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BMT Western Australia Pty Ltd PO Box 2305, Churchlands WA 6018 Western Australia Tel: +61 (08) 6163 4900 Fax: +61 (08) 6163 4979 www.bmt.org ABN 093 752 811
Rev Issue Prepared by Submitted to Date Copies
A Internal Review S Mettam H Sunarko 05/03/2019 1 elec.
B Internal Review S Mettam T Green 06/03/2019 1 elec.
C Internal Review S Mettam A Gartner / I Teakle 08/03/2019 1 elec
0 Draft for Client Review S Mettam B Atkinson / A McCreath 12/03/2019 1 elec
Tn-WAT_1334_10_003-02 Rev 0 12/03/2019 Page 1
Technical Note
Project Number: 1334_10_003 Project Name: Perth Seawater Desalination Plant 2: Dredging Engineering Advice
Date: 12/03/2019 Doc Ref: Tn-WAT_1334_10_003-02
Client: Water Corporation
Subject: Perth Seawater Desalination Plant 2: Dredging Plume Modelling Input
1 Introduction
The proposed Perth Seawater Desalination Plant 2 (PSDP2) will be located in Kwinana,
approximately 30 kilometres south of Perth. Dredging works are required at the new PSDP2
area to create two trenches to accommodate a seawater intake pipe and a brine outfall pipe
(~250 m and ~580 m, respective). BMT has been engaged by the Water Corporation to assess
for dredging works in the PSDP2 area and provide plume modelling input to inform the
Environmental Impact Assessment process.
The purpose of this assessment to assess the required dredging and provide indicative
production rates to enable dredge plume modelling analysis.
2 Dredged Material
2.1 Dredging Volume
The in situ dredging volume for PSDP2 pipe trenches were determined by BMT on the basis
of bathymetric survey data collected in April/May 2009 and January 2010. The pipe trench
design was provided by Water Corporation to cater for the intake and outfall piping
requirements (refer to Attachment 2). The calculated volumes are presented in Table 2-1, and
the associated PSDP2 difference plot drawing is provided in Attachment 1.
Table 2-1: PSDP2 Dredging Volumes
# Values may vary due to current bathymetry/seabed condition, particularly in the nearshore area
Description Units Value#
Surface Area m2 62,906
Volume to Design m3 130,459
Volume to Design + 0.5m Over-dredge Allowance m3 154,362
Volume to Design + 1.0m Over-dredge Allowance m3 180,341
Page 2
2.2 Rock Protection Volume
The calculated placed bank volumes for the pipeline protection are presented in Table 2-2.
Table 2-2: PSDP2 Rock Protection Volumes
Description Units Value#
Pea Gravel m3 30,174
Filter Rock m3 9,151
Armour Rock m3 20,197
Sand Backfill m3 79,260
# Tonnages for each material will vary depending on required detailed design specifications
2.3 Dredged Material Characteristics
The in-situ material property assessments have been based on the information provided in the
following reports:
• Oceanica (2009), Fremantle Ports, Sediment Sampling and Analysis Implementation
Report: Diver and Geotechnical Survey (Reference no. 560_005/4)
• Golder Associates (2009), Fremantle Ports, Outer Harbour Geotechnical Investigation
Factual Report (Reference no. 087642339 002 R Rev1)
2.3.1 Sediment Sampling and Analysis Implementation Report
Sediment sampling and analysis was undertaken by Oceanica in 2008/09 for Fremantle Ports
proposed Kwinana Quay Development and Kwinana Bulk Berth No.1 projects for Fremantle
Ports. The purpose of this investigation was to assess the suitability of sediment for use in land
reclamation and offshore disposal.
Two different sampling techniques were used to obtain material from the seabed surface down
to below dredge design depths. A diver survey was undertaken in August 2008 to assess the
top 1m of sediment using a PVC core. A geotechnical survey undertaken in late 2008 and early
2009 was carried out using a ‘PQ3 triple tube’ drill string set up.
Based on Oceanica’s field observations, the dredged material characteristic was described as
follows (underlining by BMT; Attachment 3):
• The sediment in all areas was generally free of metal contaminants. Results also indicate
that there is no risk of acid sulphates soil development if the material is exposed to
oxygen during land reclamation
• Particles in the top 0-50 cm and bottom 50-100 cm across the area were mainly silt and
clay, followed by fine sand with some shell, occasional rocks and seagrass rhizome
remnants. The cores were not layered, and most samples had a sulphurous odour.
Page 3
Particle size distribution (PSD) data are presented in Table 2-3.
Table 2-3: PSD data
Fines (%) Coarse (%)
<38µm >38µm >63µm >125µm >250µm >500µm >1000µm >2000µm
BH1_top 53.1 7.0 16.8 8.3 4.9 2.9 2.3 4.7
BH1_bot 63.0 6.8 7.4 4.0 3.6 3.5 6.2 5.5
BH2_top 56.8 10.3 13.6 4.4 3.4 2.1 1.7 7.6
BH15_top 51.7 13.1 21.1 6.5 1.7 0.5 0.3 5.1
BH16_top 39.0 9.2 18.2 8 6.7 3.9 2.5 12.6
BH16_bot 32.7 7.0 22.2 7.2 5.3 4.9 4.0 16.6
BH17_top 25.2 3.7 8.2 4.3 4.2 4.1 4.0 46.3
Average 45.93 8.16 15.36 6.10 4.26 3.13 3.00 14.06
2.3.2 Outer Harbour Geotechnical Investigation Factual Report
The Golder Associates geotechnical site investigation was undertaken in 2009 for the
proposed Outer Harbour development at the Port of Fremantle. The purpose of this
investigation was to determine the subsurface conditions in the channel and berthing areas
known to be shallower than the design depths.
J&S Drilling were commissioned directly to carry out the drilling programme using an Edson
3000 drilling rig and jack up barge.
The site geotechnical condition can be described as follows (underlining by BMT):
The marine sediment observed over the site were generally up to 2.5m thick and composed
of sandy clay with low plasticity, fine grained sand and abundant shell fragments. Below the
marine sediments, a siliceous calcarenite, calcarenite and calcisiltite (limestone) layer was
encountered. These sediments were very weakly to well cemented, fine to medium grain
with abundant large shell fragments and pale grey to pale yellow in colour.
Unconfined compressive strength (UCS) ranges up to 2.33MPa
Page 4
PSD data are presented in Table 2-4
Table 2-4: PSD data
Fines (%)
Coarse (%)
Depth
(m) <75 µm
<150 µm
<300 µm
<425 µm
<600 µm
<1180 µm
<2360 µm
<4750 µm
<9500 µm
<19000 µm
<37500 µm
K3 -12.25 82 7 3 1 1 3 1 1 1 0 0
OH17 -13.2 46 27 8 2 3 4 3 2 1 4 0
OH18 -12.3 45 29 17 3 2 2 1 1 0 0 0
OH18 -13.5 25 12 8 3 5 10 8 7 10 7 5
Average 49.50 18.75 9.00 2.25 2.75 4.75 3.25 2.75 3.00 2.75 1.25
3 Dredging Method
Dredge plume modelling was initially used to assess the relative impact to water quality
(turbidity) of a backhoe dredge (BHD) versus cutter suction dredge, where it was determined
that the BHD approach would induce far less impact, Accordingly, a BHD will form the basis
for the plume modelling inputs:
• Backhoe Dredging - using a backhoe to excavate/remove marine sediment to the
required designed dredging depth. Excavated material is placed onto a barge which
travels to an approved nearby harbour location or temporary facility for offloading.
3.1.1 Assumptions and Exclusions
The dredging methodologies provided in this technical note are based on the following
assumptions:
• As directed by the Client, dredged material will not be placed in an offshore placement
area (i.e. no sea dumping)
• Dredged material characteristics have been assumed based on historical geotechnical
and sediment data (Fremantle Outer Harbour – Golder, 2009 & Oceanica, 2009)
• Dredged material from BHD will be transferred to land via a land back wharf facility,
such as those available in Henderson. The dredged material will be placed in an
onshore placement area. The location and management of dredged material are
excluded from the scope of this services. The BHD will be supported by adequate
number of barges to enable continuous dredging operation, i.e. BHD won’t be required
to sit on standby while the Hopper Barges travels and being unloaded in a wharf facility
• This report only considers the use of BHD. Other options or combination of options
have not been assessed, which may include the use of different sizes BHD and hopper
barges, use of a grab dredger and offshore dredged material placement. The use of
Cutter Suction Dredge (CSD) was assess in Technical Note No. Tn-
WAT_1334_10_003-01.
• Soil improvement works following the completion of reclamation works have not been
included in this study
Page 5
• Assessment for suitable reuse of the dredged material is not included in this study
• A project specific geotechnical site investigation campaign should be undertaken in the
future as part of detailed design phase. BMT wish to highlight that a calcisiltite limestone
layer with UCS of 30.6MPa was recorded in KP5 at depth of ~17m CD (Golder, 2009).
Geotechnical site investigation should be carried out to confirm that this hard limestone
layer is not within the design envelope as it will significantly impact the selection of
appropriate dredge plant.
3.2 Backhoe Dredging
3.2.1 General Methodology
A BHD is a combination of equipment consisting of a backhoe/excavator mounted on a barge
and equipped with a spud system to control the stability of the equipment. A picture of a BHD
vessel is shown in Figure 3-1 below.
Figure 3-1: Backhoe Dredger Vessel
A general working methodology of a BHD is outlined below:
• BHD will be positioned using its spud and can maneuver to the required dredging
location using its excavator arm or with support tugs (for longer distances)
• Excavated material will be placed onto hopper barges moored alongside the BHD
• The loaded barges can then be towed to a nearby land back wharf facility for
off-loading. Self-propelled barges may also be used
• BHD is also anticipated to be used for the placement of pipeline rock protection system.
3.2.2 Indicative BHD Dredging Production Parameters
The following dredging parameters have been adopted to estimate the proposed staged
dredging duration:
• 24-hour operations are assumed
• 4.8 – 7.2 hours per day for standby time (for delay due to sea state, maintenance and
repair)
• 3 m3 BHD bucket size
• Estimated dredging production rate of 60 - 82 m3/operational hour.
Page 6
The above are the key parameters for determining the scope, and timeframe required to
complete the proposed dredging works. BHD sequencing should commence in Area A and
progress towards Area C, followed by Area D.
Table 3-1: Backhoe Dredging Duration
Estimated Dredging Duration
Work Area Design Volume +1.0m
Overdredge (m3) High (days) Low (days)
Area A 41,519 22.4 29.1
Area B 45,928 24.7 32.1
Area C 22,018 11.9 15.4
Area D 70,875 38.2 49.6
Total: 180,341 ~97 ~126
3.2.3 Indicative BHD Rock Placement Production Parameters
In both dredging scenarios a BHD will be required once the pipe trench dredging is completed
to install the intake and outfall pipelines. The BHD will facilitate the placement of pea gravel,
filter rock, armour rock and sand backfill in that order to restore the natural seabed surface.
The following dredging parameters have been adopted to estimate the proposed rock
placement and backfill duration:
• 24-hour operations are assumed
• 4.8 – 7.2 hours per day for standby time (for delay due to sea state, maintenance and
repair)
• 3 m3 BHD bucket size
• Estimated rock placement production rate of 44 - 55 m3/operational hour
• Estimated backfill production rate of 59 - 73 m3/operational hour.
The above are the key parameters for determining the scope, and timeframe required to
complete the proposed rock placement and backfill works.
Table 3-2: Backhoe Dredging Duration
Estimated Dredging Duration
Work Area Design Volume (m3) High (days) Low (days)
Pea Gravel 30,174 23.5 30.2
Filter Rock 9,151 7.1 9.2
Armour Rock 20,197 15.7 20.2
Sand Backfill 79,260 46.2 61.6
Total: 138,781 ~93 ~121
Page 7
4 References
Golder Associates (2009), Fremantle Ports, Outer Harbour Geotechnical Investigation Factual
Report (Reference no. 087642339 002 R Rev1)
Oceanica (2009), Fremantle Ports, Sediment sampling and analysis implementation report:
Diver and geotechnical survey (Reference no. 560_005/4)
Page 8
ATTACHMENT 1:
DREDGING WORK AREAS
Drg No. Revision Title
WAT-1334-10-01-01 A
Perth Seawater Desalination Plant 2
Intake and Outfall Dredging Options
Colour Coded Differences
Natural Surface to Trench Design
0
SCALE 1 : 1000
METRES
10 0 100
0.0
-1.0
-2.0-3.0-4.0
-5.0-1
0.0
0.0
-1.0
-2.0-3.0
-4.0
-5.0-1
0.0
-11.0 AREA D
AREA C
AREA B
AREA A
LEGEND
K 3
K 4
K 5
B16
B2
B1
K 6
643580
0 mN
643600
0 mN
643620
0 mN
383400 m
E
383400 m
E
383600 m
E
383800 m
E
384000 m
E
384000 m
E
643580
0 mN
643600
0 mN
643620
0 mN
383400 m
E
383400 m
E
383600 m
E
383800 m
E
2.
DoW LIDAR SURVEY 2008
NATURAL SURFACE CONTOURS FROM COMBINED DoT SURVEYS 2003 TO 2012 INCLUDINGS.MOUCHEMORE
INTAKE AND OUTFALL DREDGING OPTIONS
WATER CORPORATION
PERTH SEAWATER DESALINATION PLANT 2
COLOUR CODED DIFFERENCES
NATURAL SURFACE TO TRENCH DESIGN
WAT 1334 10 - 01 - 01
S.METTAM 06/03/2019
06/03/2019
06/03/2019
06/03/2019
DRAWING NUMBER
CHECK
DRAFTING
REV
DRAWN
ENGINEER
PROJECT MGR
APPROVED
CHECK
ENGINEERING
C.LIVINGSTONE
H.SUNARKO
DATUM
NOTES
REV DATE AMENDMENT
06/03/19
APP
INITIAL ISSUE
DRN
SM
ORIG SIZE
A1WAT_1334_10-01-01A.dgnARCHIVE
MAP GRID OF AUSTRALIA BASED ON GDA 94, ZONE 50
VERTICAL
HORIZONTAL BebbCart
CLIENT
PROJECT
TITLE
A
A
1.AERIAL PHOTOGRAPHY JANUARY 2018
AHD
3.
IMPLEMENTATION REPORT: DIVER AND GEOTECHNICAL SURVEY (REFERENCE NO. 560_005/4)
OCEANICA (2009), FREMANTLE PORTS, SEDIMENT SAMPLING AND ANALYSIS
4.
GEOTECHNICAL INVESTIGATION FACTUAL REPORT (REFERENCE NO. 087642339 002 R REV1)
BOREHOLE DATA FROM GOLDER ASSOCIATES (2009), FREMANTLE PORTS, OUTER HARBOUR
K 4
B16 (REFER NOTE 3)
SEDIMENT SAMPLING SITES
(REFER NOTE 4)
BOREHOLES
GENERAL
FROM THE ORIGINAL SURVEYS
CALCULATED USING DATA INTERPOLATED
THE VALUES ON THE PLAN HAVE BEEN
GRIDDING PARAMETERS 2.0m GRID
TH
AN D
ESIG
N
DE
EP
ER
TH
AN D
ESIG
N
SH
ALL
OW
ER
-5.0
-4.0
-3.0
-2.0
-1.0
-0.7
-0.2
0.0
0.2
0.7
1.0
2.0
3.0
4.0
5.0
5.
MR93-096-004-01A4
FOR TRENCH DESIGN AND LOCATION REFER GHD PLANS MR93-096-003-02A2 AND
Page 9
ATTACHMENT 2:
REFERENCE DRAWINGS
Drg No. Revision Title
MR93-096-003-02 A2
Perth Seawater Desalination Plant
Expansion Investigation
Perth Seawater Desalination Plant 2
Intake and Outfall – Plan and Longitudinal Sections
MR93-096-004-01 A4
Perth Seawater Desalination Plant
Expansion Investigation
Perth Seawater Desalination Plant 2
Intake and Outfall –Sections
Level 10, 999 Hay Street Perth WA 6000 Australia
T 61 8 6222 8222 F 61 8 6222 8555
E [email protected] W www.ghd.com.au
PR
EL
IM
IN
AR
Y - N
OT
F
OR
C
ON
ST
RU
CT
IO
N
Page 10
ATTACHMENT 3:
SEDIMENT QUALITY ASSESSMENT
D0c No. Revision Title
WAT-1334-10-03-01 0 Perth Seawater Desalination Plan 2: Sediment Quality
Report
Perth Seawater Desalination Plan 2: Sediment
Quality Report
1334_10_003_Rev0 October 2018
P:\WaterCorp\1334_10PSDP EIA\003_PSDP2DredgingAdvice\Reports\Sediment Report\PD_Sediment_Report_Rev0_20181024.docm
Perth Seawater Desalination Plan 2: Sediment Quality Report
Prepared for
The Water Corporation (Western Australia)
Prepared by
BMT
October 2018
Report No. 1334_10_003_Rev0
Client: The Water Corporation (Western Australia)
Document history
Distribution
Revision Author Recipients Organisation No. copies
& format Date
A G Cummins B Davis BMT 1 x docm 22/10/18
B G Cummins A Gartner BMT 1 x docm 23/10/18
0 G Cummins B Atkinson Water Corporation 1 x pdf 24/10/18
Review
Revision Reviewer Intent Date
A B Davis Technical 22/10/18
B A Gartner Technical and editorial 24/10/18
Status
This report is 'Draft' until approved for final release, as indicated below by inclusion of signatures from: (i) the author and
(ii) a Director of BMT Western Australia Pty Ltd (BMT) or their authorised delegate. A Draft report may be issued for
review with intent to generate a 'Final' version, but must not be used for any other purpose.
Approved for final release:
Author Director (or delegate) Date: 23/10/18 Date: 23/10/18
Disclaimer
This report has been prepared on behalf of and for the exclusive use of The Water Corporation (Western Australia), and
is subject to and issued in accordance with the agreed terms and scope between The Water Corporation (Western
Australia) and BMT Western Australia Pty Ltd (BMT). BMT accepts no liability or responsibility for it in respect of any
use of or reliance upon this report by any third party.
Copying this report without prior written consent of The Water Corporation (Western Australia) or BMT is not permitted.
© Copyright 2018 BMT
BMT: The Water Corporation (Western Australia): Perth Seawater Desalination Plan 2: Sediment Quality Report i
Contents
Acronyms ................................................................................................................................... iii
1. Introduction ....................................................................................................................... 1
2. Sediment Sampling and Analysis .................................................................................... 2
Sediment sampling methods ................................................................................ 2
2.1.1 Quality assurance and quality control ........................................................... 3
Sediment analysis methods .................................................................................. 3
2.2.1 Sediment analytes ........................................................................................ 3
Data analysis methods .......................................................................................... 3
2.3.1 Normalisation of organics ............................................................................. 4
2.3.2 Computation of test statistics and assessment against guidelines ................ 4
3. Sediment Analysis Results ............................................................................................... 6
Physical sediment characteristics ........................................................................ 6
3.1.1 Particle size distribution ................................................................................ 6
3.1.2 Visual and odour characterisation ................................................................. 6
Metals ..................................................................................................................... 9
Hydrocarbons ...................................................................................................... 13
Organotins............................................................................................................ 14
3.5 Acid Sulfate Soils ................................................................................................. 14
Quality assurance/quality control ....................................................................... 15
4. Conclusions ..................................................................................................................... 16
5. References ....................................................................................................................... 17
ii BMT: The Water Corporation (Western Australia): Perth Seawater Desalination Plan 2: Sediment Quality Report
List of Figures
Figure 1.1 Perth Seawater Desalination Plant 2 dredge footprint and sediment sites
selected for analysis ............................................... Error! Bookmark not defined.
Figure 3.1 Particle size distribution of sediment samples collected in August 2008 ................ 6
List of Tables
Table 1.1 Sediment sites coordinates .................................... Error! Bookmark not defined.
Table 3.1 Wentworth scale ................................................................................................... 6
Table 3.2 Sediment characteristics and penetration depth of diver cores sampled in
August 2008 .......................................................................................................... 7
Table 3.3 Total metal concentrations in sediments sampled in August 2008 ........................11
Table 3.4 Polycyclic aromatic hydrocarbons concentrations normalised in sediment
samples collected at Kwinana Quay in 2008 ........................................................13
Table 3.5 Total organotin concentrations in sediment samples collected at Kwinana
Quay in 2008 ........................................................................................................14
Table 3.6 Acid sulfate soil analysis and acid base accounting for sediment samples
collected at Kwinana Quay in 2008 ......................................................................15
BMT: The Water Corporation (Western Australia): Perth Seawater Desalination Plan 2: Sediment Quality Report iii
Acronyms
ASS Acid sulfate soils
CSIRO Commonwealth Scientific and Industrial Research Organisation
EILs Ecological Investigation Levels
HILs Health Investigation Levels
LoR Limit of reporting
NAGD National Assessment Guidelines for Dredging
PAHs Polycyclic aromatic hydrocarbons
PSD Particle size distribution
SAP Sediment sampling and analysis plan
TOC Total organic carbon
TPH Total petroleum hydrocarbons
QA/QC Quality assurance and quality control
UCL Upper confidence limit
BMT: The Water Corporation (Western Australia): Perth Seawater Desalination Plan 2: Sediment Quality Report 1
1. Introduction
Water Corporation of Western Australia is proposing a second seawater desalination plant (Perth
Seawater Desalination Plan 2, PSDP2) adjacent to the existing PSDP1 in Kwinana, south of
Fremantle Western Australia. Construction of the PSDP2 outfall and intake pipelines requires
dredging and infilling of a trench, ~ 550 m long and 70 m wide (Error! Reference source not
found.).
Extensive sediment sampling and analyses have previously been undertaken in Cockburn Sound
to assess the suitability of sediment for use in land reclamation and offshore disposal. One
example is the Fremantle Port Kwinana Quay Development and Kwinana Bulk Berth No. 1 projects
(Oceanica 2009). Results available from a subset of selected sites from Oceanica (2009) that are
close in alignment with the PSDP2 dredge footprint (Figure 1.1) have been summarised in this
report to determine potential risk of contamination in sediments in the planned PSDP2 dredge area.
To ensure this assessment is contemporary, results were compared against current guidelines.
Figure 1.1 Perth Seawater Desalination Plant 2, Kwinana
2 BMT: The Water Corporation (Western Australia): Perth Seawater Desalination Plan 2: Sediment Quality Report
2. Sediment Sampling and Analysis
Site selection
A subset of ten sites (out of 94), located closest to the planned dredge area alignment
(Figure 2.1,Table 2.1), were selected from the broader sediment quality sampling program
undertaken by Oceanica (2009).
Note:
1. Sites were sampled by Oceania (2009)
Figure 2.1 Perth Seawater Desalination Plant 2 planned dredge footprint and sediment
sites selected for analysis
Table 2.1 Sediment sites coordinates
Site Easting Northing
A3 383713 6435812
A5 383612 6435868
A7 383550 6435897
B1 383644 6435987
B15 383075 6436250
B16 383331 6436250
B17 383158 6436227
B18 382906 6436436
B19 383152 6436513
B20 383372 6436582
Note:
1. Sites were by Oceanica (2009)
BMT: The Water Corporation (Western Australia): Perth Seawater Desalination Plan 2: Sediment Quality Report 3
Sediment sampling methods
Sediment sampling was completed between 11—20 August 2008 (Oceanica 2009) inline with
methods described in the Fremantle Port Kwinana Quay Development sediment Sampling and
Analysis Plan (SAP; Oceanica 2008). At each site, a diver hammered a PVC core into the sediment
until the target depth of 100 cm or until core refusal. Once target depth was reached the core was
sealed and retrieved to the vessel. The core was de-watered and extracted into a core tray, so
that the sediment profile was retained. Once extracted, the core was photographed, length
recorded, and sediment characteristics noted. The cores were sub-sampled at 50 cm increments
for laboratory analysis (Oceanica 2008).
All sampling equipment was cleaned with Decon 90 and rinsed in clean seawater between each
sampling event. Samples were placed in glass jars and zip-lock bags as described in the SAP
(Oceanica 2008) and stored on ice. At the end of each field day the samples were transported in
eskies to a freezer for storage prior to transport to the laboratory.
2.2.1 Quality assurance and quality control
Two types of field quality assurance/quality control (QA/QC) samples were recovered in the
broader program (Oceanica 2008):
• Triplicates, where three cores were obtained at the same location and analysed individually
• Replicates, where one sample was collected, homogenised, split into two in the field and
analysed individually in the laboratory.
Of the subset of sites selected for this review, two triplicate samples were analysed
Sediment analysis methods
2.3.1 Sediment analytes
Sediment samples from each of the ten sites (Figure 1.1,Table 2.1, were analysed for the
contaminants of concern listed in the SAP (Oceanica 2008):
• metals (Sb, As, Ba, Cd, Cr, Co, Cu, Pb, Mn, Mo, Ni, Ag, Sn, Hg and Zn)
• total petroleum hydrocarbons (TPH)
• polycyclic aromatic hydrocarbons (PAHs)
• benzene, toluene, ethylene and xylene (BTEX)
• organotins (monobutyltin: MBT, dibutyltin: DBT, tributyltin: TBT)
• total organic carbon (TOC)
• particle size distribution (PSD)
• acid sulphate soils (ASS; only 20% of the original 94 sites sampled in Oceanica 2009 were
analysed for ASS. This included 4 of the 10 sites from Error! Reference source not found.,
Error! Reference source not found.).
PSD analysis was completed at the Division of Minerals/Particle Analysis Service at CSIRO.
National Measurement Institute completed analysis of remaining contaminants of concern using
standard methods in National Association of Testing Authorities accredited methods.
Data analysis methods
Data analysis was completed as per Oceanica 2009, with the following amendments:
• test and summary statistics were computed across the ten sites (Figure 1.1,Table 2.1)
4 BMT: The Water Corporation (Western Australia): Perth Seawater Desalination Plan 2: Sediment Quality Report
• current guidelines were used (the National Assessment Guidelines for Dredging: CA 2009,
NEPC 2013 and DER 2014).
2.4.1 Normalisation of organics
As TOC is the main binding constituent for organic substances in marine sediments, CA (2009)
requires organics (TBT, TPH, PAH and BTEX) to be normalised to 1% TOC for comparison with
the NAGD Screening Levels. The normalised results provide a measure of the bioavailability of
the organic analytes. When TOC is significantly greater than 1%, the additional binding capacity
will result in organics being less biologically available, and therefore, normalisation will reduce the
measured value proportionally (the reverse also applies). Normalisation is only appropriate over a
TOC range of 0.2–10%. In accordance with the NAGD (CA 2009), if the organic data were below
the laboratory limit of reporting (LoR), half the LoR value was used for normalisation purposes.
2.4.2 Computation of test statistics and assessment against guidelines
Test statistics were computed from the analyte datasets (where possible) for comparison with the
relevant guidelines. The different guidelines stipulate different types of statistical analysis; each of
which is summarised below.
National Assessment Guidelines for Dredging Screening Levels
Concentrations of metals and organics in sediments were compared to the NAGD Screening Levels
(CA 2009). This comparison required calculation of the 95% upper confidence limit (UCL) of the
mean (CA 2009). Where there were not enough samples to complete the calculations, the
maximum concentrations were compared to the relevant NAGD Screening Levels (CA 2009).
Ecological investigation levels and health investigation levels
Concentrations of metals in sediment samples were assessed against the ecological investigation
levels (EILs) and health investigation levels (HILs) from the National Environmental Protection
Council (NEPC) guidelines (NEPC 2013) that are referenced in the contaminated sites guidelines
(DER 2014). Sediment contaminant concentration levels were compared to the EILs for "urban
residential/public open space" and HIL "C" which is acceptable for public open space (NEPC 2013).
The maximum concentration value and the 95% UCL of the arithmetic mean was used for
comparison against the EILs and HILs (NEPC 2013). For assessment against the relevant levels,
the following criteria are also specified in NEPC (2013):
• the standard deviation of the sample data must be less than 50% of the relevant value
• no single value must exceed 250% of the relevant value.
The EILs (for chromium III, copper, nickel and zinc) are typically derived by the addition of the
ambient water quality background analyte concentrations (determined from reference site data) to
the guideline values which represent added contaminant levels. However, sampling was
completed to different guidelines, and therefore there was no collection of reference site data or
ambient background data required for EIL calculation. As such, metal concentration results were
compared to the EILs range. Once the onshore disposal area location has been determined,
background reference site data will be collected and EILs calculated prior to dredging..
Analysis of analyte concentrations below the limit of reporting
Analyte concentrations that are too low to be detected using laboratory methods were recorded as
below the LoR. Generally, CA (2009) recommend that half the laboratory LoR value should be be
used as a substitute for data below the LoR; however, a large proportion of the data below the LoR
has the capacity to bias subsequent analyses. The USEPA (2007) does not consider a 95% UCL
BMT: The Water Corporation (Western Australia): Perth Seawater Desalination Plan 2: Sediment Quality Report 5
of the mean calculated based upon few detected values to be reliable. Therefore, where the data
contain values below the LoR, the following protocol was applied:
• Where >25% of values are below the LoR, descriptive statistics (means and percentiles) or
inferential analysis (including the calculation of confidence limits) were not calculated. Instead,
individual results were compared to the triggers and discussed accordingly.
• Where ≤25% but >0% of values are below the LoR, confidence limits were calculated based on
half the LoR as the replacement value.
6 BMT: The Water Corporation (Western Australia): Perth Seawater Desalination Plan 2: Sediment Quality Report
3. Sediment Quality Results
Physical sediment characteristics
3.1.1 Particle size distribution
Sediment was classified according to the Wentworth Scale sediment classifications (Table 3.2).
Sediments at the majority of sites were predominantly comprised of silts and clay, followed by fine
sands, with the exception of sites B17 and B19, which were predominantly comprised of gravel
(Figure 3.1).
Table 3.1 Wentworth scale
Particle size Description
<63 µm silt and clay
63-250 µm fine sand
250-500 µm medium sand
500-2000 µm coarse sand
>2000 µm gravel
Note:
1. A3 & B18= mean of a triplicate
Source: Oceanica (2009)
Figure 3.1 Particle size distribution of sediment samples collected in August 2008
3.1.2 Visual and odour characterisation
Sediment characteristics, core penetration depth and photographs of the cored are detailed in
Table 3.2. Core penetration varied from refusal at 10 cm to full recovery of 100 cm (Table 3.2).
The sediments samples were predominantly grey silts and fine sands (Table 3.2). Seagrass
rhizomes were observed in samples collected at sites A3, B18 and B20, and seagrass matting was
found in the site B16 sample. More than half of the sites had sulphur odour associated with the
sediment samples (Table 3.2).
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
gravel coarse sand medium sand fine sand silt and clay
0-50 cm 50-100 cm
BMT: The Water Corporation (Western Australia): Perth Seawater Desalination Plan 2: Sediment Quality Report 7
Table 3.2 Sediment characteristics and penetration depth of diver cores sampled in August 2008
Site Date Core length (cm)
Section
Top = 0-50cm
Bottom = 50-100cm
Sample characteristics - type of material, colour, odour Photograph
A3 Triplicate A 15/08/08 100
Top Grey fine silt, rhizome at about 30 cm, some smell
Bottom As above, small amount of rhizome, thick, very dark grey clay, light grey
limestone at bottom
A3 Triplicate B 15/08/08 100
Top Grey fine silt, rhizome at about 30 cm, some smell
Bottom As above, small amount of rhizome, thick, very dark grey clay, light grey
limestone at bottom
A3 Triplicate C 15/08/08 100
Top Grey fine silt, rhizome at about 30 cm, some smell
Bottom
As above, small amount of rhizome, thick, very dark grey clay, light grey
limestone at bottom
A5 15/08/08 10 (surface scrape)
Top Grey silt, no smell
Bottom NA
A7 (replicate sample) 15/08/08 30 (surface scrape)
Top Dark grey/black silt, some smell
Bottom NA
B1 11/08/08 100
Top
Corer did not reach compacted material, soft, grey fines, compacted
during coring, sulphur smell
Bottom No layering but deeper was slightly coarser
B15 12/08/08 50
Top Grey fine silt. Some sulphur smell
Bottom NA
B16 12/08/08 100
Top Grey silt/sand, shell layer at 30 cm, seagrass matt at 20 cm
Bottom Grey silt/sand, some shells
8 BMT: The Water Corporation (Western Australia): Perth Seawater Desalination Plan 2: Sediment Quality Report
Site Date Core length (cm)
Section
Top = 0-50cm
Bottom = 50-100cm
Sample characteristics - type of material, colour, odour Photograph
B17 12/08/08 10 (surface scrape)
Top Grey sand, lots of shell grit
Bottom NA
B18 Triplicate A 12/08/08 100
Top
Light grey sand/silt and shell, some sulphur smell, some rhizome mat
Bottom
B18 Triplicate B 12/08/08 100
Top
Light grey sand/silt and shell, some sulphur smell, some rhizome mat
Bottom
B18 Triplicate C 12/08/08 100 Top
Light grey sand/silt and shell, some sulphur smell, some rhizome mat See above photograph Bottom
B19 12/08/08 10 (surface scrape)
Top Shell, coarse sand and grit
Bottom NA
B20 12/08/08 100
Top Grey sand, sulphur smell, rhizome at 20 cm
Bottom Grey sand, sulphur smell, some shell
Source: Oceanica (2009)
BMT: The Water Corporation (Western Australia): Perth Seawater Desalination Plan 2: Sediment Quality Report 9
Metals
Test statistics (95% UCL, maximum, mean and standard deviation) were calculated for all metal
analyte concentrations in the surface layer (0–50 cm) sediments, with the exception of antimony
and cadmium (Table 3.3) as antimony and cadmium concentrations were below the LoR for all or
>25% of sites (Table 3.3). For surface sediments (0–50 cm), the 95% UCL of total metals was
below the respective NAGD Screening Levels for each analyte (Table 3.3). Individual mercury
surface sample concentrations exceeded the NAGD Screening Levels at sites A3 and A5
(Table 3.3).
The sample size was too small (n=5) to calculate a meaningful 95% UCL in the bottom layer (50-
100 cm) of sediments, and as such, individual concentrations were compared to the NAGD
Screening Levels (CA 2009). All maximum concentration for total metals in bottom sediments were
below the respective NAGD Screening Levels, with the exception of arsenic, which was equal to
the NAGD Screening Level at site B1
The 95% UCL concentrations for arsenic, total chromium, copper, lead, zinc and nickel, for surface
sediment samples were below their respective EILs, or within acceptable EIL ranges for disposal
to 'urban residential and public open space' requirements (Table 3.3, NEPC 2013). All individual
metal concentrations in surface samples and bottom samples were below their respective HILs "C"
for public open spaces, satisfying the conditions of the NEPC (2013; Table 3.3).
BMT: The Water Corporation (Western Australia): Perth Seawater Desalination Plan 2: Sediment Quality Report 11
Table 3.3 Total metal concentrations in sediments sampled in August 2008
Analyte/Site Sb As Ba Cd Total Cr Co Cu Pb Mn Hg Mo Ni Sn Ag Zn
Unit mg/kg
NAGD Screening Level1 2 20 – 1.5 80 – 65 50 – 0.15 – 21 – 1 200
EIL2 – 50 – – 75-160 – 30-120 270 – – – 10-170 – – 25-500
HIL2 – 300 – 90 – 300 17000 600 19000 80 – 1200 – – –
LoR 0.2 0.5 0.2 0.1 0.2 0.2 0.2 0.2 0.2 0.01 0.2 0.2 0.2 0.2 0.2
A3_S* 0.2 7.5 8.9 0.24 46.0 1.5 35.0 14.0 77.3 0.167 2.6 10.3 0.9 0.1 75.7
A5_S <0.2 8.9 11.0 0.23 51.0 1.7 40.0 16.0 72.0 0.160 1.4 11.0 1.0 0.1 80.0
A7_S <0.2 11.0 11.0 0.17 47.0 1.8 25.0 12.0 78.0 0.110 3.7 10.0 0.8 0.1 55.0
B1_S <0.2 7.7 7.6 0.20 27.0 1.2 14.0 26.0 42.0 0.028 2.0 6.6 0.5 0.1 46.0
B15_S <0.2 6.3 8.9 0.14 28.0 1.1 8.8 17.0 25.0 0.110 1.5 5.4 0.1 0.1 29.0
B16_S <0.2 4.7 7.7 <0.05 20.0 1.0 6.1 9.3 16.0 0.054 1.9 4.3 0.1 0.1 45.0
B17_S <0.2 6.6 8.0 <0.05 20.0 1.1 3.3 6.6 20.0 0.032 1.1 3.9 0.1 0.1 9.9
B18_S* <0.2 3.4 8.4 <0.05 14.1 0.8 2.0 4.7 9.6 0.016 2.0 2.3 0.1 0.1 6.7
B19_S <0.2 1.2 12.0 <0.05 7.0 0.7 19.0 4.1 8.2 0.014 0.4 0.7 0.1 0.1 7.2
B20_S <0.2 4.5 6.2 <0.05 17.0 1.0 4.2 6.6 12.0 0.045 1.4 3.3 0.1 0.1 9.3
Maximum NA 11.0 12.0 NA 51.0 1.8 40.0 26.0 78.0 0.167 3.7 11.0 1.0 NA 80.0
Mean NA 6.2 9.0 NA 27.7 1.2 15.7 11.6 36.0 0.074 1.8 5.8 0.4 NA 36.4
Standard deviation NA 2.84 1.82 NA 15.27 0.36 13.65 6.84 29.11 0.058 0.89 3.59 0.36 NA 28.25
95% ProUCL3 NA 7.82 10.03 NA 36.56 1.395 23.65 15.6 52.89 0.107 2.32 7.86 0.58 NA 52.75
A3_0.5-1.0* 0.15 9.2 8.6 0.22 29 1.24 9.1 5.8 57.7 0.039 5.4 6.5 0.3 0.1 23.0
B1_0.5-1.0 0.20 20.0 13.0 0.05 50 2.4 6.4 9.3 94 0.005 15 11 0.3 0.1 8.5
B16_0.5-1.0 0.20 9.8 10.0 0.05 23 1.4 1.6 4.4 29 0.005 3 5 0.1 0.1 2.7
B18_0.5-1.0* <0.2 5.3 5.9 0.05 15.7 0.9 0.8 2 10.7 0.005 3.4 2.7 0.1 0.1 1.4
B20_0.5-1.0 0.16 8.3 8.5 0.05 21.5 1.4 1.6 4.05 23.5 0.005 4.5 4.6 0.1 0.1 1.4
Maximum 0.20 20.0 13.0 0.22 50 2.4 9.1 9.3 94 0.039 15.0 11.0 0.3 NA 23.0
Mean 0.16 10.52 9.18 0.08 27.83 1.47 3.90 5.12 42.97 0.012 6.28 5.97 0.2 NA 7.4
Standard Deviation 0.04 5.57 2.60 0.08 13.27 0.55 3.65 2.71 33.31 0.015 4.97 3.12 0.12 NA 9.2
Notes:
1. NAGD Screening Levels from CA (2009).
2. EIL = range of Ecological Screening Levels for "urban residential/public open spaces" (NEPC 2013)
3. HIL = health investigation level "C" for commercial/industrial areas (NEPC 2013)
4. Calculation of 95% UCL only possible or surface data (not possible for bottom data due to small dataset size).
5. Bold text indicated exceedance of NAGD Screening Level, italicised text indicates exceedance of Ecological Investigation Level (EIL) for public open space.
6. * = triplicate results which were averaged for inclusion in this table.
7. NA = not applicable; test statistics were not calculated for analytes with >25% below LoR.
8. LoR = limit of reporting.
BMT: The Water Corporation (Western Australia): Perth Seawater Desalination Plan 2: Sediment Quality Report 13
Hydrocarbons
Concentrations of TPH and BTEX were below the LoR in all samples (Oceanica 2009). Therefore,
results were not normalised and sediments are considered to be uncontaminated by TPHs and
BTEX.
While there were low concentrations of PAHs recorded in all sediment samples (results for PAH
sum ranged from 0.0466–0.5896 mg/kg; Table 3.4), numerous PAH species were below the LoR,
and not all PAH species now required for comparison to the NAGD (CA 2009) Screening Level
(10 000 mg/kg) were originally analysed by Oceanica (2009). This prohibited a meaningful
comparison to the NAGD (CA 2009) Screening Levels. Given the extremely low concentrations of
PAHs in sediments, the risk of contamination to the marine environment due to disturbance
associated with dredging is considered extremely low.
Table 3.4 Polycyclic aromatic hydrocarbons concentrations normalised in sediment
samples collected at Kwinana Quay in 2008
Analyte/Site Total organic carbon Sum 15 PAHs1
Unit % mg/kg
NAGD Screening Level2 – 10 000
A3* 5.0 0.1196
A5 3.9 0.0918
A7 2.8 0.1911
B1 2.4 0.5896
B15 1.9 0.2711
B16 1.9 0.1389
B17 1.2 0.0792
B18* 1.5 0.0682
B19 1.0 0.0910
B20 1.3 0.0869
A3* 3.7 0.0466
B1 2.1 0.0610
B16 1.0 0.0750
B18* 1.1 0.0714
B20 0.8 0.0938
Notes:
1. 95% UCL could not be calculated as >25% results were below the limit of reporting (LoR). Only 15 PAHs (napthalene,
acenaphthalene, acenaphtene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo(a)anthracene,
chrysene, benzo(b)fluoranthene and benzo(k)fluoranthene, benzo(a)pyrene, indeno(1,2,3-c,d)pyrene,
dibenzo(a,h)anthracene and benzo(g,h,i)perylene) were analysed, therefore the sum of these is compared to the 18
PAHs NAGD Screening Level
2. NAGD Screening Levels from CA (2009)
3. Italicised results = non-normalised result was below the LoR and half the LoR was used in calculation purposes
4. * = triplicate samples which were averaged for inclusion in this table
14 BMT: The Water Corporation (Western Australia): Perth Seawater Desalination Plan 2: Sediment Quality Report
Organotins
Normalised TBT concentrations were below both the NAGD (CA 2009) Screening Level and the at
all sites in both the top and bottom sediment samples (Table 3.5).
Table 3.5 Total organotin concentrations in sediment samples collected at Kwinana
Quay in 2008
Organotin TOC MBT DBT TBT Normalised TBT2
Unit % μgSn/kg μgSn/kg μgSn/kg μgSn/kg
Screening Level1 – – – – 9
Top samples 0–50 cm
A3_Top* 5.0 3.1 4.4 2.2 0.44
A5_Top 3.9 3 4.7 2.4 0.62
A7_Top 2.8 3.1 4.8 2.7 1.13
B1_Top 2.4 <0.5 1.4 0.79 0.33
B15_Top 1.9 <0.5 1.5 0.64 0.34
B16_Top 1.9 <0.5 0.97 0.59 0.31
B17_Top 1.2 <0.5 0.77 0.60 0.50
B18_Top* 1.5 <0.5 0.67 <0.5 0.17^
B19_Top 1.0 0.83 0.74 0.87 0.87
B20_Top 1.3 0.62 <0.5 <0.5 0.19^
Bottom samples 50–100 cm
A3_Bottom* 3.7 1.1 1.4 0.85 0.43
B1_Bottom 2.1 <0.5 <0.5 <0.5 0.12^
B16_Bottom 1.0 <0.5 <0.5 <0.5 0.25^
B18_Bottom* 1.1 <0.5 <0.5 0.31 0.30
B20_Bottom 0.8 <0.5 <0.5 <0.5 0.32^
Notes:
1. As per NAGD (CA 2009)
2. TBT was normalised to 1% total organic carbon. Normalisation is only appropriate over the total organic carbon
range 0.2–10% (equates to multiplication factors of 5 times –0.1 times, respectively)
3. * = triplicate samples which were averaged for inclusion in this table
4. ^= half limit of reporting used in calculation
5. TOC = total organic carbon, MBT = monobutyltin, DBT = dibutyltin, TBT = tributyltin, - = no guideline value
3.5 Acid Sulfate Soils
A subsection (20%) of the original sites sampled were analysed for ASS (Oceanica 2009). Of the
ten sites examined within this report, four were included in the 20% analysed for ASS (Table 3.6).
At each site, the sulfur (%S) was above the potential sulfidic acidity Action Criteria of 0.03%
(DER 2015) and therefore identified as potential ASS.
However, the acid-based accounting completed for these sediment samples indicated that the
potential acidity was sufficiently buffered by the acid neutralising capacity of the sediment and
therefore the total net acidity for every sample was negative (Table 3.6). Therefore, the samples
exhibited sufficient neutralising capacity within the sediments to result in no net acidity formation
after disturbance of the sediments during dredging within the water column.
BMT: The Water Corporation (Western Australia): Perth Seawater Desalination Plan 2: Sediment Quality Report 15
Table 3.6 Acid sulfate soil analysis and acid base accounting for sediment samples
collected at Kwinana Quay in 2008
Analyte/Site pHKCl %S (SCr) Equivalent
Acidity
Existing
Acidity
ANC
existing %
ANC (mol
H+/tonne)
Net
Acidity
(mol
H+/tonne)
Action
Criteria1 – 0.03 18.7 – – – –
A3c_Bottom 9.0 0.45 280.7 none 63 12587.4 -8110.9
B15_Top 9.2 0.18 112.3 none 57 11388.6 -7480.1
B18a_Bottom 9.3 0.11 68.6 none 66 13186.8 -8722.6
B20_Top 9.1 0.10 62.4 none 48 9590.4 -6331.2
Notes:
1. Samples assigned DER (2015) action criteria for >1000t material.
2. pHKCL = pH in potassium chloride suspension, S = sulfur, SCr = chromium reducible sulfur, ANC = acid neutralising
capacity
3. – = no guidelines available
4. A positive net acidity indicates excess acid
Quality assurance/quality control
QA/QC analyses was completed on the full set of sediment data (n=94) collected by Oceanica
(2009), and laboratory duplicate and blank samples had a relative percentage difference of within
±35% between results, which is considered acceptable (Oceanica 2009). Further QA/QC
assessment was not completed in this report.
16 BMT: The Water Corporation (Western Australia): Perth Seawater Desalination Plan 2: Sediment Quality Report
4. Conclusions
The unconsolidated surface material in the upper 1 m of the seabed from sampling in 2008 was
considered to be clean and met NAGD (CA 2009) Screening Levels.
BMT: The Water Corporation (Western Australia): Perth Seawater Desalination Plan 2: Sediment Quality Report 17
5. References
CA (2009) National Assessment Guidelines for Dredging. Commonwealth of Australia, Canberra,
ACT
DER (2014) Assessment and management of contaminated sites. Contaminated sites guidelines.
Department of Environment Regulation, Perth, Western Australia, December 2014
DER (2015) Identification and Investigation of Acid Sulfate Soils and Acidic Landscapes.
Department of Environment Regulation, Perth, Western Australia, June 2015
NEPC (2013) National Environment Protection (Assessment of Site Contamination) Amendment
Measure 2013 (No. 1) National Environment Protection Council, April 2013
Oceanica (2008) Fremantle Ports Kwinana Quay Project Sediment Sampling and Analysis Plan.
Prepared for Fremantle Ports by Oceanica Consulting Pty Ltd. Report No. 560/1 Draft,
Perth, Western Australia, July 2008
Oceanica (2009) Fremantle Ports Kwinana Quay Sediment sampling and analysis implementation
report diver and geotechnical survey. Prepared for Fremantle Ports by Oceanica Consulting
Pty Ltd. Report No. 560_005/4_Rev0, Perth, Western Australia, October 2009
USEPA (2007) ProUCL version 4.0. Available from <http://www.epa.gov/esd/tsc/ software.htm>.
United States Environmental Protection Authority
PO Box 2305 Churchlands
WA 6018 Australia
Tel: +61 8 6163 4900
www.bmt.org
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