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ROLE OF SOIL PHYSICAL AND CHEMICAL CHARACTERISTICS AND LANDSCAPE FACTORS IN
DEFINING SOIL BEHAVIOUR UNDER LONG TERM WASTEWATER DISPERSAL
A Thesis by Publication Submitted in Partial Fulfilment of the Requirements of the
Degree of Doctor of Philosophy (PhD)
Les Dawes
Bachelor of Applied Science (Geology)
Centre for Built Environment and Engineering Research Faculty of Built Environment and Engineering
Queensland University of Technology
February 2006
i
Abstract
The use of on-site wastewater treatment systems for the treatment and dispersal of
domestic effluent is common in urban fringe areas which are not serviced by
centralised wastewater collection systems. However, due to inappropriate siting and
inadequate evaluation of soil characteristics, the failure of these systems has become
a common scenario. The current standards and guidelines adopted by many local
authorities for assessing suitable site and soil conditions for on-site dispersal areas
are coming under increasing scrutiny due to the public health and environmental
impacts caused by poorly performing systems, in particular septic tank-soil
adsorption systems. In order to achieve sustainable on-site wastewater treatment with
minimal impacts on the environment and public health, more appropriate means of
assessment of long term performance of on-site dispersal areas are required.
The research described in the thesis details the investigations undertaken for the
development of robust assessment criteria for on-site dispersal area siting and design
and assessment of the long term performance of soil dispersal areas. The research
undertaken focused on three key research areas; (i) assessment of site and soil
suitability for providing adequate treatment and dispersal of domestic wastewater;
(ii) understanding sorption, purification and transport processes influencing retention
and release of pollutants and the natural controls governing these processes and (iii)
the development of assessment criteria for long term behaviour of soils under
effluent dispersal.
The research conducted was multidisciplinary in nature, with detailed investigations
of the physical and chemical processes involved in on-site wastewater treatment and
dispersal. This involved extensive field investigations, sampling and monitoring,
laboratory and soil column testing and detailed data analysis across the fields of soil
science, groundwater quality, subsurface hydrology, chemical contamination, and
contaminant fate and transport processes. The interactions between these different
disciplines can be complex which resulted in substantial amounts of data being
generated from the numerous field and laboratory investigations and sampling
undertaken. In order to understand the complex relationships that can occur,
ii
multivariate statistical techniques were utilised. The use of these techniques
was extremely beneficial. These techniques not only allowed not only the respective
relationships between investigated parameters to be identified, but also adequate
decisions based on the correlations were able to be formulated. This allowed a more
appropriate assessment of the influential factors, and the prediction of ongoing
changes to soil properties due to effluent disposal.
The primary outcomes for this research were disseminated through a series of peer
reviewed scientific papers centred on these key disciplines. The assessment of site
and soil suitability was achieved through extensive soil sampling throughout the
study areas and detailed laboratory testing and data analysis. The study identified and
investigated the role of influential site and soil characteristics in the treatment
performance of subsurface effluent dispersal areas. The extent of effluent travel and
the ability of the soil to remove pollutants contained in the effluent by adsorption
and/or nutrient uptake were investigated. A framework for assessing the renovation
ability of the major soil groups located throughout Southeast Queensland was also
developed. The outcomes provide a more rigorous scientific basis for assessing the
ability of soil and evaluating site factors to develop more reliable methods for siting
effluent dispersal areas. The resulting assessment criteria developed was compared
with soil column studies to determine the robustness and validity of the outcomes.
This allowed refinement of the assessment criteria in developing a more reliable
approach to predicting long term behaviour of soils under sewage effluent dispersal.
Multivariate techniques assisted in characterising appropriate soils and to determine
their long-term suitability for effluent treatment and dispersal.
The assessment criteria developed included physical, chemical and sub-surface
hydrological properties of a site and soil which can be used to predict suitability for
long term effluent treatment and dispersal. These include:
Moderate to slow drainage (permeability) to assist the movement of effluent
(percolation) through the soil profile and allow adequate time for treatment and
dispersal to occur. With longer percolation times, the opportunity for exchange
and transport processes increase.
Significant soil cation exchange capacity and dominance of exchangeable Ca2+ or
exchangeable Mg2+ over exchangeable Na+. Although a soil dominated by Mg2+
iii
is found to promote dispersion of soil particles to some extent, its impact is far
less than that of Na+. A stable soil would have a Ca: Mg ratio > 0.5.
Low exchangeable Na+ content to maintain soil stability.
Minimum depth of 400mm of potentially unsaturated soil before encountering a
restrictive horizon, to permit adequate purification to take place.
Clay type with Illite and mixed mineralogy soils being the most sensitive to Na+.
In general, significant increases in ESP occur in soils with 30 to 40% clay and in
the presence of illite clay. Small amounts of smectite clays enhance treatment
potential of a soil.
The research outcomes have significantly contributed to the knowledge base on best
practice in on-site dispersal area siting and design. The developed predictive site and
soil suitability assessment criteria allows more appropriate evaluation of site and soil
characteristics for providing long term effluent renovation. This is generally not done
in the current assessment techniques for on-site dispersal areas. The processes and
techniques used in the site and soil suitability assessment, although based on the
common soil types typical of South East Queensland, can be implemented in other
regions, provided appropriate soil information is collected or available.
The predictive assessment criteria have been developed at a generic level, allowing
easy implementation into most assessment processes. This gives the framework the
flexibility to be developed for other areas specifically targeting the most influential
on-site dispersal area siting and design factors, and assessment of long term
performance under wastewater application.
Keywords: On-site wastewater treatment systems, soil dispersal areas, soil chemistry, multivariate analysis, physical and chemical soil parameters.
iv
List of publications by Candidate Peer Reviewed Journal Papers
1. Dawes, L. and Goonetilleke, A., 2003. An Investigation into the Role of
Site and Soil Characteristics in On-site Sewage Treatment, Journal of
Environmental Geology, 44(4): 467-477.
2. Carroll, S., Goonetilleke, A. and Dawes, L. 2004. Framework for soil
suitability evaluation for sewage effluent renovation. Environmental
Geology 46(2): 195-208.
3. Dawes, L., Goonetilleke, A. and Cox, M., 2005. Assessment of physical
and chemical attributes of sub-tropical soils to predict long term effluent
treatment potential”, Journal of Soil and Sediment Contamination, 14(3):
211-230.
4. Dawes, L. and Goonetilleke, A., 2004. Using multivariate analysis to
predict the behaviour of soils under effluent irrigation, Water Air and Soil
Pollution, In Press
Journal papers under Review
1. Carroll, S., Goonetilleke, A., Thomas, E., Hargreaves, M., Frost, R. and
Dawes, L. 2005. Integrated Risk Framework for On-site Wastewater
Treatment Systems.
Peer Review completed and resubmitted to Environmental Management.
2. Dawes, L., Goonetilleke, A. and Khalil, W., 2005. Using undisturbed
columns to predict long term behaviour of effluent irrigated soils under
field conditions.
Submitted to Journal of Environmental Quality. Under review.
v
Peer Reviewed International Conference Papers
1. Dawes, L., 2005. Evaluating the long term behaviour of soils under effluent
dispersal using soil columns, In: Proceedings of On-site ’05 Conference:
Performance Assessment for On-Site systems: Regulation, operation and
monitoring, Patterson, R.A. and Jones, M.J. (eds). Armidale, Australia, pp. 155-
162.
2. Dawes, L. and Goonetilleke, A., 2004. Assessing changes in soil physical and
chemical properties under long term effluent disposal, In: On-site Wastewater
Treatment X: Proceedings of Tenth National Symposium on Individual and Small
Community Sewage Systems, Mankin, K. (ed). ASAE, Sacramento, California,
USA. pp. 349-357
3. Dawes, L. and Goonetilleke, A., 2003. Soil physical and chemical attributes for
effective sewage effluent renovation, In: Proceedings of On-site ’03 Conference:
Future Directions for On-Site systems: Best Management Practice, Patterson, R.A.
and Jones, M.J. (eds). Armidale, Australia, pp. 123-130.
4. Khalil, W., Goonetilleke, A. and Dawes, L., 2003. Correlation of soil data with
treatment performance of subsurface effluent disposal systems, In: Proceedings of
On-site ’03 Conference: Future Directions for On-Site systems: Best Management
Practice, Patterson, R.A. and Jones, M.J. (eds). Armidale, Australia, pp. 225–232.
5. Dawes, L. and Goonetilleke, A., 2001. The importance of site assessment in
designing effluent disposal areas, In: Proceedings of 2nd Australia and New
Zealand Conference on Environmental Geotechnics, Newcastle, Australia, pp 287-
294
6. Dawes, L. and Goonetilleke, A., 2001. Importance of Designing Effluent Disposal
Areas for Site and Soil Characteristics, In: Proceedings of On-site ’01 Conference:
Advancing On-site Wastewater Systems, Patterson, R.A. and Jones, M.J. (eds).
Armidale, Australia, pp. 133-140
7. Goonetilleke, A. and Dawes, L., 2001. Audit of Septic Tank Performance, In:
Proceedings of On-site ’01 Conference: Advancing On-site Wastewater Systems,
Patterson, R.A. and Jones, M.J. (eds). Armidale, Australia, pp. 155-162.
vi
Statement of Original Authorship
The work contained in this thesis has not been previously submitted for a degree or diploma at any other higher education institutions to the best of my knowledge and belief. This thesis contains no material previously published or submitted for publication by another person except where due reference has been made. Signed: Date: (Leslie Dawes)
vii
Acknowledgments
Completion of this Doctoral research would not have been possible without the
support and assistance of numerous people throughout the research project. I would
like to express my appreciation to my Principal Supervisor, A/Prof Ashantha
Goonetilleke, and Associate Supervisors Dr Malcolm Cox and Professor Keith
Wallace. Their support, guidance and professional advice provided to me throughout
the duration of the research has been invaluable and I am extremely grateful for their
assistance.
To my colleagues Mr Steve Carroll and Mr Wael Al-Shiekh Khalil for their
assistance and advice in conducting field investigations, soil column studies,
sampling and undertaking laboratory analysis of samples.
I wish to acknowledge the generous support provided by Bill Kweicien, School of
Natural Resource Sciences, for his assistance in the soil and effluent analysis.
I would also like to acknowledge Sam Bass and Jeff Fisher for their assistance in
conducting the soil and effluent analysis for the research project.
Finally, appreciation is extended to the staff of the former School of Civil
Engineering for their support throughout my Doctoral research studies.
viii
Dedication
I would like to dedicate this thesis to my wife, Helen, and to my beautiful children,
Brittany and Samuel. Their patience and understanding throughout the completion of
this doctoral research is gratefully appreciated.
ix
Abbreviations AEC
Al3+
C
Ca2+
Ca: Mg
CEC
Cl-
CCR
EC
ECEC
ESC
ESI
ESP
FC
k
K+
Mg2+
Na+
NH4+
NO3-
OC
OM
OWTS
PO43-
SAR
TDS
TOC
TP
TN
XRD
Anion Exchange Capacity
Aluminium Cation
Carbon
Calcium Cation
Calcium: Magnesium Ion Ratio
Cation Exchange Capacity
Chloride Ions
Clay Activity Ratio
Electrical Conductivity
Effective Cation Exchange Capacity
Exchangeable Sodium Content
Electrochemical Stability Index
Exchangeable Sodium Percentage
Feacal Coliforms
Hydraulic Conductivity (Permeability)
Potassium Cation
Magnesium Cation
Sodium Cation
Ammonium Ions
Nitrate Ions
Organic Carbon
Organic Matter
On-Site Wastewater Treatment Systems
Orthophosphate Ions
Sodium Absorption Ratio
Total Dissolved Solids
Total Organic Carbon
Total Phosphorus
Total Nitrogen
X-ray Diffraction
x
TABLE OF CONTENTS
Abstract ....................................................................................................................... i
List of publications by Candidate............................................................................... iv
Statement of Original Authorship .............................................................................. vi
Acknowledgments .................................................................................................... vii
Dedication ................................................................................................................viii
Abbreviations............................................................................................................. ix
CHAPTER 1.0 INTRODUCTION...................................................................1 1.1 Background to Research Project.......................................................................1
1.2 Research Project and Justification ....................................................................3
1.3 Research Aims and Objectives .........................................................................5
1.4 Scope ................................................................................................................6
1.5 Study Area.........................................................................................................7
1.6 Research Methodology....................................................................................11
1.7 Linkage of Scientific Papers ............................................................................14
CHAPTER 2.0 ANALYTICAL TECHNIQUES.............................................17 2.1 Multivariate Data Analytical Techniques..........................................................17
2.1.1 Principal Component Analysis (PCA) ............................................18 2.1.2 Discriminant Analysis (DA) ............................................................19 2.1.3 PROMETHEE and GAIA................................................................20
2.2 Analytical Procedures......................................................................................21
CHAPTER 3.0 ON-SITE WASTEWATER TREATMENT............................25 3.1 Introduction......................................................................................................25
3.2 On-site Wastewater Treatment Systems.........................................................26 3.2.1 Septic Systems ..............................................................................27
3.2.1.1 Overview.....................................................................................27 3.2.1.2 Operation and Maintenance........................................................29
3.2.2 Aerobic Systems............................................................................30 3.2.2.1 Overview.....................................................................................30
xi
3.2.2.2 Operation and Maintenance........................................................31 3.2.3 Other On-site Systems...................................................................32 3.2.4 Summary of Key Research Literature Findings .............................33
3.3 Subsurface Effluent Dispersal .........................................................................33 3.3.1 Siting and Design...........................................................................37 3.3.2 Regulatory Framework...................................................................38 3.3.3 Clogging Mat Formation.................................................................39 3.3.4 Summary of Key Research Literature Findings .............................42
3.4 Performance of On-site Systems.....................................................................43 3.4.1 Surrounding Soil ............................................................................43 3.4.2 Fate and Transport of Pollutants....................................................47 3.4.3 Failure Consequences ...................................................................51
3.4.3.1 System Failure ............................................................................51 3.4.3.2 Consequences of Failure ............................................................53
3.4.4 Summary of Key Research Literature Findings .............................56
3.5 Soil and Site Conditions ..................................................................................56 3.5.1 Soil Processes ...............................................................................57
3.5.1.1 Chemical Mechanisms................................................................57 3.5.1.2 Physical Mechanisms .................................................................60
3.5.2 Physical Parameters ......................................................................62 3.5.2.1 Soil Profile Evaluation .................................................................62 3.5.2.2 Clay content and mineralogy ......................................................64 3.5.2.3 Permeability/ Drainage Characteristics.......................................66
3.5.3 Chemical Parameters ....................................................................67 3.5.3.1 Exchangeable sodium percentage (ESP) or Exchangeable
sodium content (ESC)...................................................................................67 3.5.3.2 Ca:Mg ratio .................................................................................68 3.5.3.3 Cation exchange capacity (CEC) and exchangeable cations .....69 3.5.3.4 Chloride concentration ................................................................71 3.5.3.5 Organic Matter ............................................................................71 3.5.3.6 Nutrients......................................................................................71
3.5.4 Site Factors....................................................................................74 3.5.5 Summary of Key Research Findings .............................................77
3.6 Conclusions from Literature Review................................................................78
xii
CHAPTER 4 AN INVESTIGATION INTO THE ROLE OF SITE AND
SOIL CHARACTERISTICS IN ON-SITE SEWAGE TREATMENT ..............81 Statement of Contributions of Joint Authorship ........................................................81
Linkage of Paper to Research Methodology and Development ...............................82
Abstract ....................................................................................................................84
Introduction...............................................................................................................85
Materials and methods .............................................................................................86 The research project........................................................................................86 Analytical program...........................................................................................88 Sampling program ...........................................................................................89 Field data collection.........................................................................................92
Results and discussion.............................................................................................92 Changes in soil chemical properties................................................................92 Subsurface effluent travel................................................................................95 Effluent renovation...........................................................................................98 Subsurface drainage .......................................................................................99 Landscape factors .........................................................................................101
Summary ................................................................................................................102
References .............................................................................................................104
CHAPTER 5 FRAMEWORK FOR SOIL SUITABILITY EVALUATION FOR SEWAGE EFFLUENT RENOVATION .......................................................109 Statement of Contributions of Joint Authorship ......................................................109
Linkage of Paper to Research Methodology and Development .............................110
Abstract ..................................................................................................................112
Introduction.............................................................................................................113
Materials and methods ...........................................................................................115 Project area ...................................................................................................115 Soil sample collection ....................................................................................115 Soil analysis...................................................................................................118 Soil suitability framework ...............................................................................119 Data analysis .................................................................................................120 Principal Component Analysis.......................................................................120 PROMETHEE and GAIA ...............................................................................121
xiii
Results and Discussion ..........................................................................................124 PCA, PROMETHEE and GAIA......................................................................124 Permeability and drainage.............................................................................132 Soil suitability ranking ....................................................................................133
Conclusions............................................................................................................136
Acknowledgements ................................................................................................137
References .............................................................................................................137
CHAPTER 6 ASSESSMENT OF PHYSICAL AND CHEMICAL PROPERTIES OF SUB-TROPICAL SOIL TO PREDICT LONG TERM EFFLUENT TREATMENT POTENTIAL.................................................... 141 Statement of Contributions of Joint Authorship ......................................................141
Linkage of Paper to Research Methodology and Development .............................142
Abstract ..................................................................................................................144
Introduction.............................................................................................................145
Materials and Methods ...........................................................................................146 Research Project ...........................................................................................146 Site Selection.................................................................................................146 Soil Sampling.................................................................................................147 Analytical Program Soil .................................................................................149 Soil Water Sampling ......................................................................................149 Analytical Program Soil Water .......................................................................150 Research Rationale .......................................................................................153
Results and Discussion ..........................................................................................153 Soil Water .....................................................................................................153 Physical Characteristics ................................................................................155 Chemical Properties ......................................................................................161 Hydrological Sequence..................................................................................166
Conclusions............................................................................................................167
References .............................................................................................................168
CHAPTER 7.0 USING MULTIVARIATE ANALYSIS TO PREDICT THE BEHAVIOUR OF SOILS UNDER EFFLUENT IRRIGATION .................... 173 Statement of Contributions of Joint Authorship ......................................................173
xiv
Linkage of Paper to Research Methodology and Development .............................174
Abstract ..................................................................................................................176
Introduction.............................................................................................................177
Materials and Methods ...........................................................................................179 Site Selection and Sampling..........................................................................179 Soil Analysis ..................................................................................................180 Classification of Soil and Sampling Sites ......................................................182 Statistical analysis .........................................................................................183
Results ...................................................................................................................185 Soil and Site Characteristics..........................................................................185 Principal Component Analysis.......................................................................186 Correlations and Contrasting Variables.........................................................187
Discussion ..............................................................................................................189 Role of Exchangeable Cations in Effluent Dispersal .....................................189 Sodic Soils in Effluent Dispersal....................................................................191
Conclusions............................................................................................................193
References .............................................................................................................194
CHAPTER 8.0 USING UNDISTURBED COLUMNS TO PREDICT LONG TERM BEHAVIOUR OF EFFLUENT IRRIGATED SOILS UNDER FIELD CONDITIONS.............................................................................................199 Statement of Contributions of Joint Authorship ......................................................199
Linkage of Paper to Research Methodology and Development .............................200
Abstract ..................................................................................................................202
Introduction.............................................................................................................203
Materials and Methods ...........................................................................................205 Collection of Soil Columns and Setup ...........................................................205 Soil Sampling and Analysis ...........................................................................211 Effluent Application and Sampling.................................................................212 Field Studies..................................................................................................214 Multivariate data analysis ..............................................................................217
Results and Discussion ..........................................................................................220 Impact on Soil Properties (Columns).............................................................220
xv
Physical Characteristics ................................................................................222 Chemical Properties ......................................................................................224 Assessment of Soil Columns with Field Study Sites......................................226 Multivariate Analysis ......................................................................................228
Influential soil characteristics ......................................................................228 Identifying impacts on soil after effluent application ...................................231 Prediction of long term behaviour ...............................................................233
Conclusions............................................................................................................235
References .............................................................................................................236
CHAPTER 9.0 DISCUSSION ................................................................... 239 9.0 General Discussion .......................................................................................239
9.1 Soil and Site Processes involved in Effluent Treatment and Dispersal .........241
9.2 Sorption, Purification and Transport Processes influencing Availability of
Pollutants.......................................................................................................245
9.3 Assessment Criteria for Long Term Behaviour..............................................249
CHAPTER 10.0 CONCLUSIONS AND RECOMMENDATIONS .............. 253 10.1 Conclusions ...................................................................................................253
10.2 Recommendations.........................................................................................255
CHAPTER 11.0 CONSOLIDATED LIST OF REFERENCES................... 257
APPENDIX A EFFLUENT QUALITY DATA FROM SAMPLING SITES ... 283
APPENDIX B SITE DATA FROM SAMPLING SITES, BRISBANE AND LOGAN ...................................................................................................... 289
APPENDIX C SOIL DATA FROM SAMPLING SITES, BRISBANE AND LOGAN ...................................................................................................... 291
APPENDIX D SOIL COLUMN DATA ........................................................ 299
APPENDIX E SOFTWARE ALGORITHMS .............................................. 306
1
CHAPTER 1.0
INTRODUCTION
1.1 Background to Research Project
Over the last several years, there has been increasing recognition that on-site
wastewater treatment systems should be considered as treatment systems rather than
disposal systems. This view is due to the acknowledgement that such systems
provide a means of dispersing treated wastewater back to the environment or
recycling it in a manner that protects both public health and the environment
(USEPA 2002). The provision of conventional sewage collection and treatment
facilities has not kept pace with urban development primarily as a result of economic
constraints. Consequently, the on-site treatment of sewage is the most practical
option under these circumstances. In Australia, over 3 million people or about 16%
of the population are dependent on on-site systems for the treatment and dispersal of
sewage (Carroll and Goonetilleke 2004).
Subsurface effluent dispersal areas are common features in most on-site wastewater
treatment systems. These systems are also commonly referred to as “soil absorption
areas”. The subsurface effluent dispersal area is an important part of this treatment
train. Unfortunately, the effluent dispersal area is the component most susceptible to
failure, resulting in undesirable surface and groundwater contamination (Scandura
and Sobsey 1997, DeBorde et al 1998, Lipp et al 2001).
Sewage effluent can contain high concentrations of organic matter, suspended solids,
nutrients and micro-organisms and as a consequence is not suitable for discharge to
the environment without further treatment. This further treatment is achieved by
discharging the effluent into a trench or bed. Typically, infiltration and percolation
occur through the underlying unsaturated zone and recharge to the local groundwater
system. The natural soil system offers a medium for not only absorbing pollutants,
but also for treating and utilising waste constituents. The porous nature of soil can
provide an ideal media for absorbing and transmitting effluent. Purification occurs
2
through a range of processes, such as physical filtration, chemical treatment
through ion exchange, adsorption and transformation, biological decomposition by
micro-organisms as well as enrichment of the nutrient pool for uptake by plants
(Jenssen and Siegrist 1990). Despite satisfactory purification performance observed
in controlled experiments and field studies with appropriate site evaluation and
properly constructed systems, transport of high concentrations of chemical and
biological pollutants from subsurface effluent dispersal areas to groundwater has
been widely reported (e.g. Hagedorn et al 1981, Harris 1995, Harman et al 1996,
Wilhelm et al 1996, and van Cuyk et al 2001).
The health and environmental consequences of inadequately treated effluent can be
serious, as impacts can be widespread (Beard et al 1994, Mote et al 1995, Geary and
Whitehead 2001, Carroll and Goonetilleke 2004). Furthermore these highly
undesirable impacts are gradual and not immediately visible. The dependency on
visual factors such as surface ‘break-out’ of effluent from a subsurface dispersal area
is not always reliable. For example, it could well be that a dispersal area had failed
at a particular site without surface indications. Under such conditions partially
treated effluent could percolate into the groundwater rather than resulting in the
surface appearance of effluent.
The performance of soil based effluent dispersal systems and the need to consider
soil characteristics in their siting and design have been investigated by numerous
researchers such as Brouwer and Bugeja (1983) in Victoria, and more recently Geary
(1993), Martens and Warner (1995), Jelliffe (1995) and Martens and Geary (1999) in
New South Wales, Whitehead and Geary (2000) in Tasmania, and Bouma et al
(1972), Bouma (1974) and Hoover et al., (1998) in USA. Most of these studies
focussed primarily on effluent quality and not on changes to soil characteristics or
relationship to site factors in the effluent dispersal area.
Recent studies on the performance evaluation of on-site sewage treatment systems
within the Brisbane and Logan City local government regions confirmed that more
than 70% of the investigated systems were not meeting the stipulated standards for
effluent treatment (Goonetilleke et al 1999, 2000; Dawes 2000). In 35% of these sites
failure of the effluent dispersal area due to poor site and soil evaluation prior to the
3
installation of the dispersal area was the common cause (Dawes and Goonetilleke
2003). Commonly, stereotypical site evaluations are undertaken, regardless of the
sensitivity, or lack thereof, to the receiving environment. Consequently, this has led
to the poor performance and failure of effluent dispersal areas. The outcomes of
these studies confirm much of the anecdotal evidence that many dispersal areas fail
due to hydraulic overloading and an inadequate consideration of key soil physical
and chemical characteristics.
1.2 Research Project and Justification
Subsurface effluent dispersal areas are common throughout South East Queensland.
However, the specific physical and chemical processes involved in wastewater-soil
interactions are not completely known. Additionally, the impact of other factors such
as topography and subsurface drainage processes on the life of the dispersal system
and in the renovation of sewage effluent is poorly understood. The main focus of this
investigation was to incorporate strong scientific knowledge into assessment criteria
to reflect the complex nature of the soil system on which treatment and dispersal is
based. Both internal soil properties and external landscape factors need to be
integrated in defining long term performance prediction.
The behaviour of soil dispersal areas in the treatment of sewage effluent is inherently
complex. The processes taking place and the degree of influence exerted by various
parameters are highly variable. In evaluating the treatment performance of soil
absorption areas, it is essential that the primary factors governing these processes are
identified and critical relationships defined. The research project assessed treatment
performance at a series of study sites using common failure scenarios associated with
on-site wastewater systems as defined by USEPA (2002). Classification of dispersal
area behaviour was categorised into hydraulic or purification failure or satisfactorily
performing. Collection and analysis of field observations, soil water sampling,
detailed site history, surface and subsurface site conditions allowed a comprehensive
examination of failure mechanisms at specific sites. This enabled relationships
between site criteria to be developed and a better understanding of the subsurface
drainage processes in predicting long term behaviour of soils under effluent dispersal.
4
An investigation into soil and site suitability for providing appropriate effluent
treatment was conducted. Detailed analysis of soil physical and chemical parameters
allowed definition of critical processes and development of correlations between soil
and site characteristics involved in the effluent treatment process. The research
focused on the assessment of soil physico-chemical characteristics and associated
landscape features. These factors are responsible for attenuating and removing
effluent pollutants as the effluent percolates through the soil matrix, as well as soil
hydraulic characteristics necessary for effluent dispersal. An assessment of treatment
performance specifically related to the uptake and release of pollutants from soil
dispersal areas identified the critical processes influencing the movement and
availability of nutrients and salts within the soil profile. This assessment involved
collecting information on water table depth, presence of effluent flows, depth of soil
horizons, and detailed analysis of soil and soil water sampling data. The
identification of critical site and soil characteristics led to an initial field assessment
of long term behaviour of soils under sewage effluent dispersal. The initial field
evaluation of long term behaviour was validated with undisturbed laboratory soil
column data from comparable soil types, to confirm the developed relationships and
to identify critical parameters obtained from the field investigations. The outcomes
of this research were utilised in developing assessment criteria for long term
behaviour of South East Queensland soils. These criteria were developed to improve
prediction of long term performance of on-site effluent dispersal areas.
The field study included thirty four sites selected from the unsewered urbanised areas
of South East Queensland covering an area of over 700 km2. Over two hundred soil,
water and effluent samples were collected from the various soil depths, piezometers
and septic system distribution boxes and analysed for their physico-chemical
characteristics along with detailed site classification and the collection of historical
data. The supporting column study included twelve soils with soil samples extracted
for physico-chemical analysis at different time intervals. Data summaries for all
sampling and monitoring sites can be found in Appendix A, B, C, D.
Limited research has been conducted with regard to investigating the role played by
soil and subsurface hydrological processes in on-site effluent dispersal systems
5
within South East Queensland. Most research has been carried out in the United
States (Wilhelm et al 1994b, Hoover et al 1998, Siegrist et al 2000, Day 2004) where
the soil characteristics and soil types are markedly different to Australian soils. The
current study has significant applicability Australia wide as similar soils occur
throughout the eastern regions of the continent.
The development of long term performance criteria for soil dispersal areas was
described as one of the single most important needs in the assessment of these
systems at the recent National Research Needs Conference: Risk-based decision
making for on-site wastewater treatment (Siegrist et al 2000). This research project
was aimed at contributing to the knowledge base relating to the indicators of
treatment performance. In particular, the development of enhanced assessment
criteria for evaluating on-site soil dispersal areas, that is both universally acceptable
and scientifically robust to reduce uncertainty in predicting the life expectancy of
such systems. Such an assessment scheme would be beneficial in the evaluation of
soil dispersal areas and would minimise the inherent risks associated with poor
performance. This is particularly important for areas such as South East Queensland
due to the current high rate of development, high failure rates of on-site effluent
dispersal areas, and the numerous environmentally sensitive areas within the region.
1.3 Research Aims and Objectives In summary, the primary aims of this research project were:
1. To develop a comprehensive understanding of how site and soil characteristics
influence on-site effluent treatment processes;
2. To develop a comprehensive understanding of the fate and transport of specific
pollutants from on-site systems, such as nutrients and salts; and
3. To investigate the extent to which natural controls such as soil mineralogy, site
drainage and landscape features influence the treatment potential of subsurface
effluent dispersal areas in South East Queensland soils.
The primary objectives of the research project were:
6
1. To identify relationships between soil characteristics, drainage and
landscape factors in order to define critical parameters and primary controls
involved in on-site effluent treatment processes;
2. To develop a detailed understanding of the critical processes which influence the
changes in availability of nutrients and salts in soils receiving effluent; and
3. To develop robust assessment criteria to predict long term behaviour of sites and
soils under on-site effluent dispersal by incorporating scientific knowledge from
improved evaluation of site and soil characteristics.
The outcomes of the project are expected to contribute to strengthening the long term
sustainability of sewage effluent dispersal systems. The creation of effective and
robust assessment criteria will help in the development of predictive methodology for
determining performance of on-site dispersal areas under transient conditions.
1.4 Scope
The research undertaken was specifically formulated around the performance issues
associated with the treatment of effluent discharged from on-site systems. The
treatment capabilities and performance of the actual treatment units and respective
technologies were not investigated. The study was confined to South East
Queensland where the soils are highly weathered and are generally acidic and
representative of a subtropical coastal zone.
Only single home subsurface dispersal systems were investigated and the assessment
of soil and site suitability was developed on the basis of effluent infiltration through
the soil matrix comparing control sites with sites where effluent dispersal had
occurred. The focus of this research was subsurface soil dispersal areas associated
with septic tanks where a significant portion of the effluent treatment occurs. Though
the focus of the study was South East Queensland, the field sites selected for data
collection were confined to Brisbane and Logan local government areas. The reasons
for selecting these two areas are discussed below (Section 1.5). The research
outcomes are applicable to comparable soils in similar geomorphological and
climatic settings within Queensland and Eastern Australia.
7
The investigations were designed to specifically focus on physical filtration, ion
exchange and adsorption processes involved in wastewater-soil interaction as the
effluent percolates through the soil. Biological processes, heavy metals precipitation
and oxygen demand occurring within the soil dispersal system were not investigated.
Evaporation processes and vegetation can provide additional treatment of effluent.
Vegetation and soil within the dispersal area are closely interacting agents in
renovating sewage effluent. Plants play an important role by taking up water and
nutrients, providing cover and by maintaining the soil physical properties and
biological activities through rooting. The moisture regime of the soil can affect the
rate and degree to which chemical changes occur within the soil profile.
Microbiological processes in the soil are dependant on vegetation as it is commonly
the source of organic carbon in the soil. This research complements past research
conducted specifically focussing on evapotranspiration by vegetation (Gardner and
Davis 1998, NZLTC, 2000).
1.5 Study Area
The study was confined to the South East Queensland region incorporating the
unsewered areas in Brisbane and Logan local government areas. This region was
selected as:
• the soils are representative of subtropical soils in South East Queensland
• broad scale baseline data (soil maps) were available
• good mix of system ages was available for investigation
South East Queensland is Australia’s largest growth area where extensive
urbanisation is occurring. Due to the escalating cost of infrastructure, on-site
treatment systems are the most economical and accepted means of wastewater
treatment within the rapidly developing urban fringe areas. The Brisbane and Logan
local government areas currently have over 12,000 on-site wastewater treatment
systems with a majority of them being conventional septic tank-soil dispersal areas.
Large clusters of on-site systems exist in various locations throughout these regions
8
and their cumulative effect has become a major concern for regulatory
authorities. Some areas have high system densities (>100 systems/km2) and
unsatisfactory site and soil characteristics often lead to ineffective effluent treatment
and dispersal and high system failure rates (Goonetilleke et al 2000, Dawes et al
2004).
The study area has a diverse range of soil types as shown in Figure 1.1. The most
prominent soils are the Chromosol, Kurosol and Dermosol groups, as classified
under the Australian Soil Classification (Isbell 2002). These soils constitute
approximately 75% of the entire study area. The remaining soil groups found in the
region consist of a mixture of Ferrosols and Kandosols soils with minor areas of
Sodosols and Podosols.
Sites were selected within the western and northern suburbs of Brisbane and western
and eastern suburbs of Logan. Figure 1.2 and 1.3 show the thirty four sites selected
for investigation. Table 1.1 presents the site and soil description recorded at each of
the 34 sites. Some sites needed to be subsequently abandoned due to the inability to
collect soil water samples of sufficient quantity or due to the closeness of the rock
shelf to the ground surface.
Site selection was based on the following criteria: soil type, site drainage, soil
permeability, soil profile (duplex, uniform), soil sequence (slope), type of household
(single family with minimum of 2 persons), age and type of system (septic tank with
trenches). Other factors that influenced site selection included known or suspected
failure of soil dispersal areas as well as known efficiently functioning systems
(established with local government assistance) and areas where there is potential for
more intensive residential development taking place in the future. 60% of the study
sites selected were less than 8 years of age and designed according to AS1547, 1994.
Older systems were designed with trench lengths of 9 metres regardless of the soil
type. Among the older on-site systems (>8 years) only 40% were known to have
failed. All the failed soil dispersal areas were over 17 years old and as such it is
difficult to determine whether poor design was a factor as design life is generally
considered to be 15 to 20 years.
9
Figure 1.1 Soil Association Map Brisbane and Logan (extract from CSIRO Soil Landscapes Brisbane and South East Environs Map 60, Beckmann et al 1987) (Different soil units shown by colour and symbol) Not all sites shown. Legend Symbol Soil Landscape Dominant Soil Groups Landscape As Aspley Ferrosols Undulating hills B Beenleigh Kurosols, Chromosols Low undulating hills Be Brisbane River Kandosols, Kurosols Low plains, alluvium En Enoggera Dermosols, Kurosols Steep hills of granite Je Jamboree Chromosols, Kurosols Low undulating hills K Kenmore Chromosols Undulating hills L Logan Chromosols, Sodosols Flood plains MCk Moggill Creek Podosols, Sodosols Alluvium MCo Mount Cootha Dermosols Steep hills of phyllite Sa Samford Kandosols, Kurosols Low hills of granodiorite T Toowong Chromosols Low hills of phyllite
10
8
1Anstead
Bellbowrie
Moggill
PullenvalePinjarra Hills
KenmoreBrookfield
11
3
The Gap
Upper Kedron
Kepperra
Ferny Hills
14
City
Chermside
Bridgeman Downs
Carseldine16
Cen
tena
ry H
ighw
ay
Moggi
ll Rd
Mt Crosby Road
Ipswich Road
Rafting
Ground
Road
Waterworks Rd
Settl
emen
t Rd
Samford Road
Bec
kett
Roa
d
Sand
gate
Roa
d
Sand
gate
Roa
d
∗
97
45
12
13
15
26
10
Figure 1.2 Location of selected sites Brisbane
Figure 1.3 Location of selected sites Logan
N City of Brisbane
* Monitoring Sites
0 6 12 Kilometers
N
Moreton Bay
Creek
Dog
Native
Tevi
ot
Carbrook
Mt.
Cotto
n
Rd.
Ster
n R
d.
16
Rd.
Serpentine
14
15
5Kilometers
0 2.5
Bay
Redland
Creek
Gramzow Rd.Mt.
Cornubia
West
Cotton
13
11
12
Rd.
Highway
City of Gold Coast
17
Tanah Beenleigh
Rd.
Shailer
Loganholme
Ford
Redland Shire18
PriestdaleRd.Rd.
Saw
mill
Rd.
Park
Bryants
Rd.
Logan
River
Rd.
DaisyHill Venman Rd.
Plantain
St.Lyndale
Merah
Dai
sy
Springwood
Rd.
Hil lChatswood Rd.
CreekMotorway
Meadowbrook
Slacks
Pacific
Slacks Creek
Rd.
Underwood
S.E.Freew
ay Roachdale
Priestdale Rd.
Roa
chda
leR
d.
Rd.
Logan
Loganlea
Rd.
UnderwoodSouth
Springwood
Queens Rd.
CentralLogan
Bee nlei gh
Rd.
Compton Rd.
Woodridge
Kingston
Rd.
KingstonBardon
Fifth
A
ve.
Marsden
Third
Ave
.
Firs
t
A
ve.
2Creek
1
Wembly
Berrinba
PlanesBrowns
City of Brisbane
Scrubb
y
High
way
Railw
ay
Rd.
Rd.Johnson
4
6
Rd.
Stap
ylto
n R
d.
5
Cre
ek
Oxley
7
∗
Goodna - Browns Plains
West
School Rd.
Waterford
Rd.
L oga
nlea
LoagnReserve
Flat
Crestmead
Julie
S
t.
Rd.
Rd.
BumsteadRd.
Cha
mbe
rs
Xoplick Rd.
Rosia Rd.
Beaudesert Shire
ParkHeritage
Park Ridge
Cla
rke
Rd.
Park Ridge3
Park
Green Rd.
Wal
ler
Regents
Hillcrest
Andrew Rd.
Mt.
Lind
esay
Sydn
ey
Rd.
Boronia Heights
10
Rd.
Middle
Stoney Camp
Greenbank
Forestdale
9
8
Brisb
ane
-
Oxley
Greenbank Army Camp
Creek
Rd.
Monitoring Sites
17
18
19
2021 22
23
24
25 26
32
31 30
29
2827
33
11
Table 1.1 Site and soil descriptions Site No.c
System age (yr)
Disposal Area(m2)
Australian Soil Classificationa
Soil Drainageb
Hydraulic Loading Rate
(mm/day)
Slope (˚)
1 4 56 Red Chromosol Moderately well drained
35 >15
3 5 70 Brown Chromosol Imperfectly drained 40 <10 4 3 72 Brown Chromosol Imperfectly drained 40 <5
7 2.5 60 Red Chromosol Moderately well drained
35 >10
8 4 60 Red Sodosol Poorly drained 20 <5 9 17 40 Grey Sodosol Poorly drained - <5 11 4.5 40 Red Kandosol Well drained 50 >15
12 19 56 Brown Kurosol Moderately well drained
- >10
14 14 72 Brown Chromosol Moderately well drained
- >15
15 3 48 Red Ferrosol Moderately well drained
50 >5
16 4 36 Red Ferrosol Poorly drained 35 <5
17 12 48 Yellow Chromosol Moderately well drained
- >5
18 8 84 Brown Kurosol Very poorly drained - <5 19 6 60 Yellow Chromosol Moderately well
drained 35 >5
20 19 54 Brown Chromosol Imperfectly drained - <5
21 5 39 Yellow Chromosol Well drained 50 >5
22 1 126 Brown Chromosol Moderately well drained
35 >5
23 6 72 Brown Chromosol Moderately well drained
35 >10
24 18 72 Brown Chromosol Imperfectly drained - >5 25 5 72 Brown Chromosol Imperfectly drained 20 >5 26 14 126 Brown Chromosol Imperfectly drained - <5
27 12 48 Grey Dermosol Well drained - >15 28 11 72 Brown Kurosol Poorly drained - >5
29 5 72 Brown Chromosol Imperfectly drained 20 >10 30 7 144 Brown Kurosol Poorly drained 20 <5
31 8 72 Red Chromosol Imperfectly drained - >5
32 6 72 Brown Chromosol Moderately well drained
35 >10
33 7 72 Brown Kurosol Poorly drained 35 <5 34 20 48 Brown Chromosol Well drained 20 >15
a Australian Soil Classification after Isbell (1996) b the classification used complies with AS/NZS 1547:2000 (Standards Australia, 2000), McDonald et al. (1990). c missing numbers are sites abandoned due to insufficient soil water sample and unreliable historical site information
1.6 Research Methodology
The implementation of a suitable methodology which encompasses the specific
research aims and objectives set out for this project was essential. The process of
progressing from the initial problem formulation to the field investigation and
12
analysis involved developing sampling strategies, selecting identifying critical
soil and effluent parameters, site selection for field investigations and establishing
field monitoring sites. Figure 1.4 outlines the methodology adopted for the research
project. The methodology involved several stages including an initial assessment
based on field studies which was refined with the collection of data from undisturbed
soil columns and progressive analysis being undertaken. This process allowed the
development of a more reliable approach for predicting long term behaviour of soils
under wastewater application by incorporating appropriate scientific data and
relevant site information.
The research conducted was reported as a series of linked publications. Each of the
five peer reviewed papers cited focus on a specific stage of the research with the
respective outcomes utilised in the development of predictive assessment criteria for
long term behaviour of soil under sewage effluent dispersal. The overall
methodology and development of these scientific papers in the context of the
research project is also depicted in Figure 1.4. Detailed descriptions of the linkages
between these scientific papers and their respective outcomes in relation to the
research project are provided in Section 1.7.
To determine the prevalence of distinct soil groups in the unsewered areas, the South
East Queensland UBD 1:20,000 maps were overlaid on the Soil Landscapes Map of
Brisbane and Surrounding Areas (Beckmann et al 1987). The extent of each soil
group was outlined to enable ease of recognition on the ground and was utilised to
calculate the percentage area of soil groups according to the soil map developed by
Beckmann et al (1987). Due to the wide range of parent materials and different
intensities of soil weathering, there is an infinite variety of soil types. Therefore it
was important to base the research on a broad scale soil classification system. The
unsewered areas with potential for more intensive residential development in the
future were identified. Sites with septic tank/sub-surface soil dispersal areas were
selected in proportion to the prevalence of the different soil types in the unsewered
urbanised areas of Brisbane and Logan local government areas. Chromosol and
Kurosol soils comprised 75% of the unsewered areas and thus the majority of sites
were selected in these soil types.
13
Figure 1.4 Schematic diagram showing detail of research program highlighting methodology and sequence of scientific papers (shading identifies stages where scientific papers were developed)
Identify critical soil physical and chemical parameters, drainage and
landscape features
Develop criteria for site selection and sampling strategy
Selection of field study sites
Literature Review and Desktop Study
Field investigation and data analysis
Field soil and sewage effluent sampling, monitoring and testing
at existing on-site systems. Site and landscape analysis
Development of relationships between soil characteristics, drainage and landscape factors
Initial assessment of long term behaviour of soils under sewage effluent dispersal
Performance evaluation
Column study on Undisturbed soils
Develop assessment criteria to predict long term behaviour of soils in on-site dispersal areas
Detailed evaluation of field and column studies, identifying failure criteria
Paper 1
Paper 2
Paper 4
Paper 3
Paper 5
Analysis of critical site and soil characteristics involved in effluent treatment
Evaluate Treatment Performance and confirm desktop study outcomes
14
1.7 Linkage of Scientific Papers
Satisfactory performance of on-site wastewater treatment systems, in particular
septic systems, depends mainly on the ability of the underlying soil to treat and
transmit the discharged effluent. One of the most important issues regarding the
appropriate use of on-site effluent dispersal systems is the proper assessment of the
site and soil characteristics which play a vital role in the treatment and dispersal of
discharged effluent.
The concept of soil effluent renovation ability, the ability of the soil to attenuate and
remove pollutants and provide adequate dispersal is described in detail through
Papers 1 and 2. Paper 1 (An Investigation into the Role of Site and Soil
Characteristics in On-site Sewage Treatment) identifies and investigates the role of
influential site and soil characteristics in the treatment performance of subsurface
effluent dispersal areas. The treatment performances of a number of septic systems
on a range of site and soil conditions were investigated together with detailed soil
analysis. The changes to soil physico-chemical characteristics of the dispersal area
due to effluent application and its effluent renovation ability were found to be
directly related to the subsurface drainage characteristics.
Paper 2 (Framework for soil suitability evaluation for sewage effluent renovation)
outlines a framework for assessing the renovation ability of the major soil groups
located throughout South East Queensland. The data collected in Paper 1 and Paper
2 were combined to consolidate and update soil databases for sub-tropical soils in
South East Queensland. Using multivariate statistical methods, the assessed soils
were ranked in order of their ability to provide suitable effluent renovation based on
their physical and chemical characteristics. The most significant outcome from this
study was that Chromosol soils were found to have the best overall renovation ability,
followed closely by the Ferrosol and Dermosol soils. These soils were found to
provide adequate renovation ability, and therefore were considered as suitable for on-
site wastewater treatment.
However, although the study described in Paper 2 discussed the renovation
suitability of major soil groups within South East Queensland, the suitability ratings
15
were established based on scientific analysis of soils which had not been previously
exposed to effluent. Consequently, further validation of these suitability rankings in
relation to field conditions under long term effluent exposure was necessary.
Paper 3 (Assessment of physical and chemical properties of sub-tropical soil to
predict long term effluent treatment potential) highlighted the role of soil physical
and chemical properties in the treatment performance of existing subsurface effluent
dispersal fields. The changes in soil properties of the dispersal area due to effluent
application were found to be directly related to the subsurface drainage
characteristics including permeability, clay content and clay type. Monitoring of
changes in these properties permitted improved prediction of the treatment potential
of a soil. The study confirmed that an in-depth knowledge of the local soil
characteristics and associated sub-surface soil hydrology is essential for better
prediction of long term treatment potential of subsurface effluent dispersal systems.
Together Papers 1, 2 and 3 investigated the ability of common soil types found in
South East Queensland to effectively renovate effluent and identified the critical
parameters and primary controls involved in the effluent treatment processes. The
combined outcomes from Papers 1, 2 and 3 provided a more rigorous scientific basis
for assessing the ability of soil and relevant site factors to develop more reliable
methods for siting of effluent dispersal systems. However, although these papers
employed various univariate and multivariate statistical techniques to assess the soil
physical and chemical data, a detailed description of the statistical methods adopted
were not the main focus of these papers.
Consequently, Paper 4 (Using multivariate analysis to predict the behaviour of soils
under effluent irrigation) provided a more detailed discussion on the multivariate
methods used for assessing long term behaviour of soils under effluent irrigation,
with a major focus on principal component analysis. This paper identified Principal
Component Analysis (PCA) as a reliable and versatile tool for characterising a soil’s
ability to adequately treat sewage effluent. Multivariate statistical methods provided
the ability to differentiate the most suitable soils for long-term effluent irrigation and
to determine the most influential soil properties and associated site factors in order to
characterise them.
16
As a result of detailed evaluation of field sites, laboratory testing and data
analysis, identification of critical processes in effluent treatment, analysis of critical
site and soil characteristics and relationships developed, assessment criteria were
developed and compared with soil column studies on similar soil types in order to
determine the robustness and validity of the outcomes. This is discussed in Paper 5
(Using undisturbed columns to predict long term behaviour of effluent irrigated soils
under field conditions). Findings confirmed that accelerated undisturbed soil column
studies can be useful in predicting long term behaviour of effluent irrigated soils.
Incorporation of soil column data allowed refinement of the assessment criteria in
developing a more reliable approach to predicting long term behaviour of soils under
sewage effluent dispersal.
17
CHAPTER 2.0
ANALYTICAL TECHNIQUES
2.1 Multivariate Data Analytical Techniques
Soil, site and wastewater data analysis needed for the research was complex,
resulting in large amounts of data being generated from numerous field
investigations, soil column studies and sampling undertaken. The complexity and
large amount and variance of environmental data limited the use of univariate
statistical methods in developing a better understanding and assessment of soil
processes. Multivariate statistical methods are able to detect similarities between
variables and allow a more profound interpretation of relevant data (Gallego et al
2002, Sena et al 2002, Einax and Soldt 1998, Carlon et al 2001). Multivariate data
analysis is beneficial in that large amounts of data can be processed for exploring and
understanding relationships between different parameters. This is typically achieved
through the procedures of pattern recognition, classification and prediction
techniques. The multivariate approaches utilised for assessing the data obtained
through soil and water investigations consisted of three common methods, which are
discussed below.
One of the strengths of a large data set is that changes in several variables can be
considered simultaneously, and multivariate analyses provide powerful methods to
achieve this. The major drawback of such methods is that they are complex, both in
their theoretical structure and in their operational methodology. Care must be taken
to adhere to assumptions underlying the tests, for the results to be logical and valid.
The techniques must be applied with diligent reference to manuals and specialist
statistical advice.
18
2.1.1 Principal Component Analysis (PCA)
PCA is the most common pattern recognition method used in multvaraite analysis. It
has been successfully applied to a range of data sets in previous research. Sparling et
al (2001) in a study on three soils under effluent irrigation in New Zealand found
PCA useful in revealing overall treatment differences between soils irrigated with
wastewater; short and long term and non-irrigated soils. Carroll and Goonetilleke
(2004) used PCA to assess chemical and microbiological data from shallow
groundwater and to relate to the density of on-site wastewater treatment systems.
Wang et al (2003) demonstrated the utility of principal component analysis in
selecting the most appropriate parameters for evaluating soil quality under long term
wastewater irrigation.
PCA is a multivariate statistical data analysis technique which reduces a set of raw
data into a number of principal components which retain the most variance within the
original data to identify possible patterns or clusters between objects and variables.
Detailed descriptions of PCA are found in Massart et al (1988), Adams (1995) and
Kokot et al (1998). All raw soil data used in PCA was subjected to pre-treatment in
order to reduce irrelevant sources of variance or ‘noise’ which may interfere in the
analysis (Einax 1998). Firstly, the raw data was log transformed to reduce data
heterogeneity. As an example electrical conductivity data varied from 40 to 3000
uS/cm whilst exchangeable cations varied between 0.01 and 39 meq/100g. This
removed the skewness of the data. Following this, the transformed data was column-
centred (column-means subtracted from each element in their respective columns)
and standardised (individual column values divided by the column standard
deviations).
After decomposition of the raw data matrix, principal components (PCs) were chosen
so that PC1 describes most of the data variance, followed by PC2 which retains the
next largest amount of data variance and is orthogonal to PC1. This meant that PC2
is independent of PC1. The advantage of PCA is that most of the data variance is
contained within the first few PC’s, thus reducing the dimensionality of the
multivariate data matrix (Kokot et al 1998).
19
Objects (in this case soil, site and water samples) that retain similar variances in the
analysed variables will have similar PCA scores which will cluster together when
plotted. Likewise, relationships between variables can be easily identified by the
respective coefficients. Strongly correlated variables will generally have the same
magnitude and orientation when plotted, whereas uncorrelated variables are typically
orthogonal (perpendicular) to each other. Clusters of object data and their respective
relationships with the analysed variable can clearly be seen when respective scores
and coefficients are plotted on a biplot. This allows relationships between analysed
variables and respective objects to be identified. Results can be displayed graphically
in terms of the original variables, using the first two or three factors as axes, as they
account for most of the variance. This emphasises those variables which best explain
changes in the nature of the system, including those which are directly or inversely
correlated.
The software used in this research to undertake PCA was MatLab and StatisiXL. The
PCA algorithms used were adopted from Kramer (1993) and are summarised in
Appendix E.
2.1.2 Discriminant Analysis (DA)
Carroll et al (2005) utilised discriminant analysis (DA) for classification of soils
from the Gold Coast region, Queensland State, Australia based on physical and
chemical characteristics and to identify changes in soil properties as a result of
effluent application. Bakhsh and Kanwar (2004) used DA to show that soil and
landscape variables (organic matter, soil texture, nutrient profiles) are contributing
factors to subsurface drainage zones.
Discriminant analysis (DA) was employed to discriminate between major soil
characteristics influencing the relevant processes. Discriminant analysis is a
multivariate statistical analysis technique where a data set containing X variables is
separated into a number of pre-defined groups using linear combinations of analysed
variables. This allows analysis of their spatial relationships and identification of the
respective discriminative variables for each group (Wilson 2002). Objects (soil type)
20
that retain similar variances in the analysed variables will have similar
discriminant scores and when plotted will cluster together. Likewise, relationships
between variables can be easily identified by the respective coefficients. Strongly
correlated variables will generally have the same magnitude and orientation when
plotted, whereas uncorrelated variables are typically orthogonal to each other.
Clusters of object data and their respective relationships with the analysed variable
can clearly be seen when respective discriminant scores and coefficients are plotted
on a biplot, generally plotting the first two discriminant functions. Visualising these
biplots is undertaken in the same manner as the PCA biplot. DA was employed to
analyse the differences between two or more groups of multivariate data using one or
more discriminant functions in order to maximally separate the identified groups.
DA can be highly sensitive to outliers in the original data and is not suited to the
complexity of exploratory analysis of large irregular data sets (Davis 1986). It is
considered more suitable for follow-up analysis, to allow grouping of samples
established by classification procedures such as Cluster analysis.
2.1.3 PROMETHEE and GAIA
PROMETHEE and GAIA are multicriteria decision making (MCDM) aids that rank
actions according to specific criteria and thresholds. The details of PROMETHEE
and GAIA are described elsewhere (Visual Decision Inc. 1999, Keller et al 1991) and
therefore only a brief summary of the methods is provided here. The PROMETHEE
method uses a pair-wise comparison system in which each action (soil sample) is
compared to all other actions one-by-one defined by the preference functions, with
thresholds and weights adopted by the decision-maker (Visual Decision Inc. 1999).
Khalil et al (2004) presents a detailed discussion on the use of preference functions
for site selection for on-site sewage treatment systems. PROMETHEE establishes
preference flows (Φ) for each action and ranks these based on the preference flows.
Partial ranking (PROMETHEE I) utilises the Φ+ and Φ- preference flows for ranking
the actions. The positive flow, Φ+, determines the degree to which each soil sample
is preferred over other samples, with higher positive values receiving a higher rank.
The negative flow Φ- determines the degree to which other soil samples are preferred
21
over a particular sample. However, if samples have conflicting flows or preferences,
they are considered incomparable in the PROMETHEE I ranking (Visual Decision
Inc. 1999). The net flow Φ (Φ = Φ+ - Φ-), also called the Pi score, represents the
complete ranking (PROMETHEE II) of samples, with higher flow values ranked
more highly. Both PROMETHEE I and II rankings were analysed to establish which
soils were more suitable for effluent renovation.
GAIA provides a diagrammatic representation of the ranking methods of
PROMETHEE, utilising a PCA technique. PCA is applied to the net preference
flows (Φ), and a biplot or GAIA plane, of the first two PCs developed. Although no
initial pre-treatment of data is needed to be undertaken, the preference functions
established by PROMETHEE act to normalise the data, thereby providing some pre-
treatment of the initial data. Carroll et al. (2004) found PROMETHEE and GAIA
enabled correlations between different soil types and ranked the soils on their ability
to renovate effluent.
2.2 Analytical Procedures This section details the physical and chemical analytical methods applied to the soil
and effluent samples collected. The physical and chemical soil tests were conducted
according to the Australian Laboratory Handbook of Soil and Water Chemical
Methods by Rayment and Higginson (1992). All effluent characterisation was
conducted according to APHA (1999). Analytical methods are listed in Table 2.1. All
instrumentation (field and laboratory) was checked and calibrated on a regular basis,
generally when each batch of samples was processed.
Soil is naturally heterogeneous both vertically and horizontally. Therefore strict
attention to obtaining representative samples was essential. Even with representative
samples, analytical variability can add further errors to final results. Sources of errors
include sub-sampling for analysis, small variations in the conditions of extraction
(time, temperature and vigour of shaking) and the precision of the analytical
determination. Reference soils were used for each batch of analysis to monitor
variability. Repeat tests were performed if the results for the check soils differed by
22
more than 2 standard deviations. Where sufficient sample was available,
replicate soil samples were analysed and results presented as averages.
Soil parameter selection was based on the suite of tests normally carried out in land
resource evaluation by Agricultural Chemistry Branch of Queensland Department of
Natural Resources. These tests have been developed through widespread agricultural
research and are designed to distinguish between deficient, adequate and toxic supply
of elements in soil and between degraded and non-degraded soil conditions.
Effluent parameter selection was based on standard parameters currently required for
approval by the Queensland Department of Local Government and Planning (On-Site
Sewerage Code, 2003) and accepted by industry as an adequate measure of a
domestic on-site wastewater treatment plant performance. In addition to the effluent
samples collected from the monitoring sites, blanks and known concentration spikes
were included in every batch as a quality control measure. Table 2.1 Analytical methods – soil and effluent
Parameter Analytical Method pH Soil Effluent
4A1: pH of 1:5 soil/water suspension at 25°C (Rayment and Higginson 1992) TPS-81 pH-conductivity meter
Electrical Conductivity (EC) Soil Effluent
3A1 EC of 1:5 soil/water suspension at 25°C (Rayment and Higginson 1992) 2520-Conductivity (APHA 1999)
Chloride ions (Cl-) Soil Effluent
5A1 chloride 1:5 soil/water filtered suspension at 25°C (Rayment and Higginson 1992) and measured using 4500-Cl-E Automated Ferricyanide Method (APHA 1999) 4500-Cl-E Automated Ferricyanide Method (APHA 1999)
Total Kjeldahl Nitrogen Soil and (TKN = organic + ammonia) Effluent
Wet oxidation method (Kjeldahl 1983) 4500-Norg C (APHA 1999)
Nitrates (NO3-) Soil
Effluent
7CB1 Water Soluble Nitrate 1:5 soil/water filtered suspension at 25°C (Rayment and Higginson 1992) Measured using 4500-NO3
- F Automated Cadmium Reduction (APHA 1999)
Orthophosphate (PO43-) Soil
Effluent
9G2 Acid extractable phosphate 1:200 soil/0.005M H2SO4 at 25°C (Rayment and Higginson 1992) and measure using 4500-P C Vanadomolybdophosphoric Acid Colourmetric method (APHA 1999) 4500-P F Automated Ascorbic Acid Reduction (APHA 1999)
Total Phosphorus (TP) Soil only
Digestion of soil using 4500-P F Automated Ascorbic Acid Reduction (APHA 1999)
23
Table 2.1 Analytical methods – soil and effluent (continued) Total Organic Carbon (TO)C Effluent
Combustion Method (APHA 1999) TOC Analyser Schimadzu TC500A
Sodium Absorption Ratio (SAR) Effluent
SAR = Sodium concentration Sq Root
Organic Matter (%OM) Soil oxidised with 50% H2O2 and heated to 1300°C to burn organic matter. Weight loss difference equal to organic matter content
Cation Exchange Capacity (CEC) Ammonium selective electrode method (Borden and Giese 2001) Ammonia Standards made as per 4500-NH3 E (APHA
1999)
Effective Cation Exchange Capacity (ECEC)
ECEC = exchangeable cations + exchangeable acidity = (Ca + Mg + Na + K) + (Al + H)
Exchangeable Cations (Al, Fe, Mg, Na, Ca and K)
Measured using Varian AA6 Flame Atomic Absorption Spectrophotometer. Acetylene flame used to measure Fe, propane used to measure Na and K, and nitrous oxide used to measure Ca, Mg and Al
Exchangeable Sodium Percentage (ESP)
ESP = (100 x Exchangeable Na+)/ECEC
Soil Mineralogy (Clay type) Samples prepared using method developed by Bish and Post (1989) Mineralogy determined via X-ray diffraction using Phillips PW1050/25 vertical goniometer, with a graphite diffracted beam monochromator
Particle Size Distribution: Percent Clay (%C), Silt (%Si) and Sand (%S)
Hydometer method using sample pre-treatment. Determined from Soil mineralogy fractions (%S = % Quartz; %C = ∑% Clay fractions eg. %Kaolinite, %Illite, %Smectite) measured using X-ray Diffraction
25
CHAPTER 3.0
ON-SITE WASTEWATER TREATMENT
3.1 Introduction
In non-sewered urban and rural residential developments, domestic wastewater is
usually treated and dispersed on-site. The safe dispersal of final effluent from an on-
site wastewater treatment system is of crucial importance. The process adopted can
have far reaching consequences including public health, environmental, social and
legal ramifications. Numerous cases of system failure have been reported over the
past years, increasing the concerns of regulatory authorities that on-site systems are
not providing adequate treatment of domestic wastewater. As an example, Geary and
Gardiner (1998), Martens and Geary (1999), Carroll and Goonetilleke (2004) have
raised concerns about the fact that inadequately treated effluent seepage into surface
and groundwater is leading to environmental and public health impacts. Several local
government authorities such as Maroochy Shire Council (Jelliffe 1995a), Coffs
Harbour City Council (Jelliffe 1995b), Sorell Shire Council (Geary et al 1999),
Brisbane City Council (Dawes et al 2000), Logan City Council (Goonetilleke et al
2000) have conducted studies that confirm these concerns.
Most domestic on-site systems are “truly” dispersal systems where wastewater is
partially treated and then dispersed into the soil for further purification. Soils are
used as a simple filter or assimilation system, where its sorption capacity is used to
attract and hold nutrients, while the treated effluent percolates away from the site.
Treatment also occurs within the soil dispersal area through removal (filtration of
suspended solids or sorption of phosphorus), transformation (nitrification of
ammonium or biodegradation of organic matter), destruction processes (die-off of
bacteria or inactivation of virus) and plant uptake by transpiration. The soil dispersal
area relies solely on the natural biogeochemical processes to assimilate various
wastewater pollutants.
26
This chapter provides a review of the common forms of on-site wastewater
treatment systems that are currently used for the treatment of domestic wastewater in
Australia in order to provide a comprehensive understanding of the processes
involved in effluent treatment and dispersal. The issues and concerns dealing with
system failure are reviewed, including a discussion on the transport and fate of the
major pollutants of concern, including nutrients and salts. The resultant hazards
arising from the inadequate treatment of wastewater are also described.
Identification of soil processes and properties that are crucial in the effluent
treatment process and are sensitive to changes in other soil functions are detailed.
The extent to which soil mineralogy, site drainage and landscape features influence
effluent treatment and dispersal processes are reviewed.
3.2 On-site Wastewater Treatment Systems
The need for on-site wastewater treatment systems is increasing at a significant rate
due to new developments in urban and rural residential areas which do not have
access to centralised treatment plants and sewer systems. In the past, on-site systems
were typically installed as temporary systems until centralised treatment systems
could be implemented. However, this situation has not changed with on-site
treatment systems becoming a permanent feature in most semi-urban areas. In many
cases, centralised systems are neither cost effective, nor sustainable due to a variety
of factors such as sparse population, rugged topography and limited water supply. In
these situations on-site systems can and should be considered as long term solutions
(USEPA 1997). Approximately 25% of all homes in the United States are connected
to on-site treatment systems (Loomis et al 2001, Siegrist 2001), and this number is
ever increasing. This trend is also evident in Australia where currently 16% of
households employ on-site wastewater treatment systems (O'Keefe 2001).
In general terms, on-site treatment systems consist of three primary components; (1)
the treatment unit; (2) the dispersal field; and (3) the soil (USEPA 2002). Typically,
these systems can be broadly classified as either anaerobic systems or aerobic
systems followed by a dispersal system, either subsurface or surface. The most
common form of anaerobic treatment system consists of a septic tank-soil absorption
27
system. In reality, for the system to provide acceptable treatment, the soil absorption
area needs to be aerobic (unsaturated zone). A typical system is shown in Figure 3.1.
A septic tank together with a subsurface effluent dispersal system can be defined as a
conventional wastewater treatment system. Due to its low cost and low operation and
maintenance requirements, it is the most economical and popular system in use.
Various other effluent dispersal options for septic tanks can also be utilised, such as
mounds and evapotranspiration systems, where typical subsurface soil absorption
systems are not suitable. However, Aerobic Wastewater Treatment Systems (AWTS)
employing surface irrigation for final treatment and dispersal of effluent are steadily
becoming more popular, mainly due to their improved treatment performance. Sand
filters have also had significant success in providing effluent polishing before
ultimate dispersal.
Figure 3.1 Common on-site wastewater treatment systems used in Australia. (adapted from AS/NZS1547: 2000)
3.2.1 Septic Systems
3.2.1.1 Overview The conventional septic system has two major components: an anaerobic chamber
which is used to provide partial treatment of raw sewage, and the dispersal field,
Septic tank
Distribution box
Gravel or crushed rock fill
Effluent disposal
Unexcavated area Effluent dispersal area
28
where final treatment and dispersal of effluent discharged from the anaerobic
chamber takes place (Figure 3.1). Both are generally installed below ground.
Dispersal fields are typically subsurface trenches filled with aggregate, from where
effluent is leached to the unsaturated soil underneath.
Figure 3.2 Typical single chamber septic tank, showing the developed scum, clear
liquid and sludge layers.
A septic tank can be defined as a watertight receptacle designed and constructed to
be a combined settling and flotation tank that detains the wastewater discharged from
the household for an expected minimum period of 24 hours. It acts as an unmixed
anaerobic digester providing digestion of organic matter, as a sludge storage tank and
allows clarified liquid to be discharged for further treatment (Goonetilleke et al
1999). Settleable solids and partially decomposed sludge known as septage settle to
the bottom of the tank whilst a scum of lightweight material rises to the top. This
layer of scum, comprising of lightweight material, including fats and greases, rises to
the surface of the clarified liquid (USEPA 1980). Regular removal of the
accumulated septage, approximately every three to five years is necessary to ensure
that the system continues to function appropriately. Figure 3.2 illustrates a typical
septic tank used in Queensland and the various zones developed within the treatment
chamber.
Sludge
Scum
Supernatant
Effluent
Inspection Ports
Influent
29
In a review of septic tank performance data from seven different countries, Cotton et
al (1996) found that septic tanks in warmer climates provide far greater treatment
performance in terms of BOD and suspended solids removal when compared to those
in temperate climates. They have attributed this to enhanced kinetics of BOD and
suspended solids removal due to the relatively higher atmospheric temperatures. The
removal of suspended solids in temperate climates was found to be due only to
sedimentation, whereas in the case of tropical climates, mineralisation of the volatile
fractions was also found to play a major role. Removal rates are also dependent on
the sizing and design features of the tank such as overall dimensions which define
hydraulic retention time, compartmentation of the tank and the inclusion of
appurtenances such as various inlet and outlet devices (Bounds 1997, Caldwell
Connell 1986, Cotteral and Norris 1969, Fimmel and Troyan 1981, Otis et al 1974,
Troyan et al 1981).
Considering the above, it is not surprising that the effluent characteristics from septic
tanks are highly variable covering a broad range for all the parameters. This is
evident in results from several researchers, such as Laak (1986) who found that the
passive anaerobic treatment of septic tank wastewater results in the removal of
approximately 40-60% BOD, 50-70% SS, 10-20% Total Nitrogen, less than 30%
Total Phosphorus.
3.2.1.2 Operation and Maintenance The proper operation and maintenance of septic tanks is crucial if they are to
continually provide adequate sewage treatment. Hydraulic retention times are critical
parameters that need to be considered in septic tank designs. The hydraulic retention
time dictates the treatment process, defining how efficient the septic tank is at
settling out suspended solids. The longer the retention time, the more time suspended
solids have for settling, thus improving effluent quality. This provides a larger clear
water volume and accumulation of sludge, which in turn demands a large septic tank
capacity (Goonetilleke et al 1999). Shorter retention times provide less time for
suspended solids to settle, reducing the volume of clear water. This increases the
level of sludge and scum accumulation in the tank, which in turn increases the level
of solids in the effluent which is discharged to the soil absorption trench, thus
30
accelerating the clogging of the trench. There is general consensus that the
most appropriate retention time suitable for adequate treatment performance is 24
hours (USEPA 1980, Bounds 1997, AS/NZS 1547: 2000).
Although septic tank systems are capable of providing suitable treatment of effluent,
failure is common. One of the most significant issues related to on-site systems and
their poor performance record is that regular maintenance is not undertaken. Recent
performance evaluations of on-site sewage treatment systems conducted in
Queensland, Australia by Goonetilleke et al (2000a, b) and Goonetilleke et al (2002),
showed that the failure rates of septic systems are directly related to poor
maintenance regimes. Goonetilleke et al (2000a, b) found that 70% of septic systems
investigated in the Brisbane and Logan regions exhibited poor treatment performance
as sludge was not regularly removed. This poor treatment performance resulted in
many systems failing by hydraulic overloading in the soil dispersal area (Dawes et al
2000). It was evident that householders lack knowledge regarding appropriate
maintenance and management of on-site wastewater treatment systems. In order to
overcome the common “out of sight, out of mind” attitude, more effective education
in relation to on-site wastewater treatment system maintenance and management,
needs to be undertaken (Allee et al 2001).
3.2.2 Aerobic Systems
3.2.2.1 Overview As the title implies, the breakdown of pollutants in the wastewater is carried out in an
aerobic environment. The aerobic environment is generally provided by mechanical
means (Bailey and Wallman 1971). Aerobic biological treatment processes can be
employed to remove substantial amounts of BOD and suspended solids that are not
removed by simple sedimentation such as in a septic tank. An additional feature of
the process is the nitrification of ammonia in the waste under appropriate conditions
and the significant reduction of pathogenic organisms (Hanna at al 1995). The
common features of Aerobic Wastewater Treatment Systems (AWTS) are oxygen
transfer to the wastewater, intimate contact between micro-organisms and waste and
solids separation and removal (USEPA 1980). Since the early 1980s these systems
have been rapidly gaining in popularity (Martin 1999).
31
There are two generic types of systems that are in common use. The first type is
where the entire treatment process is aerobic. This generally includes suspended
growth and fixed growth systems. The second type of system is where an anaerobic
chamber is employed as an initial pre-treatment process. An anaerobic process
always precedes the aerobic treatment process. There are a large number of
proprietary systems available within this category. The anaerobic and the aerobic
processes can take place in different compartments within the same tank or
alternately, the aerobic process can be separate such as a sand filter. Each system has
its own advantages and limitations, but in general, the same common features of
oxygen transfer to the wastewater, contact between microorganisms and wastes, and
solids separation and removal are utilised by each system (USEPA 2002).
A major advantage of AWTS compared to septic tanks is that the effluent has a much
lower clogging effect on the soil effluent dispersal area, because a significant
component of the suspended organic matter is oxidised to harmless by-products. The
main disadvantages of the systems are:
• higher operating costs;
• greater susceptibility to shock loadings due to episodic hydraulic or organic
loading or intermittent usage;
• sludge bulking;
• periodic solids discharges and the variation in effluent quality as a result of
such treatment upsets; and,
• greater volume and dry mass of sludge produced when compared to
anaerobic systems
(Geary and Gardner 1997, Otis et al 1974, USEPA 1980).
Also as in the case of septic tanks, some organic materials in the waste stream will
resist oxidation. Therefore, there is a gradual build-up of sludge that must be
removed to prevent periodic discharge of sludge particles with the effluent.
3.2.2.2 Operation and Maintenance An important issue relating to the operation of aerobic wastewater treatment systems,
as compared to septic tanks, is the mechanical devices employed to achieve aeration
32
and recycling of biomass. These can have implications on the performance of
AWTS, particularly through the malfunction of mechanical components or improper
maintenance and design procedures (Hanna et al 1995, Khalife and Dharmappa 1996,
Beavers et al 1999). Generally, AWTS manufacturers are required to undertake
maintenance associated with mechanical malfunctions and equipment to ensure the
system is operating correctly (in Australia this occurs approximately every three
months). However, as with septic tanks, regular routine maintenance is left to the
householder, who, in most cases, is not experienced to undertake the maintenance
required.
Despite the technically sound basis used in the development of these systems, their
field performance has not always lived up to expectations. Numerous evaluation
studies have been undertaken over the years in Australia and overseas on these
systems. The results have shown that a significant number of systems generally do
not perform to stipulated standards (Beavers 1999, Khalife 1995, Kayaalp 1997,
Kinhill 1997).
3.2.3 Other On-site Systems
Although septic tank and AWTS systems are the most common system types utilised
in Australia, other alternative systems are also available. A number of variations to
the conventional systems have been developed based on the method in which
effluent is distributed or dosed along with a range of alternative treatment and
dispersal systems. These include additional treatment after the septic tank such as
sand mounds, sand filters, wetlands and a variety of alternative dispersal methods
such as mounds and surface irrigation systems.
There has been increased use of waterless toilets either composting or incinerating in
remote, non-residential areas where access to water and wastewater facilities is
costly. Composting toilets have no water added to the system, with aerobic
decomposition and odour control facilitated by an electric fan assisting aeration.
These system types are generally utilised for specialised purposes, including
33
achieving improved effluent quality compared to current systems; reduced water
usage, or to allow suitable recycling of treated wastewater.
3.2.4 Summary of Key Research Literature Findings
The review of current research literature has indicated that several alternative
wastewater treatment systems are available for the treatment and dispersal of
domestic wastewater. However, the most common system types currently utilised in
Australia are the septic and aerobic wastewater treatment systems (AWTS) with
subsurface dispersal areas. Although these systems are capable of providing suitable
treatment of wastewater, a number of issues have been discussed in the reviewed
literature that can influence the overall treatment performance. The two most
common issues involve appropriate operation and maintenance and effluent quality.
For any on-site wastewater treatment system, undertaking regular maintenance is
essential in order to ensure acceptable treatment of effluent is obtained prior to
discharging to the dispersal field. Improper maintenance results in poor effluent
quality that can eventually lead to failure of the dispersal field, and subsequent
environmental and public health impacts.
3.3 Subsurface Effluent Dispersal Subsurface wastewater treatment and dispersal refers to the application of partially
treated wastewater to a subsurface environment, with infiltration and percolation
through the vadose zone (unsaturated zone), and finally into the saturated soil and
underlying groundwater (Siegrist et al 2000). The vadose zone is the final buffer
between groundwater and the contaminants contained in effluent applied to the soil.
The depth of the soil vadose zone to groundwater can affect hydraulic function, and
in turn purification, by influencing the soil water content, aeration status, media
surface area as well as hydraulic retention time (Van Cuyk et al 2001). Typically, a
depth of at least 1m is regarded as appropriate for sufficient treatment of effluent
(Siegrist et al 2000, USEPA 2002). Effective unsaturated soil depths ranging from
0.6m to 2m have been quoted in research studies (Johnson and Atwater 1988, Mote
et al 1995, Siegrist and Van Cuyk 2001). In a detailed twelve month study on two
septic tanks with absorption trenches, O’Sulleabhain at al (2004) found the majority
34
of chemical and biological treatment occurred within 0.3m of the bottom of the
trenches.
Effluent leaving the treatment chamber is most commonly dispersed in subsurface
trenches or beds. Subsurface dispersal is the only suitable method for the dispersal of
septic tank effluent. The effluent from a septic tank has a high concentration of BOD,
nutrients and faecal microorganisms, thus making it unsuitable for discharge into
open water or the land surface. Figure 3.3 shows the major components and
pathways involved in the subsurface dispersal process.
For the purposes of this study, the subsurface dispersal area boundaries include the
inlet to the soil absorption unit through the underlying vadose zone which varies in
thickness from site to site and into the lower limit of the saturated zone. This is based
on that in a given environmental setting (soil type, temperature) conditions are such
that the key treatment processes occur at a rate and to an extent that advanced
treatment is reliably achieved before groundwater recharge occurs. Depending on
local conditions the saturated zone and groundwater flow may provide some
treatment of wastewater pollutants and mitigate environmental and public health
effects.
The subsurface dispersal area is essentially the ‘last line of defence’ to prevent the
contamination of water sources by sewage. As Goonetilleke et al (1999), based on a
review of a large number of published research studies have noted, poor treatment
performance of septic tanks is more the rule than the exception. They noted that the
subsurface dispersal area plays a more important role than what is generally
envisaged.
The ability of the soil to treat effluent is an important consideration environmentally
in view of the fact that septic tanks do not provide effluent of a quality suitable for
direct surface dispersal. However the continuous application of effluent causes a
clogging mat to form at the infiltrative surfaces of the absorption area. This has
beneficial aspects, but it can substantially reduce the infiltrative rate through the soil.
Fortunately, the clogging mat seldom seals the infiltrative surface completely.
Generally an equilibrium condition is reached where effluent will percolate through
35
at an almost constant rate. This will vary for different soil characteristics (Bouma
1974, Bouma et al 1972, Siegrist 1987, Beal et al 2004).
Figure 3.3 Major components and pathways in subsurface effluent dispersal (adapted from Bouma et al 1972)
Trenches or beds are the most commonly employed systems in the subsurface
dispersal of effluent. The typical arrangement of these systems is shown in Figures
3.4 and 3.5. They are acceptable in situations where the soils are moderately
permeable and remain unsaturated for a reasonable depth below the system. Trenches
are dependent on the upper soil horizons for treatment. Kommalapati and Noman
(1999) concluded from their literature review that permeable surface layers above
clayey subsoils play an important role in effluent movement from trenches. They also
suggested that lateral flow above the restrictive layers and probable macropore flow
through them are the primary factors for successful operation of septic systems.
The bed and sidewalls of the excavation act as infiltrative surfaces. At the initial
stages of commissioning a subsurface dispersal field, most of the effluent would
infiltrate through the soil. However with time and as the clogging layer develops,
ponding of effluent will take place. Losses due to evapo-transpiration would still take
place, but there would be a net collection of effluent in the absorption bed. At this
stage, the sidewalls would also contribute to the infiltration process (Bouma et al
1972, Caldwell Connell 1986, USEPA 2002). However in the case of a bed, the
Stream/lake
evapotranspiration
Soil layers
Groundwater mound
Purification
Subsurface effluentdisposal area
Septictank
36
proportion of the side wall area will be relatively small and may not play a
significant role. This is one of the main advantages in the use of trenches over beds.
Figure 3.4 Typical trench system used for effluent treatment and ultimate dispersal
(adapted from AS/NZS 1547:2000)
Figure 3.5 Typical bed system used for effluent treatment and ultimate dispersal (adapted from AS/NZS 1547:2000)
There are other advantages in using trenches. In the case of sloping ground
conditions, trenches can be laid following ground contours. There is less likelihood
of damage to the infiltrative surface by construction machinery as these can straddle
the trench rather than having to move on the surface.
Several other subsurface system alternatives are available for use in areas where the
typical trench and beds systems are considered inappropriate for providing adequate
treatment and dispersal of discharged effluent due to restrictions in site and soil
characteristics. These include:
• Mound systems
37
Mound Systems are designed to overcome problems of treating and dispersing
partially treated effluent in areas where the soil has a relatively low permeability or
high ground water table, or where slowly permeable subsoils or subsoils overlying
cracked bedrock exist (Bouma et al 1972, Magdoff et al 1974a,b , Bouma et al 1974).
The general mound system consists of an above grade soil adsorption system which
relies on selected sand fill and top soil layers to purify the discharged effluent
(Converse and Tyler 1984, 1987, 1998, USEPA 2002). Mound systems are not
widely used in Australia due to cost considerations and the need to provide a
pressure distribution system.
• Evapotranspiration systems
Evapotranspiration systems utilise the natural climatic conditions to evaporate
effluent from shallow trenches, combined with transpiration through the use of
vegetation specifically planted to utilise the available water and nutrients. However,
these systems are directly related to the climatic conditions. Evapotranspiration
systems are receiving increasing recognition in Australia, primarily due to its
favourable climatic conditions which are necessary for the treatment and dispersal of
effluent.
3.3.1 Siting and Design
It is only recently in Australia that factors relating to the soil and site conditions have
become important with regard to system siting and design. Previously, designs were
reliant on simple percolation tests to evaluate site suitability. There is a continuing
dependency on practices found to be inadequate in assessing soil dispersal area
behaviour, particularly the use of the percolation test (van der Graaff 1996).
Researchers have shown that the percolation rate can be misleading and does not
directly measure any soil characteristic that could be used in the design of the
subsurface dispersal system (Healy and Laak 1974, Gunn 1988). The current
standard, AS/NZS 1547:2000 has noted the limitation of the standard clean water
percolation test, which has been used for many years as the sole design approach.
Consequently, the use of site and soil related factors in the siting and design process
38
are gaining significant importance. The various soil and site factors that play an
important role in selecting an appropriate system include:
• topography, such as site elevation and slope;
• subsurface conditions, including soil characteristics and profile, groundwater
pathways, water table depth and variability and the depth to the limiting
restrictive soil layer;
• area available for treatment and dispersal;
• climatic conditions, such as rainfall and temperature;
• flooding frequency; and
• presence, location and distance to specific topographic features, such as
waterways or wells.
(Geary 1987, USEPA 2002, Siegrist et al 2000, Dawes and Goonetilleke 2003)
In order for treatment and dispersal systems to accommodate the long term
acceptance of effluent, it is crucial that these factors are considered in the design and
siting. The importance of soil morphology and physical/chemical properties in the
siting and design of on-site systems has been recognised in the USA for the past 20
years (Siegrist et al 2000).
3.3.2 Regulatory Framework
Local authorities administer domestic wastewater regulations in Australia, although
policy advice and the approval of treatment and dispersal systems is the
responsibility of State departments. Queensland has incorporated AS/NZS 1547:2000
into the On-site Sewerage Code (2003) across the state as the regulation for
performance requirements and criteria for on-site system management. Some local
authorities have developed their own guidelines (local laws) and requirements
resulting in wide variations in approach to site assessment and system design. Some
have acknowledged the limitations of sewage treatment and effluent dispersal
systems and prepared detailed policies on domestic wastewater dispersal, whilst the
majority have not adequately addressed the situation. While local knowledge is
important, the poor understanding which exists regarding soils and their effluent
39
renovation capabilities and the lack of standardised procedures has led to many
inconsistencies in design, system sizing, and performance. Martens and Geary (1999)
note that one of the primary reasons for this lack of guidance is that there has been
very limited research undertaken on on-site systems in Australia and in the
characterisation of Australian soils.
Significant advances in the past ten years with release of revised guidelines and
codes of practice in South Australia (South Australian Health Commission 1995),
Victoria (Environmental Protection Agency 1996), Tasmania (Australian Institute of
Environmental Health 1998), New South Wales (Department of Local Government
1998) and Queensland (Department of Natural Resources 2003) has led to a more
rigorous evaluation of ground conditions. Both AS/NZS 1547:2000 and the more
recent state government guidelines have moved away from the prescriptive approach
to site assessment and system design, and have adopted the performance-based
approach.
In AS/NZS 1547:2000 and the Queensland On-site Sewerage Code (2003) the
standard clean water percolation test, has been replaced by design loading rates
(DLR), which are based on soil texture and structure, indicative permeability and
indicative drainage class. However limiting soil factors such as shallow soil depth,
highly dispersal soils, or reactive clays may require special design of the land
application system and special consideration for what is an appropriate design
loading rate. This will rely more on the knowledge and professional judgement of
the site evaluator/designer. This should ensure that more appropriate loading rates for
specific soil conditions can be determined and adjusted in the light of local
experience gained from long term performance of dispersal systems. These changes
bring AS1547:2000 into line with approaches already successfully adopted in New
Zealand and the United States (Whitehead and Geary 2000).
3.3.3 Clogging Mat Formation In the case of subsurface dispersal of sewage effluent, a clogging mat will inevitably
form at the soil-liquid interface. An understanding of the mechanisms of clogging
40
mat formation, its behaviour and implications is important in evaluating soil
dispersal area performance. Based on a literature review, Siegrist (1986) has
summarised the environmental factors which influence clogging mat formation. In
relation to important soil characteristics:
• Soil morphology – this includes soil organic matter, porosity of the soil and the
initial saturated hydraulic conductivity of the soil (Laak 1970).
• Soil temperature – research studies have noted that low temperature could either
inhibit or stimulate soil clogging depending on the absence or the presence of
suspended solids in the effluent (De Vries 1972, Gupta and Swartzendruber 1962,
Simons and Magdoff 1979).
• Soil moisture content – this has an indirect impact as high moisture, results in
low air filled pores, which will accelerate clogging (Jones and Taylor 1965,
Simons and Magdoff 1979).
• Soil aeration status – anaerobic conditions have been found to accelerate
clogging mat formation (Thomas and Phillips 1979, Simons and Magdoff 1979).
The formation of a clogging mat in soil dispersal areas has attracted considerable
research over the years. Its adverse impacts leading to the failure of soil dispersal
areas have been well documented. The clogging mat is composed of microorganisms
living off the organic material percolating through the soil. The formation of the
clogging mat occurs when bacterial growth and their by-products, and accumulated
solids reduce soil pore diameters, resulting in the reduction of the soil infiltration
capacity. Soil absorption systems often fail hydraulically due to clogging and
subsequent reduction in infiltration through the soil at the soil-gravel interface
(Kristiansen 1981).
However, even though the formation of the clogging mat is considered a major
problem for the soil dispersal area, it can also be beneficial. The infiltrative capacity
of the clogging mat has been shown to reach an equilibrium state after a period of
time (Otis 1984, Siegrist et al 2000). As such, effluent will still be able to seep
through the layer, but at a much lower rate. The development of this zone can
enhance purification by increasing biogeochemical reactions within the zone, as well
as creating unsaturated conditions beneath it due to the reduced permeability rate
41
below the clogging mat. It also permits greater contact between the effluent and soil
particles as effluent flow is only through the smaller pores.
The occurrence of unsaturated flow is very significant for the filtration of effluent. It
means that only a part of the voids in the soil will be occupied by liquid, which will
move relatively slowly through the smaller pores in a soil material in which aerated
conditions prevail (Bouma et al 1972). Jnad et al (2001) found that the application of
wastewater to soil resulted in increased soil water retention, decreased volume of
pores with large radii, and a decrease in saturated hydraulic conductivity.
It should be noted that the phenomenon of soil filtration of the unsaturated flow
beneath the biomat does not apply to nitrogen removal. The nitrification process
taking place in the unsaturated region below the clogging mat will produce nitrates,
which will not be removed by the soil particles. It can percolate down to the
groundwater leading to groundwater pollution (Johnson and Atwater 1988). In theory
the stronger the clogging mat, the greater the purification of the effluent. Van Cuyk
et al (2001) noted that in most wastewater soil infiltration systems, clogging zone
genesis must occur to a balanced extent to foster enhanced purification before
discharge to groundwater. They also found in large scale three dimensional lysimeter
tests that if clogging zone development is retarded or absent altogether, for example
due to the application of highly pretreated effluent, removal of pathogens and other
pollutants of concern may be less than predicted or desired. Conversely, if soil
clogging is too excessive due to the application of high strength effluents, clogging
can be detrimental by causing hydraulic dysfunction, soil anaerobiosis and reduced
purification.
What is important to realise is that the formation of a clogging mat is inevitable in
the case of a soil dispersal area. Under these circumstances, the failure of a soil
dispersal area can in fact be attributed to the hydraulic impedance posed by the
clogging mat to effluent infiltration. Due to the formation of the clogging mat, the
capacity to load the soil with effluent is no longer governed by the soil’s hydraulic
conductivity as measured by the percolation test, but rather by the infiltration rate
through the clogged zone (Miller and Wolf 1975, Siegrist and Van Cuyk 2001).
Bouma et al (1972) noted the remarkable similarity in the hydraulic resistance
42
between systems of different ages but located on similar soil types. This means
that in the design of soil dispersal areas, a relatively constant infiltration parameter
for a particular soil type could be used independent of the soil permeability.
3.3.4 Summary of Key Research Literature Findings
The dispersal area is one of the most important components in the on-site wastewater
treatment train. Consequently, it is essential that the proposed dispersal area is
adequately assessed to ensure that proper treatment and dispersal is achieved without
causing environmental and public health impacts. However, although the subsurface
dispersal area is generally an acceptable means of providing suitable treatment and
dispersal of discharged effluent, the review of research literature indicated that
several issues can significantly influence overall performance. The main issues
involve effluent quality from the on-site system itself. Poor quality effluent can cause
clogging of the soil pores, resulting in hydraulic failure of the dispersal field.
Therefore, in order to ensure that proper treatment and dispersal of discharged
effluent is achieved, it is essential that these issues are adequately addressed.
In determining site suitability for on-site dispersal areas, understanding the soil’s
ability to accept, treat and disperse the discharged effluent is crucial. Due to its
heterogeneous nature, the assessment of a single soil parameter cannot provide a
comprehensive overview of its suitability for a particular purpose (Diack and Stott
2001). As an example, the simple soil percolation test traditionally used as a means
of assessment for effluent dispersal, will indicate the soil’s ability to disperse effluent,
but will not show if the effluent will undergo sufficient treatment prior to percolating
into the groundwater. Phillips (2002) supports this finding by concluding that
impacts of wastewater on the receiving environment cannot be assessed based on a
single chemical component.
Permeable surface layers play an important role in controlling effluent movement
through soil. For successful operation of effluent dispersal systems, lateral flow
above restrictive layers and macropore flow is essential. There is continuing debate
about the effective unsaturated soil depth required to provide sufficient treatment
43
before effluent leaves the site. In some cases the restrictive soil layer may protect
groundwater from the vertical movement of pollutants or may cause hydraulic failure.
3.4 Performance of On-site Systems The performance of on-site wastewater treatment systems imposes several critical
issues on the surrounding environment. Improper system siting, design and operation
can result in biological and chemical contamination of water sources (Hagedorn et al
1981, Harman et al 1996, Wilhelm et al 1996). The performance of an on-site
wastewater system is not only related to the level of treatment produced by the
treatment unit (septic tanks or aerobic treatment systems), but is also dependent on
the capability of the soil to treat the discharged effluent percolating through the soil
matrix. The soil is considered suitable if it has the capacity to percolate the incoming
effluent load and provide the necessary treatment to meet public health, ground and
surface water standards, and protect the environment.
3.4.1 Surrounding Soil
The soil surrounding the dispersal area plays a crucial role in the further treatment of
the effluent. Therefore the subsurface characteristics of the dispersal area are among
the most important parameters governing the performance of the treatment process.
Under suitable conditions, the soil is an excellent treatment medium and the effluent
requires minimal pretreatment (USEPA 2002). Soil material can be an effective filter,
both with respect to faecal micro-organisms and to chemical compounds, where
conditions are suitable. Clayey soils are generally better suited for effluent treatment
and dispersal due to the presence of finer pores providing more contact surface area
for percolating effluent. Both, the amount and type of clay present has a major
influence on the ability of the soil to treat the effluent. Generally, the purification
potential increases as the clay content increases, but the probability of clogging is
also increased (Bouma 1974). The amount of clay is significant as higher percentages
can be impermeable, preventing vertical infiltration of effluent. As the effluent
percolates through the soil, the processes of sorption, filtration and oxidation will
purify it (Bouma et al 1972, Ellis 1973; Miller and Wolf 1975, Mote et al 1995,
44
Siegrist and Van Cuyk 2001). Bioprocesses also influence effluent treatment in
the form of biotransformation (ammonium to nitrate), biodegradation (mineralisation
of organic matter), and predation/inactivation (die-off of bacteria or virus).
Sorption processes are important for effluent treatment. The process of sorption
refers to the binding of one substance to another. This occurs through one of three
mechanisms:
1. Absorption: a substance is totally taken in by another by molecular or
chemical attraction.
2. Adsorption: a substance is bound to the surface of another.
3. Persorption: adsorption of substances in pores only slightly wider than the
diameter of the adsorbed molecule.
The sorption processes in soil are beneficial for the effective treatment of effluent,
provided the soil profile allows adequate transmission of effluent. The large surface
area within the soil pore space is chemically and electrostatistically active and
possesses a great capacity for the sorption of suspended solids and dissolved
substances (Miller and Wolf 1975). Soil adsorption ability is reliant on the type of
soil and its cation exchange capacity (CEC), which in turn is dependent on the
amount and type of clay present in the soil and the amount of organic matter.
The physical properties of the soil matrix provide an effective medium for filtering
out solid material from wastewater. The mineral skeleton of the soil and the
subsequent crust formation acts as an efficient physical filter. This not only helps to
remove suspended solids, but also serves to retain micro-organisms and facilitate the
biological treatment of dissolved and suspended organic matter (Miller and Wolf
1975, Siegrist and Van Cuyk 2001).
Effluent contains a variety of organic compounds collectively expressed in terms of
the biochemical oxygen demand, chemical oxygen demand or the total organic
carbon content. Effluent renovation requires oxygen not only for the oxidation of
carbonaceous materials, but also for the nitrification of organic and ammonia
nitrogen. In the case of a well aerated soil, this oxygen requirement is provided via
45
diffuse soil pores or dissolved oxygen percolating through the zone. Therefore as the
effluent slowly percolates through the soil it provides sufficient oxygen for the
bacteria to consume the organic loading (Wilhelm et al 1994a,b). Saturated
conditions limit oxygen supply through the soil thereby restricting aerobic
decomposition of the organic material. Clay soils have a lower permeability and may
remain saturated for longer periods of time allowing them to immobilise components
in the effluent better than sandy soils. At the same time sandy soils, being better
aerated, have greater ability to allow decomposition of organic matter. Sandy soils
are comparatively poorly buffered as they have less charged sites, and nutrient
addition from effluent can quickly alter their physico-chemical state and
consequently limit nutrient uptake (Lott et al 1999).
A soil treatment system is technically simple. However, through a complex array of
interacting natural processes, impurities can be removed and degraded, ultimately
returning the percolating water towards natural purity. The ability of a soil as a filter
is influenced by its capacity to immobilise metals and organic compounds (sorption)
and allow for the breakdown of organic matter by microbial decomposition. These
requirements create a challenge because clay soils have a high sorption capacity but
low permeability and sandy soils have low sorption and high permeability (Bell
1993).
Dawes et al (2000) found that the soil characteristics play an important role in
defining dispersal area behaviour. They have classified the physical and chemical
characteristics of soils suitable for effluent dispersal. This supports research
conducted by USEPA (1997) where critical factors including physical characteristics
such as soil gradation, chemical characteristics such as the presence of various
metallic cations, exchangeable sodium percentage, and biological characteristics
such as the presence of organic matter and micro-organisms, and subsurface
characteristics such as soil depth over the water table or presence of some
impermeable layer and the size of the area available for dispersal were identified.
Many South Eastern Queensland soils have impermeable ‘B’ horizons. When they
occur in an undulating landscape, these can develop perched water tables and form
shallow flow restricting horizons. However, ponding of effluent and subsequent
46
surface flow of pollutants during heavy rainfall events can lead to hydraulic
failure. This does not automatically mean that the system is not performing
adequately. Several researchers have noted the importance of lateral flow for
effective effluent dispersal. Weymann et al (1997) found that in North Carolina, for
soils with restrictive horizons, the permeable surface layers play an important role in
allowing infiltration and lateral flow from the trenches. The presence of a thin layer
of saturation at the A/B horizon interface in surrounding soil and lack of saturation
above the interface suggest that lateral flows above the restrictive layers and perhaps
macropore flow through them are the main contributors for successful operation of
systems. Tyler and Kuns (1997) in a study on Ohio soils noted that although soils
with shallow flow restricting horizons present difficult hydraulic design problems,
these horizons protect the groundwater from vertical movement of pathogens and
nitrate contamination.
Jenssen and Siegrist (1990) determined that a thorough knowledge of
sedimentological properties such as texture, layering, structure, chemical,
mineralogical, weathering and hydrogeological properties such as depth of saturated
zone, hydraulic conductivity of both saturated and unsaturated zone, hydraulic
gradients, flow directions were necessary if the pollutant retention capacity and
effluent migration rate is to be evaluated. They noted that purification processes are
more effective in the unsaturated zone than in the saturated zone. This is
substantiated by the research of Johnson and Atwater (1988), Wilhelm et al (1994a),
Wilhelm et a. (1996) and Siegrist and Van Cuyk (2001). Islam et al (2001) identified
the importance of local hydrogeological conditions such as hydraulic conductivity,
ion exchange capacity, and buffering capacity of the soil in assessing the potential
for groundwater pollution.
Reneau et al (1986) has provided a comprehensive review of treatment achieved by
soil based renovation systems and concluded that removal of pollutants such as
phosphorus and microbial pathogens is adequate as long as travel times through the
soil are of a satisfactorily duration. Travel time is obviously related to the soil depth
and also to the size of soil pores through which wastewater flows (Mote et al 1995).
They also concluded that the effluent after leaving the drain field and entering the
surrounding soil must be sufficiently dispersed among the soils pores to maintain
47
desirable soil moisture status and accommodate the contact time required for
renovation to occur.
3.4.2 Fate and Transport of Pollutants The transport of pollutants from on-site wastewater systems generally occurs via
groundwater flow, due to the use of soil dispersal areas for the final treatment and
ultimate dispersal medium for discharged effluent. The processes and mechanisms
that the soil uses to renovate effluent can achieve a relatively high level of
purification, but does not ensure the total removal of these pollutants. It is inevitable
that a certain fraction of nutrients and pathogens will reach groundwater, travelling
along available pathways to the receiving water body. However, if the soil dispersal
area fails, surfacing of effluent may occur, with fate and transportation of nutrients
and pathogens reliant on surface and climatic conditions. Surface runoff will then
inevitably be a major transportation process for pollutants.
Organic carbon and phosphorus are removed from the wastewater by retention in the
surrounding soil. In well aerated soils, most of the reduced components are
aerobically oxidized rather than retained, but retention plays an important part in
poorly aerated systems (Wilhelm et al 1994a). The clogging mat also plays a crucial
role in the removal of pathogens (die-off) and filtration of suspended solids and
organic matter.
A properly functioning soil dispersal area will retain most of the micro-organisms
and phosphorus from the effluent. However the nitrogen after conversion from
ammonia-nitrogen to nitrate-nitrogen will disperse easily through the soil as a
suitable environment for denitrification is generally not available. In these
circumstances dilution by groundwater is the only option available to mitigate the
harmful impacts of nitrogen enrichment (Bouma et al 1972, Kristiansen 1981, Miller
and Wolf 1975, Reneau et al 1989). Practical methods for the large scale removal of
nitrogen are non existent. Removal by denitrification requires an anaerobic
environment and an adequate energy source for the denitrifying bacteria. It is
difficult to provide these conditions in a soil dispersal area.
48
The contamination of shallow aquifers by sewage effluent has been noted by
numerous investigators (Carroll and Goonetilleke 2004, Hagedorn et al 1981,
Harman et al 1996, Hoxley and Dudding 1994, Reddy and Dunn 1984, Viraraghavan
1978). This not only refers to nitrogen contamination, but also to phosphorus and
microbial contamination. Research into the efficiency of pollutant removal in soil
dispersal areas has resulted in sometimes contradictory conclusions. An extensive
study on the purification efficiency of 19 soil absorption systems was undertaken by
Bouma et al (1972). They concluded that septic tank-soil absorption systems, which
exhibited proper hydraulic functioning, also served to purify sewage effluent. The
large population of micro-organisms present in the effluent was reduced to levels
associated with the control soil samples within a few metres of the percolation trench.
Similar observations were also reported by Brown et al (1979), Alhajjar et al (1988),
Cromer (2001) and Dawes and Goonetilleke (2005). Similar results for phosphorus
have been reported by Reneau (1979), Reneau et al (1989), Viraraghavan and
Warnock (1976).
There are numerous studies which report more extensive travel distances for
pathogens (Hagedorn et al 1981). Similarly there is evidence of nutrient travel over
long distances and enrichment of groundwater aquifers despite other research
conclusions to the contrary (DeBorde et a. 1998, Harman et al 1986, Reddy and
Dunn 1984, Robertson et al 1991, Heisig 2000).
According to research literature, the transport of biological and chemical pollutants
over long distances is not necessarily confined to poorly drained soils. This type of
situation also arises in the case of well-drained sandy soils. Whelan and Barrow
(1989a,b) found that effluent nitrogen apart from that removed by vegetation moved
unchanged in concentrations into the groundwater largely in the form of nitrate.
However what is important to note in the study was the soil pH change associated
with the oxidation of ammonia to nitrate. The soil pH below the oxidation zone was
low, but above, it was high. The differences in pH will also impact on the retention
of phosphates in the soil column. Above the zone of oxidation and the presence of
high pH, phosphate is removed by the formation of a phosphate precipitation reaction.
However below it, the most likely reaction for removal is sorption. The primary
sorbing surfaces are calcium carbonate, iron and aluminum hydroxide soil coatings
49
and solid organic carbon in the soil (Harman et al 1996, Sikora & Corey, 1976).
Therefore as Whelan and Barrow (1984a,b) and Gerritse (2000) have noted, soils
have a finite capacity for the sorption of phosphorus. Once this capacity is exceeded,
the phosphorus discharged into the soil dispersal area will not be retained but will
gradually move into the groundwater or to other soil outside the defined field. This
phenomenon will eventuate in any dispersal area after a period of time depending on
the soil physical and chemical characteristics.
Robertson et al (1998) have further refined this concept by concluding that the
oxidation of sewage effluent will lead to acidic conditions only in non-calcareous
soils or beneath old dispersal areas where soil calcium carbonate had been depleted.
They have further noted that the phosphate plume migration velocity in groundwater
appear to be controlled by sorption processes, but the phosphate concentration
present in the plume is strongly controlled by the precipitation reactions that occur in
close proximity to the effluent infiltration pipes. The long-term persistence of
phosphorus in the soil has been confirmed for example by Harman et al (1996),
Robertson et al (1991, 1998) and Viraraghavan and Warnock (1976).
In research on effluent dispersal in Queensland, Hu (1999) indicated that phosphorus
is the most limiting nutrient and that it is important to measure the phosphorus
sorption capacity of soils in the dispersal area. Patterson and Chapman (1998)
showed that where effluent has been irrigated in excess of thirty years, the movement
of phosphorus was restricted by the sorption capacity of the soil and there was very
little lateral movement of phosphorus away from the application area.
The relatively high mobility of phosphorus in sandy soils has also been observed by
other researchers. Robertson et al (1991) investigated septic systems at two single-
family homes located on shallow unconfined sand aquifers. They noted that effluent
discharged into the soil resulted in distinct plumes of polluted groundwater with low
transverse dispersion. Sikora and Corey (1976) have confirmed these observations
noting that phosphorus contamination of groundwater is to be expected primarily in
sandy soils low in organic matter, soils with high water table or shallow soils. This
essentially refers to situations where the sorption capacity of the soil is limited.
50
The capacity of a soil to hold cations is widely used in agricultural land
assessment and is particularly important in irrigated soils (Peverill et al 1999).
Changes in the pool of exchangeable cations occur when effluent passes through the
soil. As cations are removed from soil solution, they are replaced from a pool of
exchangeable cations, which may in turn be replaced by less soluble sources of
nutrients in the soil. Other studies have used total concentrations of elements (Ca,
Mg, Na, K) whereas Dawes and Goonetilleke (2003) used exchangeable cations to
better characterise soil behaviour, as effluent dispersal is similar to natural leaching
processes. Wastewater contains relatively high concentrations of salts and is only
partially removed by primary or secondary treatment. Phillips (2002) found large
amounts of cations (Ca, Mg, K and Na) were transported to depths greater than 60cm
in undisturbed columns (Sodosol and Vertosol soils) under wastewater application.
He highlighted the potential increases in salt load not only within the soil profile, but
also to underlying groundwater or receiving water bodies. High concentration of
sodium in soil is of concern because it can cause a reduction in the soil aggregate
stability (Cameron et al 1997). This in turn can cause a decrease in infiltration rate
and an increase in the risk of runoff.
Geary (2004) and Geary and Pang (2005) found the transport of pollutants from on-
site systems commonly occur via groundwater, but attenuation of pollutants and
pathogens can occur in the groundwater/surface water interface (riparian zones) such
that no public health or environmental threat occurs.
Another process that contributes to inadequate effluent treatment and transport of
pollutants is the formation of a groundwater mound below an effluent dispersal bed
as illustrated in Figure 3.3. This situation can commonly arise in the case of shallow
permeable soil underlain by an impervious layer. These mound shaped zones of
saturation can reduce or even negate the treatment that occurs in the unsaturated soil
zone above. Depending on the soil characteristics and the design of the effluent
dispersal system, the water table beneath the discharge area could rise high enough to
reduce the unsaturated zone depth and the treatment it provides or even short-circuit
entirely. This essentially is the result of the effluent application rate exceeding the
infiltration capacity of the permeable soil layer.
51
3.4.3 Failure Consequences
3.4.3.1 System Failure Proper performance of on-site wastewater dispersal areas depends on the ability of
the soil to treat and transmit wastewater. Failure occurs if either of these functions is
not adequately achieved. Failure refers to the inability of on-site dispersal areas to
provide adequate treatment and dispersal of sewage, resulting in the increased release
of pollutants, causing adverse conditions in the environment, such as eutrophication
of waterways or increased pathogen numbers in recreational water bodies. Hydraulic
overloading, effluent surfacing (as shown in Figure 3.6), subsurface treatment
failures (insufficient treatment) and infrequent pump outs created from the
inadequate siting, design, operation and management of on-site wastewater systems,
are some of the failures that can be associated with these systems. Any treatment
system can be deemed as failing if it allows harmful pollutants to accumulate to
dangerous levels in the receiving environment (Otis et al 1974).
The failure of on-site wastewater treatment systems to treat and disperse wastewater
safely is not due to their inherent shortcomings, as they can be very safe and
effective when properly utilised. Failure results more from the inadequate assessment
of soil characteristics (Dawes and Goonetilleke 2003) along with the misuse of the
system itself (Otis et al 1974). The misuse is primarily a result of the lack of
maintenance by the householder and the lack of proper regulations for controlling
on-site wastewater treatment systems (Butler and Payne 1995).
Figure 3.6 Effluent surfacing, evidence of on-site system failure
52
Water quality and land use is a complex issue, which is currently receiving
considerable research interest. On-site sewage treatment systems play a significant
role in the degradation of water quality (Geary 1992, Geary et al 1999, Martens and
Geary 1999, Whitehead and Geary 2000). The transmission of pollutant loads to the
natural environment is the ultimate consequence. Geary (1992), Geary et al (1999),
Martens and Geary (1999), Goonetilleke et al (1999 and 2000) and Whitehead and
Geary (2000) have discussed a number of performance evaluation studies on on-site
treatment systems undertaken in South Australia, Tasmania, New South Wales and
Queensland. The type of system investigated in these studies was predominantly
septic tanks. The results of these investigations indicated the overall poor
performance of a significant number of these systems with failure rates ranging from
50% to 90%. The major reasons have been attributed to inadequate consideration of
soil characteristics at site in the design of the effluent dispersal system leading to
flawed design and eventual failure.
Table 3.1 shows the more common failure scenarios related to on-site wastewater
treatment systems. Hodges (2001) states that on-site wastewater treatment systems
are capable of adequately treating and dispersing effluent over a 15 to 20 year life
time if they are correctly designed, installed and maintained. Operation and
management of on-site wastewater treatment and dispersal systems has often resulted
in poor performance and dispersal of effluent (Charles et al 2001). This is due in part
to the traditional management and inconsistent monitoring and maintenance
processes whereby numerous assumptions have been applied to the siting, design and
installation of these systems with little consideration given to their long-term
performance (Hoover 1998 and Day 2004).
The failure of on-site sewage treatment systems can lead to serious environmental
and public health impacts. The two issues are interrelated and most environmental
impacts if they become sufficiently severe ultimately result in health impacts. These
impacts arise as a result of surface water and groundwater contamination.
53
Table 3.1 Failure Scenarios associated with on-site wastewater treatment systems (USEPA, 2002)
3.4.3.2 Consequences of Failure Groundwater pollution is the most common form of contamination due to subsurface
effluent dispersal. Groundwater contamination can result due to:
• failure of the soil dispersal area;
• high groundwater levels where the soil cover between the infiltration trench or
bed and the water table is inadequate;
• the dilution provided by the groundwater to the effluent infiltrating through the
soil matrix being inadequate.
In addition to the review of groundwater contamination undertaken by Yates (1985),
a number of studies have related septic system failure to the contamination of water
bodies. Reddy and Dunn (1984) in a three-year study of a catchment containing a
large number of septic systems found significant concentrations of nitrate,
phosphorus and chlorides in the groundwater. Hoxley and Dudding (1994) have
presented the results of two studies undertaken in Benalla, Victoria on groundwater
contamination. In the first, groundwater contamination by septic systems had
resulted in a plume of nitrate interacting with the nearby Broken River. Additionally,
significant bacterial contamination was also detected. In the second investigation, a
shallow aquifer, which acted as a water supply source as well as a repository for
septic tank effluent, was found to have such high pollutant levels that it was no
54
longer fit for human consumption without suitable treatment. In both instances,
the authors have considered and discounted the possibility of microbial
contamination from sources other than septic tanks. In both locations, the soils were
low to moderately draining but interspersed with sand and gravel layers giving rise to
shallow aquifers. Similarly DeWalle and Schaff (1980) evaluated 98 well records
obtained over a 30-year period in a 437 sq km area with a relatively high septic tank
density. A gradual deterioration of groundwater and surface water quality was noted
which could be directly attributed to sewage effluent discharges. In fact the median
coliform values in streams were found to have increased by 70% per year during the
preceding ten years.
Though most of the research emphasis in this regard has been on groundwater
contamination, surface water is not immune to this situation. Quite often surface
water contamination results from the discharge of polluted groundwater. Harris
(1995) investigating the contamination of coastal areas by pathogens and nutrient
concentrations estimated that about 55-85% of the nitrogen entering a septic tank is
available to the groundwater. Furthermore it can be assumed that a significant
percentage of this nitrogen is then discharged to surface water. Harris (1995), based
on a number of studies cited, concluded that on-site wastewater dispersal systems
contribute at least 14% to the nitrogen budget of the inland bays in Delaware, USA.
An extreme situation was Buttermilk Bay in Massachusetts, USA where it was
estimated that 74% of the nitrogen entering the bay resulted from on-site sewage
dispersal areas via groundwater discharge to the bay. Weiskel and Howes (1992)
investigated the level of ammonium nitrification by monitoring 524 on-site
wastewater treatment systems in a 53 ha residential area in the Indian Heights
subbasin located adjacent to Buttermilk Bay, Massachusetts. The effluent dispersal
areas for these systems were a sandy soil with less than 1% clay content. The study
investigated and documented the depth and surface extension of the plume of
contaminants as it flowed away from the effluent dispersal area into the Bay.
Martens and Geary (1999) investigated the small unsewered Scotland Island in
Sydney and found that many existing conventional septic systems were failing
causing very high levels of nutrient and bacterial pollution in local streams. Trench
water quality data of five separate drainfields indicated contaminant saturation with
55
limited potential for existing trenches to renovate effluent prior to discharge to the
local environment. A similar study by Geary et al (1999) at Dodges Ferry, Tasmania
found contaminated groundwater in shallow bores. They concluded that elevated
levels of pollutants were the result of surface and subsurface drainage from the high
density of on-site systems in the upstream catchment area. Carroll and Goonetilleke
(2004) concluded from a study at Jacob’s Well, Queensland that on-site wastewater
treatment systems led to significant contamination of shallow groundwater.
Unfortunately issues such as nutrient enrichment of waterways do not always draw
the attention of the public, the media or the decision-makers as the impacts are long-
term and not always visible. It can be simply relegated as a concern for the
environmental lobby. However waterborne disease outbreaks as a result of microbial
contamination are a completely different situation. Its consequences are always
unpleasant and sometimes fatal. It will invariably result in wide media coverage,
adverse publicity and public concern. This situation arose in early 1997 in New
South Wales when 444 people contacted ‘viral hepatitis A’. This is a highly
infectious viral disease which attacks the cells in the liver. The common symptoms
are anorexia, nausea, fever and jaundice. The disease outbreak was traced to the
consumption of contaminated oysters from Wallis Lake in NSW. The oysters had
been contaminated due to sewage overflows from failed septic systems in the vicinity
of the lake.
In areas with shallow freshwater systems, groundwater may easily be contaminated
from on-site systems which are typically installed close to the water table. This
situation is compounded during periods of high rainfall, which may cause flooding,
resulting in desorption of contaminants due to saturated conditions, which will then
travel through the soil into the groundwater. The transport of pollutants from on-site
systems can also be a significant source of contamination to environmentally
sensitive areas, for example the marine environment, especially in areas of restricted
circulation, such as an estuary or small embayment (Corbett et al 2001, Paul 1997,
Paul 2000).
It is unfortunate that incidents such as the above have to occur to draw the attention
to the serious implications of on-site sewage treatment system failure. This situation
56
is not due to the lack of relevant research and investigations. A direct link
between septic tank density and groundwater contamination was noted by Yates
(1985). Similarly case studies relating on-site sewage dispersal to surface water and
groundwater contamination have been undertaken for example by Bouma et al
(1972), DeBorde et al (1998), Harris (1995), Hoxley and Dudding (1994), Martens
and Warner (1991), Robertson et al.(1991). In contrast, Cromer’s (2001) study at
Lauderdale in Tasmania where 500 homes discharge into a coastal sand aquifer
found that one metre of unsaturated sand beneath the trenches provided an effective
environment to reduce bacteria and nutrients to safe levels.
3.4.4 Summary of Key Research Literature Findings
The reviewed research literature has identified important issues that can significantly
affect the overall performance of on-site wastewater treatment systems. These mostly
involve appropriate assessment of the respective site and soil characteristics which
determine the overall ability of the on-site dispersal area for providing appropriate
treatment. Inadequate assessment can lead to poor performance and eventual failure
of on-site dispersal areas resulting in severe environmental and public health impacts.
The review of research literature enabled understanding of contaminant fate and
transport processes for the major pollutants associated with on-site wastewater
treatment systems, including nutrients, salts and micro-organisms. The mechanisms
that influence the attenuation and removal of these pollutants are generally associated
with the physical and chemical characteristics of the soil medium, including filtration,
adsorption and die off (for micro-organisms). As such, the importance of ensuring
adequate site and soil assessment in order to prevent poor system performance and
the inherent environmental and public health impacts was clearly highlighted
throughout the reviewed literature.
3.5 Soil and Site Conditions
57
Researchers such as Brouwer and Bugeja (1983), Geary and Gardner (1996),
Whitehead and Geary (2000) and van de Graaff and Brouwer (1999) have identified
the serious lack of research information and in-depth knowledge of effluent
renovation processes taking place within the soil matrix and their relationship to site
conditions. This includes establishing the nature and extent of the biological,
chemical and physical processes taking place and an understanding of their
interactions. Soil is regarded as an excellent medium for the renovation of biological
and inorganic pollutants in effluent. However the ability of the soil to purify effluent
is not completely understood. The sub-surface characteristics of the dispersal area are
among the most important parameters governing the performance of effluent
treatment processes.
The soil processes and reactions ultimately determine pollutant fate, transport and
impact (O’Connor et al 2005). The processes and reactions can be categorised as
retention, transformation and movement. Bastian (2005) identified that
understanding soil reactions with pollutants represent the key to sustainable land
application waste systems.
3.5.1 Soil Processes
Soils are the product of their environment and any long term change of physical,
chemical or biological status, induced by large increase in water throughput and
nutrient/organic carbon addition (wastewater application) could give rise to a “new”
soil with altered capacity to cope with continued effluent application
(Speir 2002). Soil processes critical to on-site dispersal areas include the ability:
to accept, hold and release nutrients and other chemical constituents;
to accept, hold and release water to plants, water bodies and the subsoil;
to maintain soil biotic habitats; and
to resist soil degradation.
3.5.1.1 Chemical Mechanisms It is essential to understand the chemical processes, which affect the concentration of
ions and molecules in the soil solution. The soil solution is considered to be in quasi-
58
equilibrium with the solid phase, and where its composition can be altered by
the processes of ion exchange, solubilization/precipitation and adsorption/desorption
(Bell 1993).
Ion exchange Ion exchange is one of the most common sorption mechanisms and involves
interactions due to electrostatic forces (Phillips 1993). Ion exchange includes various
aspects of both cation and anion exchange in soil. The exchange capacity of a soil is
a reflection of mineralogy and organic matter content. The sources of cation
exchange in soils are clay minerals, organic matter and amorphous minerals. The
sources of anion exchange in soils are clay minerals, metal oxides and amorphous
materials (Sparks 1995). The ion exchange capacity of a soil is important since it
determines its capacity to retain ions so it is not susceptible to leaching from the
dispersal area into the groundwater system.
Ion exchange involves electrostatic interactions between a counter ion on a charged
particle surface and counter ions in a diffuse cloud around the charged particle. It is
usually rapid, diffusion–controlled, reversible, stoichiometric, and in most cases
there is some selectivity of one ion over another by the exchanging surface. The
selectivity or preference of the ion exchanger for one ion over another is due to the
hydrated radius of the ion. For a given group in the Periodic Table with the same
valency, ions with the smallest hydrated radius will be preferred, since ions are
hydrated in the soil environment. Generally the higher charge ion will be preferred if
the ion exchanger is dealing with ions of different valency. As an example, Al3+ will
be preferred over NH4+ (Sparks 1995), and if anions such as phosphate are present
the nitrate (NO3-), retention will be reduced due to competition for exchange sites
(Eick et al 1999)
+ 2+
59
Figure 3.7 Exchange cations on the exchanging surface
(Adapted from McBride 1994)
Esteller et al (2001) in a study on infiltration treated wastewater in Spain found that
cations were affected by ionic exchange, mainly between calcium and ammonium in
the upper soil profile and below this between potassium or sodium and calcium and
magnesium. Wilhelm et al (1994a) found that soil dispersal areas remove nitrogen
from the effluent at high rates initially, but once exchange sites equilibrate with NH4+,
the ability to remove nitrogen decreases as NO3- is not retained by soils.
Dissolution/Precipitation The dissolution of minerals is a weathering process which releases potassium,
calcium and magnesium along with other metals. In highly weathered subtropical
soils, most of these minerals may have completely dissolved in the upper part of the
soil profile (Bell 1993). Addition of waste to soils may result in the solubility
products of various compounds being exceeded, resulting in precipitation. An
induced change in pH of the soil may reduce the concentration of some ions (metallic
cations) through precipitation. The precipitation of phosphates in the presence of
calcium has been confirmed by Esteller et al (2001).
Adsorption/Desorption The process of adsorption refers to the accumulation of an ion or molecule on a
surface. Desorption is the reverse of this process. Ions can be held on soil surfaces by
columbic or electrostatic bonding (non-specific adsorption) or by the formation of
chemical bonds (specific adsorption) (Bell 1993). Non-specific adsorption is the
process by which exchangeable cations and anions are held in soils.
Specific adsorption differs from non-specific adsorption in that the ions involved in
the process are absorbed on soil surfaces in amounts far in excess of that predicted
from the relative proportion of the ion in solution. For example, if an equimolar
60
solution of chloride (non-specific adsorbed) and phosphate (specifically
adsorbed) is added to a soil, most of the phosphate will adsorb on soil surfaces,
whereas most of the chloride remains in solution. This explains the reason for
chlorides being employed as an indicator of effluent travel through soil. Specifically
adsorbed ions are held more strongly on the soil surface but can be desorbed by ions
that form stronger chemical bonds with the surface rather than the ion.
Heng et al (1999) in a study on leaching through undisturbed soil columns on
Ferrosol soil found that adsorption was influenced by the soil’s water flow
characteristics. They sampled two soils from the same field in Victoria and found
that the flow regime differed markedly. The slow flow core exhibited adsorption of
cations whilst the fast flow core did not.
3.5.1.2 Physical Mechanisms The solid particles of soil consist of granules or grains of different sizes and shapes,
which are composed of a wide variety of minerals and organic matter. The shapes of
individual grains are the result of complex processes of chemical activity,
mineralogical structure, climatic conditions and mechanical abrasion (Winegardner
1996). The compositions of minerals are of significance in the treatment of
wastewater in soil as iron, aluminium and calcium can react with phosphorus and
form insoluble compounds (Patterson 1994). Organic matter serves as a reservoir of
nutrients particularly nitrogen and phosphorus and is important in developing and
maintaining soil structure and the negative charge on its colloidal component is
important in the retention of cations and water (Bell 1993).
Water Retention and Movement Solids occupy only about half the soil volume. The remainder is composed of pores
filled with air and water. The amount of pore space is dependent on the texture,
structure and organic matter content. In clay soils, the pores are generally small. In
sandy areas the pores are large, but the total quantity of pore space is less than in
soils consisting of fine particles. The size of individual pores and the total pore space
affect the movement and retention of water. In sandy soils, water moves rapidly
through the large pores, but little is retained. The numerous micro pores of heavier
61
clay soils contribute to greater water retention. The porosity of heavy soils is affected
by the state of aggregation. Aggregates are large structural units composed of clay
and silt particles (Bell 1993).
The quantity of water contained in a soil mass and how it is contained is an important
factor of the soil’s response to its environment. Water in soil is responsible for the
transport of nutrients such as nitrogen and phosphorus. Water moves in soil in three
ways; saturated flow, unsaturated flow and vapour movement. The flow of liquid
water is due to the gradient in matric potential from one zone to another, the
direction of flow being from the zone of higher moisture potential to one of lower
moisture potential. Saturated flow occurs when the soil pores are completely filled
with water, whereas unsaturated flow occurs when the pores are only partially filled
with water. Vapour movement in soils is negligible relative to liquid movement (Bell
1993).
It is generally assumed that purification of effluent will occur with a minimum depth
of unsaturated soil. Research studies have quoted depths varying from 0.6 m to 2 m
(USEPA 2002) underneath the dispersal area and that fine grained soils are far more
effective than soils with coarser grain sizes. This is balanced by the fact that
hydraulic capacities of finer grained soils are generally lower than coarser soils. The
depth of the unsaturated zone can affect the hydraulic function and in turn the
purification by influencing the soil water content, aeration status, media surface area
and hydraulic retention time (Siegrist and Van Cuyk 2001). Therefore the infiltration
of sewage effluent is directly related to soil characteristics, which define pore size
and pore size distribution. Texture, structure and consistency of the soil can
contribute information about soil pores along with the mineralogy of the clay. This
can be predicted from soil chemistry. Valuable information in characterising soil
potential for renovation can also be derived from terrain evaluation and observing
geomorphologic features that are significant in relation to drainage (Dawes et al
2001b).
Dispersion Dispersion of fine aggregates and clay associations is a process of structural
breakdown of the soil. It is caused by either high levels of exchangeable sodium or
62
excessive mechanical disturbance of the soil when the soil is wet (Peverill
1999). On being wetted, dispersive soils undergo breakdown of the clay structures
that bind fine aggregates and larger particles together. Individual clay particles tend
to go into suspension in the soil water. This dispersed clay moves into soil pore
spaces, blocking water and air flow. Sewage effluents usually have medium to high
salinity accompanied by high concentrations of sodium relative to other cations. This
sodium can potentially result in deleterious effects on soil structure and consequently
permeability, when effluent percolates through the soil dispersal area.
Menneer et al (2001) in a study on laboratory and insitu soils irrigated with sodium
rich wastewater in New Zealand found reduced water movement through soils as a
result of dispersed clay, thereby blocking the water conducting pores and impeding
drainage. Balks et al (1998) investigated soil physical properties of Chromosols and
Kandasols under effluent irrigation at Wagga Wagga, NSW and found that although
permeability decreased and exchangeable sodium percentage increased, the changes
could not be attributed to dispersion of the soils.
3.5.2 Physical Parameters
3.5.2.1 Soil Profile Evaluation Soils are characterised by the formation of a profile consisting of several horizons.
These horizons are the surface, the subsoil and the decomposing parent material
horizons which are named A, B and C respectively. These horizons which are
developed by soil forming processes with morphological properties different from
layers below or above can be classified into sub-horizons as shown in Figure 3.8.
Soil profile descriptions including colour, texture, structure and biological activity
are generally recorded in depth increments of 100mm as described by McDonald et
al (1990).
63
Figure 3.8 Soil profile showing horizon types (McKenzie et al 2004)
A soil profile develops as the weathering front penetrates more deeply into the parent
material while organic matter residues accumulate on the surface layer (Bell 1993).
The nature of these processes is dependent on climate, parent material, topography,
micro-organisms present and time. The most important factor determining the type of
soil formed is the parent material. It determines the texture that can develop and
provides the mineral make up that largely determine soil physical and chemical
properties (Beckmann et al 1987). Next in importance as a differentiating factor is
topography, which affects the drainage in the landscape and the energy of the water
moving over the soil surface and through the soil. The soil profile, and particularly
texture, structure and moisture regime can be used to determine the effect of
movement of water into and through the soil (Baker and Eldershaw 1993). The
particle size controls the soil texture. The physical and chemical behaviour of soil is
influenced by its particle size distribution, a measure indicating the relative
proportions of mineral particles of various sizes (sand, silt and clay).
64
3.5.2.2 Clay content and mineralogy
The type and amount of clay present in a soil influences many soil physical
properties such as cracking, swelling, pore space and stability. Clay mineral analysis
is not commonly undertaken due to the complex and time consuming preparation.
Generally clay mineralogy is inferred by referring to the soil Cation Exchange
Capacity (CEC).
In gradational profiles, the increasing clay content with depth may result from greater
exposure to leaching and intense weathering in surface horizons than at depth. The
movement of clay in virtually impermeable clay subsoils is unlikely to occur. As
well as the downward movement of fine clay during rainfall events, fine particles can
be washed down slope, adding finer soils to lower slopes and possibly enriching
nutrients.
Clay minerals offer three advantages for sorption of pollutants as effluent passes
through the soil matrix. They have a large specific surface area in comparison to
other solid phase components (Johnston 1996). The specific surface area of a soil is
the ratio of surface area to volume, which is measured as the surface area per unit
mass, assuming a constant particle density. Secondly, this large surface area is often
associated with electrical charges. These charges result in accumulation of inorganic
and organic cations and are responsible for the high water retention capacity of many
types of clays (Farrell and Reinhard 1994). Finally, naturally occurring clay mineral
particles can be coated by amorphous oxide hydroxides and humic materials and thus
serve as efficient templates for secondary solid phases (Johnston 1996). The
adsorption of effluent pollutants by clay particles depends not only on their large
specific surface area but also on the nature of the clay minerals present in the soil.
The pH level controls the type of charges available for adsorption mechanisms and
also desorption, if the pH changes.
The basic structural units of most clay minerals consist of sheets of silicon tetrahedra
and aluminium octahedra. The basic clay sheets combine either in a 1:1 or 2:1 ratio
to form the clay minerals such as kaolinite, illite and smectites.
65
The kaolinite structure is based on a single sheet of silicon tetrahedra combined with
a single sheet of aluminium octahedra. Most of the sorption activity occurs in
kaolinite along the edges and outside surfaces. Soils with large quantities of kaolinite
are expected to have a low percolation rate due to the compact structure. Kaolinite
exhibits less plasticity, stickiness, cohesion, shrinking and swelling and can hold less
water than other clays. Kaolinite is considered the least active clay compared to other
types of clay and has a low cation exchange capacity (Suraj et al 1998).
The illite structure is based on layers consisting of octahedral sheet of alumina
sandwiched between two tetrahedral sheets of silica. In the octahedral sheet, there is
a partial substitution by Mg2+ and Fe3+ and in the tetrahedral sheet there is a partial
substitution of silicon by aluminium. Soils that contain illite have a higher cation
exchange capacity than kaolinite due to their surface charge. McLaren et al (2003)
found that soils dominated by illite clays have substantial K+ fixing capacity.
Smectites are characterised by a 2:1 layer structure in which two tetrahedral sheets
form on either side of an octahedral sheet through sharing of apical oxygen. The
smectite structure is similar to illite, but in the octahedral sheet, there is possible
partial substitution of Al3+ by Mg2+, Fe2+ or Fe3+ and Al-Si substitution in the
tetrahedra sheet is also possible (Sawhney 1996). Water molecules and exchangeable
cations other than K+ can occupy the space between the layers, forming a weak bond.
Considerable swelling of smectites may occur due to additional water being adsorbed
between the layers. The cation exchange capacity is much higher than for illite and
kaolinite.
Shaw et al (1994) found that soils with mixed mineralogy are the most sensitive to
sodium variations and will form the least permeable matrix if the clay content is
about 40 to 50%. Subsurface effluent dispersal involves a series of wetting and
drying cycles which would align the clay and restructure the soil. In soils with
minimal shrink swell characteristics (kaolinite and illite clay), a dense soil matrix
will form, whereas in soils with appreciable shrink swell properties (smectite clay),
some regeneration of soil properties and porosity would result. Thus soils with a
predominance of smectite clays have the ability to efficiently renovate effluent even
with moderately high exchangeable sodium. Shaw et al (1998) found that soils with
high smectite clay content (high CEC and those that shrink and swell) can tolerate
66
higher Exchangeable Sodium Percentage (ESP) when compared to clay soils
with limited capacity to shrink and swell.
3.5.2.3 Permeability/ Drainage Characteristics van de Graaff and Brouwer (1999) found that intermittent soil waterlogging does not
inevitably lead to effluent dispersal system failure, and that the maximum level to
which a perched water table may rise in a soil profile has no bearing on the site
suitability for on-site effluent dispersal. They also concluded that permeability tests
should be used only for determining soil permeability in sizing dispersal systems and
not in assessing soil water regimes. Micro-hydrogeology assessment of soil profiles
including position and movement of perched and true water tables and duration of
saturation can be derived from soil profile characteristics (colours and mottles) and
hydrological monitoring (water table levels) (Cresswell et al 1999).
Soils containing slowly permeable horizons commonly develop perched water tables
during periods of high rainfall. These perched water tables can result in saturated
flow of effluent, lateral flow and/or transport of the effluent to the soil surface. As
such an in-depth understanding of the drainage characteristics is important in
determining the behaviour of sewage effluent in soils (van der Graaff and Brouwer
1999). These characteristics are due to a complexity of factors such as layering or
stratification of the soil, the permeability of the various soil horizons, presence of
restrictive layers, position in the landscape and the weather conditions. It is
worthwhile noting that downward and lateral drainage and effluent absorption that
continues under waterlogged conditions will be faster than if the soil is drier.
Penninger and Hoover (1998) provided hydrometric evidence that downslope
effluent flow occurred from a septic system through the upper soil horizons of a
clayey soil, as a result of perched saturation over an impeding B/C horizon.
Restricted vertical percolation in an on-site dispersal area increases the risk of
surface effluent ponding and thus failure. Sherlock et al (2002) in a field study on
loam soils with shallow slopes (2 to 8 degrees) found that lateral hydraulic gradients
were 10 times smaller than vertical gradients and that soil water had a long residence
time within the vadose zone. Thus effluent movement was confined to the soil matrix
pore space.
67
3.5.3 Chemical Parameters
Menneer et al (2001), NZLTC (2000), Schipper et al (1996), Sparling et al (2001),
and Wang et al (2003) suggested pH, electrical conductivity (EC) and the following
chemical parameters discussed below as possible reliable indicators in assessing the
likely deterioration of soil structure and soil quality due to effluent dispersal.
Chemical parameters represent quantitative information needed to support field
descriptions (Bridge and Probert 1993). Levine et al (1980) noted that soil chemistry
monitoring at existing infiltration facilities provides a convenient method for
evaluating renovation efficiency and an insight into renovation mechanisms.
3.5.3.1 Exchangeable sodium percentage (ESP) or Exchangeable sodium content (ESC)
ESP is a measure of the proportion of sodium ions present in the soil and is used for
assessing the likely physical behaviour of soil horizons under irrigation. ESP is used
to define the sodicity of the soil. The detrimental effects of sodicity are exhibited
through swelling and dispersion. Dispersion is thought to be the dominant process
occurring at low ESP, whereas swelling is thought to dominate at high ESP values.
CECNaleExchangeabx100ESP
+=
With increased ESP comes the risk of deterioration of the physical properties of the
soil (Balks et al 1998). At high ESP (>6), soils tend to lose aggregation and to
undergo clay dispersion, impermeability, surface crusting and poor aeration (Baker
and Eldershaw 1993). The threshold value of ESP at which the adverse impacts of
exchangeable Na+ becomes significant depends on the clay mineralogy and the
amount of organic matter present in the soil. In soils with a high clay fraction, the
threshold ESP value at which clay particles becomes dispersive is lowered (Baker
and Eldershaw 1993). A number of researchers such as Bridge and Probert (1993)
and Northcote and Skene (1972), have suggested a threshold ESP limit of 6 for clay
soils, above which physical problems would occur.
Patterson and Chapman (1998) found that exchangeable Na+ together with electrical
conductivity can be used to predict soil structural stability and potential problems of
68
hydraulic conductivity for effluent dispersal. Summer (1993) noted that even
soils with ESP values<1% can exhibit sodic behaviour depending on soil properties
and EC of the applied water. Balks et al (1998) found that wastewater application
increased sodicity and resulted in an increased tendency for the soil to disperse for all
soil textures. Mamedov et al (2000) in a study on Israeli soil found that ESP
increased from 2% to >6% after 15 years of effluent application. Menneer et al.,
(2001) investigated silty loam soils irrigated with wastewater in New Zealand and
found that mineralogy and possibly topographic setting caused larger increases in
ESP in low lying areas. The soils investigated had relatively low CEC, which
enabled small amounts of exchangeable sodium to have large impacts on ESP.
Crescimanno et al (1995) suggested that a continuum may exist between soil
structural properties and ESP, with an ESP as small as 2 to 5% causing adverse
effects if soil water has low cationic concentration.
Cook and Muller (1997) concluded that Exchangeable Sodium Content (ESC) is a
better index of soil sodium levels across all soil types. Their study compared the
abilities of ESP and ESC to explain variation in soil structural stability across soil
types. There were no consistent differences in soil type, clay mineralogy or clay
content between the data sets analysed.
3.5.3.2 Ca:Mg ratio The Ca:Mg ratio in a soil can be employed to indicate cation distribution, particularly
in the case when the subsoil is dominated by Mg2+. An excess of one cation may
inhibit the uptake of another. The relationship between Ca2+ and Mg2+ can be related
to soil physical behaviour (Baker and Eldershaw 1993). Emerson (1977) found that
ratios less than 0.5 are associated with soil dispersion. Ca2+ ions tend to aid in
flocculation of soils while Na+ ions and possibly Mg2+ ions disperse soils. Mg2+
associated with Na+ is commonly thought to aid soil dispersibility (Emerson and
Bakker 1973). Curtin et al (1994) in a study to evaluate the effects of Mg2+ on the
cation exchange relationships and structural stability of Canadian soils found that
exchangeable Ca:Mg ratio can have an effect on dispersion even in the absence of
Na+. They determined that Mg2+ rich soils were more susceptible to surface sealing
caused by aggregate disintegration and clay dispersion than a Ca2+ rich soil. This is
69
supported by Shaw et al (1987) who postulated that low Ca:Mg ratios in conjunction
with high ESP indicate enhanced dispersion.
3.5.3.3 Cation exchange capacity (CEC) and exchangeable cations The electrostatic charge developed on soils can be quantified in terms of CEC and is
an indication of its mineralogy and nutrient holding capacity. The ions held on the
surface are exchangeable and can be replaced by other ions added to the soil. Cation
exchange is important in soils, as it measures the basic nutrient holding capacity
(Bell 1993). Bridge and Probert (1993) have noted that soils with low CEC (< 10%)
are poor at holding cationic nutrients.
CEC is a measure of the soil particles’ ability to exchange cations with freely mobile
cations added to the soil matrix, in this particular case those associated with
percolating effluent (Borden and Giese 2001, Manahan 2000). Therefore, if the soil
has a low CEC, it will not have a strong ability to adsorb pollutants, and will rely
wholly on filtration and microbiological decomposition processes. On the other hand,
soils with a high CEC will have excellent adsorption ability, and provide suitable
effluent renovation, provided the effluent can physically percolate through the soil.
Clayey soils generally retain greater sorption ability due to the smaller size of the
clay particles, and hence provide a greater, more active adsorption area. Clay soil
particles which have a coating of iron, aluminium and hydrous oxides have
exceptional sorption ability. The electrostatic properties of soils with high clay
content, as well as organics, provide a good CEC which is capable of sorbing ionic
and biological material, commonly contained within the percolating effluent (Miller
and Wolf 1975).
In the case of the exchangeable cations in a soil being predominantly Ca2+ or Mg2+,
the clay particles interact or repel each other only to a limited extent and as such the
particle separations are not large. However, when the proportion of Na+ ions is
appreciable, considerably greater swelling is encountered. This leads to a diminution
of the favourable characteristics conferred on a soil by its macroporosity (Quirk
1971). This postulate is supported by the findings of Emerson (1983), that
exchangeable Ca2+ has the important effect of flocculating individual clay particles
and imparting a stable structure to the soil through interparticle and interaggregate
70
bonds. This structure creates pore space that allows movement of water and air
through the soil. Exchangeable Na+ produces undesirable impacts such as crusting
and low infiltration, which is related to the fact that the ion increases dispersion of
the soil colloid. Jnad et al (2001) found that an increase in Na+ concentration
associated with a reduction in Ca2+ concentration will increase the hazard of clay
particle swelling and dispersion. This in turn could lead to a reduction in soil pore
size and consequently an increase in soil water retention.
Hartmann et al (1998) concluded that if water moves more slowly through a soil,
there is greater opportunity for exchangeable cations to be adsorbed. They found a
correlation between quantity of exchangeable cations and the percolation volume
became significant with decreasing hydraulic conductivities. This finding is
supported by Heng et al (1999) who described the effects of flow rate on cation
exchange and adsorption on a Ferrosol soil. Tarchitzky et al (1999) in a study on
wastewater effects on smectite soils found that dissolved organic matter and
ammonium caused desorption of Na+, K+ and Mg2+ from the upper soil layer. The
Mg2+ and K+ were then adsorbed in the deeper soil layers, whereas the Na+ was
leached out.
The routinely measured exchangeable cations in soil analyses are Ca2+, Mg2+, Na+
and K+. The first three cations exert a significant influence on the soil structure. In
neutral to alkaline soils, the total CEC equals the sum of the exchangeable cations.
However in the case of acidic soils, the summation should also include the
exchangeable acidity. Therefore in acidic soils, the traditional methods of measuring
CEC, using concentrated salt solutions at pH 7 or higher, sometimes yield unrealistic
results. Modern methods have been developed to determine an effective cation
exchange capacity appropriate to field conditions. The ‘Effective Cation Exchange
Capacity’ (ECEC), is being used to characterise acidic soils instead of CEC (Baker
and Eldershaw 1993). This is defined as:
ECEC = exchangeable cations + exchangeable acidity = Exchangeable (Ca + Mg + Na + K) + Exchangeable (Al + H)
71
Baker and Eldershaw (1993) have also noted that the actual values of CEC obtained,
have limited use in interpreting soil properties and that it may be better used in cross
checking other soil properties.
3.5.3.4 Chloride concentration Chloride ion concentration is a good indicator of effluent movement as it is highly
mobile, undergoes no biochemical transformation and is easy to measure. It is not
consumed in the renovation process (Mote et al 1995). Chloride levels are
considerably higher in the domestic water supply than in rainfall and even higher in
septic tank effluent. Therefore the chloride concentration can be a reliable indicator
of effluent travel.
3.5.3.5 Organic Matter Organic matter content is material directly derived from plants and animals, and
supports most of the important microfauna and microflora in the soil. The organic
matter breakdown interacts with other soil constituents and is largely responsible for
much of the physical and chemical reactions in a soil. The organic matter content in
the soil is important for understanding the soils’ capacity for nutrient release and
uptake. The application of wastewater effluent is expected to increase the organic
matter through the soil horizons. The change of organic matter content in the soil is
important to understand as it affects the soil’s capacity to remove pollutants from the
soil, especially nitrogen and phosphorus. Soil organic matter is often responsible for
half the cation exchange capacity and acts as a stabilising agent for soil aggregates
(McKenzie et al 2004). It can reduce the bulk density and increase total porosity and
hydraulic conductivity in heavy clay soils (Anikwe 2000).
3.5.3.6 Nutrients Nitrogen
On-site treatment systems can typically remove around 20% of the nitrogen
contained in the effluent depending on the specific site related factors, such as soil,
topography and climate ( Siegrist and Jenssen 1989). Anaerobic conditions generally
72
prevail in septic tanks, which provide excellent conditions for organic-N to be
transformed into NH4+.
Nitrogen is often the most complex nutrient because it can be stored in the plant, in
new soil organic matter, lost via gaseous pathways during irrigation (ammonia
volatilisation) or after irrigation (denitrification), leached below the root zone
(nitrate) and slowly converted from the organic form to inorganic forms (NH4+
and
NO3-) available for plant uptake and leaching. In an effluent dispersal field, soil
processes such as ion exchange or adsorption retard either ammonium or nitrate
formation, Ammonium gets reduced to nitrate, and nitrate is further reduced to
nitrogen gas and can escape to the atmosphere through the process of denitrification.
Most soils have limited ability to adsorb nitrogen and therefore cannot be
continuously loaded without leakage of nitrogen.
Johnson and Atwater (1988) tested the role of the saturated and unsaturated zone in
an effluent dispersal field for the removal of nitrogen in two soil types; loamy sand
and sand. They found that substantial reduction in ammonia concentrations could be
obtained regardless of groundwater table position, but that ammonia reduction in
sand was substantially better than in the loamy sand. Sumner et al (1998) in field
experiments to examine nutrient transport and transformation beneath an effluent
dispersal field concluded that the nitrification reaction could occur not only in the
unsaturated zone but also in the shallow saturated zone. Findings indicated that
substantial organic nitrogen was retarded in the upper part of the unsaturated zone
and that nitrification converted this to nitrate.
Strong adsorption and desorption of NH4+ can be evident in soil horizons high in
organic carbon. Organic carbon can be positively correlated with potential NH4+
buffering capacity and labile NH4+ for soils (Wang and Alva 2000). However, soils
low in organic carbon have little or no adsorption and desorption of NH4+, as the
organic carbon sources in the wastewater are oxidated to carbon dioxide in the septic
system. Consequently, the NH4+ will be oxidised to nitrate in the unsaturated zone
(Wilhelm et al 1996).
73
Soils containing significant quantities of variable charge minerals have a substantial
anion exchange capability (AEC). AEC has the potential to retard NO3- movement
and mitigate contamination of groundwater. The net positive charge and NO3-
retention is dependent on the type and quantity of both variable and permanently
charged minerals found in the soil and the composition of the exchange complex.
Although a soil may have significant amounts of variable charge minerals that would
generate AEC, this positive charge may be masked by the presence of a high cation
exchange capability (CEC). Anions such as phosphate can reduce NO3- retention
through competition for exchange sites. Even though competing anions are present, it
has a potential for retardation of NO3- in soils (Eick et al., 1999). This compares
favourably with research by Black and Waring (1976). They found that in a Ferrosol
soil, the adsorption could be a significant mechanism in restricting the movement of
nitrate under field conditions.
Phosphorus
Phosphorus can be strongly held by soils through both electrostatic and non-
electrostatic mechanisms and usually does not leach in most soils. Patterson (1994)
found that sandy soils usually have much less capacity to sorb and hold phosphorus
than finer textured soils. In sandy soils that contain little clay, aluminium, iron oxides,
or organic matter, phosphate can leach through the soil and impact groundwater
quality (Sparks 1995). However Mehadi and Taylor (1988) noted that sand may have
higher adsorption capability under some circumstances. Two highly weathered soils,
clay loam and sandy loam, were tested to establish their phosphorus adsorption
capacity. They established that sandy loam, which had lower pH and higher
exchangeable aluminium and free iron oxide, adsorbed more phosphorus than the
clay loam soil. Sumner et al (1998) undertook field experiments to examine nutrient
transport and transformation beneath an effluent dispersal field. The dispersal system
consisted of fine to medium grained sand, with small amounts of silt and clay. Iron
and aluminium were present as coatings on the sand grains and were abundant in the
oxidising environment of the unsaturated zone. They concluded that phosphorus
concentrations were reduced, and that was probably due to adsorption by abundant
iron and aluminium hydroxides. Phosphorus that reached the watertable was
74
predominantly organic, but was immobilised by adsorption or precipitation
reactions under lower loading rates.
The digestion processes established in on-site treatment systems convert most of the
phosphorus into soluble orthophosphates. This form of phosphorus is therefore able
to move through saturated soil, ground and surface waters. Typically, phosphorus
undergoes two sorption processes; fast sorption and slow ionic reaction. Fast sorption
processes are generally confined to the sorption of phosphorus ions to the surfaces of
soil physical and chemical elements. Generally, this occurs on the clay and organic
matter particles. The slower, ionic reactions between phosphorus and chemical
elements, such as aluminium, iron and calcium also occur, typically below the
surface of the individual particles (McGechan and Lewis 2002).
Phosphorus availability in soil is a complex issue that is dependent on pH, certain
minerals and microbial activity (Winegardner 1996). The pH of the soil can influence
the chemical processes significantly. Soils that have a lower pH generally have
higher levels of aluminium and iron available, which enhances these slower ionic
reactions. Similarly for soils with higher pH, more calcium is generally available in
the soil for these reactions to occur.
The removal of phosphorus from wastewater is by fixation in the dispersal field.
Fixation is a retention process where the phosphorus can be adsorbed or incorporated
into a crystal structure. Mobile elements such as phosphorus, migrating with the
wastewater are retained by soil particles. A properly functioning soil absorption field
will retain most of the phosphorus in the soil. Phosphate is usually attenuated in soil
by sorption and precipitation. Most Australian soils have high capacity to immobilise
phosphate ions and limit the sub-surface transport of this nutrient.
3.5.4 Site Factors
A comprehensive soil profile evaluation can define the limitations of a site for
effective effluent treatment. A soil profile evaluation undertaken to describe a soil
should take into consideration a number of site features such as:
75
• topography - defines the drainage and aeration of the soil and whether there is
soil movement down a slope
• climate - temperature, rainfall and evaporation affect profile development
through leaching and weathering.
• parent material - exerts the primary influence on soil development.
• native vegetation - reflects the nutrient status and water availability.
• biological activity - can impact infiltration and water storage in the soil.
This assessment can be supported by the observation and description of colour,
texture and structure of the soil which may be used to qualitatively assess the
hydrology of the soil profile whilst the physical and chemical soil data can provide
an insight into soil stability and its ability to absorb applied nutrients (Bridge and
Probert 1993, Dawes et al 2000, Lindbo et al 2004)
Other valuable information for designing and siting an on-site dispersal area can be
derived by geomorphologic features affecting drainage such as flow of surface water
through the site, flood potential and discharge of surface and ground water. Geary et
al (1999), in their study at Dodges Ferry, Tasmania, found groundwater pollution at
the bottom of drainage areas below catchments containing high densities of on-site
systems. They also noted that both surface and subsurface drainage flowed towards
clusters of development where elevated concentrations of pollutants occurred.
Many Australian soils have “duplex” profiles, which have heavier clay texture with
clay content increasing to form impermeable ‘B’ horizons. When they occur in an
undulating landscape, these can develop perched water tables, which predisposes to
reducing conditions and gleying and mottling in the profile. This is a common
phenomenon in “duplex” soils on the lower slopes and foothills of the Great Dividing
Range in South Eastern Australia (White 1997). These sites can be problem sites for
effective effluent dispersal, and need characterising carefully by a combination of
site factors along with chemical and physical criteria (Dawes et al 2000).
Kommalapati and Noman (1999) found that in soils with restrictive horizons, the
permeable surface layers play an important role in allowing infiltration and lateral
flow from the trenches. Thus it is vital that the dispersal trenches are sited at the most
76
suitable depth in the soil profile allowing lateral flow of effluent above the
restrictive layers.
A large number of the soils have distinctly differentiated profiles, equivalent to the
duplex profiles described by Northcote and Skene (1972), ie. soils with coarse
textured sand-sandy loam surface horizons fairly sharply separated from sandy clay
or clay ‘B’ horizons. Generally in undulating landscapes on permeable material, the
soils near the top of the slope tend to be free draining with the watertable at depth,
whilst the soils at the valley bottom are poorly drained with the watertable at or near
the surface. The succession of soils forming under different drainage conditions on
relatively uniform parent material comprises a hydrological sequence. This is
illustrated in Figure 3.9. As the soil drainage deteriorates, the oxidised soil profile is
transformed into the mottled and gleyed profile of a waterlogged soil. The sequence
of soils on a slope described above is an example of a catena or landscape pattern.
This is illustrated in Figure 3.10.
Figure 3.9 - Hydrological soil sequence (adapted from White 1997)
77
Uniform‘oxidized’
colours
Mottles
Muchmottling
in adark-grey
matrix
Rustymottlesaroundroots
Prominentmottles
grading intoblue-grey
matrix
Predominantlyblue-grey
Dark,peaty
0
25
50
75
Well drained Moderatelywell drained
Imperfectlydrained
Poorlydrained
Very poorlydrained
Uniformcolours
Uniformcolours
Orangemottles
grey matrix
Figure 3.10 Sequence of soils in a landscape catena (adapted from White 1997)
A soil profile is subjected to continuous changes to its drainage characteristics due to
illuviation or migration of fine particles to the lower profile. In addition to the
drainage modifications due to this process, there is a net movement of soil along the
slope. A mid-slope site will continually receive soil and solutes from upslope whilst
continually losing material to sites below (White 1997). Therefore the location of a
site on the catena is an important factor in terms of its drainage characteristics.
3.5.5 Summary of Key Research Findings The reviewed research literature has identified important issues involving the role of
soil physical and chemical characteristics and site factors in effluent treatment that
can significantly affect the long term performance of on-site dispersal areas. This
included identification of important parameters and controls involved in the
treatment and dispersal process. The application of wastewater to soil increases soil
water retention, decreases the volumes of pores and decreases the saturated hydraulic
conductivity.
Various studies have found contradictory findings in relation to the mobility and
retention of phosphorus and nitrogen in soils under wastewater dispersal. Little
research has been conducted on the impact of exchangeable cations (Ca2+, Mg2+, Na+
and K+) and associated salts on the receiving soil environment.
78
The review of research literature enabled understanding of the significant role
played by soil physical and chemical parameters in effluent treatment and dispersal.
The mechanisms that influence the attenuation and removal of these pollutants are
generally associated with the physical and chemical characteristics of the soil
medium and related site factors. These site factors are controlled by a complexity of
issues such as layering or stratification of the soil, the permeability of the various soil
horizons, presence of restrictive layers, position in the landscape and climatic
conditions.
3.6 Conclusions from Literature Review On-site wastewater treatment systems are capable of providing adequate treatment
and dispersal of domestic effluent provided they are situated in areas that have
appropriate site and soil characteristics and are maintained on a regular basis.
However, failure of on-site wastewater treatment systems is a common scenario,
particularly for septic tank-soil dispersal areas. This is related to several issues
including unsatisfactory site and soil characteristics, general maintenance of systems,
and the improper siting of on-site dispersal areas. Poor performance can lead to
serious environmental and public health impacts. Consequently, more appropriate
assessment criteria and evaluation techniques need to be developed to safeguard
against the impacts associated with the failure of the soil dispersal area. These
assessment criteria for on-site dispersal area siting and design can be considered as
the next improvement to the current standards and codes employed in on-site
wastewater treatment systems.
Satisfactory dispersal area design and subsequent performance is critically dependant
on sound site and soil assessment and appropriate consideration of hydraulic,
climatic, and nutrient factors for correct system selection, siting and sizing.
Performance can be dominated by a single factor or by a complex interaction of
factors. Site and soil assessment/evaluation should not rely on a simplified
consideration of a few terrain and soil factors, rather on an integrated analysis of
these factors. The design and siting of an on-site system to meet regulatory
expectations and adequately protect the environment and public health is rarely
straightforward. System selection has often been based on what has been
79
traditionally acceptable and cost efficient. Lack of attention to the relevant site and
soil related topographic and geomorphological factors often result in inappropriate
dispersal area location, leading to poor performance. Careful consideration of the
range of site and soil characteristics can result in a robust design which will deliver
effective long term performance.
From the reviewed literature, several important issues were highlighted which
needed to be investigated in order to develop a robust, scientifically based
assessment criteria to predict long term behaviour of on-site soil dispersal areas.
These issues are:
• An in-depth understanding of the complex physical and chemical soil
processes that influence effluent treatment and dispersal;
• More comprehensive assessment and evaluation of soil and site
characteristics, based on scientific investigation and analysis is required to
ensure adequate effluent treatment is achieved through appropriate siting and
design of on-site dispersal areas;
• Identify the crucial role played by drainage and landscape features in effluent
treatment and dispersal. The interaction of these features together with soil
physical and chemical characteristics is a primary factor that governs the
resulting treatment process within the soil dispersal area;
• Identification and assessment of the critical factors that influence contaminant
fate and transport from on-site dispersal areas; and
• Developing improved knowledge of soil processes affecting chemical release
and retention rates along with measurement of changes in soil physical
properties that will be indicative of long term sustainability of effluent
dispersal.
The research conducted explores these issues through a series of peer reviewed
scientific papers, with the respective outcomes used for the development of
assessment criteria to predict long term behaviour of on-site soil dispersal areas.
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CHAPTER 4
AN INVESTIGATION INTO THE ROLE OF SITE AND SOIL CHARACTERISTICS IN ON-SITE SEWAGE
TREATMENT
LES DAWES AND ASHANTHA GOONETILLEKE
School of Civil Engineering, Queensland University of Technology
Published: Environmental Geology 44(4): 467-477
Statement of Contributions of Joint Authorship Dawes, L: (Candidate)
Established methodology, data analysis, preparation of tables and figures, writing
and compilation of manuscript.
Goonetilleke, A: (Principal Supervisor)
Supervised and assisted with manuscript compilation, editing and co-author of
manuscript.
This Chapter is an exact copy of the journal paper referred to above.
109
CHAPTER 5
FRAMEWORK FOR SOIL SUITABILITY EVALUATION FOR SEWAGE EFFLUENT RENOVATION
STEVEN CARROLL, ASHANTHA GOONETILLEKE AND LES DAWES
School of Civil Engineering, Queensland University of Technology
Published: Environmental Geology 46(2): 195-208
Statement of Contributions of Joint Authorship Carroll, S: (Research Colleague)
Established methodology, data collection and analysis, preparation of tables and
figures, writing and compilation of manuscript.
Goonetilleke, A: (Principal Supervisor)
Supervised and assisted with manuscript compilation, editing and co-author of
manuscript.
Dawes, L: (Candidate)
Assisted the first author in establishing methodology, data collection and analysis,
editing, compilation and co-author of manuscript.
This Chapter is an exact copy of the journal paper referred to above.
141
CHAPTER 6
ASSESSMENT OF PHYSICAL AND CHEMICAL PROPERTIES OF SUB-TROPICAL SOIL TO PREDICT LONG TERM EFFLUENT
TREATMENT POTENTIAL
LES DAWESa, ASHANTHA GOONETILLEKEa AND MALCOLM COXb
aSchool of Civil Engineering, bSchool of Natural Resource Sciences Queensland University of Technology
Published: Soil and Sediment Contamination 14(3): 211-230
Statement of Contributions of Joint Authorship Dawes, L: (Candidate)
Established methodology, data collection and analysis, preparation of tables and
figures, writing and compilation of manuscript.
Goonetilleke, A: (Principal Supervisor)
Supervised and assisted with manuscript compilation, editing and co-author of
manuscript.
Cox, M: (Associated Supervisor) Editing and co-author of manuscript.
This Chapter is an exact copy of the journal paper referred to above.
173
CHAPTER 7.0
USING MULTIVARIATE ANALYSIS TO PREDICT THE BEHAVIOUR OF SOILS UNDER EFFLUENT
IRRIGATION
LES DAWES AND ASHANTHA GOONETILLEKE
School of Urban Development, Queensland University of Technology
Article accepted: Journal of Water, Air and Soil Pollution (In Press)
Statement of Contributions of Joint Authorship Dawes, L: (Candidate) Established methodology, data analysis, preparation of tables and figures, writing
and compilation of manuscript.
Goonetilleke, A: (Principal Supervisor) Supervised and assisted with manuscript compilation, editing and co-author of
manuscript.
This Chapter is an exact copy of the journal paper referred to above.
199
CHAPTER 8.0
USING UNDISTURBED COLUMNS TO PREDICT LONG TERM BEHAVIOUR OF EFFLUENT IRRIGATED SOILS UNDER FIELD
CONDITIONS
LES DAWES AND ASHANTHA GOONETILLEKE
School of Urban Development, Queensland University of Technology
Article submitted to: Journal of Environmental Quality (under review)
Statement of Contributions of Joint Authorship Dawes, L: (Candidate)
Established methodology, data analysis, preparation of tables and figures, writing
and compilation of manuscript.
Goonetilleke, A: (Principal Supervisor)
Supervised and assisted with manuscript compilation, editing and co-author of
manuscript.
This Chapter is an exact copy of the journal paper referred to above.
239
CHAPTER 9.0
DISCUSSION
9.0 General Discussion
Rapid development around the urban fringes and attractiveness of living in rural
areas close to cities in South East Queensland has dramatically increased the
need for on-site wastewater systems for the treatment and dispersal of domestic
wastewater. Due to the difficulty in providing centralised treatment facilities,
on-site systems are the most economical and feasible alternative for treatment of
wastewater. However, on-site system failure is a common issue both in Australia
and internationally (Harman et al 1996, Geary 2004, Harris 1995, Goonetilleke
et al 2000, Goonetilleke et al 2002). Typically, poor treatment performance is a
result of several factors including unsuitable soil and site characteristics, poor
operation and maintenance practices and a general lack of knowledge by
householders regarding appropriate use and general maintenance of on-site
systems (Whitehead and Geary 2000, Alle et al 2001). The current standards and
guidelines used for the assessment of on-site wastewater treatment systems have
been shown to be inadequate for preventing system failure, leading to possible
environmental and public health impacts (Whitehead and Geary 2000, Paul et al
1995, Carroll and Goonetilleke 2004). The assessment of on-site wastewater
treatment systems generally falls within the responsibility of individual local
governments. There are wide variations in adopted standards and guidelines
between regulatory authorities. The need to develop scientifically robust siting
and design guidelines is necessary. To achieve this objective, improved
evaluation and assessment of site and soil characteristics is needed. This in turn
will help to safeguard against impacts associated with the failure of soil
dispersal areas.
In Queensland site and soil assessment is carried out by certified evaluators
according to the Queensland On-site Sewerage Code (2003) guidelines which
240
incorporates AS/NZS 1547:2000. The Queensland Department of Local
Government and Planning have also developed guidelines for effluent quality
and separation distances to assist in the sustainable design of on-site systems.
Whilst AS/NZS 1547 (2000) provides detailed coverage on most aspects of on-
site wastewater system design, it does not address some key aspects of design,
such as nutrient loading and nutrient assimilation.
Some local governments maintain a register of site and soil assessors and only
use qualified trained professionals to conduct assessments and subsequent
design. Many local governments use professionals who are not trained in the
multidisciplinary areas required to understand the processes involved in on-site
wastewater treatment. This can result in extra cost to the homeowner or lead to
premature failure of the soil dispersal area. Site and soil assessment should take
into account a full range of site and soil characteristics including: aspect, slope,
landform, slope stability, erosion potential, drainage characteristics, soil
landscape, soil texture, structure, colour, mottling, moisture and their bearing on
the selection, location and sizing of on-site soil dispersal areas. Many of these
characteristics are dependent on each other and should be carefully evaluated.
The research conducted will contribute to overcoming the constraints associated
with on-site dispersal area siting, and design, including more extensive soil and
site evaluation techniques, assessment of the inherent factors associated with the
sorption, purification and transport of pollutants from on-site wastewater
treatment systems, and the integration of this research into the development of
assessment criteria. The research outcomes achieved were applied in the
development of predictive assessment criteria to characterise long term
behaviour of sites under on-site effluent dispersal. The primary objectives for
the research project were achieved by addressing the specific research aims,
which included investigations into soil and site processes for effluent treatment
and dispersal, the natural controls governing these processes, understanding
sorption, purification and transport processes influencing retention and release
of pollutants and the development of assessment criteria for long term behaviour
of soils under effluent dispersal.
241
9.1 Soil and Site Processes involved in Effluent Treatment and Dispersal
The current methods for assessing site suitability for on-site wastewater systems
are typically focused on the dispersal of effluent, with little attention given to
whether the soil is capable of providing adequate treatment or site conditions
inhibit or enhance treatment processes and to understand soil behaviour in the
long term. The ever-increasing need to pay more attention towards site and soil
evaluation in the treatment of effluent has been recognised due to the high
failure rates of on-site systems reported both nationally and internationally
(Geary 1992, Hoover et al 1998, Whitehead and Geary 2000, Carroll et al 2004,
Day 2004, Dawes and Goonetilleke 2004).
The major deficiency in the current means of assessing site suitability for on-site
dispersal areas is the lack of scientific methodology for identifying which soils
and sites are suitable for providing adequate treatment and dispersal of
discharged effluent. These shortcomings were addressed by investigating the
site and soil characteristics of operating on-site wastewater treatment system soil
dispersal areas and relating the controlling parameters to treatment performance
for a number of common soil types found in South East Queensland.
Comparison with control sites allowed identification of physical and chemical
processes and parameters involved in soil-wastewater interactions. The
importance of comprehensive soil and site assessment to assist in defining the
limitations of sites was highlighted. Subsurface drainage processes, topography
and depth to restrictive soil horizon impacted on the treatment process and life
of the dispersal area.
The developed soil suitability framework further addresses these deficiencies by
assessing the renovation suitability of a number of different soil types common
throughout South East Queensland. This was based on three major mechanisms,
soil renovation ability, soil permeability and soil drainage. Soil renovation
ability was evaluated by analysing a number of soil physical and chemical
characteristics. The analysed soils were ranked based on their effluent
renovation ability. The main focus of the soil research undertaken was to
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determine which of the major physical and chemical characteristics influenced
soil renovation ability, and thereby assess the different soil types based on their
overall suitability.
The major soil groups identified as the most suitable for effluent renovation and
dispersal include Chromosol, Ferrosol and Dermosol. These results are
significant as soils previously thought to be incapable of providing appropriate
treatment of sewage effluent based purely on soil physical characteristics were
subsequently found to be suitable. However, this particular finding signifies the
necessity for identifying suitable soils based on the combination of renovation
ability, permeability and drainage characteristics. Similar results to those
derived were also found by Khalil et al (2004) in a study undertaken to assess
land capability for on-site sewage effluent renovation for the Logan City
Council region. Soils with a higher ability for attenuating and removing
pollutants were determined based on CEC and organic matter content in soil. It
is important to note that the suitability ratings in these studies were established
based on scientific analysis of soils which had not previously been exposed to
effluent.
Detailed analysis of soil physical and chemical parameters allowed definition of
critical processes and development of correlations between soil and site
characteristics involved in effluent treatment and dispersal processes. The
research focused on the assessment of soil physical and chemical parameters and
associated landscape features responsible for attenuating and removing
pollutants as the effluent percolated through the soil matrix, as well as soil
hydraulic characteristics necessary for effluent dispersal. Soil sampling and
monitoring of effluent and soil water at established subsurface effluent dispersal
systems were used as a convenient method for evaluating renovation efficiency
and to obtain an insight into subsurface drainage mechanisms.
The multivariate analysis undertaken on the influential soil parameters showed
that there are several primary variables that influence the ability of soil to
renovate effluent. These include the type and content of clay present in the soil,
Cation Exchange Capacity (CEC) or ECEC, organic matter content (%OM), as
243
well as soil permeability and drainage characteristics. Electrical conductivity
(EC) and exchangeable sodium content of soils are also critical parameters in
determining soil structural change and subsequent soil degradation. CEC defines
the ability of a soil for attenuating and removing effluent pollutants, and can be
significantly influenced by the amount and type of clay present as well as
the %OM. Therefore, more suitable soils would exhibit higher CEC values.
However, both the permeability and drainage can also be influenced by the
amount and type of clay present in the soil. For a soil to provide suitable long
term treatment and dispersal of effluent, it must meet both the treatment and
dispersal criteria.
A review of recommended hydraulic loading rates for the various soils at the
study sites found that 5 out of 17 systems (30%) designed to AS1547:1994 had
failed due to hydraulic overloading. Soil type was not a contributing factor. Poor
site evaluation was more likely the cause. Drainage characterisation, depth of
restrictive horizon and adequate soil classification to depth critical factors need
to be assessed to prevent premature failure of the dispersal areas. Several of the
failed sites were designed with hydraulic loading rates of 20mm/day in poorly
drained areas and clayey soils. Small dispersal areas compared to the current
standard AS/NZS 1547:2000 design may have also lead to early failure. As a
result of the column study discussed in Chapter 8 and work by Beal et al (2005)
design loading rates (DLR) will need to be re-evaluated especially for clay soils
and potential sodic soils.
Treatment performance of dispersal areas at each study site was categorised into
hydraulic or purification failure or satisfactorily performing to allow a
comprehensive examination of failure mechanisms at specific sites. This led to
an initial field assessment of long term behaviour of soils under sewage effluent
application. Multivariate statistical methods provided the ability to differentiate
the most suitable soils for long-term effluent application and to determine the
most influential soil properties and associated site factors in order to characterise
them. Principal Component Analysis (PCA) was identified as a versatile tool for
characterising a soil’s ability to adequately treat and disperse sewage effluent.
244
To further clarify the site suitability analysis and assessments obtained from
previous work (Chapters 4 and 5), the effluent treatment and dispersal capacity
of several of the most common soil types found in South East Queensland were
investigated using undisturbed soil columns. The use of soil columns for
assessing different soil types for treating effluent have been investigated in
numerous past research studies (Magnesan et al 1999, Van Cuyk et al 2001,
Coppola et al 2004). The majority of these studies have been used for hydraulic
conductivity assessment involving repacked columns (homogeneous soil
repacked into columns) due to the difficulty in obtaining undisturbed samples.
Although indicating the capacity of the soil to remove contaminants, the results
can be misleading as the medium is not equivalent to in-situ conditions.
Additionally, other studies used soil columns for investigating specific processes.
For example, soil columns have been used for assessing pollutant attenuation
and removal characteristics with little regard to the effluent dispersal process of
the soil (Lam et al 1993, Menneer et al., 2001). Additionally, several studies
have used soil columns for assessing long term effluent acceptance rates through
the development of a biological clogging layer (Laak 1970, Daniel and Bouma
1974, Kristiansen 1981, Siegrist 1987). However, investigation into the
treatment and dispersal mechanisms of the soil medium itself had not been
investigated.
The purpose of the column study was initially to assess the suitability of
different soil types for effluent treatment, including pollutant attenuation and
removal, as well as the soil dispersal processes. The findings were compared
with the outcomes of detailed field studies. The respective changes occurring to
the soil medium as a result of effluent application were also investigated. This
included pollutant leaching processes, soil degradation, permeability and
drainage processes. The long-term behaviour of the soil cores under effluent
application was also investigated, with particular reference to the treatment and
dispersal characteristics, simultaneously with changes in the soil’s textural and
physical and chemical properties. This multifaceted approach has not been
conducted in other soil column studies published to-date, particularly in relation
to effluent treatment and dispersal processes. The results obtained from this
column study after twelve months of effluent application agreed with the
245
previous site suitability analysis and assessments discussed in Chapter 4, 5 and
6. Soils that retained an initially high CEC, %OM, medium clay content (<40%),
moderate permeability and good drainage were found to provide more suitable
treatment and dispersal of effluent in the long-term. However, several soil
columns that had very high clay content did not adequately transmit the applied
effluent to satisfactorily permit long term use. Comparatively, it was observed
that soils with a high permeability, and low CEC, %OM and clay content did not
provide sufficient attenuation and removal of effluent pollutants. Hence, these
soil types are not suitable for the treatment and dispersal of effluent from on-site
wastewater treatment systems.
The outcomes of these studies are generic and as soil types investigated are
common to the region, are of significance to South East Queensland in general
and to similar soils throughout Eastern Australia. The results and established site
assessment criteria will be beneficial to other geographic areas with similar site
and soil characteristics. Adoption of the improved site assessment techniques
will provide more appropriate identification of problem soils and thereby
minimise the high number of poorly performing systems due to unsuitable soil
conditions.
9.2 Sorption, Purification and Transport Processes influencing Availability of Pollutants
The movement of pollutants from on-site dispersal areas into the groundwater,
and eventually surface water are reliant on a number of physical and chemical
processes which may either hinder or advance contaminant transport. The most
critical factor that influences these mechanisms is the soil. Some soils,
particularly sandy soils, soils with restrictive horizons within 400mm of the
ground surface or soil influenced by seasonal or permanent saturation, do not
provide adequate treatment. Numerous studies have shown that the siting of on-
site dispersal areas on these soil types increase the risk of contamination of both
groundwater and surface water, particularly in areas with high system densities
(Robertson et al 1991, Paul et al 1995, Geary and Whitehead 2001, Carroll and
246
Goonetilleke 2004). These studies have indicated that significant nitrate and
faecal contamination of shallow groundwater aquifers were evident in urban
developments utilising on-site dispersal areas for treatment and dispersal of
effluent. The high correlation found between contaminants typical of effluent
indicated that the major source of the contamination were on-site systems. This
can be further exacerbated by high densities of on-site systems situated in areas
with unsuitable soil and site characteristics.
A range of changes occur as the effluent travels through the subsurface. The
constituents of the effluent react with each other as well as with the soil matrix.
Cation exchange in soils has a significant influence on the nutrient holding
capacity and is a significant process occurring in soil dispersal areas. The
continued application of effluent will cause a redistribution of ions on the
exchange sites of the receiving soils. Cation exchange has the ability to aid the
adsorption of cations throughout the soil profile. The degree to which a
particular cation is adsorbed will depend on its concentration relative to other
cations and its relative affinity for the absorbing surface. Studies indicated that
high cation exchange capacity and clay content provided greater cation
exchange and therefore contaminant adsorption characteristics. Mass losses or
gains due to the exchangeable reactions related to transport distance were
greater in the unsaturated zone than in the saturated zone. The organic matter,
clay type and content along with effluent flow conditions which governed ion
movement were critical in evaluating the distribution of these cations.
The research study investigated the extent of effluent travel and the ability of the
soil to remove pollutants contained in the effluent by adsorption and/or nutrient
uptake. Results found that the subsurface application of domestic sewage
effluent caused appreciable changes in pH, EC, exchangeable cations such as Ca,
Mg, Na and CEC (or ECEC), compared to control soils, but this was dependant
on the position of the site within the landscape and depth to the restrictive
horizon. By monitoring these parameters, specific site characteristics and
treatment performance allowed comprehensive assessment of each site for the
likely deterioration of the soil structure due to sewage effluent dispersal. A
significant increase in sodium concentration occurred together with a decrease
247
in calcium concentration through many soil profiles. The detrimental impact of
an increase in sodium concentration associated with a reduction in calcium
concentration is the increased hazard of clay particle swelling and dispersion.
This deterioration will lead to soil dispersion from increased exchangeable Na.
Thus increased Exchangeable Sodium Percentage (ESP) will lead to a reduction
in soil pore size and consequently a reduced soil hydraulic conductivity. High
concentrations of cations such as Na and Mg were found to cause dispersion of
the clay particles and strongly impede water flow through the soil.
Similar to the study by Heng et al (1999) on a Red Ferrosol soil which examined
the leaching behaviour of applied cations and anions under contrasting flow
conditions, the column study found the leaching process was dominated by the
soil’s water flow characteristics and when the flow was greater than 50mm per
day, showed little influence of surface chemical reactions. This demonstrates
that the rate of water movement influences the soil cation exchange reactions by
determining how much of the soil’s CEC interacts with the percolating solution.
Thus at low flow rates, solutes are in significant contact with the soil matrix as
effluent percolates through the soil, allowing greater opportunity for chemical
reactions to take place.
The porous nature of soil can provide an ideal media for absorbing and
transmitting effluent. A sinuous flow path through soil pores that is neither too
rapid nor too slow allows for a variety of natural treatment processes to take
place. Research findings indicated that the improvement in soil water quality
appeared to take place within the initial 1 metre of travel away from the soil
dispersal area even in sites that are poorly drained. The amount of purification
would be determined by the soil processes taking place in the initial few metres
of travel. This is based on the premise, that the amount of pollutants removed
from sewage effluent will be determined by the site specific soil characteristics
while the remainder of the pollutants will eventually percolate into the
groundwater. In a given area, the total quantum of pollutants percolating into the
groundwater will be determined by the density of on-site sewage treatment
systems. This will be a crucial issue particularly in the case of poor soil
conditions or environmentally sensitive groundwater resources.
248
A strong correlation was identified between the depth to the restrictive horizon
measured at a site and observed treatment performance. In cases where the
restrictive horizon was less than 0.4m from the surface, inadequate purification
of effluent was a common outcome.
Limited studies have specifically investigated the dynamics of cation movement
in soils which are important in processes such as effluent dispersal and salt
removal. Phillips (2002) and Redding et al (2001) conducted leaching studies on
land application areas under piggery effluent. Transportation of cations through
soil can cause potential increases in salt load not only in the soil profile, but also
groundwater or receiving water bodies. A good understanding of the interaction
between cations in solution and soils will help in developing better design
strategies for effluent application. In both field and column studies where
effluent ponding was observed, salt accumulation in the soil significantly
increased, independent of drainage class. This indicated that structural
breakdown of the soil or clogging of soil pores by organic matter would lead to
restricted water entry and change the moisture regime of the soil. Where salt is
continually added to the soil by the effluent, it is important that there is
continuous movement of water for leaching of salt through the profile. Without
this continuous leaching, salt can build up to levels that may be harmful to the
landscape and vegetation. Monitoring of electrical conductivity (EC) within the
soil profile allows warning of any adverse salt build-up.
Multivariate analytical techniques (PCA, Cluster analysis and Discriminant
analysis) identified similarities in the soil data sets. The analysis assisted in
characterising appropriate soils and determined their long-term suitability for
effluent treatment and dispersal which otherwise would be extremely difficult to
detect using univariate statistical methods. The PCA and Cluster analysis
provided new insights into the long-term assessment of soil behaviour under
effluent dispersal. The studies enabled the detection of similarities or differences
between soils and correlations among properties that were clearly not evident
from the univariate statistical data analysis where few differences in specific
parameters were noted. Multivariate statistical methods provide the ability to
differentiate the most suitable soils for long-term effluent application. This
249
makes it possible to predict which soils are likely to fail hydraulically taking
into consideration the clay content, electrical conductivity and exchangeable
sodium content. The assessment of long term behaviour of soils under effluent
dispersal should be conducted as a multivariate study to investigate the
significance of all related factors. Although certain individual factors may
indicate a stronger influence, the cumulative effect caused by several minor
factors could be more significant in influencing the long term sustainability of
on-site dispersal areas.
For continued long term application of effluent to be successful, it is essential
that infiltration and drainage characteristics of soil dispersal areas do not decline
to levels where flow is impeded. Also critical is how the long term application
of nutrients and cations alters the capacity of a soil to cope with continued
effluent application and whether any leaching occurs.
9.3 Assessment Criteria for Long Term Behaviour
The need for developing reliable assessment criteria for on-site dispersal areas
has become more imperative in recent years due to the inherent environmental
and public health concerns caused by poor performance of on-site wastewater
treatment systems. Although AS/NZS1547:2000 outlines approaches that have
been developed for the assessment of on-site wastewater dispersal areas, several
deficiencies in these approaches have however undermined their overall
usefulness and acceptance. These include:
1. lack of scientific data and knowledge for the development of the
assessment criteria associated with the failure of on-site wastewater
dispersal areas;
2. current methods are typically focussed on the dispersal of effluent with
little attention given to whether the soil is capable of providing adequate
treatment; and
3. on-site dispersal areas should be designed to conform to the site conditions
encountered rather than requiring the site conditions to conform to criteria
250
established for prescriptive designs. This allows more flexibility to meet
site constraints.
In developing scientifically robust predictive assessment criteria that is generic
and can be universally applied, these deficiencies need to be investigated. This
will allow the integration of scientific knowledge into assessment criteria and
design concepts that lead to the successful long term performance of on-site
dispersal areas.
Detailed characterisation and analysis found that poor site and soil evaluation
was the most likely cause of premature failure of the soil dispersal areas.
Comprehensive drainage characterisation, depth of unsaturated soil (seasonally
and permanently), depth to restrictive horizon, ion exchange capability and
adequate soil classification to depth are critical factors that need to be addressed
to improve long term performance and sustainability of on-site soil dispersal
areas.
The results of the studies confirmed that by determining the site location, its
position in the landscape, slope and other relevant topographic features, that it is
possible to determine whether more detailed soil chemical investigations are
justified. Soil chemistry in conjunction with soil physical characteristics and
drainage factors are an invaluable predictive tool for evaluating the long-term
performance of effluent dispersal areas. However, soil chemistry does not
necessarily add value to a suitability assessment in the case of a well-drained
site on an upper position on a landscape unless the depth to the restrictive
horizon is less than 400mm from the surface. Its greater value is in the case of
soils in the lower position in the landscape. These soils generally exhibit poor
drainage and need further evaluation and characterisation in terms of soil
physical and chemical analysis to assess their suitability for effective effluent
treatment and dispersal. Very poorly drained sites can be deemed unsuitable for
subsurface effluent dispersal especially in small lot developments, even without
further analysis.
251
It is generally considered that a major consequence of wastewater application is
that Na+ can induce changes in soil properties with the likelihood of soil ESP
increase, leading to decreased permeability of water through the soil and
subsequent hydraulic failure (Halliwell et al 2001, Balks et al 1998 and
Magnesan et al 1998). Research findings confirm this and describe how the type
of clay and clay content along with electrical conductivity and exchangeable
sodium content have the potential to be used as possible indicators of soil
degradation under effluent application. Some of these chemical properties can
be measured in the field by portable instruments and these properties would be
useful in determining the most suitable soils for sustainable effluent irrigation.
These parameters would also help to predict gradual adverse changes in other
soil properties such as hydraulic conductivity, leaching of nutrients and
structural integrity of the soil. By identifying soil properties that are sensitive to
minor changes can ensure that continued effluent application is sustainable in
the long-term and will not eventually lead to soil degradation.
In the course of the research undertaken, assessment criteria were developed to
reflect the dynamic and complex nature of the soil dispersal area in which
treatment and dispersal of effluent occurs. The physical and chemical properties
of a site and soil which can be used to predict suitability for long term effluent
treatment and dispersal include:
Moderate to slow drainage (permeability) to assist the movement of effluent
(percolation) through the soil profile and allow adequate time for treatment
and dispersal to occur. With longer percolation times, the opportunity for
exchange and transport processes increase.
Significant soil cation exchange capacity and dominance of exchangeable
Ca2+ or exchangeable Mg2+ over exchangeable Na+. Although a soil
dominated by Mg2+ is found to promote dispersion of soil particles to some
extent, its impact is far less than that of Na+. A stable soil would have a Ca:
Mg ratio > 0.5.
Low exchangeable Na+ content to maintain soil stability.
Minimum depth of 400mm of potentially unsaturated soil before
encountering a restrictive horizon, to permit adequate purification to take
place.
252
Clay type with Illite and mixed mineralogy soils are the most sensitive to
Na+. In general, significant increases in ESP occur in soils with 30 to 40%
clay and in the presence of illite clay. Small amounts of smectite clays
enhance treatment potential of a soil.
Along with the need to integrate the factors described above in understanding
soil structure stability, the research highlighted that in-depth knowledge of the
local soil characteristics and associated soil hydrology is essential for a better
prediction of long-term performance of effluent dispersal areas.
253
CHAPTER 10.0
CONCLUSIONS AND RECOMMENDATIONS
10.1 Conclusions
Due to the inherent treatment performance issues associated with on-site
wastewater treatment systems, failure of the dispersal area is a common scenario
and can lead to environmental and public health impacts. Typically, these issues
are related to the inadequate assessment of site and soil characteristics, and the
general management of these systems. In order to obtain adequate wastewater
treatment using on-site systems, more scientifically robust methods of assessing
site suitability is essential. The main focus of this research project was to
develop an integrated approach for assessing long term performance of sites
under wastewater application. Both internal soil properties and external
landscape factors were integrated for predicting long term performance. The
research aims and objectives were achieved through the development of three
fundamental processes. These were:
• Identification of critical site and soil processes and characterisation.
• Integration of site and soil factors and analysis of treatment performance
(i) assessment of soil suitability for effluent treatment and dispersal;
(ii) assessment of contamination of soil and groundwater as a result
of dispersal area failure; and
(iii) integrated assessment of treatment performance and
identification of failure mechanisms relating to dispersal area
siting and design.
• Development of assessment criteria for long term performance of sites.
Detailed characterisation of both site and soil factors and analysis of treatment
performance found that poor site and soil evaluation was the most likely cause
254
of premature failure of the majority of soil dispersal areas monitored during the
research. Site and soil assessment should include comprehensive drainage
characterisation, depth of unsaturated soil (seasonally and permanently), depth
to restrictive horizon, ion exchange capability and adequate soil classification to
depth as critical factors that need to be addressed to improve long term
performance and sustainability of on-site soil dispersal areas. This lead to
forming an integrated approach to assessing long term performance of soil
dispersal areas with the following assessment criteria developed:
Moderate to slow drainage (permeability) to assist the movement of effluent
(percolation) through the soil profile and to allow adequate time for
treatment and dispersal to occur. With longer percolation times, the
opportunity for exchange and transport processes increase.
Significant soil cation exchange capacity and dominance of exchangeable
Ca2+ or exchangeable Mg2+ over exchangeable Na+. Although a soil
dominated by Mg2+ is found to promote dispersion of soil particles to some
extent, its impact is far less than that of Na+. A stable soil would have a Ca:
Mg ratio > 0.5.
Low exchangeable Na+ content to maintain soil stability.
Minimum depth of 400mm of potentially unsaturated soil before
encountering a restrictive horizon, to permit adequate purification to take
place.
Clay type with Illite and mixed mineralogy soils being the most sensitive to
Na+. In general, significant increases in ESP occur in soils with 30 to 40%
clay and in the presence of illite clay. Small amounts of smectite clays
enhance treatment potential of a soil.
In order to overcome the inherent risks associated with the poor performance of
on-site dispersal areas, more universal and scientifically robust assessment
criteria are needed. The assessment criteria developed in the course of the study
were specifically aimed at limiting the inherent failures associated with on-site
dispersal areas. Detailed investigations allowed the incorporation of scientific
information into the assessment of on-site dispersal area siting and design and
will help to reduce poor on-site system performance.
255
10.2 Recommendations
Further evaluation, testing and review of the assessment criteria formulated and
developed in this research needs to be carried out. An integrated analysis of site
and soil factors needs to be undertaken by an assessor/evaluator who has the
analytical skills to assess changing field conditions. This will lead to an
improved determination of the assimilative capability of soils at a particular site
and more appropriate siting and design which is crucial for the sustainable and
successful operation of on-site dispersal areas.
Although the developed predictive assessment criteria will help to strengthen the
current standards and guidelines, there still remain several important areas that
have not been addressed through this research. Therefore, further research in
these areas is recommended to strengthen the effectiveness of the assessment
criteria developed. These are:
System density is an important issue relating to the siting and design of on-
site wastewater treatment systems. Increased densities of on-site systems are
well recognised for increasing the potential for contamination of water
bodies, particularly groundwater. The acceptable density of on-site dispersal
areas will differ depending on the respective soil and site characteristics.
However, there currently exists no scientifically defensible criteria that helps
to understand the optimum density of on-site systems based on soil
conditions in order to avoid detrimental impacts to water bodies.
Previous research has focussed on the behaviour and environmental
consequences of N and P in receiving soil and water bodies, whereas the
impact of large losses of cations has been ignored. Significant loss of cations
from soils has been found to be detrimental to soil structure and may lead to
increasing soil salinity. Further investigation of on-site wastewater dispersal
sites is required to determine the impact of cations such as Ca2+, Mg2+, K+
and Na+ on soil and water quality. Relationships between cations and nitrate
leaching need to be evaluated as nitrate anions are generally accompanied by
cations to maintain charge neutrality.
256
Further research needs to be conducted on clay soils as many of the reported
failing or poorly operating on-site systems occur in clay soils, whereas most
research literature relates to studies on sandy soils. Detailed soil studies need
to be conducted on well structured clay soils (Ferrosols, Dermosols and
Kandosols) to enhance the current knowledge base. This may include long
term monitoring and instrumentation of new on-site treatment systems. This
in turn will provide knowledge on a broad range of soils and site
characteristics and a greater understanding of the interactions between
hydraulic and treatment mechanisms.
Understanding the critical processes and controls involved in on-site dispersal
areas and determining a site’s ability to effectively treat and disperse effluent
will result in substantial improvement on the long term performance of on-site
wastewater treatment systems.
257
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283
APPENDIX A
EFFLUENT QUALITY DATA FROM SAMPLING SITES
284
Average (range) concentrations of effluent quality data from sample monitoring locations Table A.1 Effluent quality parameters analysed and notation Parameter Notation Unit Chemical Contaminants pH pH Electrical Conductivity EC mS/cm Chlorides Cl- mg/L Total Nitrogen TN mg/L Total Organic Carbon TOC mg/L Total Dissolved Solids TDS mg/L
Microbiological Contaminants Feacal Coliforms FC cfu/100mL
NOTES:
1. Under ‘sample code’, the first digit refers to the site no. and the second letters
refer to the piezometer locations.
• A refers to the location 1 m away from the effluent disposal area and B refers
to the location 3 m away.
• T refers to the sample taken from the distribution box.
2. ‘ns’ refers to no sample taken.
3. ‘NR’ refers to no result.
285
Table A.2 Average concentrations of chemical constituents at sample monitoring locations
Effluent Samples 19 to 22 July, 1999
Sample Code Soil Type pH EC(mS/cm)
Total N (mg/L)
TOC (mg/L)
TDS (mg/L)
Faecal Coliforms (Count)
1A Chromosol 2 32 420 340 1B Chromosol 2.6 17 420 9 2A Chromosol ns 2B Chromosol 4.8 59 550 700 3A Chromosol 31 30 1350 <1 3B Chromosol 4.9 42 1180 <1 4A Chromosol 60 16 900 1 4B Chromosol Sample spilled - - - <1 5A Chromosol Abandoned ns - - - 5B Chromosol Abandoned ns - - - 6A Dermosol Abandoned ns - - - 6B Dermosol Abandoned ns - - - 7A Chromosol Relocated ns - - - 7B Chromosol Relocated ns - - - 7C Chromosol Relocated ns - - - 7D Chromosol Relocated ns - - - 8A Sodosol 62 27 3230 2800 8B Sodosol 63 22 2270 3000 9A Sodosol 2.5 31 1090 >6000 9B Sodosol 1.5 25 660 580
10A Kandosol Abandoned ns - - - 10B Kandosol Abandoned ns - - - 11A Kandosol 2.2 17 150 12 11B Kandosol ns - - - 12A Kurosol 1.5 28 420 2200 12B Kurosol 21 58 760 >6000 13A Kurosol Abandoned ns - - - 13B Kurosol Abandoned ns - - - 14A Chromosol 7.3 0.562 2.6 37 720 >6000 14B Chromosol 7.6 0.374 2.3 28 390 >6000
286
Table A.2(cont) Average concentrations of chemical constituents at sample monitoring locations
Effluent Samples 9 to 11 August, 1999
Sample Code Soil Type pH
EC (mS/cm)
Total N
(mg/L)TOC
(mg/L)TDS
(mg/L)
Faecal Coliforms (Count)
Chloride (mg/L)
1A Chromosol 6.9 1.42 1.7 30 340 120 41 1B Chromosol 6.9 1.27 4.6 23 410 30 51 IT Chromosol 8.1 4.22 71 87 760 >6000 3A Chromosol 7.2 2.73 24 33 1170 <10 340 3B Chromosol 7.5 2.23 3.8 44 1020 <10 230 3T Chromosol 5.9 1.75 43 16 560 >6000 4A Chromosol 5.1 1.95 54 11 820 <10 240 4B Chromosol 6.2 1.45 4.5 13 450 <1 220 4T Chromosol ns ns ns ns ns <1 7A Chromosol ns ns ns ns ns ns 7B Chromosol 6.2 0.98 8.3 46 310 <10 33 7C Chromosol 6.7 1.16 1.7 9.6 230 4 45 7D Chromosol 6.8 0.89 2.3 15 240 10 43 7T Chromosol 6.7 3.61 240 93 690 >6000 8A Sodosol 6.6 10.06 43 28 4280 1100 2300 8B Sodosol 6.7 8.15 14 19 3200 4900 1700 8T Sodosol 8.1 3.36 170 110 580 >6000 9A Sodosol 7.3 2.9 7 18 1300 30 390 9B Sodosol 6.9 2.39 2.3 24 1040 70 500 9T Sodosol 7.5 2.17 75 50 380 3000
11A Kandosol 6.1 0.77 5.7 30 190 20 7.9 11B Kandosol 6.9 1.33 4.7 35 260 4100 15 11T Kandosol 8.6 1.48 6.3 19 400 <1 12A Kurosol 7 0.47 4.4 26 580 <100 49 12B Kurosol 6.6 0.37 4.3 45 2540 300 47 12T Kurosol 8.1 1.61 158 52 620 >6000 14A Chromosol 7.4 0.67 2.5 26 440 >6000 46 14B Chromosol 7 0.49 2 20 520 >6000 36 14T Chromosol 8.3 2.07 170 86 550 >6000 NR 15A Ferrosol 5.8 1.03 27 7 320 10 36 15B Ferrosol 5.8 1.3 29 5 340 <10 41 15T Ferrosol 7.7 1.78 49 78 320 >6000 NR 16A Ferrosol 7.2 2.07 46 46 870 5600 400 16B Ferrosol 5.8 1.26 6 5 620 <10 330 16T Ferrosol 7.4 3.4 150 100 1240 >6000 NR 16T Ferrosol 7.7 3.44 66 130 1000 >6000 380
287
Table A.2(cont) Average concentrations of chemical constituents at sample monitoring locations
Effluent Samples 30 August, 1999
Sample Code Soil Type pH
EC (mS/cm)
Total N
(mg/L)TOC
(mg/L)TDS
(mg/L)
Faecal Coliforms (Count)
Chloride (mg/L)
1A Chromosol 6.6 1.19 3.7 40 460 800 37 1B Chromosol 6.88 1.07 4.8 23 470 40 54 IT Chromosol 7.83 2.35 190 72 600 14000 3A Chromosol 6.75 1.3 3.4 41 460 1 54 3B Chromosol 6.47 1.3 7.6 34 500 10 44 3T Chromosol 5.8 1.85 56 24 680 >6000 4A Chromosol 5.1 1.95 54 11 820 <10 240 4B Chromosol 6.2 1.45 4.5 13 450 <1 220 4T Chromosol 7.63 2.26 162 68 660 14000 7A Chromosol 5.75 1.16 24 36 410 7000 31 7B Chromosol 5.79 0.7 7.9 99 1220 >60000 25 7C Chromosol 7.94 3.49 300 170 280 >60000 7D Chromosol 6.3 1.05 1.7 17 290 1800 45 7T Chromosol 6.18 0.98 1.3 15 820 56 43 8A Sodosol 5.65 6.37 60 29 3000 200 1600 8B Sodosol 6.2 4.75 34 22 1830 190 970 8T Sodosol 7.98 3 280 180 820 >60000 9A Sodosol 6.85 2.75 2.3 25 1260 1100 420 9B Sodosol 6.18 2.05 3.1 31 940 >60000 290 9T Sodosol 6.25 0.87 34 110 410 37000
11A Kandosol 5.7 0.83 1.7 25 190 390 8.5 11B Kandosol ns ns ns ns ns ns ns 11T Kandosol 6.9 1.14 28 84 460 40 12A Kurosol 6.1 1.09 21 25 500 10 38 12B Kurosol 5.6 0.78 7.9 50 2300 <10 29 12T Kurosol 8.15 1.81 171 61 855 >6000 14A Chromosol 6.8 1.18 6.5 30 590 >60000 40 14B Chromosol 6.5 1.07 5.2 29 690 450 30 14T Chromosol 7.2 3.01 320 180 720 >60000 15A Ferrosol 5.23 0.75 34 7 430 14 56 15B Ferrosol 5.7 0.88 25 5 260 <1 36 15T Ferrosol 7.14 1.13 53 83 330 >60000 16A Ferrosol 5.9 1.64 14 7 800 <1 340 16B Ferrosol 5 1.4 3.9 7 670 <1 330 16T Ferrosol 6.92 3.4 200 110 1270 >60000
288
Table A.2(cont) Average concentrations of chemical constituents at sample monitoring locations
Effluent Samples 13 September, 1999
Sample Code Soil Type pH
EC (mS/cm)
Total N (mg/L)
TOC (mg/L)
TDS (mg/L)
Faecal Coliforms (Count)
Chloride (mg/L)
3A Chromosol 6.6 1.49 7.9 38 390 140 61 3B Chromosol 6.6 2.51 ns ns ns 7000 ns 7A Chromosol 6.5 1.63 ns ns ns 600 ns 7B Chromosol 6.5 1 6 37 320 12000 32 7C Chromosol 6.7 0.97 3.6 16 260 5 58 7D Chromosol 6.7 0.95 2.6 21 270 120 52 7T Chromosol 7.8 3.27 330 100 680 800000 -
12A Kurosol 6.3 1.16 24 29 460 20 38 12B Kurosol 5.8 0.69 6.5 60 2150 5 29 12T Kurosol 8.05 1.67 153 82 935 >6000 15A Ferrosol 5.4 0.92 33 7 390 20 55 15B Ferrosol 5.7 0.9 23 7 260 31 37 15T Ferrosol 7.2 1.77 70 100 330 220000 - 16A Ferrosol 5.6 1.8 18 7 740 35 390 16B Ferrosol 4.95 1.74 3.3 8 560 1700 310 16T Ferrosol 6.95 3.52 220 130 1370 1E+07 -
289
APPENDIX B
SITE DATA FROM SAMPLING SITES, BRISBANE AND LOGAN
290
Table B.1 Site data at sample monitoring locations Site No.d
System age (yr)
Australian Soil Classificationa
Soil Textureb
A – A horizon B – B horizon
Soil Drainagec
Depth to Restrictive layer (m)
Slope (˚)
Observed Performance
A – Sandy loam 1 4 Red Chromosol B – Clay loam
Moderately well drained
0.6 >15 Satisfactory
A - Sandy loam 3 5 Brown Chromosol B – Light Clay
Imperfectly drained
0.5 <10 Trenches waterlogged
A - Sandy loam 4 3 Brown Chromosol B- Clay loam
Imperfectly drained
0.6 <5 Satisfactory
A - Sandy loam 7 2.5 Red Chromosol B – Sandy clay loam
Moderately well drained
0.7 >10 Satisfactory
A - Clay loam 8 4 Red Sodosol B – Heavy clay
Poorly drained 0.3 <5 Trenches extended
A – Clay loam 9 17 Grey Sodosol B – Heavy clay
Poorly drained 0.3 <5 Trenches replaced
A - Sandy loam 11 4.5 Red Kandosol B – Sandy clay loam
Well drained 0.7 >15 Satisfactory
A -Loamy sand 12 19 Brown Kurosol B – Sandy clay loam
Moderately well drained
0.7 >10 Satisfactory
A - Loam 14 14 Brown Chromosol B – Clay loam
Moderately well drained
0.7 >15 Satisfactory
A - Sandy loam 15 3 Red Ferrosol B- Light clay
Moderately well drained
0.7 >5 Satisfactory
A - Clay loam 16 4 Red Ferrosol B- Medium clay
Poorly drained 0.4 <5 Ponding
17 12 Yellow Chromosol Sandy Loam Moderately well drained
0.5 >5 Satisfactory
18 8 Brown Sodosol Heavy clay Very poorly drained
0.1 <5 Ponding
19 6 Yellow Chromosol Loamy sand Moderately well drained
0.5 >5 Satisfactory
A – Loamy sand 20 19 Brown Chromosol B – Clay loam
Imperfectly drained
0.3 <5 Trenches clogged
A – Loamy sand 21 5 Yellow Chromosol B – Clay loam
Well drained - >5 Satisfactory (high perm)
A – Loamy sand 22 1 Brown Chromosol B – Clay loam
Moderately well drained
0.6 >5 Satisfactory
A – Loamy sand 23 6 Brown Chromosol B – Medium clay
Moderately well drained
0.7 >10 Satisfactory
24 18 Brown Chromosol Clay loam Imperfectly drained
0.6 >5 Trenches clogged
25 5 Brown Chromosol Clay loam Imperfectly drained
0.6 >5 Satisfactory
A – Clayey sand 26 14 Brown Chromosol B – Light clay
Imperfectly drained
0.4 <5 Satisfactory
27 12 Grey Dermosol Clay loam Well drained 0.7 >15 Satisfactory A – Silty loam 28 11 Brown Kurosol
B – Medium Clay Poorly drained 0.6 >5 Satisfactory
29 5 Brown Chromosol Medium clay Imperfectly drained
0.3 >10 Trenches replaced
A - Silty loam 30 7 Brown Kurosol B - Medium, clay
Poorly drained 0.2 <5 Ponding
A - Loamy sand 31 8 Red Chromosol B - Medium clay
Imperfectly drained
0.4 >5 Satisfactory
A - Loamy sand 32 6 Brown Chromosol B – Light clay
Moderately well drained
0.8 >10 Satisfactory
A – Sandy loam 33 7 Brown Kurosol B – Light clay
Poorly drained 0.4 <5 Satisfactory
A – Clay loam 34 20 Brown Chromosol B – Medium clay
Well drained 0.2 >15 Trenches replaced
a Australian Soil Classification after Isbell (1996) b soil texture based on McDonald et al. (1990) c the classification used complies with AS/NZS 1547:2000 (Standards Australia, 2000), McDonald et al. (1990). d missing numbers are sites abandoned due to insufficient soil water sample and unreliable historical site information
291
APPENDIX C
SOIL DATA FROM SAMPLING SITES, BRISBANE AND LOGAN
292
Table C.1 Average concentrations of soil chemical constituents at sample monitoring locations – Brisbane Site No.
Depth (m)
SoilType
%Clay
pH Conductivity (mS/cm)
Cl N (mg/kg)
P (mg/kg)
Organic Carbon
%
Nitrogen %
OC/N Ratio
ESP
%
ECEC Ca:Mg Ratio
Ca
(meq/100g)
Mg
(meq/100g)
Na
(meq/100g)
K
(meq/100g)
Al
(meq/100g)
RC1 0-0.1 5 5.6 0.20 7.40 1.60 44.00 1.80 0.15 12.00 1 19 1.88 12.00 6.40 0.24 0.35 0.00
RC1 0.2-0.3 5 6.0 0.15 <1 1.80 1 24 1.56 14.00 9.00 0.32 0.26
RC1 0.5-0.6 25 6.7 0.12 6.40 <1 3 40 0.95 19.00 20.00 1.10 0.20
RC1 0.8-0.9 20 7.2 0.09 <1 <1 4 46 0.76 19.00 25.00 2.00 0.19
RC1 1.0-1.1 15 7.3 0.10 <1 <1 5 50 0.68 19.00 28.00 2.40 0.22
RC1 1.1-1.2
R
ed C
hrom
osol
15 7.4 0.06 <1 <1 5 42 0.67 16.00 24.00 2.00 0.16
BC1 0.0-0.1 5 5.3 0.12 7.30 1.00 19.00 1.75 0.11 15.91 1 4 1.67 2.50 1.50 0.06 0.40
BC1 0.2-0.4 10 5.3 0.06 <1 <1 1 2 1.29 1.10 0.85 0.06 0.14
BC1 0.5-0.6 50 5.0 0.09 25.90 <1 18 9 0.06 0.41 6.50 1.60 0.27
BC1 0.8-1.0 15 5.3 0.08 58.50 <1 20 12 0.07 0.58 8.30 2.30 0.35
BC1 1.0-1.1
B
row
n C
hrom
osol
15 5.3 0.09 88.80 2.40 20 17 0.02 0.28 13.00 3.50 0.56
BC2 0.3 14 4.5 0.06 1 0.65 4.49 0.19 23.63 4 4 0.74 0.74 1.00 0.06 0.17 1.1
BC2 0.6 29 4.2 0.08 26 0.65 4 9 0.12 0.41 3.40 0.68 0.21 2.9
BC2 0.9 Bro
wn
Chr
omos
ol
35 4.1 0.08 37 7 5 8 0.04 0.14 3.80 0.94 0.16 3.5
RC2 0.3 9 5.9 0.12 6 1.4 1 25 4.30 19.0 4.4 0.36 0.40
RC2 0.6 Red
C
hro
16 7.3 0.17 8 1.0 2 34 5.60 28.0 5.0 0.41 0.29
RS1 0.0-0.1 15 5.7 0.14 15.50 <1 9.00 1.65 0.13 12.69 4 7 1.23 3.80 3.10 0.28 0.27
RS1 0.2-0.3 20 5.8 0.11 47.50 <1 9 7 0.59 2.20 3.70 0.56 0.11
RS1 0.5-0.6 60 5.0 0.14 126.80 <1 15 9 0.13 0.91 7.10 1.40 0.09
RS1 0.8-0.9 65 4.7 0.37 454.50 <1 28 14 0.07 0.69 9.50 4.10 0.10
RS1 1.0-1.1
G
rey
Sodo
sol
75 4.6 0.55 680.90 <1 34 18 0.08 0.88 11.00 6.20 0.11
293
Table C.1 (cont) Average concentrations of soil chemical constituents at sample monitoring locations – Brisbane Site No.
Depth (m)
Soil %Clay
pH Conductivity (uS/cm)
Cl N (mg/kg)
P (mg/kg)
Organic Carbon
%
Nitrogen %
OC/N Ratio
ESP ECEC Ca:Mg Ratio
Ca
(meq/100g)
Mg
(meq/100g)
Na
(meq/100g)
K
(meq/100g)
Al
(meq/100g)
GS1 0.2 24 5.8 0.11 31 2 9 1.42 4.7 3.3 0.22 0.4
GS1 0.5 58 5.5 0.37 264 6 8 0.52 3.0 5.8 0.47 0.2
GS1 0.8
R
ed S
odos
ol
49 5.2 0.48 315 16 11 0.05 0.45 8.8 1.4 0.15
RKa1 0.0-0.1 5 5.4 0.30 13.30 <1 63.00 3.15 0.29 10.86 2 34 1.75 21.00 12.00 0.65 0.28
RKa1 0.2-0.3 15 5.8 0.22 10.90 0.90 2 30 2.15 20.00 9.30 0.53 0.18
RKa1 0.5-0.6 20 5.4 0.11 6.90 <1 4 43 1.05 21.00 20.00 1.80 0.16
RKa1 0.8-0.9 20 5.5 0.07 12.00 <1 11 39 0.84 16.00 19.00 4.30 0.16
RKa1 0.9-1.1
R
ed K
anda
sol
20 6.0 0.08 7.00 <1 11 50 0.83 20.00 24.00 5.70 0.18
BKu1 0.3 7 4.9 0.12 20 0.65 3.35 0.198 16.92 1 5 1.38 2.20 1.60 0.05 0.15 0.4
BKu1 0.5 21 4.7 0.07 22 0.65 1 2 0.20 0.22 1.10 0.12 0.08 0.6
BKu1 0.8
B
row
n l
27 4.9 0.13 83 0.65 13 10 0.02 0.10 6.80 1.20 0.16 0.6
BC3 0.1 20 5.1 0.06 26.00 <1 2 5 0.30 0.70 2.30 0.10 0.20 1.20
BC3 0.4 50 4.6 0.07 41.00 <1 3 13 0.00 0.01 7.30 0.44 0.20 4.10
BC3 0.5
Bro
wn
Chr
omos
ol
40 4.5 0.09 67.00 <1 4 17 0.00 0.03 9.70 0.61 0.30 4.40
RF1 0.2 18 5.3 0.07 17 0.65 0.42 0.07 6.00 1 7 1.42 3.70 2.60 0.60 0.21 0.05
RF1 0.5 37 4.8 0.11 12 1.5 1 7 1.44 3.60 2.50 0.09 0.21 0.03
RF1 0.8
R
ed F
erro
sol
44 4.1 0.16 9 12 1 6 0.87 2.70 3.10 0.12 0.16 0.12
294
Table C.1 (cont) Average concentrations of soil chemical constituents at sample monitoring locations – Brisbane Site No.
Depth (m)
Soil %Clay
pH Conductivity (uS/cm)
Cl N (mg/kg)
P (mg/kg)
Organic Carbon
%
Nitrogen
%
OC/N Ratio
ESP
%
ECEC
meq/100g
Ca:Mg Ratio
Ca
(meq/100g)
Mg
(meq/100g)
Na
(meq/100g)
K
(meq/100g)
Al
(meq/100g)
RF2 0.0-0.1 20 4.6 200 8.90 <1 39.00 2.15 0.15 14.33 3 7 1.36 3.80 2.80 0.19 0.55
RF2 0.2-0.4 30 4.6 140 18.00 <1 5 8 0.38 2.10 5.50 0.41 0.18
RF2 0.5-0.6 50 4.3 100 45.60 0.70 6 6 0.09 0.47 5.40 0.40 0.15
RF2 0.8-1.0 60 4.0 100 49.10 <1 6 7 0.03 0.16 6.00 0.42 0.19
RF2 1.0-1.1
R
ed F
erro
sol
65 4.0 90 46.90 <1 7 7 0.02 0.14 6.30 0.50 0.26
295
Table C.2 Average concentrations of soil chemical constituents at sample monitoring locations - Logan Site No
Depth (m)
Soil Type
% Clay
pH EC (mS/cm)
Cl mg/kg
NO3 (mg/kg)
Ca (meq/100g)
Mg (meq/ 100g)
Na (meq/ 100g)
K (meq/100g)
Al (meq/100g)
17C 0 -0.1 7 5.1 0.07 19.5 0.9 0.64 0.56 BQ 0.08 0.36
17C 0.2-0.3 20 4.8 0.04 16.9 1.4 0.27 0.64 0.13 0.06 0.64
17C 0.4-0.5 16 4.5 0.06 18.2 <1 0.14 3.5 0.43 0.21 3.98
17C 0.7-0.8 34 4.4 0.05 36.7 0.8 0.04 2.9 0.32 0.13 5.51
17C 1.0-1.2
Y
Chr
omos
ol
32 4.4 0.04 37.3 <1 0.05 2.5 0.3 0.14 4.67
18C 0.0-0.1 75 4.4 0.11 56.7 <1 0.45 0.65 0.33 0.08 0.74
18C 0.2-0.3 75 6.1 0.2 162.3 <1 0.19 3.4 2.2 0.03
18C 0.3-0.4 70 7.5 0.3 262.4 1 0.17 0.9 4 0.06
18C 0.5-0.6 79 8.2 0.35 347.1 1.3 0.15 5.6 5.4 0.06
18C 0.9-1.0
B
Sod
osol
74 9 0.58 647.6 1 0.25 8 9.4 0.19
19C 0.0-0.1 0 6.6 0.07 6.1 3.9 2.7 1.3 0.23 0.24 0.05
19C 0.1-0.2 0 6.6 0.05 8.2 1.1 1.1 0.49 0.08 0.13 0.15
19C 0.3-0.4 7 5.9 0.04 8.2 0.7 0.44 0.29 0.02 0.10
19C 0.4-0.5 10 5.8 0.04 <1 0.7 0.25 0.18 0.06 0.15
19C 0.8-0.9
Y
Chr
omos
ol
13 5.6 0.03 6.0 <1 0.09 3.3 0.17 0.10
20C 0.0-0.1 15 5 0.08 <1 1.8 1.7 1.1 0.03 0.24 0.66
20C 0.2-0.3 14 4.8 0.06 <1 <1 0.35 2.6 0.04 0.03 0.87
20C 0.3-0.4 28 4.7 0.07 <1 <1 0.22 5 0.13 0.04 1.09
20C 0.6-0.7 34 4.3 0.09 71 <1 0.14 3.7 0.23 0.04 2.72
20C 1.0-1.1
B
Chr
omos
ol
47 3.9 0.14 75 <1 0.08 5.8 1.1 0.07 4.78
21C 0.0-0.1 4 5.2 0.08 <1 1.8 1.7 0.88 BQ 0.10 0.16
21C 0.3-0.4 3 5.2 0.04 <1 0.9 0.54 0.64 0.04 0.03 0.4
21C 0.5-0.6 9 5.2 0.03 <1 0.7 0.16 0.65 0.05 0.02 0.29
21C 0.7-0.8 10 4.9 0.03 <1 <1 0.06 2.6 0.11 0.0.05 0.29
21C 1.1-1.2
Y
Chr
omos
ol
28 5 0.03 <1 0.9 0.07 2.6 0.14 0.09 0.71
22C 0.0-0.1 0 5.1 0.06 <1 0.8 1.3 0.89 0.07 0.07 0.48
22C 0.3-0.4 12 5.1 0.04 <1 1.2 0.7 0.73 0.06 0.02 0.23
22C 0.5-0.6 0 4.7 0.04 <1 0.7 0.27 0.86 0.05 0.02 0.56
22C 0.6-0.7 19 4.6 0.04 <1 <1 0.22 1.6 0.09 0.04 0.73
22C 0.9-1.0
B
Chr
omos
ol
27 4.8 0.04 <1 1.5 0.24 3.9 0.2 0.04 1.5
23C 0.0-0.2 5 5.1 0.04 <1 <1 0.47 0.26 0.07 0.05 0.23
23C 0.3-0.4 4 5.1 0.03 <1 <1 0.21 0.29 0.04 BQ 0.34
23C 0.6-0.7 27 4.6 0.04 <1 <1 0.04 0.84 0.05 BQ 7.97
23C 0.7-0.8 26 4.4 0.04 <1 <1 0.04 1.5 0.08 0.02 0.47
23C 1.0-1.1
B
Chr
omos
ol
52 4.5 0.03 <1 0.9 0.07 1.5 0.2 0.05 0.69
24C 0.0-0.1 0 5.1 0.06 <1 <1 0.74 0.36 0.02 0.07 0.72
24C 0.3-0.4 0 4.8 0.04 <1 <1 0.11 0.27 0.03 0.06 2.38
24C 0.6-0.7 16 5.1 0.03 <1 <1 0 0.4 0.03 BQ 3.32
24C 0.8-0.9 23 5.1 0.02 <1 <1 0.04 1 0.06 BQ IS
24C 1.1-1.2
B
Chr
omos
ol
31 5.5 0.03 <1 <1 0 2.7 0.19 0.03 3.96
25C 0.1-0.2 30 5 0.04 <1 <1 0.11 0.32 0.07 0.03 7.48
25C 0.2-0.3 33 5.1 0.04 <1 1.2 0.09 0.37 0.05 BQ 7.16
25C 0.5-0.6 18 5.1 0.05 8.0 0.8 0.05 1.3 0.16 BQ 8
25C 0.7-0.8 20 5.2 0.04 <1 <1 0.03 2.2 0.17 BQ 8.55
25C 1.0-1.1
B
Chr
omos
ol
21 5 0.04 6.0 <1 0.05 3.6 0.27 BQ 1.69
296
Table C.2 Average concentrations of soil chemical constituents at sample monitoring locations - Logan
Site No
Depth (m)
Soil Type
% Clay
pH EC (mS/cm)
Cl mg/kg
NO3
(mg/kg)Ca
(meq/100g)
Mg (meq/100g)
Na (meq/ 100g)
K (meq/ 100g)
Al (meq/100g)
26C 0.0-0.2 10 5.5 0.07 7 <1 1.1 0.65 0.05 0.13 5.82
26C 0.2-0.3 13 5.8 0.03 <1 <1 0.18 0.21 0.03 BQ 6.69
26C 0.3-0.5 15 5.6 0.02 <1 <1 0.1 0.14 0.03 BQ 2.39
26C 0.6-0.65 45 4.3 0.08 <1 <1 0.26 4.6 0.04 0.13 1.76
26C 0.9-1.0
B
Chr
omos
ol
25 4.6 0.07 15 <1 0.09 9.5 1.1 0.11 0.83
27C 0.0-0.1 15 4.9 0.16 16 28.5 4.8 1.4 0.09 0.14 1.7
27C 0.2-0.3 14 4.9 0.13 7 26 3.4 1.1 0.07 0.09 1.5
27C 0.3-0.4 16 4.9 0.11 8 18.7 3.3 1.2 0.09 0.10 1.37
27C 0.5-0.6 26 4.7 0.09 14 5.8 1.2 0.9 0.11 0.13 3.19
27C 0.6-0.7
G
Der
mos
ol
39 5 0.11 15 10.9 2.5 0.93 0.13 0.17 1.04
28C 0.0-0.1 10 4.6 0.18 54 <1 2 1.9 0.21 0.24 0.69
28C 0.1-0.2 11 4.6 0.11 23 <1 0.66 1.3 0.14 0.13 0.87
28C 0.3-0.4 30 4.7 0.08 <1 <1 0.35 1.3 0.12 0.12 1.3
28C 0.6-0.7 58 4.5 0.07 <1 0.8 0.26 2.8 0.42 0.09 2.68
28C 0.8-0.9
B
Kur
osol
34 4.4 0.08 <1 0.7 0.36 4.6 0.59 0.14 2.51
29C 0.0-0.1 40 6.6 0.16 <1 1.9 11 1.1 0.13 0.13 0.16
29C 0.2-0.3 43 4.5 0.1 17 0.7 1.3 2.9 0.52 0.07 2.61
29C 0.3-0.4 27 4.5 0.09 14 <1 0.69 4.3 0.71 0.10 2.9
29C 0.4-0.5 34 4.6 0.1 27 0.7 0.65 4 0.81 0.13 1.92
29C 0.5-0.6
B
Chr
omos
ol
74 4.5 0.16 131 0.7 0.04 6.9 1.7 0.15 1.65
30C 0.0-0.1 50 4.9 0.1 15 <1 1.4 1.2 0.32 0.05 0.95
30C 0.1-0.2 49 4.7 0.08 6 <1 0.35 1 0.28 0.04 1.41
30C 0.3-0.4 17 4.1 0.18 66 0.7 0.32 5.7 1.3 0.16 6.23
30C 0.5-0.6 28 4.1 0.27 131 0.9 0.05 7.3 2.8 0.14 6.89
30C 0.7-0.8
B
Kur
osol
30 4.2 0.33 254 <1 0 9 4.2 0.14 4.8
31C 0.0-0.1 12 4.8 0.13 <1 2.9 4.3 1.3 0.11 0.16 0.19
31C 0.2-0.3 25 4.6 0.09 <1 <1 2.2 1.2 0.1 0.12 1.8
31C 0.4-0.5 34 4 0.08 7 0.8 0.042 4.3 0.43 0.14 7.81
31C 0.9-1.0 33 4.2 0.07 16 <1 0.12 4.7 1.1 0.19 12.7
31C 1.1-1.2
R
Chr
omos
ol
40 4.6 0.06 29 <1 0.06 3.9 1.1 0.13 7.97
32C 0.0-0.2 8 4.8 0.09 <1 <1 1.6 0.76 0.04 0.06 0.47
32C 0.3-0.4 10 4.7 0.04 <1 <1 0.2 0.25 0.03 0.05 0.69
32C 0.7-0.8 5 4.7 0.03 <1 <1 0.37 0.52 0.03 0.07 0.72
32C 0.8-0.9 25 4.3 0.04 <1 <1 0.24 3.3 0.14 0.10 2.38
32C 1.0-1.1
B
Chr
omos
ol
20 4.3 0.03 <1 <1 0.3 3.9 0.18 0.08 3.32
33C 0.0-0.1 9 4.1 0.14 26 <1 0.39 1.7 0.22 0.10 3.96
33C 0.2-0.3 13 3.9 0.14 20 <1 0.23 3.8 0.43 0.10 7.48
33C 0.5-0.6 37 4 0.09 9 0.7 0.08 2.4 0.37 0.08 7.16
33C 0.8-0.9 47 3.7 0.07 13 0.7 0.03 1.4 0.3 0.08 8
33C 1.1-1.2
B
Kur
osol
77 3.9 0.07 26 <1 0 1.7 0.35 0.06 8.55
34C 0.0-0.1 14 4.9 0.13 12 0.8 3.9 4.9 0.42 0.65 1.69
34C 0.3-0.4 14 4.2 0.08 <1 0.7 0.24 2.6 0.19 0.21 5.82
34C 0.6-0.7 18 3.9 0.07 6 <1 0.08 2.4 0.22 0.17 6.69
34C 1.0-1.1 35 4.3 0.06 <1 <1 0.1 4.7 0.79 0.10 2.39
34C 1.1-1.2
B
Chr
omos
ol
34 4.5 0.06 10 <1 0.05 5.2 0.92 0.07 11.8
297
Table C.2 Average concentrations of soil chemical constituents at sample monitoring locations - Logan Site No
Depth (m)
Soil Type
ECECa
ESPb
Ca:Mg Ratio
Organic Carbon %
Total Nitrogen %
C/N Ratio
Permeability mm/day
17C 0 -0.1 2 BQ 1.14 1.31 0.06 22
17C 0.2-0.3 2 BQ 0.42
17C 0.4-0.5 9 5 0.04 2.0 @ 0.6m
17C 0.7-0.8 10 3 0.01
17C 1.0-1.2
Y
Chr
omos
ol
9 3 0.02
18C 0.0-0.1 3 BQ 0.69 1.14 0.10 11
18C 0.2-0.3 6 38 0.06
18C 0.3-0.4 11 44 0.19
18C 0.5-0.6 11 48 0.03
18C 0.9-1.0
B
Sod
osol
18 53 0.03 5.2 @ 0.8m
19C 0.0-0.1 5 5 2.08 1.46 0.08 18
19C 0.1-0.2 2 BQ 2.24
19C 0.3-0.4 1 BQ 1.52
19C 0.4-0.5 1 BQ 1.39 7.2 @ 0.6m
19C 0.8-0.9
Y
Chr
omos
ol
4 4 0.03 1.8 @ 1.2m
20C 0.0-0.1 4 BQ 1.55 0.95 0.05 19
20C 0.2-0.3 4 BQ 0.13
20C 0.3-0.4 7 2 0.04
20C 0.6-0.7 7 3 0.04 5.6 @ 0.7m
20C 1.0-1.1
B
Chr
omos
ol
14 8 0.01
21C 0.0-0.1 3 BQ 1.93 1.21 0.09 13
21C 0.3-0.4 2 BQ 0.84
21C 0.5-0.6 1 BQ 0.25
21C 0.7-0.8 2 BQ 0.02 5866 @ 0.8m
21C 1.1-1.2
Y
Chr
omos
ol
4 4 0.03
22C 0.0-0.1 3 BQ 1.46 0.88 0.08 11
22C 0.3-0.4 2 BQ 0.96
22C 0.5-0.6 2 BQ 0.31
22C 0.6-0.7 3 BQ 0.14 2.4 @ 0.8m
22C 0.9-1.0
B
Chr
omos
ol
6 3 0.06
23C 0.0-0.2 1 BQ 1.81 3.47 0.20 17
23C 0.3-0.4 1 BQ 0.72
23C 0.6-0.7 11 BQ 0.05
23C 0.7-0.8 2 BQ 0.03 0.2 @ 0.8m
23C 1.0-1.1
B
Chr
omos
ol
3 BQ 0.05
24C 0.0-0.1 2 BQ 2.06 3.75 0.18 21
24C 0.3-0.4 3 BQ 0.41
24C 0.6-0.7 4 BQ 0.00
24C 0.8-0.9 IS IS 0.04 3.2 @ 0.9m
24C 1.1-1.2
B
Chr
omos
ol
8 2 0.00
25C 0.1-0.2 10 BQ 0.34 2.89 0.15 19
25C 0.2-0.3 9 BQ 0.24
25C 0.5-0.6 11 1 0.04
25C 0.7-0.8 13 1 0.01 1.1 @ 0.9m
25C 1.0-1.1
B
Chr
omos
ol
5 4 0.01
298
Site No
Depth (m)
Soil Type
ECECa
ESPb
Ca:Mg Ratio
Organic Carbon %
Total Nitrogen %
C/N Ratio
Permeability mm/day
26C 0.0-0.2 9 BQ 1.69 2.43 0.13 19
26C 0.2-0.3 9 BQ 0.86
26C 0.3-0.5 3 BQ 0.71
26C 0.6-0.65 8 6 0.06 0.4 @ 0.6m
26C 0.9-1.0
B
Chr
omos
ol
12 9 0.01
27C 0.0-0.1 9 BQ 3.43 1.91 0.16 12
27C 0.2-0.3 6 BQ 3.09
27C 0.3-0.4 5 BQ 2.75
27C 0.5-0.6 4 2 1.33
27C 0.6-0.7
G
Der
mos
ol
5 3 2.69
28C 0.0-0.1 6 4 1.05 1.62 0.10 16
28C 0.1-0.2 4 4 0.51
28C 0.3-0.4 4 3 0.27 48 @ 0.5m
28C 0.6-0.7 7 6 0.09
28C 0.8-0.9
B
Kur
osol
9 7 0.08
29C 0.0-0.1 12 1 10.00 3.11 0.17 18
29C 0.2-0.3 8 6 0.45
29C 0.3-0.4 10 7 0.16
29C 0.4-0.5 6 10 0.16
29C 0.5-0.6
B
Chr
omos
ol
11 15 0.01
30C 0.0-0.1 4 7 1.17 2.04 0.16 13
30C 0.1-0.2 3 8 0.35
30C 0.3-0.4 16 8 0.06
30C 0.5-0.6 19 15 0.01 1.1 @ 0.6m
30C 0.7-0.8
B
Kur
osol
21 20 0.00
31C 0.0-0.1 6 2 3.31 3.69 0.22 17
31C 0.2-0.3 6 NA 1.83
31C 0.4-0.5 15 3 0.01
31C 0.9-1.0 22 5 0.03 0.4 @ 0.7m
31C 1.1-1.2
R
Chr
omos
ol
16 7 0.02
32C 0.0-0.2 3 NA 2.11 3.05 0.19 16
32C 0.3-0.4 2 NA 0.80
32C 0.7-0.8 2 NA 0.71 36.4 @ 0.6m
32C 0.8-0.9 7 2 0.07
32C 1.0-1.1
B
Chr
omos
ol
8 2 0.08 0.5 @ 1.1m
33C 0.0-0.1 7 3 0.23 1.52 0.14 11
33C 0.2-0.3 14 3 0.06
33C 0.5-0.6 11 3 0.03 1.0 @ 0.7m
33C 0.8-0.9 12 3 0.02
33C 1.1-1.2
B
Kur
osol
13 3 0.00
34C 0.3-0.4 12 3 0.80 2.37 0.16 15
34C 0.6-0.7 10 2 0.09 6.2 @ 0.4m
34C 1.0-1.1 11 2 0.03
34C 1.1-1.2 9 9 0.02
34C 0.3-0.4
B
Chr
omos
ol
9 11 0.01
BQ below quantification IS insufficient sample NA not analysed
299
APPENDIX D
SOIL COLUMN DATA
300
Table D.1 Average soil chemical constituents of soil columns
OM pH EC Cl- PO43-PO43-
- P TP NO3- -
N TKN CEC Quartz Kaolinite Illite Mixed KI Smectite Soil Type Sample % µs/cm mg/Kg mg/Kg mg/Kg mg/Kg mg/Kg mg/Kg meq/100g % % % % %
1org 20.50 6.08 170.70 155.00 0.20 0.06 3.90 28.00 31.30 3.2 55.3 16.2 9.3 0.0 0.0 2org 7.90 4.71 130.30 96.00 5.50 1.77 1.92 9.00 156.00 6.0 29.3 42.4 0.0 0.0 3.0 3org 4.70 4.75 65.00 36.00 0.50 0.16 1.00 10.00 147.00 51.2 39.8 21.0 0.0 0.0 7.8 1 col 16.00 6.17 1361.00 44.00 0.32 0.10 6.05 13.00 281.00 35.1 68.4 28.2 0.0 0.0 0.9 2 col 24.30 5.20 388.00 140.00 5.30 1.71 1.77 25.00 195.00 27.3 42.0 23.2 0.0 0.0 0.0
Col 1 Brown
Kurosol
3 col 27.30 4.90 149.00 48.00 1.52 0.49 0.55 31.00 180.00 14.6 38.9 20.1 0.0 0.0 6.8
1org 22.02 5.00 48.90 120.00 1.25 0.40 3.10 5.20 243.75 3.2 13.8 57.4 27.0 0.0 0.0 2org 18.78 4.36 42.20 103.00 0.40 0.13 0.15 10.00 170.31 27.3 9.1 67.1 21.4 0.0 0.0 3org 13.24 4.08 50.70 68.00 1.83 0.59 0.63 8.00 54.69 27.3 21.6 66.0 0.0 0.0 10.4 1 col 31.59 4.63 1441.00 18.00 0.11 0.04 0.16 9.00 93.75 27.3 10.4 76.0 12.0 0.0 0.0 2 col 26.62 4.68 435.00 34.00 0.12 0.04 0.21 19.00 93.75 21.2 26.6 61.5 9.4 0.0 0.0
Col 2 Ferrosol (Beech)
3 col 24.94 4.18 407.00 67.00 1.04 0.34 0.34 40.00 154.69 16.5 21.4 75.1 0.0 0.0 0.0
1org 4.43 5.27 20.84 72.00 2.10 0.68 0.81 13.00 132.81 14.6 94.1 3.3 0.0 0.0 0.0 2org 0.02 6.41 1912.00 85.00 0.69 0.22 0.45 29.00 204.69 7.8 95.9 0.0 0.0 0.0 0.0 3org 0.32 6.21 15.02 160.00 0.00 0.00 0.38 29.00 167.19 14.6 89.9 3.4 0.0 0.0 0.0 1 col 1.41 6.66 431.00 42.00 1.10 0.35 0.81 95.00 209.38 10.0 86.7 0.0 0.0 0.0 0.0 2 col 0.28 6.32 401.00 45.00 1.21 0.39 0.92 75.00 78.13 7.8 96.3 0.0 0.0 0.0 0.0
Col 3 Hydrosol
3 col 3.82 3.82 530.00 100.00 0.61 0.20 0.32 110.00 206.25 51.2 83.7 0.0 0.0 0.0 0.0
1org 10.18 4.65 1820.00 65.00 2.60 0.84 1.32 30.00 140.63 14.6 68.9 16.5 0.0 0.0 0.0 2org 6.59 4.82 458.00 161.00 1.60 0.52 0.65 9.00 400.00 27.3 68.4 28.2 0.0 0.0 0.2 3org 21.00 5.37 495.00 92.00 1.21 0.39 0.65 45.00 190.63 27.3 38.9 20.1 0.0 0.0 6.1 1 col 25.84 6.61 434.00 43.00 1.20 0.39 3.32 60.00 59.38 35.1 29.3 42.2 0.0 0.0 3.0 2 col 12.37 6.17 1001.00 21.00 0.01 0.00 1.55 2.00 151.56 14.6 39.8 21.0 0.0 0.0 7.8
Col 4 Brown
Chromosol
3 col 20.65 4.68 1534.00 41.00 0.13 0.04 0.16 3.00 154.69 45.1 55.3 16.2 0.0 0.0 9.3
301
Table D.1 (cont) Average soil chemical constituents of soil columns
OM pH EC Cl- PO43-PO43-
- P TP NO3- -
N TKN CEC Quartz Kaolinite Illite Mixed KI Smectite Soil Type Sample % µs/cm mg/Kg mg/Kg mg/Kg mg/Kg mg/Kg mg/Kg meq/100g % % % % %
1org 8.00 5.82 1129.00 68.00 0.36 0.12 109.68 18.00 32.81 16.5 75.0 2.0 0.0 0.0 0.0 2org 3.03 5.66 49.20 55.00 0.20 0.06 88.71 9.00 100.00 24.1 76.9 3.9 3.7 0.0 0.0 3org 14.56 6.54 435.00 156.00 0.42 0.14 251.61 12.00 110.94 11.3 51.4 39.1 0.0 0.0 0.0 1 col 21.43 5.36 643.00 86.00 2.21 0.71 138.71 120.00 243.75 12.8 58.4 5.0 6.8 0.0 0.0 2 col 21.24 5.12 496.00 100.00 0.21 0.07 161.29 35.00 162.50 35.1 55.4 10.9 6.2 0.0 0.0
Col 5 Red
Dermosol
3 col 25.76 6.36 432.00 69.00 1.20 0.39 111.29 45.00 226.56 35.1 58.4 36.5 2.9 0.0 0.0
1org 1.23 4.47 790.00 65.00 1.89 0.61 0.84 11.00 203.13 10.0 61.4 23.3 0.0 4.6 0.0 2org 5.20 4.49 151.20 270.00 2.80 0.90 1.32 0.00 79.69 14.6 75.4 14.1 0.0 4.2 0.0 3org 7.08 6.20 439.00 93.00 0.80 0.26 0.71 13.00 215.63 8.8 64.3 24.0 0.0 3.8 0.0 1 col 17.78 5.45 458.00 69.00 1.72 0.55 0.98 50.00 59.38 10.0 43.8 21.5 0.0 4.1 0.0 2 col 18.16 6.10 546.00 96.00 3.40 1.10 1.27 48.00 95.31 14.6 63.1 11.8 0.0 4.0 0.0
Col 6 Brown
Sodosol
3 col 21.10 6.40 1127.00 80.00 0.02 0.01 2.89 14.00 95.31 11.3 51.9 13.6 0.0 3.6 0.0
1org 3.12 5.81 156.40 145.00 2.40 0.77 1.19 40.00 195.31 14.6 82.0 12.0 0.0 0.0 0.0 2org 2.89 5.34 149.60 114.00 0.10 0.03 0.56 11.00 228.13 5.3 75.7 19.7 0.0 0.0 0.0 3org 8.00 3.99 146.80 132.00 4.40 1.42 2.69 100.00 143.75 10.0 55.8 43.1 0.0 0.0 0.0 1 col 17.94 5.54 1563.00 65.00 1.30 0.42 8.87 21.00 171.88 6.9 78.2 15.6 0.0 0.0 0.0 2 col 16.36 5.98 1339.00 22.00 0.02 0.01 0.66 13.00 225.00 6.9 70.3 16.3 0.0 0.0 0.0
Col 7 Brown
Kurosol
3 col 22.17 4.41 441.00 52.00 3.20 1.03 2.13 45.00 214.06 10.0 58.8 40.0 0.0 0.0 0.0
1org 10.01 4.30 45.00 65.00 5.50 1.77 1.94 1.10 103.13 5.3 87.1 11.3 0.0 1.1 0.0 2org 5.20 4.49 151.20 270.00 8.50 2.74 1.32 0.00 79.69 14.6 75.4 14.1 0.0 4.2 0.0 3org 7.08 6.20 439.00 93.00 0.30 0.10 0.71 8.00 215.63 14.6 64.3 24.0 0.0 3.8 0.0 1 col 17.78 5.45 458.00 69.00 4.23 1.36 0.98 72.00 59.38 2.2 43.8 21.5 0.0 4.1 0.0 2 col 18.16 6.10 546.00 96.00 0.81 0.26 1.27 65.00 95.31 8.8 42.5 27.1 0.0 4.0 0.0
Col 8 Brown
Dermosol
3 col 21.10 6.40 1127.00 80.00 2.70 0.87 2.89 85.00 95.31 8.8 51.9 13.6 0.0 3.6 0.0
302
Table D.1 (cont) Average soil chemical constituents of soil columns
OM pH EC Cl- PO43-PO43-
- P TP NO3- -
N TKN CEC Quartz Kaolinite Illite Mixed KI Smectite Soil Type Sample % µs/cm mg/Kg mg/Kg mg/Kg mg/Kg mg/Kg mg/Kg meq/100g % % % % %
1org 2.13 5.12 453.00 115.00 1.80 0.58 0.71 16.00 237.50 3.7 90.9 3.2 0.0 0.0 0.0 2org 3.26 5.38 1110.00 23.00 0.12 0.04 0.58 8.00 95.31 10.0 94.4 3.3 0.0 0.0 0.0 3org 5.07 5.56 322.00 65.00 0.05 0.02 0.48 4.00 85.94 4.5 82.0 10.0 5.0 0.0 0.0 1 col 3.72 6.34 478.00 25.00 1.10 0.35 8.55 40.00 31.25 4.7 81.0 3.5 0.0 0.0 0.0 2 col 18.92 6.08 829.00 65.00 0.68 0.22 2.85 16.00 34.38 6.0 56.7 5.6 7.6 0.0 0.0
Col 9 Yellow
Dermosol
3 col 29.76 5.90 1001.00 183.00 0.11 0.04 1.56 2.00 106.25 4.1 66.6 10.5 15.6 0.0 0.0
1org 3.91 5.01 100.00 103.00 2.21 0.71 1.15 5.30 8.28 3.7 79.2 18.9 0.0 0.0 0.0 2org 5.22 5.20 65.00 65.00 4.05 1.31 2.11 7.20 11.25 7.8 66.3 15.6 0.0 0.0 0.0 3org 6.81 5.60 37.50 81.00 1.70 0.55 0.88 9.00 14.06 7.8 60.0 31.0 0.0 0.0 0.0 1 col 15.89 6.33 1200.00 68.00 2.20 0.71 1.14 15.00 23.44 4.7 77.3 4.1 0.0 0.0 0.0 2 col 22.16 6.22 1103.00 65.00 1.10 0.35 0.57 8.00 12.50 6.0 71.9 10.3 0.0 0.0 0.0
Col 10 Yellow
Chromosol
3 col 25.18 6.10 1124.00 31.00 0.30 0.10 0.16 9.00 14.06 4.1 60.2 29.9 0.0 0.0 0.0
1org 5.03 6.22 241.20 154.00 1.50 0.48 1.03 80.00 125.00 6.0 90.7 3.9 0.0 0.0 0.0 2org 2.95 6.03 160.70 114.00 0.00 0.00 0.63 9.00 14.06 8.8 70.9 4.7 0.0 0.0 0.0 3org 11.60 5.90 751.00 44.00 0.14 0.05 0.37 11.00 17.19 3.7 40.3 47.9 8.9 0.0 0.0 1 col 14.53 6.35 1086.00 56.00 0.15 0.05 0.52 8.00 12.50 1.5 80.0 4.0 0.0 0.0 0.0 2 col 23.79 6.16 1508.00 13.00 0.02 0.01 0.76 18.00 28.13 4.1 56.3 6.8 3.5 0.0 0.0
Col 11 Grey
Chromosol
3 col 25.76 4.46 1215.00 39.00 0.01 0.00 0.08 1.00 1.56 2.8 51.4 38.1 2.9 0.0 0.0
1org 3.00 5.91 221.00 153.00 0.15 0.05 0.63 2.00 189.06 2.8 88.5 4.8 4.7 0.0 0.0 2org 5.30 6.03 240.00 171.00 0.70 0.23 0.89 0.00 209.38 5.3 57.4 13.8 27.0 0.0 0.0 3org 11.94 5.65 150.30 126.00 0.80 0.26 0.58 6.00 159.38 3.7 67.1 9.1 21.0 0.0 0.0 1 col 18.74 5.94 1657.00 16.00 0.61 0.20 0.81 2.00 145.78 4.1 66.0 21.6 10.0 0.0 0.0 2 col 29.38 6.50 464.00 63.00 1.21 0.39 1.79 80.00 206.25 2.5 68.0 9.6 19.0 0.0 0.0
Col12 Red
Kandosol
3 col 8.40 5.82 1620.00 27.00 0.02 0.01 7.74 9.00 85.94 1.5 55.4 38.9 4.8 0.0 0.0
303
Table D.2 Average soil chemical constituents of soil columns Albite Anorthite Amorphous Total clay Al Fe Mg Na Ca K Ca:Mg ECEC ESP
Soil Type % % % % % meq/100g meq/100g meq/100g meq/100g meq/100g meq/100g meq/100g % 13.9 4.4 0.7 99.8 25.5 0.01 0.00 2.18 0.13 1.08 0.15 0.50 3.56 4.04 24.0 0.0 1.0 99.7 45.4 0.03 0.00 4.22 0.35 0.18 0.04 0.04 4.82 7.26 30.4 0.0 0.9 99.9 28.8 0.01 0.00 6.82 0.54 0.13 0.09 0.02 7.67 7.04 0.0 0.0 2.0 99.5 29.1 0.00 0.01 1.48 0.20 1.11 0.28 0.75 3.07 6.50
32.0 0.0 2.6 99.8 23.2 0.00 0.00 1.52 0.15 0.22 0.04 0.14 1.93 7.77
Col 1 Brown
Kurosol
34.1 0.0 0.0 99.9 26.9 0.03 0.00 4.70 0.74 0.09 0.02 0.02 5.55 13.33
0.0 0.0 1.6 99.8 84.4 0.03 0.01 1.58 0.13 1.13 0.11 0.72 2.99 4.47 0.0 0.0 2.2 99.8 88.5 0.01 0.00 0.37 0.10 0.35 0.07 0.95 0.90 11.12 0.0 0.0 1.3 99.3 76.4 0.00 0.00 0.73 0.14 0.59 0.05 0.81 1.51 9.26 0.0 0.0 1.4 99.8 88.0 0.03 0.01 0.22 0.20 0.21 0.02 0.95 0.72 4.47 0.0 0.0 2.3 99.8 70.9 0.00 0.00 0.51 0.11 0.43 0.00 0.84 1.06 10.42
Col 2 Ferrosol (Beech)
0.0 0.0 3.3 99.8 75.1 0.02 0.00 0.45 0.08 0.21 0.00 0.47 0.75 10.18
0.0 0.1 2.1 99.6 3.3 0.02 0.00 0.66 0.07 0.39 0.02 0.59 1.17 0.48 0.3 0.0 3.6 99.8 0.0 0.00 0.00 0.18 0.14 0.30 0.05 1.64 2.33 1.80 0.0 0.5 6.0 99.8 3.4 0.02 0.00 0.26 0.13 0.14 0.02 0.54 0.57 0.89 0.0 2.6 10.7 100.0 0.0 0.00 0.00 0.82 0.10 0.54 0.02 0.66 1.47 1.00 0.0 2.1 1.4 99.8 0.0 0.00 0.00 0.22 0.12 0.09 0.02 0.41 0.46 0.82
Col 3 Hydrosol
1.6 14.4 0.2 99.9 0.0 0.28 0.00 0.12 0.10 0.14 0.02 1.17 0.45 0.19
4.4 8.2 2.0 100.0 16.5 0.01 0.00 1.48 0.20 0.50 0.11 0.34 2.30 1.36 0.0 0.0 2.2 99.0 28.4 0.00 0.00 0.03 0.04 0.01 0.02 0.33 0.10 16.01
34.1 0.0 0.0 99.2 26.2 0.03 0.00 13.98 3.49 0.15 0.13 0.01 17.78 19.63 24.0 0.0 1.4 99.9 45.2 0.06 0.01 1.31 0.28 0.35 0.00 0.27 2.00 0.80 29.0 0.0 1.1 98.7 28.8 0.00 0.01 6.16 1.25 0.30 0.09 0.05 7.81 16.01
Col 4 Brown
Chromosol
13.9 4.4 0.9 100.0 25.5 0.04 0.00 10.48 2.81 0.10 0.04 0.01 13.45 20.85
304
Table D.2 (cont) Average soil chemical constituents of soil columns Albite Anorthite Amorphous Total clay Al Fe Mg Na Ca K Ca:Mg ECEC ESP
Soil Type % % % % % meq/100g meq/100g meq/100g meq/100g meq/100g meq/100g meq/100g % 3.8 0.0 18.9 99.7 2.0 0.00 0.00 3.05 0.27 1.61 0.09 0.53 5.02 5.29 2.7 0.0 12.7 99.9 7.6 0.01 0.00 1.03 0.25 0.09 0.04 0.09 1.42 17.61 5.5 0.0 1.3 97.3 39.1 0.17 0.00 0.90 0.25 0.38 0.11 0.42 1.81 15.47
21.0 3.8 4.9 99.9 11.8 0.00 0.00 3.70 1.05 0.13 0.08 0.04 4.97 21.13 0.0 0.0 27.5 100.0 17.1 0.00 0.00 3.35 0.38 0.06 0.06 0.02 3.85 9.87
Col 5 Red
Dermosol
0.0 0.0 2.2 100.0 39.4 0.04 0.00 3.05 0.40 0.04 0.02 0.01 3.31 12.19
2.6 2.1 5.9 99.9 27.9 0.00 0.00 4.03 0.54 0.79 0.05 0.20 5.42 9.93 3.6 1.6 0.9 99.8 18.3 0.02 0.00 2.52 0.45 0.32 0.07 0.13 3.38 13.31 6.2 1.6 0.0 99.9 27.8 0.01 0.00 26.00 5.30 1.83 0.14 0.07 33.28 15.93 3.1 2.3 25.1 99.9 25.6 0.00 0.00 7.16 0.73 0.43 0.07 0.06 8.37 8.72 3.2 1.7 16.2 100.0 15.8 0.00 0.00 4.70 0.88 0.38 0.07 0.08 6.03 14.59
Col 6 Brown
Sodosol
3.9 1.5 25.5 100.0 17.2 0.00 0.00 1.20 0.15 0.04 0.04 0.03 1.43 10.62
0.4 0.0 5.2 99.6 12.0 0.02 0.00 0.91 0.14 0.66 0.16 0.73 1.89 0.96 1.3 0.0 2.5 99.2 19.7 0.02 0.00 2.11 0.24 0.35 0.12 0.17 2.84 4.51 0.3 0.0 0.3 99.5 43.1 0.00 0.00 3.30 0.31 0.06 0.06 0.02 3.73 8.31 1.6 0.0 4.4 99.8 15.6 0.05 0.01 0.52 0.22 0.26 0.07 0.50 1.14 3.21 9.6 0.0 3.5 99.7 16.3 0.00 0.00 0.61 0.10 0.11 0.06 0.18 0.87 1.46
Col 7 Brown
Kurosol
0.0 0.0 1.0 99.8 40.0 0.00 0.00 2.59 0.22 0.06 0.06 0.02 2.92 7.62
0.0 0.0 0.4 99.9 12.4 0.01 0.00 0.54 0.16 0.08 0.03 0.15 0.82 3.01 3.6 1.6 0.9 99.8 18.3 0.02 0.00 3.53 0.29 0.08 0.10 0.02 4.01 1.99 6.2 1.6 0.0 99.9 27.8 0.03 0.00 5.10 0.40 0.11 0.14 0.02 5.78 2.75 3.1 2.3 25.1 99.9 25.6 0.00 0.00 2.82 0.29 0.04 0.03 0.01 3.18 13.13 3.0 2.2 20.2 99.0 31.1 0.00 0.00 2.60 0.26 0.04 0.09 0.02 2.99 2.95
Col 8 Brown
Dermosol
3.9 1.5 25.5 100.0 17.2 0.00 0.00 5.74 1.26 0.53 0.04 0.09 7.57 14.31
305
Table D.2 (cont) Average soil chemical constituents of soil columns Albite Anorthite Amorphous Total clay Al Fe Mg Na Ca K Ca:Mg ECEC ESP
Soil Type % % % % % meq/100g meq/100g meq/100g meq/100g meq/100g meq/100g meq/100g % 0.0 0.0 5.2 99.3 3.2 0.00 0.00 0.47 0.10 0.35 0.06 0.74 0.97 2.65 0.0 0.0 1.8 99.5 3.3 0.00 0.00 0.22 0.06 0.04 0.07 0.18 0.39 0.60 0.0 0.0 2.8 99.8 15.0 0.00 0.00 0.08 0.04 0.01 0.08 0.13 0.47 0.89 9.0 0.0 6.0 99.5 3.5 0.02 0.00 0.20 0.07 0.13 0.06 0.65 0.48 1.49 1.0 0.0 29.0 99.9 13.2 0.00 0.00 2.81 0.31 0.08 0.03 0.03 3.23 5.13
Col 9 Yellow
Dermosol
4.3 0.0 2.9 99.9 26.1 0.00 0.00 4.16 0.35 0.04 0.06 0.01 4.61 8.36
0.0 0.0 1.0 99.1 18.9 0.01 0.00 0.81 0.10 0.76 0.06 0.94 1.74 2.68 0.0 0.0 17.1 99.0 15.6 0.01 0.00 0.47 0.13 0.13 0.05 0.28 0.79 1.67 0.0 0.0 8.5 99.5 31.0 0.01 0.00 2.89 0.13 0.12 0.09 0.04 3.24 4.01 0.0 0.0 16.7 98.1 4.1 0.01 0.00 0.87 0.20 0.39 0.07 0.45 1.54 4.26 0.0 0.0 16.6 98.8 10.3 0.00 0.00 0.16 0.07 0.09 0.00 0.56 0.32 1.70
Col 10 Yellow
Chromosol
0.0 4.4 3.2 97.7 29.9 0.00 0.00 0.26 0.04 0.04 0.02 0.15 0.36 0.98
0.0 0.0 3.8 98.4 3.9 0.00 0.00 0.43 0.06 0.18 0.02 0.42 0.69 0.99 0.0 0.0 23.6 99.2 4.7 0.02 0.00 1.37 0.15 0.07 0.01 0.05 1.62 1.70 0.0 2.6 0.0 99.7 56.8 0.01 0.00 4.36 0.20 0.07 0.02 0.02 4.67 4.28
12.0 2.0 98.0 4.0 0.03 0.00 0.42 0.10 0.10 0.00 0.24 0.66 6.60 20.0 0.0 13.0 99.6 10.3 0.04 0.01 0.63 0.09 0.06 0.00 0.10 0.82 2.17
Col 11 Grey
Chromosol
0.0 4.0 3.5 99.9 41.0 0.00 0.00 2.54 0.16 0.06 0.01 0.02 2.75 5.82
0.0 0.0 1.3 99.3 9.5 0.00 0.00 0.60 0.09 0.14 0.01 0.23 0.85 3.31 0.0 0.0 1.8 100.0 40.8 0.02 0.00 2.17 0.19 0.12 0.01 0.06 2.51 3.57 0.0 0.0 2.4 99.6 30.1 0.00 0.00 10.51 0.38 0.13 0.04 0.01 11.05 10.41 0.0 0.0 2.0 99.6 31.6 0.02 0.00 0.48 0.18 0.07 0.00 0.15 0.76 4.35 0.0 0.0 3.2 99.8 28.6 0.00 0.00 2.45 0.15 0.05 0.00 0.02 2.63 5.99
Col12 Red
Kandosol
0.0 0.0 0.5 99.6 43.7 0.00 0.00 3.28 0.13 0.06 0.01 0.02 3.49 8.81
306
APPENDIX E
SOFTWARE ALGORITHMS
307
PCA Algorithm used in MatLab
Res;
[vs,vl,veigen] = pca(Res,'yes');
scree(veigen);
pcaplota(vl,veigen,Res_var, 1,2);
pcaplot3d(vl,veigen,Res_var,1,2,3); pcaploto(vs,veigen,Res_obj,1,2);
Biplot(Res,Res_var,Res_obj,’yes’); Biplot3d(Res,Res_var,Res_obj,’yes’);
Data matrix loaded (Res)
Scores (vs), loadings (vl)
and eigenvalues (veigen) are
calculated based on the original data
matrix. The data is also pre-
treated using the standardise option
('yes')
A scree plot of the eigenvalues is
plotted to determine the number of
principal components to use in the
analysis
The loadings of each variable (Res_yar
contain variable names) are plotted
on the first two principal components
The loadings of each variable are
plotted on the first three principal
components in a three-dimensional plot
The scores of each object (Res_obj
contain object names) are plotted on the
first two principal components
The scores of each object are plotted on
the first three principal components in
a three-dimensional plot
Loadings and scores are combined in
a two-dimensional biplot
Loadings and scores are combined in
a three-dimensional biplot
pcaplot3d(vs,veigen,Res_obj, 1,2,3);
308
The pcaplota function in MatLab (adapted from Kramer (1993)) function pcaplota(y, veigen, lbls, pcl, pc2) % PCAPLOT(y, lbls, pcl, pc2)
%
% Constructs a plot from the output data of the PCA or SPCA functions. It
% can be used to create either a loadings vs loading plot or a scores vs
% scores plot.
%
% input: y is a loadings or scores matrix returned from PCA or SPCA
%
% lbls is: vector of strings containing text labels for the variables
% (columns)
%
% optional arguments (if these argument are omitted then a PCI vs PC2
% plot is assumed:
%
% pc 1 is the first principal component to plot
% pc2 is the second principal component to plot
%
[m, n]=size(y);
if (nargin = 3) % assume a PCI vs PC2 plot is required
pc1 = 1;
pc2 = 2;
elseif (nargin ~= 5) % pcl and pc2 contain PCs to plot
disp('Error: Incorrect number of input arguments')
end
plot(y(:,pcl), y(:,pc2), 'ro', 0, 0, ‘b+') % include (0, 0) in plot
text(y(:,pcl), y(:,pc2), lbls) % annotate plot
for i = l:n
line([ 0 y(i,pcl)], [0 y(i,pc2)],'color', [1 0 0])
end
309
title('Principal Component Analysis')
strl = ['PCI (' num2str(veigen(l)* 100,3) ' %)'];
str2 - [TC2 (' num2str(veigen(2)* 100,3) ' %)'];
xlabel(strl)
ylabel(str2)
k = axis; % find axis coordinates
% draw in axis lines to mark quadrants
line([k(l) k(2)], [0 0],'color',[0 0 1])
line([0 0], [k(3) k(4)],'color')[0 0 1])
310
The biplot function in MatLab (adapted from Kramer (1993))
function biplot(x, lblsv, lblso, standardise)
% BIPLOT(x, lbls, standardise)
%
% Constructs a biplot from the input matrix x for principal component
% analysis using singular value decomposition algorithm.
%
% input: x is a (nxp) data matrix whose columns represent variables and
% whose rows represent samples (or observations).
%
% lblsv is: vector of strings containing text labels for the variables
% (columns)
% lblso is: vector of strings containing text labels for the objects
% (columns)
%
% Standardise is one of: 'none'
% yes'
% 'no'
% A "standardise" option of "no" mean centers the x data but does not
% standardise to unit variance. Whereas the "yes" option mean centers (by
% removing the mean from each column) and then standardises the x data to unit
% variance. When "none" is specified, then neither centering nor
% standardisation is carried out.
%
if (nargin = 4)
[m ,n] = size(x);
mx = mean(x);
if strcmp(standardise, 'yes')
% column centre and normalise to unit variance
sx = std(x);
fori = l:n
x(:,i)=(x(:,i) –mx(i))/sx(i);
311
end
elseif strcmp(standardise, 'no')
% just column centre
for i = l:n
x(:,i)=(x(:,i) –mx(i)
end
elseif ~strcmp(standardise, 'none')
disp('Error: Invalid option specified')
end
else
disp('Error: Incorrect number of input arguments')
end
[u, s, v] = svd(x);
evals = diag(s).^2;
evals = evals./sum( evals);
plot(u(:,l), u(:,2), ‘bo’, v(:,l), v(:,2), 'ro')
legend('objects', Variables')
title('Principal Component Analysis Biplot')
strl = ['PCI (' num2str(evals(l)* 100,3) ' %)'];
str2 = [TC2 (' num2str(evals(2)* 100,3) ' %)'];
xlabel(strl)
ylabel(str2)
% draw vectors from origin to variables
for i=l:n
line([ 0 v(i,l)], [0 v(i,2)], 'Color', [1 0 0])
end
text(v(:,l),v(:,2),lblsv) % annotate variables
text(u(:,l),u(:,2),lblso) % annotate objects
a = axis; % find axis coordinates
% draw in axis lines (in lt. grey) to mark quadrants
line([a(l) a(2)], [0 0], 'Color', [0.75 0.75 0.75]);
line([0 0], [a(3) a(4)], 'Color1, [0.75 0.75 0.75]);
