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Southern Seawater Desalination Plant 2016 Performance Review Report

Contents

i SSDP 2016 Performance Review Report

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Glossary and Definition of Terms _________________________________________ 1

1. Introduction ____________________________________________________ 3

1.1 Environmental Approval _________________________________________________ 3

1.2 Report Objective _______________________________________________________ 3

2. Environmental Factors, Risks and Impacts _____________________________ 4

2.1 Key Environmental Factors _______________________________________________ 4

2.2 Key Risks and Impacts __________________________________________________ 4

3. Environmental Monitoring Framework ________________________________ 6

3.1 Environmental Quality Objectives __________________________________________ 6

3.2 Marine Environment Monitoring Programs ___________________________________ 6

3.2.1 Marine Environment Monitoring Program _________________________________ 6

3.2.2 Dissolved Oxygen Monitoring Program __________________________________ 6

3.2.3 Diffuser Performance Monitoring Program ________________________________ 7

3.2.4 Whole Effluent Toxicity Monitoring Program ______________________________ 7

3.3 Revegetation Management Plan ___________________________________________ 7

4. Environmental Performance ________________________________________ 9

4.1 Benthic Health Monitoring _______________________________________________ 13

4.2 Greenhouse Gas Emissions ______________________________________________ 13

5. Benchmarking, Best Available Technology and Improvements in Environmental Management ________________________________________________________ 14

5.1 Diffuser Re-orientation _________________________________________________ 14

5.2 Backfilling ___________________________________________________________ 14

5.3 Seawater Recirculation _________________________________________________ 14

5.4 Diffuser Capping ______________________________________________________ 14

6. Conclusion _____________________________________________________ 16

Appendix 1 – Ministerial Statement 792 __________________________________ 17

Appendix 2 – Report and recommendations of the EPA Report 1302 ____________ 17

Appendix 3 – Marine Environment Monitoring Program _______________________ 17

Appendix 4 – Dissolved Oxygen Monitoring Program_________________________ 17

Appendix 5 – Diffuser Performance Monitoring Program ______________________ 17

Appendix 6 – Whole Effluent Toxicity Monitoring Program ____________________ 17

Appendix 7 – Revegetation Management Plan ______________________________ 17

Appendix 8 – 2015 Marine Environment Monitoring Annual Report ______________ 17

Appendix 9 – 2016 Marine Environment Monitoring Annual Report ______________ 17

Appendix 10 – Letter from OEPA acknowledging completion of dissolved oxygen monitoring _________________________________________________________ 17

SSDP 2016 Performance Review Report

1 SSDP 2016 Performance Review Report

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Glossary and Definition of Terms Actual Dilution The Actual Dilution achieved at the SSDP LEPA boundary is calculated from the results of the Diffuser

Performance Monitoring Program. The method to calculate the Actual Dilution is provided in Section

3.3.3 of the DPMP.

Bottom Saline Layer The bottom saline layer is the whole bottom saline layer, a layer of higher salinity to that of the

background salinity. The layer commences at the first salinity reading above the background salinity.

DER Department of Environment Regulation (previously Department of Environment and Conservation)

Desalination Effluent Desalination effluent consists of the brine stream from the RO system, neutralised clean-in-place (CIP)

streams and wastewater originated from the backwash of the membrane filters and seawater strainers.

The desalination effluent is discharged to the marine environment via a 320m diffuser array.

DPMP Diffuser Performance Monitoring Program (Revision D, 2015)

DO Dissolved Oxygen

DOMP Dissolved Oxygen Monitoring Program

Environmental

Quality Objectives

The Environmental Quality Objectives identified by the OEPA and specified in MS792 Schedule 1 for the

marine environment surrounding the SSDP ocean diffuser.

EPA Environmental Protection Authority

Full Production Full Production of the SSDP is the combined Stage 1 and Stage 2 operations, which produces 100GL of

drinking water per year.

GL Gigalitres

IWSS Integrated Water Supply Scheme

Key Environmental

Factors

The Key Environmental Factors identified as relevant to the construction and operation of the SSDP in

the Report and recommendations of the Environmental Protection Authority (EPA) (Appendix 2 – Report

and recommendations of the EPA Report 1302).

LEPA Low Ecological Protection Area

Marine Environment

Monitoring

Environmental monitoring undertaken in the marine environment as per the MEMP, DOMP, DPMP and

WETMP.

MEMP Marine Environmental Monitoring Program, including Discharge Water Quality Monitoring and Benthic

Health Monitoring.

MF Membrane Filtration

MS792 Ministerial Statement 792

NOEC No Observed Effect Concentration

OEPA Office of the Environmental Protection Authority

OEMF SSDP Operation Environmental Management Framework developed to address MS792 requirements.

ppt Parts per thousand

Recirculation Seawater entering through the seawater intake pipelines is recirculated directly back into the

desalination effluent diffuser pipeline to increase on-shore dilution prior to diffusing into the marine

environment.

RMP Revegetation Management Plan

RO Reverse Osmosis

SSDP Southern Seawater Desalination Plant

SSWA Southern Seawater Alliance

Target Dilution The minimum number of dilutions required to meet the ANZECC (2000) 99% species protection trigger

at the boundary of the LEPA as per the latest valid WET testing results provided by the WET testing

consultant. The 99% species protection trigger is theoretical or statistically inferred based on the results

of sub-lethal toxicity testing and species sensitivity distributions.

WET Whole Effluent Toxicity



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WETMP Whole Effluent Toxicity Monitoring Program

Worst Case Dilution The Worst Case Dilution achieved at the SSDP LEPA boundary can be calculated from the Actual Dilution

results of the Diffuser Performance Monitoring Program (salinity monitoring). If the number of marine

salinity monitoring events (n) is less than 20, then the worst dilution result calculated for all of the

salinity monitoring events in the reporting period will be used to represent the Worst Case Dilution. If

the number of marine salinity monitoring events (n) is greater than 20 then the lower 5th percentile of

the dilution results calculated for all of the salinity monitoring events in the reporting period will be used

to represent the Worst Case Dilution.



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1. Introduction

The Southern Seawater Desalination Plant (SSDP) consists of offshore marine infrastructure

(intake and diffuser systems) and onshore infrastructure (treatment and storage infrastructure)

on Taranto Road, Binningup, WA. Drinking water is supplied to Water Corporation’s Integrated

Water Supply Scheme (IWSS) via a storage tank facility near Harvey.

The SSDP was designed and constructed in two stages, each capable of producing 50 GL of

water annually. Stage 1 of the plant began commercial operations on the 12 March 2012. Stage

2 was commissioned on 17 January 2014. The combined plant is capable of producing 100GL of

drinking water annually.

1.1 Environmental Approval

In July 2007 Water Corporation referred the proposal to construct and operate the SSDP to the

Minister for Environment for assessment under Section 38 of the Environmental Protection Act

1986. It was formally assessed at the level of Public Environmental Review under the State

process. The Proposal was approved by the Minister for Environment, with Ministerial Statement

792 (MS792) published on the 14 April 2009 (provided in Appendix 1 – Ministerial Statement

792). The approval acknowledged that construction and operation of the desalination plant will

have an impact on the marine environment.

The project was referred to the Commonwealth Department of Environment, Water, Heritage

and the Arts (now Department of the Environment) for assessment under the Environment

Protection and Biodiversity Conservation Act 1999. The project was approved under conditions

published in approval EPBC2008/4173 on 24 June 2009.

1.2 Report Objective

Water Corporation is required to submit a Performance Review Report (PRR) at the conclusion

of the second, forth, and sixth year after commencement of operation in accordance with

MS792 condition 5-1.

Condition 5-1 specifies that the PRR is required to address the following items:

1. The major environmental risks and impacts; the performance objectives, standards and

criteria related to these; the success of risk reduction/impact mitigation measures and

results of monitoring related to the management of the major risks and impacts;

2. The level of progress in the achievement of best practice environmental performance,

including industry benchmarking, and the use of best available technology where

practicable; and

3. Improvements gained in environmental management which could be applied to this and

other similar projects.

This PRR is the second PRR for the SSDP. The first PRR was submitted in 2014.



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2. Environmental Factors, Risks and Impacts

2.1 Key Environmental Factors

The following Key Environmental Factors were identified as relevant to the construction and

operation of the SSDP in the Report and recommendations of the Environmental Protection

Authority (EPA) (Appendix 2 – Report and recommendations of the EPA Report 1302):

Water quality and Marine Biota – impacts from construction and operation of the desalination

plant;

Terrestrial Fauna – impacts from clearing of habitat;

Terrestrial Vegetation and Wetlands – impacts from clearing during infrastructure

construction; and

Greenhouse Gas Emissions – proposed no net greenhouse gas emissions.

2.2 Key Risks and Impacts

MS792 acknowledges that the discharge of desalination effluent will have an impact in the

immediate vicinity of the discharge to the marine environment. A Low Ecological Protection Area

(LEPA) has been established to limit the extent which the local marine ecosystem will be

impacted. The LEPA is 100 metres by 600 metres (50 metres either side of the diffuser array),

as required by MS792 Condition 6-1. A High Ecological Protection Area exists beyond the LEPA

boundary, at which 99% protection of species must be met.

The environmental risks and impacts for the construction and operation of the SSDP according

to each key environmental factor are shown in Table 1.

Table 1: SSDP Environmental Risks and Impacts

EPA Key Environmental

Factor

Environmental risk Potential environmental impact

Water Quality and Marine Biota - impacts from construction and operation of the desalination plant

Discharge water quality

Desalination effluent discharge quality exceeds trigger values (combination of 80th percentile of baseline results and ANZECC 2000 triggers) at the LEPA boundary, causing a risk of adverse biological impacts.

Dissolved Oxygen (DO)

Desalination effluent discharge results in a DO concentration at the LEPA boundary below MS792 condition 6-7 criteria of 60% saturation. DO is a key environmental quality indicator which may impact marine ecosystem integrity (structure biomass and

biota abundance) if the concentration is below 60%

saturation.

Salinity Desalination effluent discharge results in salinity levels at the LEPA boundary of 1 ppt above background more

than 5% of the time and/or salinity levels above 1.3 ppt above background on any occasion resulting in non-compliance with MS792 conditions. Note – a salinity level of 1 ppt above background at the LEPA boundary equates to a dilution factor of 24.6. The 2015 WET testing determined that the Target Dilution (the dilution required to meet 99% species protection at

the LEPA boundary) for Full Production operations is 9.6. Therefore a salinity level of 1 ppt above



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background is protective of more than 99% species. The salinity of the bottom saline layer would need to be above 2.68 ppt above background to not meet 99% species protection at the LEPA boundary.

Whole Effluent Toxicity (WET)

N/A no risk of adverse impacts from WET testing – WET Testing is required to establish the Target Dilution (the dilution required to protect 99% species at the LEPA boundary). The 2015 WET Testing results,

representative of Full Production operations, determined that a dilution of 9.6 is required to meet 99% species protection.

Dilution The Worst Case Dilution does not achieve the Target Dilution (dilution required to achieve 99% species protection at the LEPA boundary) resulting in a risk of adverse impact to marine species.

Benthic Health (construction and operation)

Construction of SSDP infrastructure has a long-term adverse impact on benthic seagrass health. Discharge of desalination effluent during SSDP operation has an adverse impact on benthic seagrass health.

Marine fauna & flora (construction phase)

Applicable for stage one construction only (i.e. dredging, blasting, construction) during the completion of all marine infrastructure works.

Terrestrial Fauna - impacts from clearing of habitat

Terrestrial fauna Applicable for construction only. The revegetation of areas not required for above-ground infrastructure according to MS792 and EPBC2008/4173 requirements

will minimise the impact from clearing on terrestrial fauna.

Terrestrial Vegetation and Wetlands- impacts from clearing

during infrastructure construction

Terrestrial flora & vegetation

Applicable mainly to construction phase, with the exception of ongoing revegetation as part of the Revegetation Management Plan. Risk of revegetation

not meeting regulatory requirements (MS792 and EBPC2008/4173 conditions) due to internal or external factors.

Greenhouse Gas Emissions – proposed no net greenhouse gas emissions

Greenhouse gas emissions

It is intended to purchase renewable energy or carbon offset credits to offset SSDP’s electricity usage. Therefore there is no risk from greenhouse gas emissions.



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3. Environmental Monitoring Framework

3.1 Environmental Quality Objectives

The following Environmental Quality Objectives were identified by the OEPA and specified in

MS792 Schedule 1 for the surrounding marine environment:

Maintenance of ecosystem integrity at a low level of ecological protection within the Low

Ecological Protection Area (LEPA) and at a high level of ecological protection at the

designated LEPA boundary;

Maintenance of aquatic life for human consumption assigned to all parts of the marine

environment surrounding the ocean outlet;

Maintenance of primary contact recreation values assigned to all parts of the marine


Maintenance of secondary contact recreation values assigned to all parts of the marine


Maintenance of aesthetic values assigned to all parts of the marine environment surrounding

the ocean outlet;

Maintenance of cultural and spiritual values assigned to all parts of the marine environment

surrounding the ocean outlet; and

Maintenance of Industrial Water Supply.

3.2 Marine Environment Monitoring Programs

The following programs were designed to meet the Environmental Quality Objectives for the

marine environment specified in MS792 Schedule 1:

Marine Environment Monitoring Program (MEMP), including discharge water quality

monitoring and benthic habitat monitoring;

Diffuser Performance Monitoring Program (DPMP);

Dissolved Oxygen Monitoring Program (DOMP); and

Whole Effluent Toxicity Monitoring Program (WETMP)

3.2.1 Marine Environment Monitoring Program

The MEMP was developed by Water Corporation and endorsed by the former Department of

Environment and Conservation (now Department of Environment Regulation (DER)). The MEMP

outlines the monitoring commitments for the discharge of desalination effluent to the Indian

Ocean via the marine outfall diffuser as per the requirements of MS792 condition 6-2.

Specifically the MEMP includes commitments for desalination effluent discharge quality

monitoring and benthic habitat health monitoring.

The Southern Seawater Alliance (SSWA) engaged an external contractor to undertake a review

of the Marine Monitoring Programs (MEMP, DPMP, DOMP and WETMP) to assess the current

requirements and determine which requirements have been met, which requirements are still to

be completed and the anticipated completion dates. Water Corporation submitted the findings,

including a new version of the MEMP to the OEPA on 7 October 2015. The MEMP is provided in

Appendix 3 – Marine Environment Monitoring Program.

3.2.2 Dissolved Oxygen Monitoring Program

The Dissolved Oxygen Monitoring Program (DOMP) was developed:



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To address MS792 condition 6-5 which requires Water corporation to monitor dissolved

oxygen levels at least weekly, either by deploying data loggers or by hand, at sites agreed by

the CEO of the Department of Environment and Conservation to determine whether the

“trigger” values are being achieved, for a period of 12 months immediately following:

o Completion of commissioning phase or six months from commencement of the

commissioning phase, whichever is sooner; and

o The initiation of full production (according to design specifications).

To address MS792 condition 6-7 which specifies a trigger of 60% DO saturation at the

boundary of the LEPA.

The DOMP is provided in Appendix 4 – Dissolved Oxygen Monitoring Program.

3.2.3 Diffuser Performance Monitoring Program

The Diffuser Performance Monitoring Program (DPMP) was developed:

To determine compliance against the salinity trigger levels defined in MS792 condition 6-2-4

of 1 parts per thousand (ppt) salinity increase above background 95% of the time and not

exceeding an increase of 1.3 ppt above background at the boundary of the Low Ecological

Protection Area; and

To assess the diffuser performance in terms of number of dilutions achieved at the LEPA

boundary required by MS792 condition 6-8.

The DPMP was revised in 2015 as recommended by a third party. The DPMP is provided in

Appendix 5 – Diffuser Performance Monitoring Program.

3.2.4 Whole Effluent Toxicity Monitoring Program

The Whole Effluent Toxicity Monitoring Program (WETMP) was developed to meet MS792

condition 6-9 which requires Water Corporation to conduct Whole Effluent Toxicity testing of

wastewater consistent with the toxicity and testing protocol at the following intervals:

One month following the initiation of the commissioning phase;

12 months following the completion of commissioning or 18 months following the initiation of

commissioning (whichever occurs first);

12 months following the commencement of full production.

The WETMP was revised in 2015 as recommended by a third party. The WETMP is provided in

Appendix 6 – Whole Effluent Toxicity Monitoring Program.

3.3 Revegetation Management Plan

The SSDP Revegetation Management Plan (RMP) (Appendix 7 – Revegetation Management

Plan) was developed to guide revegetation on the SSDP site to meet MS792 condition 9 and

EPBC2008/4173 condition 7 requirements. The plan was based on a flora and fauna survey

conducted in 2008 (360 Environmental), the Public Environmental Review (Water Corporation

2008) and the Construction Environmental Management Framework (Water Corporation 2009).

The RMP outlines the revegetation schedule and number of species that will be revegetated.

Revegetation of the SSDP commenced in July 2009 with stockpiling of topsoil, mulch and

branches and pre-planting weed spraying. Direct seeding and planting commenced in mid-2010



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and the second seeding/planting campaign commenced in mid- 2011. Planting of tubestocks

and seedlings for 1.3ha cleared at the northern area of the site was completed in 2014.

The DoE requested an amendment to the RMP to remove all references to the Harvey water

tank site based on an audit conducted in February 2015. Water Corporation provided a revised

plan to the DoE on 24 June 2015, which was subsequently approved on 4 January 2016.



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4. Environmental Performance

Table 2 provides the status of each of the monitoring programs designed to meet the Key

Environmental Factors and Environmental Quality Objectives during SSDP operations. In

general the monitoring results indicate that the SSDP is operating effectively and that the

Environmental Quality Objectives for the marine environment are being maintained.

Monitoring has demonstrated that MS792 conditions for salinity and dissolved oxygen in the

marine environment have been met. In addition the SSDP is meeting the required diffuser

performance to achieve 99% species protection at the LEPA boundary.

One of the two triggers for seagrass shoot density was not met in the 2015 benthic health

monitoring survey. Water Corporation is currently undertaking an investigation into the

reported seagrass shoot density decline. Further detail is provided in Section 4.1.



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Table 2: Status of SSDP Environmental Monitoring Programs

EPA Key Environmental

Factor

Project risk (MS792)

MS792 Criteria

Status Description

Water Quality and Marine Biota - impacts from construction and

operation of the

desalination plant

Discharge water quality

6-2-4 Compliant Discharge water quality monitoring conducted between 2014 and 2016 demonstrates that

the desalination effluent quality is within the anticipated range. There were four occasions

where the calculated contaminant concentrations at the LEPA boundary were above trigger

levels. However, the results were only very slightly above trigger levels and were not

considered to present a risk to the marine environment. In addition, the trigger levels are

the 80th percentile of the baseline measurements and as a result it is anticipated that

exceedances of the trigger levels will occur 20% of the time under normal ocean

conditions. There were no other occasions where the calculated contaminant concentration

at the LEPA boundary was above trigger levels, except on occasions where the background

seawater concentration was already above trigger levels. Details are provided in the 2015

and 2016 Marine Environment Monitoring Annual Reports (see Appendix 8 – 2015 Marine

Environment Monitoring Annual Report and Appendix 9 – 2016 Marine Environment

Monitoring Annual Report).

The final 6-monthly discharge quality monitoring event will be conducted in September

2016.

Water Corporation and the SSJV will continue to monitor in-pipe discharge effluent quality

including conductivity (and calculated salinity), dissolved oxygen, pH, turbidity and

Oxidation Reduction potential on a continuous basis for the duration of SSDP operations.

Dissolved Oxygen (DO)

6-5, 6-6, 6-7

Completed OEPA acknowledged that Water Corporation met the requirements of MS792 condition 6-5

and 6-6 in a letter dated 21 October 2015 (Appendix 10 – Letter from OEPA acknowledging

completion of dissolved oxygen monitorin). The OEPA also noted that oxygen saturation

never fell below 60% at the LEPA boundary and therefore condition 6-7 was never

triggered. Water Corporation ceased weekly DO monitoring on 21 October 2015 in

response to OEPA’s acknowledgement of the completion of MS792 conditions 6-5 and 6-6.

Salinity 6-2-4 Compliant The SSDP has implemented strategies to ensure that the salinity trigger levels specified in

MS792 condition 6-2-4 are met. This includes the optimisation of the seawater

recirculation system to turn the recirculation pumps on and off depending on the volume

of RO brine produced. This system has been shown to ensure that MS792 condition 6-2-4

salinity triggers are, and will continue to be met for future SSDP operations.



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The monthly salinity monitoring required for 12 months following the completion of Full

Production on 17 January 2014 has been completed. Condition 6-2-4 triggers for salinity

were met during the monitoring period.

Water Corporation provided the DPMP and WETMP Completion Report to the OEPA on 18

December 2015. The report advised that the salinity triggers specified in condition 6-2-4

have been met and that Water Corporation will be ceasing monthly salinity monitoring at

the SSDP LEPA boundary based on compliance with condition 6-2-4.

Water Corporation will commence annual salinity monitoring in 2016 as per DPMP

commitments. The five year monitoring period will run from 2016 until 2020.

Whole Effluent Toxicity

6-9, 6-11 Completed WET testing has been undertaken at the following intervals to meet the requirements of

MS792 condition 6-9:

One month following the initiation of the commissioning phase, on 14 December 2011;

12 months following the completion of commissioning, on 11 February 2013;

An additional sample representative of commissioning of Full Production (100GL per

year), on 14 January 2014; and

A sample on 19 March 2015, 12 months following the commencement of Full

Production.

The 2015 WET Testing results, representative of Full Production operations, determined

that a dilution of 9.6 is required to meet 99% species protection.


December 2015. The report advised that MS792 conditions 6-9 and 6-11 have been

adequately addressed and that no further WET testing will be undertaken unless there is a

change to operations which alters the components of the desalination effluent discharge.

Dilution 6-8 Compliant Monthly diffuser assessment required for 12 months following the completion of Full

Production on 17 January 2014 as per MS792 condition 6-8 has been completed.


December 2015. The report advised that MS792 condition 6-8 has been adequately

addressed and that Water Corporation will be ceasing monthly dilution assessment at the

SSDP LEPA boundary based on compliance with condition 6-8.

Water Corporation will commence annual diffuser assessment in 2016 as per DPMP

commitments. The five year monitoring period will run from 2016 until 2020.



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Benthic

Health

6-2-3 Investigation

underway

In 2015 the median shoot density measured at the impact sites was 168 shoots per m2.

This result is above the one year trigger of the 5th percentile of the reference sites of 96

shoots per m2. The median shoot density at the impact sites over two consecutive years

(2014 and 2015) was 232 shoots per m2. This result is less than the trigger value of the

20th percentile of 288 shoots per m2 measured at the reference sites over the same two

years.

There has been a year on year decrease in seagrass shoot density at both the southern

reference sites and the impact sites since 2012. The reason for the decline in seagrass

shoot density is unknown.

Water Corporation is currently undertaking an investigation into the cause of the reported

seagrass shoot density decline as advised in the letter to the OEPA dated 17 September

2015.

Marine fauna & flora (construction phase)

7-1, 7-2, 7-3, 7-4, 7-5, 7-6

Completed Applicable for stage one construction phase only (i.e. dredging, blasting, construction)

which saw completion of all marine infrastructure works.

Terrestrial Fauna - impacts from clearing of habitat

Terrestrial fauna

8-1, 8-2 Completed Applicable for construction only.

Terrestrial Vegetation and Wetlands- impacts from clearing during

infrastructure construction

Terrestrial flora & vegetation

9-7, 9-8, 9-9

Compliant The results of the 2015 Revegetation survey, the final survey required under the

Revegetation Management Plan, will be provided to the OEPA in 2016. Water Corporation

is currently finalising the results for the 2015 revegetation survey. The 2014 survey

results demonstrated that the revegetation is on track to meet MS792 and

EPBC2008/4173 requirements. The revegetation program will be considered complete

provided the criteria in MS792 condition 9-7 and EPBC 2008/4173 condition 7 are met in

the 2015 survey.

Greenhouse Gas Emissions – proposed no net greenhouse gas

emissions

Greenhouse gas emissions

11-1, 11-2

Non-compliant Water Corporation was non-compliant with Conditions 11-1 and 11-2 during the reporting

period. Water Corporation is in the process of developing a strategy for the purchase of

renewable energy and/or carbon offsets for the SSDP.



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4.1 Benthic Health Monitoring

The 2015 annual benthic health monitoring of seagrass Posidonia angustifolia was conducted by

Murdoch University Marine and Freshwater Research Laboratory between 12 and 13 May 2015.

In 2015 the median shoot density measured at the impact sites was 168 shoots per m2. This

result is above the one year trigger of the 5th percentile of the reference sites of 96 shoots per

m2. The median shoot density at the impact sites over two consecutive years (2014 and 2015)

was 232 shoots per m2. This result is less than the trigger value of the 20th percentile of 288

shoots per m2 measured at the reference sites over the same two years.

There has been a year on year decrease in seagrass shoot density at both the southern

reference sites and the impact sites since 2012. The northern reference site seagrass density

has also decreased since 2012, however not to the same extent as the impact sites and

southern reference sites. The two year trigger has been met in previous years due to the

decrease in seagrass density observed at both impact and reference sites. The reason for the

decline in seagrass shoot density is unknown.

Water Corporation is currently undertaking an investigation into the cause of the reported

seagrass shoot density decline as advised in the letter to the OEPA dated 17 September 2015.

Murdoch University Marine and Freshwater Research Laboratory and BMT Oceanica were

engaged in late 2015 to conduct the investigation into the seagrass shoot density decline. OEPA

was provided with details of the scope of the investigation in the letter dated 12 February 2016.

4.2 Greenhouse Gas Emissions

Water Corporation was non-compliant with MS792 conditions 11-1 and 11-2 during the

reporting period. Water Corporation is in the process of developing a strategy for the purchase

of renewable energy and/or carbon offsets for the SSDP.



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5. Benchmarking, Best Available Technology and Improvements in

Environmental Management

Water Corporation and the SSJV have implemented several initiatives at the SSDP based on

industry benchmarking, best available technology and improving environmental management.

These initiatives have improved the environmental performance of the SSDP. The initiatives

include:

Diffuser re-orientation;

Diffuser backfilling;

Optimisation of seawater recirculation; and

An investigation into diffuser capping.

5.1 Diffuser Re-orientation

The diffuser was re-orientated on 13 January 2014 as recommended by an independent study

on diffuser performance (Hatch 2013). Prior to the diffuser re-orientation all of the 80 diffuser

ports pointed north. This orientation exposed site 50S (50m south of the diffuser) to reduced

mixing and hence lower dilutions compared to 50N (50m north of the diffuser). Results show

that re-orientation did not have a dramatic immediately visible result on improving dilutions.

5.2 Backfilling

Backfilling of the diffuser pipeline was completed on 1 May 2015. This work has ensured that

the diffuser pipeline is covered with sand to prevent erosion of the partially exposed pipe and

hence prevent movement and potential for damage to the pipeline itself.

5.3 Seawater Recirculation

An investigation carried out with assistance from external parties in 2015 determined that

seawater recirculation is required to ensure the salinity at the LEPA boundary is less than 1 ppt

above background salinity for Reverse Osmosis (RO) brine flows of up to 300ML/day. For RO

brine flows above 300 ML/day no seawater recirculation is required to ensure the salinity at the

LEPA boundary is less than 1 ppt above background. An equation was implemented in the

continuous control system in October 2015 which turns the recirculation pumps on and off

depending on the volume of RO brine produced. This system has been shown to ensure that

MS792 condition 6-2-4 salinity triggers are, and will continue to be met for future SSDP

operations.

5.4 Diffuser Capping

An investigation conducted in July 2015 recommended capping ten of the 80 ocean outfall

diffuser ports. The analysis indicated that port capping would reduce the recirculation volume

required to meet MS792 salinity criteria through increasing discharge velocities and mixing.

OEPA were advised of the intention to cap diffuser ports in the DPMP and WETMP completion

report, submitted to the OEPA on 18 December 2015. The driver at the time was a forecast

annual drinking water production volume of approximately 63 GL. The drinking water production

profile for 2015-16 was revised in December 2016 to 92 GL, resulting in drinking water

production of approximately 285-295 ML per day for the remainder of 2016 (January to June

2016). Drinking water production of 295 ML per day results in RO brine flows of 392 ML per

day, which is above the volume at which seawater recirculation is required (300 ML per day). As



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a result diffuser capping is no longer required to reduce the recirculation volume. Diffuser

capping may be reinvestigated in the event that drinking water production volumes return to

below 226ML per day (or RO brine flows above 300ML per day).



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6. Conclusion

In general monitoring results indicate that the SSDP is operating effectively and that the

Environmental Quality Objectives for the marine environment are being maintained. Water

Corporation has demonstrated that the SSDP has met MS792 criteria for salinity and dissolved

oxygen and is achieving the required diffuser performance to meet 99% species protection at

the LEPA boundary.

One of the two triggers for seagrass shoot density was not met in the 2015 benthic health

monitoring survey. Water Corporation is currently undertaking an investigation into the

seagrass shoot density decline.

Water Corporation and the SSJV plan to undertake the following over the next two years (2016

to 2018):

Cease monthly salinity monitoring and diffuser assessment in the marine environment based

on the DPMP and WETMP Completion Report submitted to the OEPA on 18 December 2015;

Commence annual salinity monitoring and dilution assessment in the marine environment as

per DPMP commitments. Annual salinity monitoring and dilution assessment is required for a

period of five years (from 2016 to 2020);

Undertake an investigation into the benthic seagrass shoot density decline at both the

potential impact sites and the reference sites as per the letter to OEPA dated 17 September

2015;

Undertake a benthic health monitoring survey in autumn 2016 as per MEMP commitments;

Provide evidence to the OEPA to cease 6-monthly discharge water quality monitoring once

the final sampling event in September 2016 is completed provided triggers are met;

Provide evidence to the OEPA to close-out the revegetation requirements provided MS792

conditions are met.

Appendices


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Appendix 1 – Ministerial Statement 792

Appendix 2 – Report and recommendations of the EPA Report 1302

Appendix 3 – Marine Environment Monitoring Program

Appendix 4 – Dissolved Oxygen Monitoring Program

Appendix 5 – Diffuser Performance Monitoring Program

Appendix 6 – Whole Effluent Toxicity Monitoring Program

Appendix 7 – Revegetation Management Plan

Appendix 8 – 2015 Marine Environment Monitoring Annual Report

Appendix 9 – 2016 Marine Environment Monitoring Annual Report

Appendix 10 – Letter from OEPA acknowledging completion of

dissolved oxygen monitoring

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