Southern Seawater Desalination Plant. Marine Environmental Monitoring Interim Report 19 July October 2015

Transcription

1 Southern Seawater Desalination Plant Marine Environmental Monitoring Interim Report

2 Executive Summary The Southern Seawater Desalination Plant (SSDP) is located on Taranto Road, Binningup. Stage 1 of the SSDP, capable of supplying 50GL of drinking water per annum, was commissioned in March Stage 2 was commissioned on 17 January 2014 and increased the plant capacity to 100GL of drinking water per annum. Diffuser Performance Monitoring Program The Diffuser Performance Monitoring Program (DPMP) was developed: To determine compliance against the salinity trigger levels defined in Ministerial Statement 792 (MS792) Condition 6-2-4; and To assess the diffuser performance in terms of number of dilutions achieved at the Low Ecological Protection Area (LEPA) boundary required by MS792 Condition 6-8. The Southern Seawater Alliance 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 DPMP (Revision D) to the OEPA on 7 October Purpose This report provides the results of the DPMP from 19 July 2015 to 18 October This is the 12 th interim DPMP report for the SSDP. Salinity Assessment Results Ministerial Statement Condition specifies the salinity triggers for SSDP desalination effluent discharge are 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. The salinity in the bottom saline layer at the LEPA boundary has been below the in-situ triggers of +1 ppt and +1.3 ppt throughout the reporting period using the Revised Salinity Assessment Criteria (outlined in Section 3 and Appendix 1 - Salinity Assessment Criteria). As a result the SSDP has met Ministerial Statement 792 requirements to not exceed salinity levels of 1 ppt above background for more than 5% of the time and to not exceed an increase of 1.3 ppt above background at the LEPA boundary. Dilution Assessment Results The target dilution factor is the dilution required to protect 99% of species at the LEPA boundary. The target dilution factor is established through Whole of Effluent (WET) testing, which determines the toxicity of the desalination effluent i

3 on marine species, and converts the results into an equivalent dilution required to protect 99% of species. The dilution at the north LEPA boundary (50N) ranged between 26.5 and with recirculation factored in when operating. The dilution at the south LEPA boundary (50S) ranged between and with recirculation factored in when operating. The WET testing results for 2015 determined that a dilution factor of 9.6 is required to provide 99% species protection at the LEPA boundary. All dilution results at the LEPA boundary were above 9.6 and as a result 99% species protection has been met. Optimisation of Diffuser Performance An investigation carried out with assistance from external parties has determined seawater recirculation is required to ensure the salinity at the LEPA boundary is below +1ppt compared to reference salinity for Reverse Osmosis (RO) brine flows of up to 300 ML/day. For RO brine flows above 300 ML/day no seawater recirculation is required to ensure the salinity at the LEPA boundary is below + 1ppt compared to reference salinity. SSDP implemented an equation 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 salinity triggers are, and will continue to be met for future SSDP operations. Recommendations The salinity and dilution assessment results from July 2015 to October 2015, summarised in this interim report, have shown that the MS salinity triggers have been met and the dilution achieved at the LEPA boundary is above the target dilution factor of 9.6 required to protect 99% of species. Water Corporation provided the DPMP and WETMP Completion Report to the OEPA in correspondence dated 18 December This report contained the results of the 12 month monitoring period for full production (January 2014 January 2015) as well as results from additional monitoring undertaken from January This report advised that Ministerial Statement 792 Conditions 6-8, 6-9 and 6-11 have been adequately addressed and that the salinity triggers specified in condition have been met. The DPMP and WETMP Completion Report advised that Water Corporation will be ceasing monthly salinity monitoring and dilution assessment at the SSDP LEPA boundary based on compliance with conditions 6-8, 6-9, 6-11 and In addition the report advised that no further WET testing will be undertaken unless there is a change to operations which alters the components of the desalination effluent discharge. ii

4 The DPMP specifies that annual salinity monitoring will be undertaken for five years once the 12 month monitoring period is complete. Water Corporation will commence annual salinity monitoring in The five year monitoring period will run from 2016 until The results of each of the annual monitoring events will be provided to the OEPA in the Marine Environment Monitoring Program Annual Report, due to the OEPA on 17 April each year. Water Corporation will submit the results of the quarterly monitoring period between October 2015 and January 2016 as part of the MEMP Annual Report. Quarterly interim reports will no longer be required once monthly salinity monitoring is completed. iii

5 Table of Contents List of Abbreviations and Definition of Terms... vi 1 Introduction Environmental Approval Marine Monitoring Programs Diffuser Performance Monitoring Program Purpose Marine Monitoring Methodology Monitoring Frequency Monitoring Locations Field Observations and Water Quality Parameters Salinity Assessment Criteria Salinity Assessment Criteria to Determine Ministerial Statement Compliance Salinity Assessment Criteria to Trigger Reactive Monitoring Salinity Assessment Results Salinity Levels Reactive Monitoring Dilution Assessment Results Target Dilution Factor Dilution Results Optimisation of Diffuser Performance Diffuser Re-orientation Backfilling Diffuser Cleaning Diffuser Capping Optimisation of Seawater Recirculation Recommendations References Appendix 1 - Salinity Assessment Criteria Salinity Assessment Criteria to Determine Ministerial Statement Compliance Two-tiered Reference Trigger Criteria for Compliance Modified In-situ Reference Criteria for Compliance Revised Salinity Assessment Criteria for Compliance Salinity Assessment Criteria to Trigger Reactive Monitoring Two-tiered Reference Trigger Criteria to trigger reactive monitoring Modified In-situ Reference Criteria to trigger reactive monitoring Revised Salinity Assessment Criteria to trigger reactive monitoring Appendix 2 Ministerial Statement iv

6 Appendix 3 Marine Environmental Monitoring Program Annual Report Jan 2014 Jan Appendix 4 Diffuser Performance Monitoring Program Appendix 5- Independent Review of Diffuser Performance, Hatch Appendix 6 Minutes from Meeting with OEPA September Appendix WET Testing Report v

7 List of Abbreviations and Definition of Terms Bottom Layer Saline 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. cper Commonwealth Public Environmental Review CIP Clean-in-place 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 C, 2010) DoE DOMP EPBC Act IWSS LEPA Marine Monitoring Programs Australian Government Department of the Environment (previously Department of Environment, Water, Heritage and Arts and Department of Sustainability, Environment, Water, Population and Communities) Dissolved Oxygen Monitoring Program Environment Protection and Biodiversity Conservation Act 1999 Integrated Water Supply Scheme Low Ecological Protection Area Environmental monitoring undertaken in the marine environment including the MEMP, DOMP, WETMP and DPMP. MEMP Marine Environmental Monitoring Program, including Discharge Water Quality Monitoring and Benthic Health Monitoring. vi

8 MF Membrane Filtration MS792 Ministerial Statement 792 NES OEPA ppt PER Recirculation RO SSDP SSWA National Environmental Significance Office of the Environmental Protection Authority Parts per thousand Public Environmental Review 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. Reverse Osmosis Southern Seawater Desalination Plant Southern Seawater Alliance Target Factor WET WETMP Dilution The minimum number of dilutions required to meet the ANZECC/ARMCANZ 2000b guidelines 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. Whole Effluent Toxicity Whole Effluent Toxicity Monitoring Program vii

9 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. The SSDP was designed and constructed in two stages, each capable of producing 50 GL of water annually. Stage 1 plant began supplying drinking water into the Water Corporation s Integrated Water Supply System (IWSS) on the 18 November, 2011 during commissioning phase. Stage 1 of the plant officially began commercial operations on the 12 March Stage 2 was commissioned on 17 January 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 Environmental Protection Authority for assessment under Section 38 of the Environmental Protection Act It was formally assessed at the level of Public Environmental Review (PER) under the State process. The Proposal was approved by the Minister of Environment, with Ministerial Statement 792 (MS792) published on the 14th April 2009 (provided in Appendix 2 Ministerial Statement 792). The SSDP proposal was referred to the Australian Government s Department of the Environment (DoE) to determine whether the proposal constituted a Controlled Action and required assessment under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). DoE deemed that the SSDP has the potential to significantly impact on matters of National Environmental Significance (NES) protected under the EPBC Act; in particular, threatened species and listed migratory species. A Commonwealth Public Environmental Review was determined as the appropriate assessment approach by the DoE to enable a full assessment of the Proposal. DoE granted conditional environmental approval for the SSDP on 24 June 2009 (Approval EPBC 2008/4173). 1.2 Marine Monitoring Programs The Marine Environmental Monitoring Program (MEMP), Dissolved Oxygen Monitoring Program (DOMP), Whole Effluent Toxicity Monitoring Program (WETMP) and Diffuser Performance Monitoring Program (DPMP) were developed to address the requirements of MS792 Conditions (6-2, 6-5, 6-8, 6-9 and 6-12), and to minimise any potential impacts on the environment that may occur as a result of the SSDP operational activities. The results of these programs are summarised annually in the Marine Environmental Monitoring Program Annual Report, provided to the OEPA in April each year. The latest MEMP Annual Report, covering the period from 13 January 1

10 2014 until 18 January 2015 was submitted to the OEPA in April 2015 (Appendix 3 Marine Environmental Monitoring Program Annual Report Jan 2014 Jan 2015). The Southern Seawater Alliance engaged an external contractor to undertake a review of the Marine Monitoring programs (MEMP, DOMP, WETMP and DPMP). The third party review assessed the current monitoring requirements and determined which requirements have been met, which requirements are still to be completed and the anticipated completion dates. Water Corporation submitted the findings of the review, including new revisions for the MEMP, DPMP and WETMP, to the OEPA in October Diffuser Performance Monitoring Program Ministerial Statement 792 Condition 6-8 requires Water Corporation to verify diffuser performance in terms of achieving the required number of initial dilutions under a range of flow rates, low energy/calm metrological and seastate conditions to achieve a high level of ecosystem protection (99% species protection as defined by ANZECC/ARMCANZ 2000 for toxicants and 1 ppt 95% of the time for salinity) at the edge of the Low Ecological Protection Area (i.e. 50 metres either side of the diffuser array) for a period of 12 months immediately following; Completion of the commissioning phase or six months from commencement of the commissioning phase, whichever is sooner, and The initiation of full production (according to design specifications) Ministerial Statement Condition specifies the salinity triggers for SSDP desalination effluent discharge are 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. The DPMP (Revision D, 2015, provided in Appendix 4 Diffuser Performance Monitoring Program) was developed to assess the diffuser performance in terms of number of dilutions achieved at the LEPA boundary as per MS and determine compliance against the salinity trigger levels as per MS The DPMP commits to monthly monitoring of salinity at the LEPA boundary for a period of 12 months following: Completion of the commissioning phase or six months from commencement of the commissioning phase, whichever is sooner, and The initiation of full production (according to design specifications) The DPMP commits to annual salinity monitoring for a period of five years following the completion of the 12 month period. 2

11 Section 4.2 of the DPMP commits to providing the OEPA with an interim report every quarter on diffuser performance, and a final report on the completion of the monitoring program. 1.4 Purpose Water Corporation has committed to providing a report to the OEPA every quarter on diffuser performance as per Section 4.2 of the DPMP. The 12 th interim operational monitoring period for salinity commenced 19 July 2015 and concluded on 18 October This interim report includes: The salinity levels at the LEPA boundary and compliance against MS792 condition salinity triggers; and The level of dilution being achieved at the LEPA boundary compared against the target dilution factor required to protect 99% of species. 3

12 2 Marine Monitoring Methodology 2.1 Monitoring Frequency The DPMP commits to monthly salinity monitoring in the marine environment for 12 months following completion of SSDP Stage 1 commissioning and the initiation of full production (Stage 2). However, Water Corporation has monitored salinity on a weekly basis to coincide with weekly dissolved oxygen monitoring from late 2011 until the Dissolved Oxygen Monitoring Program was completed on 21 October For safety reasons, the monitoring day is determined by the monitoring subcontractor and boat skipper, and is dependent on when ocean conditions are deemed safest with regards to wind and swell. Consequently, the monitoring results are inclined towards low energy conditions and do not provide a representative view of overall diffuser performance in all weather conditions. However, it is anticipated that low energy conditions are likely to provide lower levels of dilution and represent the worst case dilution at the LEPA boundary. As a result if the MS792 salinity trigger levels and target dilution factor are achieved based on the monitoring results from low energy conditions, it is likely that in all weather conditions the diffuser is performing well above the minimum requirements. 2.2 Monitoring Locations There are six marine monitoring sites shown in Table 1 and Figure 1. Table 1: Location of Water Quality Monitoring Sites Relative to the Diffuser Site ID Easting (m) / Longitude (dd) Northing (m) / Latitude (dd) 1250m North of Diffuser (Reference) / / m North-West of Diffuser / / Diffuser 50m North (Impact) / / Diffuser 50m South (Impact) / / m South-West of Diffuser / / m South of Diffuser (Reference) / /

13 Figure 1: Location of Salinity Monitoring Sites Relative to the Diffuser 2.3 Field Observations and Water Quality Parameters Measurements are taken from a boat using a YSI 650 sonde logger probe. Measurements are taken from the bottom 5m of the seawater column to within 0.5m of the seabed. Five replicate readings at 0.5m intervals are taken, and then averaged to obtain representative figures. The following field observations are recorded by the monitoring subcontractor prior to undertaking water quality measurements at each site: Air temperature ( C) Estimated surface ocean current direction Wind speed (km/h) and direction Any other relevant general observations (i.e. recent rain/storm events, sea state) Photos at sites 500NW and 50S showing sea state/weather conditions (orientation and zoom). The water quality parameters measured (using the YSI 650 sonde logger) include: Depth (m) Water temperature ( C) ph Salinity (ppt). Salinity is used as a proxy to measure the dilution of all components of the desalination discharge at the LEPA boundary. Turbidity (NTU) Redox potential (mv) Dissolved oxygen (DO) (% saturation) Specific conductivity (ms/cm) Total dissolved solids (g/l) 5

14 3 Salinity Assessment Criteria Ministerial Statement Condition specifies the salinity triggers for SSDP desalination effluent discharge are 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. Salinity assessment criteria have been implemented for the SSDP to determine whether the MS salinity criteria have been met, and in instances where meeting the criteria is in doubt, reactive monitoring is carried out until the salinity levels return to less than 1 ppt above background. 3.1 Salinity Assessment Criteria to Determine Ministerial Statement Compliance There have been three salinity assessment criteria utilised to determine MS792 compliance since the SSDP Stage 1 was commissioned in These are: The two-tiered reference salinity trigger criteria; Modified In-situ Reference Criteria to determine the salinity level and comparison with in-situ salinity at the reference sites and seasonal salinity triggers to determine percentage of time exceedances occur; and Revised Salinity Assessment Criteria and comparison with in-situ salinity at the reference sites and seasonal salinity triggers to determine percentage of time exceedances occur. The Revised Salinity Assessment Criteria has been developed based on recommendations from an independent review on diffuser performance provided in Appendix 5- Independent Review of Diffuser Performance, Hatch The Revised Salinity Assessment Criteria method was implemented in 2014 to determine compliance against Ministerial Statement 792. The OEPA agreed to this method informally in 2014 (See Appendix 6 Minutes from Meeting with OEPA September 2014). Further detail on each of the Salinity Assessment Criteria used to determine Ministerial Statement compliance is provided in Appendix 1 - Salinity Assessment Criteria Salinity Assessment Criteria to Trigger Reactive Monitoring There have been three salinity assessment criteria utilised to trigger reactive monitoring since the SSDP Stage 1 was commissioned in These include: Two-tiered Reference Trigger Criteria; Modified In-situ Reference Criteria; and Revised Salinity Assessment Criteria (pending OEPA approval). The Revised Salinity Assessment Criteria is currently used to trigger reactive monitoring. 6

15 4 Salinity Assessment Results 4.1 Salinity Levels A total of 12 weekly routine monitoring events were undertaken for the monitoring period from 19 July 2015 until 18 October There was no monitoring undertaken during the week of August 2015 due to inclement weather. The results of the salinity monitoring are shown in Figure 2 and Figure 3. The salinity in the bottom saline layer has been below the in-situ triggers of +1 ppt and +1.3ppt throughout the reporting period. As a result the SSDP has met Ministerial Statement requirements to not exceed salinity levels of 1 ppt above background for more than 5% of the time and to not exceed an increase of 1.3 ppt above background at the LEPA boundary. There were no occasions where the salinity in the bottom saline layer at the LEPA boundary was above the seasonal +1 ppt trigger. 4.2 Reactive Monitoring Reactive monitoring is undertaken as a contingency measure when routine values are recorded in exceedance of the reference trigger value (+1.0 ppt and/or +1.3 ppt). During the reporting period there were no events where salinity levels at the LEPA boundary sites exceeded the reference trigger levels (+1.0 ppt and/or +1.3 ppt) and no reactive monitoring was instigated. 7

16 24-Jul Jul Jul Jul Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Sep Sep Sep Sep Sep Sep Sep Sep Sep Sep Sep Sep Sep Sep Sep Oct Oct Oct Oct Oct Oct Oct-15 SSDP Marine Monitoring Interim Report 1.40 Salinity in the bottom saline layer compared to in-situ triggers N 50S Ministerial Statement +1 ppt trigger Ministerial Statement +1.3ppt Trigger Figure 2: Salinity in the bottom saline layer compared to in-situ triggers for the LEPA boundary during the reporting period 8

17 Salinity (ppt) SSDP Marine Monitoring Interim Report Salinity in the bottom saline layer (50N, 50S, 500NW and 500SW) and above the bottom saline layer (1250N and 1250S) compared to in-situ and seasonal triggers In Situ Salinity Trigger Level +1.3 ppt 500NW 50S 1250S Seasonal Salinity Trigger Level +1ppt 1250N 50N 500SW In Situ Salinity Trigger Level +1ppt 95% of time Seasonal Salinity Trigger Level +1.3 ppt Figure 3: Salinity compared to in-situ and seasonal triggers for all sites during the reporting period 9

18 5 Dilution Assessment Results 5.1 Target Dilution Factor Dilution assessment is undertaken in accordance with the DPMP to determine whether the SSDP is meeting the target dilution factor at the LEPA boundary. The target dilution factor is the dilution required to protect 99% of species at the LEPA boundary. The target dilution factor is established through Whole of Effluent (WET) testing, which determines the toxicity of the desalination effluent on marine species, and then coverts the results into an equivalent dilution required to protect 99% of species. The WET testing results for 2015 determined that a dilution factor of 9.6 for the desalination effluent provides protection of 99% of species at the LEPA boundary (See Appendix WET Testing Report) It is important to note that the 2015 WET testing was conducted on a worst case sample that did not include recirculation of seawater to pre-dilute the desalination effluent stream. 5.2 Dilution Results Dilution at the LEPA boundary is calculated using the difference in salinity between the in-pipe measurements, and the salinity at the LEPA boundary. Assessment of dilution has been undertaken on a weekly basis during the reporting period to coincide with salinity readings at the LEPA boundary. The dilutions have been calculated for the boundary of the LEPA (50m north and 50m south of the diffuser) and for locations 500m north west and 500m south west of the diffuser. Dilutions have been calculated factoring in pre-dilution with recirculation of seawater when operational. All dilutions during the reporting period at the LEPA boundary (50N and 50S) were above the target dilution factor required to protect 99% of species at the LEPA boundary of 9.6, as shown in Table 2. The dilution at the north LEPA boundary (50N) ranged between 26.5 and with recirculation factored in when operating. The dilution at the south LEPA boundary (50S) ranged between and with recirculation factored in when operating. The dilution 500m North West of the diffuser (500NW) ranged between and with recirculation factored in when operating. The dilution 500m south west of the diffuser (500SW) ranged between 26.5 and with recirculation factored in when operating. 10

19 Table 2: Dilutions at the LEPA boundary (50N & 50S) Date Averaged salinity in the bottom saline layer (ppt) (or 2m from seabed if there is no bottom saline layer) Salinity Average for 1250N & 1250S (SS) Desalination Effluent Volume for the day Desalination Effluent and Recirculation Volume and Salinity Recirculation Volume for the day Desalination Effluent and Recirc Conductivity (lab) (ms/cm) Salinity of Desalination Effluent and Recirc (ppt) at 25 C Salinity of Desalination Effluent (ppt) if removing recirc at 25 C Dilution Factors - LEPA Boundary Dilution Factoring in recirculation 50N 50S 50N 50S m3 m3 24-Jul ,268 94, Jul ,274 73, Aug ,533 88, Aug ,932 87, Aug ,454 87, Sep , Sep , Sep , Sep , Sep , Oct , Oct , Note: Conductivity is converted using the Conductivity Salinity Conversion based on 1983 Technical Paper from UNESCO, "Algorithms for computation of fundamental properties of seawater". Desalination Effluent = RO Brine + MF backwash Recirculation = Recirculated seawater that does not enter the desalination process 11

20 Table 3: Dilutions 500m North and South of the Diffuser (500NW and 500SW) Date Averaged salinity in the bottom saline layer (ppt) (or 2 from seabed if there is no bottom saline layer) Salinity Average for 1250N & 1250S (SS) Desalination Effluent Volume for the day Desalination Effluent and Recirculation Volume and Salinity Recirculation Volume for the day Desalination Effluent and Recirc Conductivity (lab) (ms/cm) Salinity of Desalination Effluent and Recirc (ppt) (SB) at 25 C Salinity of Desalination Effluent (ppt) if removing recirc at 25 C Dilution Factors - Near Reference Sites Dilution Factoring in recirculation 500NW 500SW 500NW 500SW m3 m3 24-Jul ,268 94, Jul ,274 73, Aug ,533 88, Aug ,932 87, Aug ,454 87, Sep , Sep , Sep , Sep , Sep , Oct , Oct , Jul ,268 94, Note: Conductivity is converted using the Conductivity Salinity Conversion based on 1983 Technical Paper from UNESCO, "Algorithms for computation of fundamental properties of seawater". Desalination Effluent = RO Brine + MF backwash Recirculation = Recirculated seawater that does not enter the desalination process 12

21 6 Optimisation of Diffuser Performance 6.1 Diffuser Re-orientation The diffuser was re-orientated on 13 January 2014 as recommended by the 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 to reduced mixing and hence lower dilutions compared to 50N. Results show that re-orientation did not have a dramatic immediately visible result on improving dilutions. By the same token, the dilutions were slightly improved (pers. comms Jason Antenucci). 6.2 Backfilling Backfilling of the diffuser pipeline was completed on 1 May 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. 6.3 Diffuser Cleaning The SSDP undertook cleaning of the diffuser in May This work removed any of the marine growth (barnacles etc) on the diffuser ports to increase flow through the ports. The maintenance crew reported that the ports were generally free from internal growth when the work was done. The impact of the cleaning on diffuser performance was difficult to discern from already existing variability. This may be explained by the fact the diffusers were not significantly internally affected by growth. 6.4 Diffuser Capping Now that typical annual plant flows have been established, Water Corporation will at the next opportunity during routine maintenance cap several of the diffuser ports to increase dilution for the plant flow rates now thought to reflect typical operation. The capping will also be valid for full range of production profiles if required. Capping of ports will be as recommended by third party consultant and diffuser expert Jason Antenucci (formerly Hatch). Capping is purely an optimisation exercise given the compliant performance of the diffuser prior to capping. 6.5 Optimisation of Seawater Recirculation An investigation carried out with assistance from external parties has been undertaken at the SSDP to optimise the seawater recirculation system. The investigation developed a system to calculate the salinity increase at the LEPA boundary compared to the reference site salinity based on the volume of Reverse Osmosis (RO) brine produced from the plant. The calculation then 13

22 determines the volume of seawater recirculation required to meet less than +1 ppt at the LEPA boundary compared to the reference site salinity. The results of the investigation for 80 diffuser ports are shown in Figure 4. Seawater recirculation is required to ensure the salinity at the LEPA boundary is below +1 ppt compared to reference salinity for RO brine flows of up to 300ML/day with 80 ports. For RO brine flows above 300 ML/day no seawater recirculation is required to ensure the salinity at the LEPA boundary is below + 1ppt compared to reference salinity. Interaction of diffuser ports results in very little additional dilution for brine flows above 300ML/day. SSDP implemented an equation in the continuous control system in October 2015 which utilises this calculation to turn the recirculation pumps on and off depending on the volume of RO brine produced. This system will ensure that Ministerial Statement Condition salinity triggers 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 will be met for all future SSDP operations. Any change to the current configuration will only improve the situation. 14

23 Seawater Recirculation Flow (MLD) SSDP Marine Monitoring Interim Report Salinity at LEPA Boundary Brine Flow (MLD) Figure 4: Salinity Increase at the LEPA boundary compared to reference sites based on Reverse Osmosis Brine Flow Rate and Recirculation Flow Rate 15

24 7 Recommendations The 12 month monitoring period for SSDP full production was undertaken between January 2014 and January 2015 and has now been completed. The results were provided to the OEPA in the MEMP Annual Report in April The results showed that the SSDP was compliant with both the salinity triggers at the LEPA boundary and the dilution factor necessary to provide 99% species protection at the LEPA boundary. In addition the results from July 2015 to October 2015, summarised in this interim report, have shown that the MS792 salinity triggers have been met and the dilution achieved at the LEPA boundary is above the target dilution factor of 9.6 required to protect 99% of species. Water Corporation provided the DPMP and WETMP Completion Report to the OEPA in correspondence dated 18 December This report contained the results of the 12 month monitoring period for full production (January 2014 January 2015) as well as results from additional monitoring undertaken from January This report advised that Ministerial Statement 792 Conditions 6-8, 6-9 and 6-11 have been adequately addressed and that the salinity triggers specified in condition have been met. Water Corporation requested acknowledgement from OEPA of the completion of conditions 6-8, 6-9, and The DPMP and WETMP Completion Report advised that Water Corporation will be ceasing monthly salinity monitoring and dilution assessment at the SSDP Low Ecological Protection Area boundary based on compliance with conditions 6-8, 6-9, 6-11 and In addition the report advised that no further WET testing will be undertaken unless there is a change to operations which alters the components of the desalination effluent discharge. The DPMP specifies that annual salinity monitoring will be undertaken for five years once the 12 month monitoring period is complete. Water Corporation will commence annual salinity monitoring in The five year monitoring period will run from 2016 until The results of each of the annual monitoring events will be provided to the OEPA in the Marine Environment Monitoring Program Annual Report, due to the OEPA on 17 April each year. Quarterly interim reports will no longer be required once monthly salinity monitoring is completed. 16

25 8 References Hatch 2013, Operational Marine Monitoring Desktop Review. Prepared for Water Corporation of Western Australia. Minister for Environment Statement that a Proposal may be Implemented - Southern Seawater Desalination Plant (Ministerial Statement No. 792). Perth, Western Australia. Southern Seawater Alliance 2008, Engineering Design Report. SSWA, August. Southern Seawater Alliance (SSWA) 2010, Diffuser Performance Monitoring Program, document number 00-EN-PRO-0003, 15 December. Southern Seawater Alliance (SSWA) 2010b, Dissolved Oxygen Monitoring Program, SSWA document number 00-EN-PRO-0002, 15 December Southern Seawater Alliance (SSWA) 2010c, Marine Environmental Monitoring Program, SSWA document number 00-EN-PRO-0001, 15 December

26 Appendix 1 - Salinity Assessment Criteria Ministerial Statement Condition specifies the SSDP must not exceed salinity levels of 1 part per thousand (ppt) above background 95% of the time and not exceed an increase of 1.3 ppt above background at the boundary of the LEPA. Salinity assessment criteria have been implemented for the SSDP to determine whether the Ministerial Statement salinity criteria have been met, and in instances where meeting the criteria is in doubt, reactive monitoring is carried out until the salinity levels return to less than 1ppt above background. Salinity Assessment Criteria to Determine Ministerial Statement Compliance There have been three salinity assessment criteria utilised to determine Ministerial Statement compliance since the SSDP Stage 1 was commissioned in These are: The two-tiered reference salinity trigger criteria; Modified In-situ Reference Criteria to determine the salinity level and comparison with in-situ salinity at the reference sites and seasonal salinity triggers to determine percentage of time exceedances occur; and Revised Salinity Assessment Criteria (pending OEPA approval) and comparison with in-situ salinity at the reference sites and seasonal salinity triggers to determine percentage of time exceedances occur. The use of different salinity assessment criteria is primarily the result of misinterpretation of relevant documentation involving Ministerial Statement requirements and SSWA monitoring procedures, the primacy of endorsed versus non-endorsed procedures and technically incorrect procedures employed in the original assessment criteria. The first and second salinity assessment criteria listed above has been employed in the field since the commencement of commercial operations in March 2012 for the Stage 1 Plant. The third criterion has been developed based on recommendations from an independent review on diffuser performance provided in Appendix 5- Independent Review of Diffuser Performance, Hatch The Revised Salinity Assessment Criteria method has been implemented since 2014 to determine compliance against Ministerial Statement 792. Two-tiered Reference Trigger Criteria for Compliance The Two-tiered Reference Trigger Criteria was previously utilised to determine Ministerial Statement compliance until 25 th July The Two-Tiered approach is no longer utilised to determine Ministerial Statement compliance. 18

27 The two-tiered reference trigger criteria assesses whether there has been a salinity exceedance at the LEPA boundary based on the exceedance of both the baseline seasonal trigger values as the first tier, and the exceedance of in-situ values as the second tier for each monitoring event. Salinity readings are taken at 0.5m from the seabed for this approach. The average of the salinity values at the two reference sampling sites (1250N and 1250S) are used for the reference salinity, as the reference sites rarely have the same salinity level. The two-tiered reference trigger was further clarified in the Salinity Monitoring and Dilution Factor Calculation Standard Operational Procedure (SSWA 2012). This document defines the protocol used for assessing the impact of the plants desalination effluent discharge on the marine environment. A process decision flow diagram for the Two-tiered Reference Trigger Criteria approach is presented below. 19

28 Diagram for Assessment of Salinity Trigger Concentrations Extracted from the Diffuser Performance Monitoring Program review (Worley Parsons, 2012) 20

29 Modified In-situ Reference Criteria for Compliance The modified criteria represent actual in-situ concentrations for salinity. Salinity readings at sites 50N, 50S, 500NW and 500SW are taken at 0.5m from the seabed. The modified method calculates the reference mean and in turn, the reference salinity trigger using the values taken 0.5 m above the seabed at 1250N and 1250S, unless the site is affected by the desalination effluent discharge. Evidence of effect of the desalination effluent discharge is observed by a distinct bottom saline layer near the seabed. If this is the case, then the median of the unaffected water column for that site would be utilised instead and then averaged to represent background conditions as per independent recommendations. In order to determine whether a 1 ppt or 1.3 ppt exceedance has occurred, the Modified In-Situ Reference Criteria compares the salinity results at 0.5m above the seabed with both the seasonal reference triggers and the results of the salinity at the reference sites on the sampling day (1250S and 1250N). If the salinity level at the LEPA boundary 0.5m from the seabed exceeds both the seasonal reference trigger and the salinity at the reference sites on that day by +1 ppt, then an exceedance has occurred. In order to determine the percentage of time in a year that the salinity at the LEPA boundary was +1 ppt above reference sites and seasonal triggers, the number of days between sampling events is halved. For example: if sampling on the 1 May did not exceed the +1 ppt trigger sampling on 8 May did exceed the trigger the reactive monitoring event on the 9 May exceeded the +1 ppt trigger the reactive monitoring event on the 10 May did not exceed the +1 ppt Then the time of exceedance is equal to ½ time between 1 May and 8 May plus time between 8 May and 9 May, plus ½ time between 9 May and 10 May (i.e = 5 days). The Modified Method was adopted by SSWA on 25 th July Revised Salinity Assessment Criteria for Compliance An independent review on the SSDP operational marine monitoring plan was undertaken by a specialist consultant (Hatch 2013) as a result of several salinity trigger events at the LEPA boundary since the commencement of commercial operations for the Stage 1 plant in March These salinity trigger events were based on the original salinity assessment criteria for Ministerial Statement compliance (Two-Tiered Reference Trigger Criteria method). Phase 1 of the independent review ascertained the correct salinity assessment criteria (the Revised Salinity Assessment Criteria) based on a review of 21

30 monitoring data and compliance to Ministerial Statement 792 Condition 6 and OEPA endorsed SSWA monitoring procedures (such as the MEMP). Some of the recommendations from the independent review by Hatch include the following: Readings used for salinity assessment at 50N and 50S will be taken as the average reading in the bottom saline layer. Sites 1250N and 1250S do not represent the unimpacted or background state due to spatial extent of SSDP desalination effluent plume. The natural variability in salinity at the location of the outfall renders the use of seasonal triggers problematic. Both background and ambient salinity be determined based on the upper layer salinity at 50S and 50N instead of using 1250N and 1250S reference sites. Reactive monitoring is instigated for a minimum 48 hours when a minimum 1 ppt trigger occurs at either 50S or 50N based on the revised salinity assessment criteria described. In order to determine whether a 1 ppt or 1.3 ppt exceedance has occurred, the Revised Salinity Assessment Criteria compares the average salinity results in the bottom saline layer at the LEPA boundary to the seasonal reference triggers and the salinity at the reference sites 1250N and 1250S above the saline layer (if there is a bottom saline layer at the reference sites or 0.5m from the seabed if there is no bottom saline layer). If the average salinity level at the LEPA boundary in the bottom saline layer exceeds both the seasonal reference trigger and the salinity at the reference sites above the bottom saline layer on that day by +1 ppt, then an exceedance has occurred. In order to determine the percentage of time in a year that the salinity at the LEPA boundary was +1 ppt above reference sites and seasonal triggers, the number of days between sampling events is halved. For example: if sampling on the 1 May did not exceed the +1 ppt trigger sampling on 8 May did exceed the trigger the reactive monitoring event on the 9 May exceeded the +1 ppt trigger the reactive monitoring event on the 10 May did not exceed the +1 ppt Then the time of exceedance is equal to ½ time between 1 May and 8 May plus time between 8 May and 9 May, plus ½ time between 9 May and 10 May (i.e = 5 days). The recommendations of the Hatch 2013 review; including the use of the Revised Salinity Assessment Criteria was submitted to the OEPA in September 2013 for consideration and approval. Salinity Assessment Criteria to Trigger Reactive Monitoring 22

31 There have been three salinity assessment criteria utilised to trigger reactive monitoring since the SSDP Stage 1 was commissioned in These include: Two-tiered Reference Trigger Criteria; Modified In-situ Reference Criteria; and Revised Salinity Assessment Criteria (pending OEPA approval). Water Corporation currently uses the Revised Salinity Assessment Criteria to trigger reactive monitoring. Two-tiered Reference Trigger Criteria to trigger reactive monitoring The Two-tiered Reference Trigger Criteria was previously utilised to trigger reactive monitoring until 25 th July The Two-Tiered approach is no longer utilised to instigate reactive monitoring. The two-tiered reference trigger criteria assesses whether there has been a salinity trigger exceedance at the LEPA boundary based on the trigger of both the baseline seasonal trigger values as the first tier, and the trigger of in-situ values as the second tier for each monitoring event. Reactive monitoring for a minimum 48 hour period is undertaken in the event of a trigger exceedance. Salinity readings are taken at 0.5m from the seabed as per the Diffuser Performance Monitoring Program (DPMP) for this approach. The average of the salinity values at the two reference sampling sites (1250N and 1250S) are used for the reference salinity, as the reference sites rarely have the same salinity level. Modified In-situ Reference Criteria to trigger reactive monitoring Salinity readings at sites 50N, 50S, 500NW and 500SW are taken at 0.5m from the seabed. Salinity readings are taken 0.5 m above the seabed at 1250N and 1250S, unless the site is affected by the desalination effluent discharge. Evidence of effect of the desalination effluent discharge is observed by a bottom saline layer near the seabed. If this is the case, then the median of the unaffected water column for that site would be utilised instead and then averaged to represent background conditions as per independent recommendations (Hatch 2013). Reactive monitoring is triggered for instances where the average salinity 0.5m above the seabed at the LEPA boundary (50N and 50S) is +1 ppt above the average salinity 0.5m above the seabed at the reference sites (1250N and 1250S). The modified criteria has been adopted by SSWA since the 25 th July Revised Salinity Assessment Criteria to trigger reactive monitoring 23

32 Reactive Monitoring is triggered using the Revised Salinity Assessment Criteria in instances where the average salinity at the LEPA boundary in the bottom saline layer (or the average of the 2m from the seabed if there is no bottom saline layer) is +1 ppt above the average salinity at the reference sites above the bottom saline layer. Reactive monitoring is undertaken for a minimum 48 hour period. Water Corporation requested the OEPA approve the use of the Revised Salinity Assessment Criteria in September

33 Appendix 2 Ministerial Statement

34 Appendix 3 Marine Environmental Monitoring Program Annual Report Jan 2014 Jan

35 Appendix 4 Diffuser Performance Monitoring Program 27

36 Appendix 5- Independent Review of Diffuser Performance, Hatch

37 Appendix 6 Minutes from Meeting with OEPA September

38 Appendix WET Testing Report 30