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REPORT
Report prepared for:
Thames Coromandel District Council
Report prepared by:
Tonkin & Taylor Ltd
Distribution:
Thames Coromandel District Council 3 copies
Tonkin & Taylor Ltd (FILE) 1 copy
November 2012
T&T Ref: 61570.002
Thames Coromandel District Council
Moanataiari Subdivision, Thames
Phase 4 - Assessment of Response
Options
Moanataiari Subdivision, Thames Phase 4 - Assessment of Response Options T&T Ref. 61570.002
Thames Coromandel District Council November 2012
Table of contents
1 Introduction 1
2 Scope of works 2
3 Response objective 3
4 Selection of response options 4
4.1 Ministry of the Environment 4
4.2 Ministry of Health 5
5 Assessment of potential response options 6
5.1 Introduction 6
5.2 Additional information 6
5.3 Response options workshops 7
5.4 Health Precautions (Management controls) 7
5.5 Partial Capping (Containment) 9
5.5.1 Ministry for the Environment advice 9
5.6 Ministry of Health Advice 11
5.6.1 Thin cap 12
5.6.2 Thick cap 13
5.7 Land use controls 14
5.8 Summary of potential response options 15
6 Applicability 19
7 References 20
Appendix A: Figure
Appendix B: Golder HRA Figure 5
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Executive summary
This Assessment of Response Options has been prepared for the Moanataiari Project Governance
Group and Thames-Coromandel District Council (TCDC) to provide an assessment of the response
options resulting from a Human Health Risk Assessment (HRA) prepared by Golder and Associates
(Golder).
Preliminary response options for the subdivision were developed by Tonkin & Taylor in August
2012 and presented to the Moanataiari residents at a series of workshops. The preliminary
response options were then used to inform the HRA undertaken by Golder. T&T were instructed
that the results of the Golder HRA should be the starting point for this Response Options report.
This report details how contaminated land guidance published by the MfE (and to a lesser extent
the Ministry of Health) relates to the response options resulting from the HRA. The relative
advantages and disadvantages of each option are also discussed.
MfE guidance states that no one single remedy represents the optimal selection for all
contaminated sites. The selection of a response option is very site-specific and depends on many
factors. Primarily evaluation should be on the ability of an option to reduce risk, and then on its
cost-effectiveness and the future site utility.
A summary of the response options resulting from the HRA is provided in Table 3 of this report,
along with an evaluation against the key decision-making aspects. With all of the potential
response options, a management plan will be required. The level of controls required to be
included in the management plan will be dependent on the response option(s) selected.
The Golder HRA provides a plan (Figure 5) showing the minimum response options required to
meet the statutory requirements of risk in different areas of the site and this plan has been
enclosed in Appendix B of this report for convenience.
In summary, the HRA has concluded that the following options would provide the minimum
human health protection to meet statutory risk reduction requirements:
• Management controls (Health Precautions): continuation of the existing management
regime, possibly with the provision of raised planter beds (referred to as Gardening
Controls in the Golder HRA) - Minimum requirement for Zone 7.
• Management controls as above, with planters provided for vegetable growing (Health
Precautions and gardening controls) - Minimum requirement for Zones 1, 4 & 8.
• Containment (Partial Capping): constructing a cap over the contamination – Minimum
requirement in Zones 2 & 3.
Land use controls are also an option, involving purchasing properties, demolition and
redevelopment (eg as parkland or commercial properties). Such measures would be in excess of
the minimum requirement for all areas of the subdivision.
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Moanataiari Subdivision, Thames Phase 4 - Assessment of Response Options T&T Ref. 61570.002
Thames Coromandel District Council November 2012
1 Introduction
The Moanataiari Project was commissioned by the Moanataiari Project Governance Group and
Thames-Coromandel District Council (TCDC) to investigate and address potential health risks
within the subdivision as a result of soil contamination. This report relates to Phase 4 of the
project as set out in the project management plan for the Moanataiari Subdivision.
Preliminary response options for the subdivision were developed by Tonkin & Taylor in August
2012 and presented to the Moanataiari residents at a series of workshops. The preliminary
response options were used to inform a Human Health Risk Assessment (HRA) undertaken by
Golder Associates (Golder, Oct 2012). T&T were instructed that the results of the Golder HRA
should be the starting point for this Response Options report.
This report covers all 216 residential properties within the Moanataiari Subdivision as shown in
Figure 1 (Appendix A). Description of the subdivision environs and history has been provided in
previous reports, along with details of the contamination present (See References in Section 7 of
this report).
This report has been produced by Tonkin & Taylor Ltd (T&T) in general accordance with The
Ministry for the Environment’s Contaminated Land Management Guideline No. 1 “Reporting on
Contaminated Sites in New Zealand” and in accordance with our agreement with TCDC dated 21
June 2012.
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2 Scope of works
T&T’s scope of work for this report is as follows:
• Provide an assessment of the advantages and disadvantages of the range of response
options suggested by the Golder HRA.
• Produce this assessment report presenting the results of the response options assessment.
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3 Response objective
Concentrations of contaminants in the soils at the Moanataiari Subdivision, principally arsenic and
lead, are above NES soil contaminant standards (SCS) for assessing and managing contaminants in
soil to protect human health. The response objective is to reduce/manage exposure of people
within the subdivision to these contaminants down to acceptable levels and not necessarily to
reduce the levels of these contaminants to below the NES SCS.
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4 Selection of response options
4.1 Ministry of the Environment
Guidelines on the response to contaminated land in New Zealand is provided by the Ministry of
the Environment through a range of technical documents produced in the late 1990s. The health
risk-based soil acceptance criteria contained in these guidelines have been superseded by the soil
contaminant standards under the National Environmental Standard for Assessing and Managing
Contaminants in Soil to Protect Human Health (NES). The NES doesn't currently apply to this site
as it is not applied in retrospect and will only be triggered as and when activities requiring consent
are undertaken. However, these documents still provide valid guidance on the selection of
response options.
No one single remedy represents the optimal selection for all sites (MfE 1997a). The selection of a
remediation or management option is very site-specific and depends on many factors (MfE 2006),
including:
• Type, extent and depth of contamination.
• Location of contamination relative to receptors.
• Area and volume of the contamination relative to the size of the property.
• Proximity to a safe disposal location (including on-site disposal) if excavation and
replacement are being contemplated.
• Availability of clean soil.
• Future use of the site, and
• Financial resources available.
Site management options should be evaluated primarily on their ability to reduce risk, and then on
their cost-effectiveness and the future site utility (MfE 1997a). Ideally, the option that best
reduces the risk, maximises environmental merit and minimises costs would be chosen (MfE 2006).
The risks include those to site users, the general public, and the environment, during and after
implementation of the management strategy. Also important in evaluating site management
options are (MfE 1997a):
• Timing - if a site management option could take a long time to reduce contaminant
concentrations, what are the risks to human health and the environment in the intervening
period?
• Failure - if the contamination is contained [or capped] in situ, what will happen if the
containment system fails?
• Off-site disposal - if the contaminants are to be disposed of off-site what risks are associated
with moving the contaminants?
At each site, the remedial system design must (MfE 2006):
• Evaluate the practicality of using a specific remedial option.
• Attempt to evaluate the cost.
• Assess the problems that may be associated with that option, and
• Assess the timeframe for the treatment.
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4.2 Ministry of Health
Guidelines are provided by the Ministry of Health (MoH) to assist public health units in achieving
tolerable levels of lead in the environment to limit adverse health effects (MoH, 2012). Whilst this
document addresses only lead (mainly from paint), there is relevance to Moanatairi in that the
document discusses responses to lead in soil. The guidelines were first published in 1998 and
were updated in 2012 for the National Environmental Standard for Assessing and Managing
Contaminants in Soil to Protect Human Health.
The MoH lead guidelines emphasise the aim of providing a ‘lead-safe’ environment, which is not
the same as a lead-free environment. The guidelines advocate education of site occupiers that in
most circumstances, abatement cannot be considered as a complete or permanent solution, but
must be complemented by ongoing behavioural adjustments to reduce (remaining) exposure.
[Although] education to change the daily behaviour of children, caregivers, visitors and so on, is
very difficult to sustain long term.
The guidelines include abatement strategies for reducing blood-lead levels, central to which is a
management plan, typically incorporating both behavioural (educational) and environmental
(abatement) strategies, developed in consultation with the family.
The choice of soil abatement strategy will be based on the risk assessment. The key variables are:
• soil lead concentration (and bioavailability).
• location and use pattern.
• condition of existing surface cover (if any).
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5 Assessment of potential response options
5.1 Introduction
The Ministry for the Environment (and to a lesser extent the MoH) provides guidance on a range
of potential response options for contaminated land. These include:
• Land use controls (eg only allowing the land to be used for commercial purposes where
concentrations of contamination in the near-surface soils are too high to enable other land
uses without physical works).
• Management controls (eg the management controls that are currently in force across the
subdivision, controlling consumption of homegrown produce etc). Referred to as Health
Precautions in the Golder HRA.
• Intrinsic remediation (ie allowing contamination to reduce over time).
• Containment (eg capping the contamination with clean materials). Referred to as Partial
Capping in the Golder HRA.
• Remedial treatment systems (ie removing or reducing contamination concentrations), and
• Disposal to landfill.
The HRA has concluded that from the above options, the following are technically feasible for
addressing contamination within the residential properties on the subdivision:
• Management controls (Health Precautions): continuation of the existing management
regime, possibly with the provision of raised planter beds (referred to as Gardening
Controls in the Golder HRA).
• Containment (Partial Capping): constructing a cap over the contamination.
• Land use controls: purchasing properties, demolition and redevelopment (eg as parkland or
commercial properties).
A discussion of each of the options considered to be technically feasible or practical is provided in
this section, which is summarised in Table 3 at the end of the section.
The following options were not considered technically feasible:
• Intrinsic remediation: the arsenic, lead and thallium within the soils will not degrade.
• Remedial treatment systems: No practical remedial treatment systems were identified for
the subdivision. Two innovative systems were presented at workshops, in the interests of
completeness (electrokinetic and phytoremediation), however both these would require
trials to assess suitability and at this stage are likely to prove unsuitable in terms of ability
to practically reduce the contamination.
• Disposal to landfill: Removal of all the contaminated soil to landfill is unfeasible as it forms
the entire thickness of the subdivision (ie to remediate a property would require removal of
the whole property down to the original marine sediments).
5.2 Additional information
A schedule of quantities for TCDC to populate with costs for the conceptual response option(s)
was produced as a separate document to allow TCDC to develop conceptual costs for each
response option.
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5.3 Response options workshops
Three two-hour workshops were held to discuss response options with the community. Two
workshops were held on 19th
July 2012 and one on 21st
July 2012. The workshops were facilitated
by Tonkin & Taylor (with members of the Project Team in attendance). A virtual online workshop
was also broadcast by the Project Team and feedback requested.
The purpose of the workshops was to obtain early feedback from the community regarding
appropriate response options (ie feedback was required on which options would have been
appropriate to develop further for use in the health risk assessment and assessments of response
options). In line with the adopted approach of the Project Team, the workshops were undertaken
before a full assessment of response options was completed and before a preferred option(s) was
selected by the Governance Group. In particular, the Human Health Risk assessment work
package had not yet been approved at that stage, the funding arrangement had not yet been
decided. This would have affected the feedback obtained.
Those who provided feedback stated that they wanted to return the subdivision “back to normal”
and make the subdivision a healthy place to live. Preserving the financial equity in the properties
was also a main concern. Generally the feedback on the response options provided was that the
thick capping option would be the preferred solution, with some preferring the thin cap option.
The management option was viewed as being insufficient to address the human health issues.
It was stated at the time that the process whereby these options would be evaluated would
include financial analysis. If an option wasn't practical from a cost perspective it would most likely
not be implemented.
A total of 62 people attended the workshops, some of which were from the same households and
so the number of properties represented could have been of the order of 20% of the whole
subdivision. Based on our experience of consultation processes and the fact that the issues
directly affect all the properties on the subdivision, this is a relatively low attendance. We
understand that TCDC intend consulting on individual response options with individual property
owners prior to finalising a programme of works.
5.4 Health Precautions (Management controls)
Ministry for the Environment guidance states that:
Management controls [Health Precautions] are usually required where contamination is to be left
on site at depth or under structures or paving. Controls are necessary to avoid uncontrolled
excavation in the future which could result in the contamination being exposed. Imposing
management controls acknowledges that the land is not suitable for uncontrolled use (MfE
1997a).
Each of the response options discussed in this section will require a management plan, although
the extent to which the management plan will be applied will vary dependent on the option, or
combination of options, selected.
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Thames Coromandel District Council November 2012
Currently, human health risks for the residential properties on the subdivision are addressed
through application of a management plan (Health Precautions), which provides the following
advice1:
• Take care with personal hygiene (ie hand washing after handling soil).
• Make sure children don't eat or play in soil.
• Remove footwear before going indoors to avoid carrying soil dust indoors - particularly for
households with very young children.
• Cover soil (eg grassing, paving, gravel) to reduce dust and direct access by young children.
• Don’t eat home grown vegetables, especially young children, until further quantification of
the contamination is available and the risk can be assessed, unless it is known that the
garden soil is clean fill. If home grown vegetables are chosen to be eaten, then thoroughly
wash produce that may be contaminated with soil, and peel the skin off root vegetables.
If the current Health Precautions were to continue, then all soil disturbing activities would need to
be undertaken in accordance with a management plan, and bare soil would need to be minimised
as much as possible throughout the subdivision. Vegetables would need to be grown in clean
imported soil. A management plan would include procedures for handling contaminated soil to
allow for certain activities, eg excavation for a new building, driveway or swimming pool.
In addition to the above, the management plan would need to clearly define responsibilities, eg:
who is responsible for disposal of soils and provision of clean materials (is a facility provided by
council, or is it the sole responsibility of property owners). Consideration would also need to be
given to an education/awareness programme and also monitoring the implementation of the
management plan to provide confidence that this solution is effective in the long term.
Further details on this solution are as follows:
Human health risk reduction: This solution relies on self-management by the occupiers of the
properties and requires that future owners/occupiers have an awareness of the health issues
associated with the contamination within the soils on their properties.
Cost: Costs for this solution are likely to be significantly lower than other solutions. Rough order
costs have been estimated separately by TCDC.
Future site use: Continuing the current Health Precautions would rely on controls and so would
give the least flexibility to property owners. Future redevelopment of properties would possibly
require replacement of planters.
Advantages: Continuing with the current Health Precautions for the subdivision and not
undertaking significant physical works is the least intrusive option to address the potential health
risk (ie no truck movements or disturbance of properties).
Practicality: This solution is practical where contamination levels are commensurate with
acceptable levels of increased risk.
Problems associated with solution: Problems relate to future site use as described above.
Timeframe: The solution is in place now and so is the quickest solution. Provision of planters
(Gardening Controls) likely to be achievable in a matter of months.
1 “Facts Sheet 1: Moanataiari subdivision, Public health advice”, http://www.tcdc.govt.nz/Global/1_Your%20Council/
Council%20Projects/Current%20Projects/Moanataiari%20Project/Facts%20Sheet%20One%20-
%20MoH%20Public%20Health%20advice.pdf
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Thames Coromandel District Council November 2012
Community feedback: Feedback from the community was largely negative. Land owners were
concerned about the potential health effects, particularly on children, effects on property prices
long term, and how to ensure that the management plan is implemented by everyone long term.
5.5 Partial Capping (Containment)
5.5.1 Ministry for the Environment advice
Ministry for the Environment guidance (MfE 1997a, MfE 1997b) on capping contaminated land is
that:
Reduction of the exposure of site users to contaminated soil by the engineered containment of
areas of soil contamination is an acceptable remediation/management strategy in some
circumstances. Containment may involve the use of an impermeable surface cap of bitumen or
concrete paving. A well-defined management plan should accompany such a containment
strategy. Very high levels of contamination may be acceptable with such a containment strategy,
provided the contamination does not produce other off-site impacts eg via groundwater or surface
rainfall run-off.
In addition, mechanisms must be put in place to ensure the long-term integrity of any
management plan and containment works, taking into account property transfer and other
possible scenarios. The implementation of a containment strategy is most practical in the context
of ongoing commercial/industrial use, or possibly high-density residential use.
The protection offered by pavement is, however, highly dependent on the integrity of the
pavement. A relatively new area of paving of high integrity is likely to effectively eliminate
exposure of site personnel to ground contamination except where the pavement is disturbed and
the integrity of the pavement compromised. Where an area of pavement is relatively old and
broken, with say 30 to 50% of the area seriously affected, so that soil can spread from areas of
pavement failure to areas remaining intact, the pavement may provide negligible protection for
site personnel. The integrity of an area of pavement and its likely effectiveness in reducing
exposure must be evaluated on a site-specific basis.
On this basis, the guidance suggests a fivefold protection factor where paving is present, when
compared to sites where paving is absent (ie paving is appropriate where soil contamination
concentrations are less than five times the human health acceptance criteria that would be
applied if the paving were absent). Such a factor was applied to the acceptance criteria and
although those criteria are now superseded by the NES, the concept of a five-fold protection
factor still provides a basis for preliminary assessment of where paving may be appropriate.
The placement of clean fill over the site can also form an effective cap. MfE guidance states that:
The placement of such clean fill provides a barrier to the exposure of site users to soil
contamination, and therefore higher contaminant concentrations may be allowable below such
fill.
Considerations relevant to the appropriate use of such a cleanfill cover are stated in Table 2 along
with the potential relevance to the Moanataiari Subdivision.
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Thames Coromandel District Council November 2012
Table 2 – Considerations for the appropriate use of cleanfill as part of a containment
solution
MfE consideration Consideration for Moanataiari
The root zone of most home vegetables and the
depth of digging as part of gardening activities
does not generally extend beyond 0.5 m.
If plants2 and vegetables are to be grown at the site,
0.5m of cleanfill would be required, or raised garden
beds greater than 0.5m thick or with a geofabric base
would be required.
Normal maintenance activities at a residential
site (eg maintenance of underground services)
may bring contaminated soil to the surface and
spread it around.
Maintenance activities would need to be addressed in a
management plan for the site.
A greater depth of cleanfill and use of geofabric would
act to reduce the likely disturbance from maintenance
activities.
Contaminants below a cover layer should not
pose a short-term health risk to people who may
disturb the contamination.
An assessment undertaken on behalf of the
Moanataiari Project in November 2011 (PDP 2011a)
concluded that for arsenic, the principal contaminant
on the subdivision, an acute guideline value for non-
pica children is 65,000mg/kg for potentially lethal
effects, which is well above the maximum value of
4,700 mg/kg detected during the site investigation
works, and 975mg/kg for the onset of observable health
effects, which is above the upper confidence limit
values tabulated in the Golder HRA (Golder, Oct 2012,
Tables 4 and 5). Therefore no acute risk is indicated.
Contaminant concentrations below a cover layer
should not significantly impact on the health of
trees and other plants where the root zone may
extend beyond 0.5 m
No significant die-off of trees or vegetation was noted
during the property inspections and property owner
interviews, which indicates that this is not an issue at
the subdivision.
Ongoing management, and re-establishment of
the cover layer after significant works or
redevelopment, are required.
Ongoing management would be addressed in the
management plan for the site.
The use of a barrier may not be appropriate in a
flood plain zone or other areas subject to
significant erosion
Significant flooding/erosion has not occurred since the
installation of the flood protection measures around
the subdivision however a water permeable barrier may
be appropriate to reduce impacts on flooding.
The existence of contamination below any
barrier should be notified via the LIM system
administrated by the TLAs
TCDC has indicated that all relevant information will be
placed on the LIM system for all affected properties.
On this basis, preliminary assessment using the protection factor of 5 is suggested [by MfE] as
appropriate (consistent with that assigned to paving [discussed above]) to the placement of
500 mm of clean fill or topsoil, provided that an appropriate management plan is in place and the
existence of contamination beneath the barrier is recorded on a LIM [ie the guideline value is
multiplied by a factor of five for this option]. The owner, occupier, and purchaser of the site as
well as the TLA will be made aware of the contamination so that this can be taken into account
during any maintenance or construction activities.
2 Residents can come into contact with contaminated soils during planting activities.
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Thames Coromandel District Council November 2012
5.6 Ministry of Health Advice
Ministry of Health advice for addressing lead in soil by capping is that if the ground cover is poor
(ie, there are patches of bare soil exposed) at a particular location, reasons for this should be
determined, because this will influence abatement method selection. Bare soil is commonly
exposed in:
• heavily used play areas
• pathways
• areas shaded by buildings or trees.
In other situations, all that is required [to address lead exposure] is the removal of gross
contamination (visible paint chips) followed by covering the area with 25 mm of turf, 50 mm of
bark chips or similar. Usually, this will involve removal of some surface soil or a partial grass
cover, to prepare the surface for the laying of turf or bark. This may temporarily increase the
amount of bare contaminated soil potentially accessible to a child, or available to contribute by
wind transport or tracking to interior surface dust. Care should be taken to minimise disturbance
to the soil, and to contain, collect and safely dispose of any soil that has to be removed.
A grass cover has been shown to be capable of reducing exposure to soil lead by 80 percent3.
Behavioural adjustments to reduce outdoor play, relocate outdoor play areas, reduce soil
ingestion, and minimise soil transfer and tracking into the house, are necessary complementary
strategies.
More permanent [lead exposure] abatement options should be reserved for situations where a
simple grass or bark cover is unlikely to be sufficient or sustainable.
Paving is the preferred option when contaminated soil is found in high-traffic areas. Contaminated
soil should be disturbed as little as possible in preparing the surface, and precautions must again
be used in managing any soil that must be removed.
While many paving materials are available, a high-quality concrete or asphalt cover is
recommended, with appropriate allowance for thermal expansion and traffic loadings, so that
cracks will not develop over time. Any areas of bare (contaminated) soil remaining at the edges of
the paved surface should receive a grass or similar soft cover.
The guidelines state that soil removal and replacement is the most expensive and also the most
hazardous soil abatement option. It should only be considered when soil contamination is
extensive, behavioural factors are unfavourable (eg, a child with pica), and soft or hard ground
cover is unlikely to be sustainable. In this situation, core samples should be taken from the
affected area in a grid pattern to check that the expected decline in soil lead content with depth
occurs (ie, that sublayers do not have equally or even higher lead content than the surface layer,
as a result of historical events such as previous building or renovation on the site).
The guidelines refer to studies from 1993 and 2003 on the effectiveness of soil removal in
reducing blood-lead levels in children. The guidelines state that based on these studies, for soil
lead levels in the range of 1000 to 3000 mg/kg, soil removal is probably not indicated, and
measures such as improving ground cover and behaviour modification (eg, relocating the principal
play area away from the house) may suffice. At soil lead levels less than 1000 mg/kg bare soil
areas should still be covered (a soft cover such as grass or bark chips is generally adequate), if
indicated by use pattern analysis, as soil lead tracked or blown into the house will be contributing
to dust lead in the home. Care should be taken in applying this advice to Moanataiari as the
3 The Golder HRA will already have taken this reduction into account.
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studies targeted lead contamination at individual houses and were relatively short-term. The 1993
study concluded that a greater reduction in lead may have been observed if the study had
extended for longer. In addition, the 2003 study concluded that soil abatement was associated
with significant decline in children’s blood lead and indoor environmental levels of lead and
arsenic.
5.6.1 Thin cap
The thin cap solution acts to isolate people from the contaminated soils by forming a surface
barrier on top of the existing soils using:
• Imported topsoil (50mm to 100mm thick) underlain by a geofabric barrier.
• Decking.
• Paving or concrete, or
• A combination of the above.
In addition to the above, bark or river stones over geofabric may be suitable as a thin barrier for
small untrafficked areas or around trees.
At Moanataiari, a combination of these barrier-types is likely to be the most practical, eg
imported topsoil in existing grassed areas, paving in narrow trafficked areas and decking in other
small areas.
It is understood that the Ministry for Health and Waikato District Health Board would not support
any solutions that involved disturbance of soil.
Further details on this solution are as follows:
Human health risk reduction: Once installed, this solution would isolate the contaminated soils
from people on the subdivision. However, over time, the capping is likely to deteriorate, which
may allow contaminated soils to migrate to the surface. This is not indicated by the Golder HRA
to be a significant health issue at Moanataiari4.
Cost: Relatively low cost. Some disposal to landfill of surface materials (eg topsoil) likely to be
required. Rough order costs have been estimated separately by TCDC.
Future site use: This solution would address all areas of exposed soil and would allow for
everyday residential activities to be carried out without requiring special precautions. Growing of
plants and vegetables would need to be undertaken in raised gardens with clean imported soil
underlain by a geofabric barrier layer. Any activities which are likely to disturb soil beneath the
barrier layer would need to be done in accordance with a management plan. Future
redevelopment of properties would possibly require replacement of the thin cap.
Advantages: This option would involve minimal excavation of existing soils, and a relatively low
level of disruption to property and residents.
Practicality: The type of cover used could be tailored to individual properties to incorporate the
needs of individual property owners.
Problems associated with solution: See future site use above.
4 As a preliminary screen, MfE guidance indicates that this solution may not be suitable in areas where contamination
concentrations exceed five times the human health guideline values. Only a single result exceeds five times the
Golder HRA criteria.
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Timeframe: Relatively short timeframe anticipated. Assuming that the critical path installation of
a thin cap would take one week per property (ie excluding finishing works, snagging, etc), it would
take approximately three months to complete the physical works for one third of the subdivision.
Community feedback: people were concerned about drainage, ponding and flooding as a result of
changes in ground levels and increasing impervious coverage. Some people viewed this as a short
term solution only.
5.6.2 Thick cap
The thick cap solution acts to isolate people from the contaminated soils by forming a surface
barrier through either:
• Raising ground levels by say 200mm to 300mm using clean imported soil.
• Excavating 300mm to 600mm and replacing with clean soil.
• Undertaking a combination of excavation and ground raising.
TCDC have stated that they consider solutions involving ground raising to be impractical for
Moanataiari, due to natural servitude stormwater issues and the risk of inducing settlement
within the soft soils beneath the subdivision. Therefore ground raising solutions have not been
considered further in this report.
It is understood that the Ministry for Health and Waikato District Health Board would not support
any solutions that involved disturbance of soil.
The greater the thickness of clean soil, the greater the level of activity that can occur on
properties without the need for specific management actions. Placement of a geofabric barrier
layer beneath the clean soil would also act to prevent contaminated soils migrating to the surface.
Further details on this solution are as follows:
Human health risk reduction: Over time, the capping is likely to be disturbed by activities,
although the thicker the cap, the less likely this is to occur, especially with a geofabric layer placed
at the base of the cap. This is not indicated by the Golder HRA to be a significant health issue at
Moanataiari5.
Cost: Relatively high cost, due to the importation of the soil, with the highest cost being for the
excavation solution, which would involve removal of contaminated soils to landfill plus relocation
and temporary housing of displaced residents. A staged approach could be considered, with
works being undertaken in discrete stages over time as funds become available, possibly with the
application of a management plan, or even thin capping, in the interim. Rough order costs have
been estimated separately by TCDC.
Future site use: This solution would address all areas of exposed soil and would allow for
everyday residential activities to be carried out without requiring special precautions. Growing of
plants and vegetables could be undertaken wherever more than 500mm of clean soil is placed, or
a lesser thickness of clean soil (eg 300mm) with an underlying geofabric (otherwise raised garden
beds containing clean imported soil would be required). Any activities which are likely to disturb
soil beneath the barrier layer, or disturb any pre-existing soil at a property will be required to be
undertaken in accordance with a management plan.
5 As a preliminary screen, MfE guidance indicates that this solution may not be suitable in areas where contamination
concentrations exceed five times the human health guideline values. Only a single result exceeds five times the
Golder HRA criteria.
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Advantages: Less need for future management of activities, especially if a 600mm cap is placed
(few residential activities are likely to disturb soils below 600mm depth).
Practicality: This solution would probably be most practical if it were undertaken over a series of
adjacent properties (ie this solution would be more difficult than the thin cap option to tailor to
individual property owner needs). Although this solution may also be suitable for individual
properties where redevelopment is proposed and it is practical to remove all the above ground
structures;
Problems associated with solution:
• This option would involve a high level of disruption to local residents and the subdivision as
a whole and would interfere with underground services and above ground structures
(residents are very unlikely to be able to live in the properties during physical works). Also
the highest level of community disruption is associated with this solution (eg truck
movements, dust and noise).
• Would not be suitable beneath the drip line of trees that are to be retained (we note that
there are trees in the road reserve that overhang some properties on the subdivision).
Beneath drip lines a thin cap or management plan approach would be required).
• Construction of a thick cap may not be suitable for some areas where access is restricted
(eg in small areas bounded by structures). In these situations a thin cap may be more
practical.
• Occupiers would likely need to vacate the properties during the works.
• A management plan would still be required for this option (although to a lesser extent than
other options).
• MoH guidelines on addressing lead contamination in soils suggests that soil removal should
only be considered when soil contamination is extensive, behavioural factors are
unfavourable (eg, a child with pica), and soft or hard ground cover is unlikely to be
sustainable.
• The Ministry for Health and Waikato District Health Board have stated on a number of
occasions that they are concerned with the additional risk to human health associated with
dig and dump type works.
Timeframe: Relatively long timeframe anticipated, this is especially the case if staged funding
requires progressive works. Assuming that the critical path installation of a thick cap would take
three weeks per property (ie excluding finishing works, house cleaning, snagging, etc), it would
take approximately seven months to treat one third of the subdivision.
Community feedback: Feedback from the community for a thick cap option (prior to release of
the HRA and without the benefit of rough order costs) was that this option presented the most
benefit to them in terms of health benefits and property values. There was concern that the use
of a thin cap at some properties and a thick cap at other properties would result in a property
value differential. Some concerns were raised around security of properties when vacant during
physical works and where people would be relocated to. While some commented on the
disruption to the entire subdivision, practical implications of implementing the solution and the
potential change in character of the subdivision most people saw this as a permanent solution
even though it would still require a management plan highlighting restrictions on these
properties.
5.7 Land use controls
The subdivision is currently fully developed with residential housing and so land use controls
would require purchasing of property from owners, demolition and then possibly physical works
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Thames Coromandel District Council November 2012
to address exposure of people (eg so that the properties were appropriate for use as public
allotments or sold on as commercial properties). The type of response could be any of those
listed in the above sections, or a combination thereof (the Golder HRA indicates that no further
response is required for commercial land use).
Further details on this solution are as follows:
Human health risk reduction: The risk reduction will be dependent on the actual solution
adopted, however it is anticipated that the land would be operated by TCDC and so there would
be more control over activities which could occur there.
Cost: Likely to be most costly solution due to the need to purchase and demolish the properties in
the first instance. Rough order costs have been estimated separately by TCDC.
Future site use: The properties could be adapted to provide an appropriate use.
Advantages: The land use could be tailored to minimise risk from ground contamination and by
maintaining ownership or physical works could be undertaken (if required) and the properties
sold (eg for commercial use).
Practicality: This solution is most practical for a group of properties in a suitable location for a
land use change. It is not practical for all parts of the subdivision and not for properties where
owners do not wish to sell.
Timeframe: This is likely to be an expensive option and, dependent on the funds available, may
have to be undertaken over a number of years as funds become available, short term response
solutions may be required to address health risks before the land use change can be
implemented.
Community feedback: Community feedback on redevelopment options was mixed. People did
not want to see the whole of Moanataiari redeveloped, however at an individual or group level it
was considered to be viable for some properties due to the perceived health risk at that time.
5.8 Summary of potential response options
A summary of the potential response options is provided in Table 3 along with an evaluation
against the key aspects that have been considered. With all of the potential response options, a
management plan will be required. The level of controls required to be included in the
management plan will be dependent on the response option(s) selected.
The Golder HRA provides a plan (Figure 5) showing the minimum response options required to
meet the statutory requirements of risk in different areas of the site and this plan has been
enclosed in Appendix B for convenience.
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Thames Coromandel District Council November 2012
Table 3 – Summary of potential response options
Response
option
Zones6 Human health risk
reduction
Cost Future site use Timeframe Advantages Disadvantages
Health
Precautions
7 High level of self
management required.
Minimum response
options to meet
statutory requirements
of risk in Zone 7
Lowest High level of control required
into the future.
No implementation time,
already in place.
Low cost
Rapid
implementation
and no disruption.
High level of control
required.
Risk of negative public
reaction (although likely to
be welcomed by some)?
Thus careful explanation of
the HRA results likely to be
required.
Health
Precautions and
Gardening
Controls
(planters for
vegetable
gardens)
1, 4, 7 &
8
High level of self
management required.
Minimum response
options to meet
statutory requirements
of risk in Zones 1, 4 & 8
Low High level of control required
into the future.
Likely to be implemented
in a matter of weeks.
Low cost
Rapid
implementation
and little
disruption.
High level of control
required. Planting can only
occur in raised beds and
beds would possibly need
replacing if redevelopment
occurred.
Risk of relatively negative
public reaction (although
likely to be welcomed by
some)? Thus careful
explanation of the HRA
results likely to be required.
6 Zones in which this option would meet statutory risk reduction requirements. Zones are as defined in the Golder HRA figure 5 enclosed in Appendix C
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Thames Coromandel District Council November 2012
Response
option
Zones6 Human health risk
reduction
Cost Future site use Timeframe Advantages Disadvantages
Partial Capping -
Thin cap
1,2,3,4,7
& 8
Will effectively contain
contamination but may
be compromised as a
result of degradation
or site activities in
future.
Minimum response
option to meet
statutory requirements
of risk in Zones 2 & 3
Relatively
low in
comparison
with the
Thick Cap
option
Raised gardens needed for
vegetable growing. No
precautions required for most
everyday activities but
management plan applies to
all activities which disturb soil
beneath the thin cap.
Estimated three months
for treatment of one third
of the subdivision
Relatively low cost
Relatively rapid
implementation
and low disruption.
Control of everyday
activities not
required
Can be tailored to
individual
properties.
Degradation of thin cap over
time.
Will take months to
implement.
Future development of
property would possibly
require replacement of cap
Partial Capping -
Thick cap
1,2,3,4,7
& 8
Will effectively contain
contamination and is
less likely to be
compromised by
future site activities.
High (but if
it includes
temporary
relocation of
the house/
structures
then this
becomes the
most
expensive
option.)
No precautions required for
everyday activities but
management plan applies to
all activities which disturb soil
beneath the cap.
Estimated seven months
for treatment of one third
of the subdivision. Could
stage over an extended
period to meet funding
availability.
Low long-term
maintenance
required.
Control of everyday
activities not
required.
Community
feedback from the
workshops was
generally positive
about this solution.
High cost
Will take several months to
implement.
High disruption and truck
movements.
Not suitable beneath tree
drip lines.
Not suitable in restricted
access areas.
Occupiers would likely need
to vacate the property
during works.
Cannot be tailored for
individual properties (would
need several adjacent
properties to adopt this
solution).
Not supported by MoH or
Waikato District Health
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Thames Coromandel District Council November 2012
Response
option
Zones6 Human health risk
reduction
Cost Future site use Timeframe Advantages Disadvantages
Board.
Land use controls
(redevelopment)
1,2,3,4,7
& 8
Solution could be
tailored to ensure
management of health
risk.
Highest cost
as this
includes the
purchase of
the
property.
Response action can be
adapted to allow for
maximum usage under
proposed redevelopment
scenario.
Several months, especially
if properties are to be sold
on.
Site use could be
adapted to one
suitable for the
levels of
contamination.
High cost
Will take months to
implement.
Occupiers would need to
permanently vacate the
property would be removed
from the subdivision
housing stock.
Would probably require
several adjacent properties
to adopt this solution.
Community feedback mixed
for this solution.
Shading indicates advantages relative to other options. Light grey shading indicates a big advantage, dark grey shading indicates a disadvantage.
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7 References
Contaminated Site Investigation, June 2010, Moanataiari Subdivision, Thames, Scoping Report –
Historical Contamination Review, prepared for Environmental Waikato.
Golder Associates, 30 March 2012, Phase 3 – Desktop study and background sampling
methodology for Thames Area, prepared for Thames-Coromandel District Council.
Golder Associates, 29 June 2012, Interim report on bioaccessibility feasibility study, Moanataiari
Subdivision, Thames, prepared for Thames-Coromandel District Council.
Golder Associates, August 2012, Soil guideline value for thallium, Moanataiari Subdivision,
Thames, prepared for Thames-Coromandel District Council.
Golder Associates, October 2012, Health Risk Assessment, Moanataiari Subdivision, Thames,
prepared for Thames-Coromandel District Council.
Ministry for the Environment, 1997a, Guidelines for Assessing and Managing Contaminated
Gasworks Sites in New Zealand.
Ministry for the Environment, 1997b, Health and environmental guidelines for selected timber
treatment chemicals in New Zealand.
Ministry for the Environment, revised 2011a, Contaminated Land Management Guidelines No 1:
Guidelines for Reporting on Contaminated Sites in New Zealand.
Ministry for the Environment, 2011b, Methodology for deriving standards for contaminants in soil
to protect human health.
Ministry for the Environment, revised 2011c, Contaminated Land Management Guidelines (CLMG)
No. 2 – Hierarchy and Application in New Zealand of Environmental Guideline Values.
Ministry for the Environment, revised 2011d, Contaminated Land Management Guidelines (CLMG)
No. 5 – Site Investigation and Analysis of Soils.
Ministry for the Environment, 2006, Identifying, investigating and managing risks associated with
former sheep-dip sites: A guide for local authorities
Ministry for the Environment, April 2012, User’s Guide - National Environmental Standard for
Assessing and Managing Contaminants in Soil to Protect Human Health.
Ministry of Health, February 2012, The Environmental Case Management of Lead-exposed
Persons, Guidelines for Public Health Units.
Pattle Delamore and Partners, 15 November 2011a, Calculation of Acceptable Soil Concentrations
for Acute Exposure to Arsenic in Soil.
Pattle Delamore and Partners, December 2011b, Moanataiari Subdivision Site Investigation
Report, prepared for Waikato Regional Council.
Resource Management (National Environmental Standard for Assessing and Managing
Contaminants in Soil to Protect Human Health) Regulations 2011.
Tonkin & Taylor, June 2012, Moanataiari Subdivision, Thames – Phase 2 Overall Contamination
Assessment Report, prepared for Thames-Coromandel District Council