Groundwater Treatment Plant - September 2020 Annual Groundwater and Surface Water Monitoring Report

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REPORT

Groundwater Treatment Plant - September 2020

Annual Groundwater and Surface Water Monitoring

Report

Orica Botany Environmental Survey Stage 4 - Remediation

Submitted to:

Orica Australia Pty Ltd

1 Nicholson Street Melbourne VIC 3000 Submitted by:

Golder Associates Pty Ltd

Level 8, 40 Mount Street, North Sydney, New South Wales 2060, Australia

+61 2 9478 3900 20359032-001-R-Rev0 30 November 2020

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EXECUTIVE SUMMARY

This report presents the results of groundwater and surface water data collected in September 2020 as part of the Groundwater Treatment Plant (GTP) – Groundwater and Surface Water Monitoring Program. The scope of services of the September 2020 monitoring program is intended to fulfil the requirements of an annual

sampling event as specified in the 2017-2020 GTP Groundwater and Surface Water Monitoring Program (Golder 2017b).

Hydraulic Monitoring

Assessment of hydraulic data, with consideration of the six-step evaluation approach adopted by JBS&G (2019), indicates that effective hydraulic containment of the target capture zones was achieved at Botany Industrial Park (BIP), Primary Containment Area (PCA) and at the Secondary Containment Area (SCA) during the monitoring period and overall the Botany Groundwater Cleanup (BGC) Project remedy objectives were met.

The effects of reduced groundwater extraction due to the GTP maintenance shutdowns in March 2020 were compounded by high rainfall during the monitoring period. Reduced groundwater extraction rates were associated with reduced performance and efficiency caused by pump and well biofouling, particularly within the deep aquifer in the eastern portion of SCA following the failure of extraction well EWF28D in April 2019. Effective hydraulic containment at BIP and within the target capture zones of the intermediate and deep aquifers at PCA was evidenced by the achievement of target water levels and/or the assessment of reverse hydraulic gradients immediately downgradient of the containment lines for the monitoring period. Hydraulic containment in the shallow aquifer at SCA, the eastern and western portions of the intermediate aquifer and the eastern and central-eastern portion in deep aquifer was also evident on this basis. Evidence of effective hydraulic containment in the central portion of the intermediate aquifer and in the western end of the SCA in the deep aquifer was less clear.

An assessment of long-term water levels for monitoring wells located adjacent to, and at significant distances from, the containment lines indicates that observed drawdowns are similar to those predicted by groundwater modelling (Laase, 2005 and Laase, 2017) and that no long-term downward trends, that may be attributable to GTP operation, are evident. The data highlight the relatively localised effects of the hydraulic containment system and its low potential to adversely affect nearby infrastructure and licensed groundwater users.

Chemical Monitoring

The September 2020 annual chemical monitoring program is focused on collecting data critical to the assessment of groundwater and surface water quality with respect to environmental and human health receptors. The assessment includes considerations of:



Concentrations of shallow groundwater chlorinated hydrocarbons (CHCs) against long-term trends and changes in contaminant distribution (including parametric tests).



Concentrations of CHCs against assumptions and results considered in the Consolidated Human Health Risk Assessment (CHHRA) (EnRiskS, 2018).

A parametric test has been used to identify increasing/decreasing trends in contaminant concentrations at sampling locations. The assessment of data trends for monitoring locations indicates that whilst there have been a number of increases (including historical maxima) and decreases in contaminant concentrations, the changes were either relatively small or are consistent with expected plume behaviour as a result of

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iii Additional chemical monitoring was conducted during this monitoring round. These additional results will be reported separately but will be included for the future interpretation of plume dynamics and contaminant distribution in the August 2021 biennial monitoring event.

Groundwater Monitoring Wells

The September 2020 groundwater data are generally consistent with data from previous monitoring rounds. No samples were collected from Botany Industrial Park (BIP) during this monitoring period. On-site samples were only collected from Southlands.

Historical maximums were reported at:



1,2-dichloroethane (EDC) (50.7 mg/L) at MWF15 in the intermediate well. This is greater than the previous historical maximum reported in December 2007 (24 mg/L). The high concentration is likely due to two non-operational extraction wells along SCA (EWF25 and EWF28) which were recently replaced. This is not considered to represent a significant change in contamination distribution, and further

monitoring and future rounds will determine if the concentrations at this location decrease due to the new extraction wells at SCA.



EDC (0.208 mg/L), chloroform (CFM) (0.006 mg/L) and tetrachloroethene (PCE) (0.001 mg/L) at MWF19 in the intermediate well. The concentration for EDC is greater than the previous historical maximum reported in September 2010 (0.063 mg/L). There has been no detected concentration of CFM and PCE historically for this well. These concentrations are similar to those found in nearby extraction well EWF14 in the deep well and are not expected to represent a significant change in the contamination distribution.



EDC (0.002 mg/L) at WG262 in the shallow well. Historically, there has been no detected concentration

of EDC at this well. This is marginally above the limit of detection and is not considered to represent a significant change in contamination distribution.



PCE (0.161 mg/L) and trichloroethene (TCE) (3.34 mg/L) at BP117 from the 1.5 m port. These concentrations are greater than the previous historical maxima reported in March 2020 for PCE (0.03 mg/L) and in March 2012 for TCE (3.31 mg/L).



PCE (0.189 mg/L) and TCE (6.82 mg/L) at MWF18 in the deep well. These concentrations are greater than but also similar to the previous historical maxima reported in September 2010 for PCE (0.187 mg/L) and in March 2020 for TCE (3.97 mg/L).



CFM (0.001 mg/L) at WG255 in the shallow well. Historically there has been no detected concentration of CFM in this well. This is not expected to represent a significant change in contamination distribution as this concentration is marginally above the limit of detection.

No other historical maximum concentrations for the groundwater wells were reported during the September 2020 monitoring round.

Penrhyn Estuary Pore Water

In general, the September 2020 data are consistent with previous monitoring rounds with the concentrations of the chemicals of concern generally decreasing with decreasing depth towards the discharge interface. The concentrations of the key contaminants reported in the September 2020 monitoring round were less than the ANZG (2018) Trigger Values for all the samples collected at the discharge interface (0.1 m port). The samples collected from BP42 at the 0.5 m and 2.0m ports (0.428 mg/L and 1.37 mg/L respectively) were above the ANZG (2018) Trigger Value for vinyl chloride (VC) (0.1mg/L), as well as the Trigger Value for TCE (0.33 mg/L) at the 2.0 m port of BP42 (0.434 mg/L).

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iv It should be noted that the VC and TCE concentrations in surface water samples within the estuary in

proximity to BP42 were less than the ANZG (2018) Trigger Value.

No historical maximum concentrations for the Penrhyn Estuary pore water samples were reported during the September 2020 monitoring round.

Surface Water

The review of historical surface water monitoring data shows CHC concentrations have been highly variable between monitoring events. Comparison of the September 2020 surface water data with historical data shows CHC concentrations in Springvale Drain (in particular 1,2-dichloroethane (EDC)) have generally decreased several orders of magnitude compared to historical maximum concentrations. The decrease in EDC concentrations within surface water is attributable to the operation of the hydraulic containment system reducing groundwater levels and subsequently reducing groundwater seepage to Springvale Drain. Similarly, concentrations of all CHCs in Floodvale Drain and Springvale Drain significantly decreased following the commencement of groundwater extraction and remain low.

Key contaminant concentrations reported in the September 2020 monitoring round were less than the relevant ANZG (2018) Trigger Values at all locations. No historical maximum concentrations for key contaminants were reported in surface water samples collected during the September 2020 monitoring round.

Implications for Human Health Risk Assessment

A review of Springvale Drain surface water data collected in accordance with the CHHRA (EnRiskS, 2018) did not indicate potential issues during the monitoring period with respect to workplace inhalation exposures adjacent to Springvale Drain. Water levels at MWB03S, which is located close to Springvale Drain where it flows under McPherson Street, exceeded the risk review trigger level for a cumulative period of 100 days during the monitoring period. However, key contaminant concentrations were less than the relevant ANZG (2018) Trigger Values and less than considered in the CHHRA (EnRiskS, 2018) at all surface water sampling locations.

Conclusions

Assessment of hydraulic and chemical data for the September 2020 monitoring event, with consideration of the revised six-step evaluation approach adopted by JBS&G (2019), indicates that, although effective

hydraulic containment of the target capture zones was inconsistent during the period, overall the BGC Project remedy objectives were met.

There are no data presented in the September 2020 monitoring round that affect the conclusions of the CHHRA (EnRiskS, 2018) in relation to the western margin of the Northern Plumes or the Main Plumes, Penrhyn Estuary and Floodvale and Springvale Drains (i.e., provided groundwater is not extracted and used for any purpose, health risks associated with exposure to chemicals of potential concern (CoPC) are low and acceptable).

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Table 4.5 Historical Groundwater Data Trends – 1,2-Dichloroethane (EDC) - September 2020 Table 4.6 Historical Groundwater Data Trends – Tetrachloroethene (PCE) - September 2020 Table 4.7 Historical Groundwater Data Trends – Trichloroethene (TCE) - September 2020 Table 4.8 Historical Groundwater Data Trends – Vinyl Chloride (VC) - September 2020

Table 4.9 Historical Groundwater Data Trends – Carbon Tetrachloride (CTC) - September 2020 Table 4.10 Historical Groundwater Data Trends – Chloroform (CFM) - September 2020

Table 5.1 Historical Pore Water Data Trends – Tetrachloroethene (PCE) mg/L, Penrhyn Estuary – September 2020

Table 5.2 Historical Pore Water Data Trends – Trichloroethene (TCE) mg/L, Penrhyn Estuary – September 2020

Table 5.3 Historical Pore Water Data Trends – Vinyl Chloride (VC) mg/L, Penrhyn Estuary – September 2020

Table 5.4 Historical Pore Water Data Trends – 1,2-Dichloroethane (EDC) mg/L, Penrhyn Estuary – September 2020

Table 5.5 Historical Pore Water Data Trends – Chloroform (CFM) mg/L, Penrhyn Estuary – September 2020

Table 5.6 Historical Surface Water Data Trends (mg/L) – September 2020

PLATES (in the text)

Plate A: Target Capture Zones for SCA ... 8 Plate B: Target Capture Zone for PCA ... 9 Plate C: Target Capture Zones for BIP ... 9

FIGURES

Figure 2.1 Hydraulic Containment System and Monitoring Locations - September 2020 Figure 2.2 Chemical Monitoring Locations – September 2020

Figure 2.3 Surface Water Sampling Locations – September 2020

Figure 3.1 Water Table Elevation and Shallow Groundwater Flow Lines – September 2020 Figure 3.2 Water Table Elevation and Deep Groundwater Flow Lines – September 2020

Figure 4.5 Concentration of EDC (1,2-Dichloroethane) at the Shallowest Monitoring Depth- September 2020 Figure 4.6 Concentration of PCE (Tetrachloroethene) at the Shallowest Monitoring Depth – September 2020 Figure 4.7 Concentration of TCE (Trichloroethene) at the Shallowest Monitoring Depth – September 2020 Figure 4.8 Concentration of VC (Vinyl Chloride) at the Shallowest Monitoring Depth – September 2020 Figure 4.9 Concentration of CTC (Carbon Tetrachloride) at the Shallowest Monitoring Depth – September

2020

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APPENDICES APPENDIX A

Hydrographs

APPENDIX B

Properties of Volatile and Semi-Volatile Chlorinated Hydrocarbons

APPENDIX C

Data Validation Summary Reports

APPENDIX D

Glossary

APPENDIX E

References

APPENDIX F

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1.0 INTRODUCTION

The Groundwater Cleanup Plan (GCP) was developed by Orica Australia Pty Ltd (Orica) in response to condition 3B of Notice of Clean Up Action (NCUA) No 1030236. The NCUA was revoked on 3 December 2010 and replaced by a Voluntary Management Proposal (VMP) (approval No 20101714). The VMP and the

associated Groundwater Remediation and Management Plan (Orica, 2010) include a series of commitments in relation to operation of the containment lines, groundwater and surface water monitoring, assessment of risk to human health, review of alternative remediation strategies and community consultation.

The GCP included a quarterly monitoring program that was superseded by the Groundwater Treatment Plant (GTP) – Groundwater and Surface Water Monitoring Program (URS, 2005e) which was subsequently

amended in January 2007 (URS, 2007a), October 2009 (URS, 2009e), June 2013 (Golder 2013d), May 2017 (Golder, 2017b) and recently in August 2020 (Golder 2020b). The most recent revision to the GTP monitoring program includes three types of monitoring events: biannual, annual and biennial (in order of sampling program magnitude).

Groundwater and surface water monitoring completed in September 2020 was conducted in accordance with the 2017-2020 GTP monitoring program (Golder, 2017b). As specified in the amended program, the

September 2020 program is an annual event.

1.1 GTP Monitoring Program Methodology

The GTP monitoring program has two distinct monitoring functions:



Chemical monitoring of the distribution of the contaminants of concern within surface water and groundwater; and



Monitoring of hydraulic containment performance.

1.1.1 Chemical Monitoring

The chemical monitoring program (presented in Table 1.1) is based on the following methodology (Golder, 2017b):



Biannual monitoring of surface water within Springvale Drain, Floodvale Drain and Penrhyn Estuary aims to collect data critical to environmental and human health receptors. It includes collection of groundwater and pore water at the inter-tidal groundwater discharge zone at low tide in Penrhyn Estuary.



Annual chemical monitoring focuses on assessing chemical changes in areas where plume migration is expected to occur as well as detailed assessment of data with respect to the assumptions made in the Consolidated Human Health Risk Assessment (CHHRA) (EnRiskS, 2018).



Biennial chemical monitoring focuses on identifying major changes to plume geochemistry and distribution throughout the Groundwater Extraction Exclusion Area (GEEA).

1.1.2 Hydraulic Monitoring

The strategy selected to achieve hydraulic containment of groundwater contamination was described in the Botany Groundwater Cleanup (BGC) Project Environmental Impact Statement (EIS) (URS, 2004d). The hydraulic monitoring approval requirements detailed in the BGC Project EIS can be summarised as a number of specific objectives, including the monitoring of aquifer levels to demonstrate:



Capture of contaminated groundwater at the three hydraulic containment lines, comprising

▪

Botany Industrial Park (BIP);

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The Primary Containment Area (PCA); and

▪

The Secondary Containment Area (SCA).



Excessive drawdown, which could result in ground subsidence, does not occur.

Hydraulic monitoring and regular review of pumping rates are also conducted to minimise the rate of saltwater intrusion at the SCA, which is undesirable for GTP operation.

The amended hydraulic monitoring program (Golder, 2017b) is based on the use of automated data loggers and transducers to enable continuous water level monitoring in the lower GEEA (see Table 1.2 for locations). The methodology for the hydraulic monitoring program is as follows:



Biannual hydraulic monitoring to focus on assessing hydraulic containment at the SCA, PCA and BIP containment lines; and



Annual and biennial hydraulic monitoring to assess long-term data and the groundwater flow regime within the broader area of the lower GEEA.

1.2 Previous Quarterly Groundwater and Surface Monitoring

Groundwater monitoring has been regularly conducted throughout the Stage 3 and Stage 4 Surveys. Previous quarterly monitoring programs completed and reported under the GCP and GTP programs are presented in the following table.

Previous GCP and GTP Monitoring Programs

Year Month Reference

GCP

Programs 2004 March, June, September, December URS, 2004a/b/c/2005a

2005 March, June URS, 2005b/d

GTP

Programs 2005 September, December URS, 2005f/2006a

2006 March, June, September, December URS, 2006c/d/e/2007b 2007 March, June, September, December URS, 2007c/d/e/2008a 2008 March, June, September, December URS, 2008b/c/d/2009a 2009 March, June, September, December URS, 2009b/d/f/2010a 2010 March, June, September, December Golder, 2010a/b/c/2011b 2011 March, June, September, December Golder, 2011c/d/e/2012a 2012 March, June, September, December Golder, 2012b/c/d/2013a 2013 March, June, September, December Golder, 2013b/c/e/2014a 2014 March, June, September, December Golder, 2014b/c/d/2015a 2015 March, June, September, December Golder, 2015b/c/d/2016a 2016 March, June, September, December Golder, 2016b/c/d/2017a

2017 March, September Golder, 2017c/d

2018 March, September Golder, 2018a/b

2019 March, September Golder, 2019a/b

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2.0 SCOPE OF SERVICES

2.1 General

The scope of the September 2020 annual monitoring program is summarised in this section. The results of the hydraulic monitoring program are presented and discussed in Section 3.0. The results of the chemical

monitoring program for groundwater are presented in Section 4.0, while the results of the Penrhyn Estuary and surface water sampling are presented in Section 5.0. The human health risk implications (if any) of the monitoring program results are discussed in Section 6.0.

2.2 Hydraulic Containment Water Level Monitoring

A comprehensive water level monitoring program utilising automated data loggers and transducers was undertaken in accordance with the GTP monitoring program (Golder, 2017b) as shown in Figure 2.1. The monitoring well locations used for the monitoring program are presented in Table 1.2. The program involved the collection and processing of data from 277 continuously logged monitoring and extraction wells.

2.3 GTP Chemical Sampling Program

In accordance with the GTP program (see Table 1.1 and Golder, 2017b) the September 2020 sampling program represents an annual monitoring event. It includes an analytical program with sampling locations focused on assessment of volatile chlorinated hydrocarbon (CHC) concentrations in pore water, groundwater and surface water at Penrhyn Estuary and surface water at Springvale Drain and Floodvale Drain.

Porewater samples were collected from newly installed piezometers in Penrhyn Estuary to compare results to samples collected from existing piezometers. Additional groundwater and surface water samples were collected across Botany, however, this will be reported separately.

Due to dry or damaged ports at some sampling locations, minor variations to the amended GTP program were made. In most of these instances, adjacent ports were sampled. The variations to the amended GTP program are presented in the following table.

September 2020 GTP Monitoring Program Variations

Plume Scheduled Program

(see Table 1.1) Completed September 2020 Variations Location

No. Sample No. Location No. Sample No.

Southern 15 23 15 23 All samples collected as per program.

Central 9 9 8 8

▪

WG258S damaged in 2017 due to an

adjacent leaking sewerage service. Unable to sample.

▪

BP41, 2 m port dry or blocked. Substituted with 4 m port. VC SIM completed on 4 m port as a substitution.

All other samples collected as per program.

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Plume Scheduled Program

(see Table 1.1) Completed September 2020 Variations Location

No. Sample No. Location No. Sample No.

Northern 16 16 16 16 All samples collected as per program.

Penrhyn Estuary

6 18 6 18 All samples collected as per program.

Surface Water

11 11 11 11 All samples collected as per program.

2.4 Sample Analyses

Groundwater, pore water and surface water samples were analysed for a suite of volatile and semi-volatile chlorinated hydrocarbons (CHCs). The analytical suite includes the list of compounds specified in the VMP and GTP Monitoring Program (Golder, 2017b) and is presented in the table below.

Volatile Chlorinated Hydrocarbons

Carbon Tetrachloride (CTC) Chloroform (CFM)

Methylene Chloride (DCM) Chloromethane

Pentachloroethane 1,1,1,2-Tetrachloroethane

1,1,2,2-Tetrachloroethane (1,1,2,2-TeCA) 1,1,2-Trichloroethane (1,1,2-TCA)

1,1,1-Trichloroethane 1,1-Dichloroethane (1,1-DCA)

1,2-Dichloroethane (EDC) Chloroethane

Tetrachloroethene (PCE) Trichloroethene (TCE)

trans-1,2-Dichloroethene (trans-1,2-DCE) cis-1,2-Dichloroethene (cis-1,2-DCE)

Vinyl Chloride (VC)

A summary of the properties of volatile and semi-volatile CHCs is presented in Appendix B.

2.5 Quality Assurance (QA) and Quality Control (QC)

2.5.1 Quality Assurance Plan

Sample collection, sample handling and decontamination procedures were performed in general accordance with the Groundwater Treatment Plant Groundwater and Surface Water Monitoring Program 2017 – 2020 (Golder, 2017b).

2.5.2 QA/QC Samples

The analyses of laboratory and field QA/QC samples are mechanisms for checking the accuracy and

precision of analytical data in order to ensure that the program data quality objectives (DQOs) are being met. The QA/QC samples collected in the field during this sampling round included trip blanks, field duplicates and field triplicates.

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5 In addition to field QA/QC samples, the primary and secondary analytical laboratories (ALS and Envirolab, respectively) have used laboratory and batch specific QA/QC processes including laboratory duplicates, laboratory blanks, surrogate spikes, matrix spikes and laboratory control samples.

2.5.3 Data Validation

2.5.3.1 General

To ensure that data of known quality are reported and to identify whether data are suitable to fulfil the overall project objectives, analytical data validation is conducted by Golder. The validation process is based upon the following data validation guidance documents:



NEPC (2013). National Environmental Protection (Assessment of Site Contamination) Measure 1999, as amended by the National Environment Protection (Assessment of Site Contamination) Amendment Measure 2013 (No.1), and



USEPA Contract Laboratory Program National Functional Guidelines for Superfund Organic Methods Data Review (USEPA, 2008a).

The analytical data validation process involves the checking of analytical procedure compliance and the assessment of accuracy, precision and completeness of analytical data.

Analytical data validation summary sheets are presented in Appendix C.

2.6 Data Management

Analytical data for the Botany project is stored on a secure SQL server and managed via the EQuIS® 5 Environmental Data Management System (EDMS) off site. Warehoused data sets are linked to ArcGIS, proprietary Geographical Information System (GIS) software. This GIS is used in the spatial presentation of the site’s monitoring locations and the creation of contaminant distribution figures as well as geochemical and hydraulic figures.

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3.0 HYDRAULIC MONITORING

3.1 General

The September 2020 monitoring round is an annual event that focuses on assessing hydraulic containment at the SCA, PCA and BIP containment lines.

The following comments are noted with regards to the hydraulic monitoring program:



Historical (from March 2016) and current hydraulic monitoring data are tabulated and presented in Table 3.1;



Water table elevation (shallow aquifer) and inferred potentiometric surface (deep aquifer) maps, and associated groundwater flow lines are presented in Figures 3.1 and 3.2, respectively. The contours are inferred from transducer and automated logger data averaged for the period between 1 March 2020 and 31 August 2020;



A scheduled GTP maintenance shutdown occurred from 1 March 2020 to 3 April 2020. In addition, two pumps in EFW25S and EWF28S wells were switched off in August 2020 for reinstalling EWF28D and EWF25D. The effect of the shutdown on water levels in the vicinity of the BIP, PCA and SCA is evident in the hydrographs included in Appendix A. The slow migration of groundwater and the potential for increased pumping to recapture groundwater mean that hydraulic containment can still be maintained through extended periods of no, or low, groundwater extraction. The assessment of hydraulic

containment during the period is therefore focussed on the period of GTP operation following the scheduled maintenance shutdown;



Detailed hydrographs for wells equipped with transducers/loggers are presented in Appendix A.

Monitoring well hydrographs for the SCA include a representation of the target water level that is used to assess hydraulic containment. Hydrographs for wells located along Springvale Drain include a

representation of the target water levels that are used to assess the potential for groundwater to discharge to the drain. Additionally, the hydrograph for MWB03S (Figure A.16) includes a target level that is used as a basis for considering whether additional water and air quality assessments are required in the vicinity of Springvale Drain (see Section 6.3);



During the September 2020 field program, water levels were manually measured at each logger location and compared against the logged water level in order to assess data quality and reliability. A summary of these data is presented in Table 3.2. A number of minor discrepancies were identified and, where possible, the data have been corrected. In some cases, where the cause of the discrepancy was not clear, further assessment will be undertaken during the next GTP monitoring event (March 2021). The identified discrepancies are not considered to affect interpretation of groundwater flow directions and the overall data are considered suitable for assessing hydraulic containment;



A number of faulty pressure transducers and data loggers were identified during the monitoring period. An ongoing program to identify, repair/replace inoperable loggers/transducers is undertaken as part of ongoing maintenance works for the GTP. Given the historical data set and extent of monitoring at adjacent locations, the absence of reliable data at these locations is not considered to affect the quality of the overall assessment;



Each hydrograph includes a daily rainfall chart for Sydney Airport;



Rainfall during the period was slightly above the long-term average in March, May and significantly higher in July 2020. Rainfall was below the long-term averages for April, June and August 2020.

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March April May June July August

Total Monthly Rainfall (mm) 137.4 32.4 111.2 80.2 127.4 65.4

Long-Term Average Monthly Rainfall

(mm) 118.1 106.0 95.3 124.8 69.2 75.6

Source: www.bom.gov.au

3.2 Assessment of Hydraulic Containment

3.2.1 General Approach

A detailed assessment of hydraulic containment at BIP, PCA and SCA was undertaken by JBS&G (2012) using the approach presented in A Systematic Approach for the Evaluation of Capture Zones at Pump and

Treat Systems by United States Environment Protection Agency (USEPA, 2008b).

The VMP includes ongoing requirement for Remediation Strategy Review Workshops to be convened every three years. The fourth such workshop was held in February 2017, with the outcomes summarised in 2017 Botany Groundwater Strategy Review Workshop Summary Report (Orica, 2017a).

The 2017 Workshop recommended updating the 6 Step Capture Zone Analysis as defined in USEPA (USEPA, 2008b), to incorporate more recent (since 2012) data and modelled capture targets. The JBS&G assessment was recently updated (JBS&G, 2019) and addresses that recommendation. This Annual monitoring report uses the updated (2019) version as the basis for assessment of hydraulic containment performance.

The JBS&G evaluation uses multiple lines of evidence within the six ‘steps’ framework to assess hydraulic containment. It concludes that the remediation objective of the BGC Project (i.e. “to achieve protection for

slightly to moderately disturbed ecosystems using the Australian and New Zealand Guidelines for Marine and Fresh Water (ANZG, 2018)” in surface water at Penrhyn Estuary is being achieved.

The JBS&G assessment (JBS&G (2019)) provides a framework for assessment of key metrics for evaluation of the success of hydraulic containment during ongoing monitoring. The following section reviews the recent hydraulic monitoring data for the September 2020 ‘Annual’ monitoring round using the six lines-of-evidence ‘steps’ considered by JBS&G (2019).

3.2.2 Step 1 – Review Site Data, Conceptual Model and Remedy Objectives

JBS&G (2019) presented a consolidated review of the Conceptual Site Model, noting the most recent significant revision was published in 2017 (Orica, 2017b). The Orica Botany CSM is based upon extensive data collected over several decades and is widely considered to be well established and robust, following peer review by international experts. Accordingly, JBS&G (2019) considers that the CSM satisfies the prerequisites defined in USEPA (2008b) for undertaking Capture Zone Evaluation.

The remedy objective for the BGC Project is clearly stated and understood to be ‘to achieve protection for

slightly to moderately disturbed ecosystems using the Australian and New Zealand Guidelines for Marine and Fresh Water (ANZG, 2018) in surface water at Penrhyn Estuary. It is unlikely to change in the short to medium

term, thus this step (Step 1) does not require ongoing review and is not evaluated further in this report.

3.2.3 Step 2 – Define Site Specific ‘Target Capture Zones’

JBS&G (2019) provides a detailed background to system design and summarises the development of the three main Areas/Lines upon which the extraction network is based, being:

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

Primary Containment Area/Line (PCA), located along the southern (McPherson Street) boundary of Southlands Blocks 1 and 2, designed to prevent ongoing contaminant migration from Block 2, Southlands;



Secondary Containment Area/Line (SCA), located in the median strip of Foreshore Road, designed to prevent migration to Botany Bay; and



BIP Containment Line, located on and parallel to the western boundary of the BIP, designed to prevent ongoing migration from source areas on BIP.

Target capture zones were considered in JBS&G (2019), based on monitoring data collected from containment line extraction and monitoring wells. Groundwater flux-averaged contaminant concentrations were used rather than depth-averaged concentrations due to the relative paucity of vertical discretisation in contaminant concentrations at the containment lines (compared to the 2006 data used by JBS&G (2012)). Flux-averaged concentrations were estimated from extraction well data (as water quality of operating extraction wells with long well-screens across the shallow or deep aquifer is considered to represent the flux-averaged concentration across the entire thickness of the respective aquifer). Monitoring well contaminant data were also considered to conservatively supplement extraction well data.

Based upon considerations of the detailed plume geometry, pumping capacity and hydraulic performance, JBS&G (2019) refined the Target Capture Zones for each of the three lines as follows:



SCA: Hydraulic containment in the deep aquifer between EWF28D and EWF14D (Plate A);



SCA: Hydraulic containment in the shallow aquifer between EWF28S and EWF05S (Plate A)

Plate A: Target Capture Zones for SCA

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Plate B: Target Capture Zone for PCA



BIP: Hydraulic containment in the area between EWD01S/I and EWD18I/D (Plate C).

Plate C: Target Capture Zones for BIP

As for Step 1, these defined zones are unlikely to change on an ongoing basis and the need for review is likely to be by exception rather than every round. This step is not evaluated further in this report.

3.2.4 Step 3 – Water Level Analysis

The approach taken by JBS&G (2019) in evaluating water levels in target zones in Step 3 can be divided into two main assessments:

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

Water Level Maps; and



Gradient Control Pairs.

Both are metrics against which the ‘success’ of hydraulic contamination can be assessed and they warrant review during ongoing monitoring programs to consider whether the overall remedy objective continues to be met.

Background

With respect to assessing the flow of groundwater at the three containment areas it is important to highlight the following:



The primary purpose of the SCA is to reduce the mass flux of contaminants entering Penrhyn Estuary in groundwater so that surface water concentrations remain below the guideline values. Pumping priority is based on contaminant concentrations along the SCA. Consequently, the western end has been

designated a lower pumping priority. Target groundwater levels for SCA monitoring wells are based on subsidence constraints and an assessment of groundwater levels at the discharge point in the intertidal zone. Field studies (Turner et al 1996, Nielsen 1999, Cartwright & Nielsen 2001) have demonstrated the average groundwater elevation in the intertidal zone discharge point is above 0 Australian Height Datum (mAHD). The field studies show that water levels at the discharge point (even in the quiescent conditions of Penrhyn Estuary) could exceed 0.2 mAHD, which has previously been confirmed by water levels at BP117 located in the vicinity of the groundwater discharge zone at Penrhyn Estuary which typically range between 0.2 and 0.4 mAHD. As a result, a conservative target level of 0.1 mAHD has historically been adopted for long-term operation of the SCA;



While a nominal target water level of 0.1 mAHD at the SCA is presented on the hydrographs to aid interpretation, it is important to note that observed levels above these targets do not directly imply hydraulic containment was not achieved. As indicated above, assessment of hydraulic containment requires incorporation and analysis of a number of lines of evidence; and



The slow migration of groundwater and the potential for increased pumping to recapture groundwater mean that hydraulic containment can still be maintained through extended periods of no, or low, groundwater extraction.

Step 3a – Water Level Maps – September 2020

Figures 3.1 and 3.2 present water table elevations and inferred flow lines for the shallow and deep aquifers respectively.

Shallow Aquifer: Figure 3.1 is considered to illustrate a pattern of shallow groundwater flow influenced by

groundwater extraction. Flow lines at BIP and SCA are consistent with hydraulic containment of the relevant target capture zones having occurred during the period. Hydraulic containment of the shallow aquifer at PCA is considered to be broadly evident, but more intermittently expressed. It is noted, however, that this area is characterised by relatively low contaminant concentrations in the shallow aquifer. The averaged water levels were generally higher than the previous monitoring period. The higher groundwater elevations are likely to be associated with the consistently higher than average rainfall during the monitoring period. Groundwater contours of averaged water levels show a pattern of groundwater flow influenced by groundwater extraction.

Deep Aquifer: Figure 3.2 is considered to reflect a pattern of intermediate and deep groundwater flow heavily

influenced by groundwater extraction. Flow lines at BIP, PCA and SCA are consistent with hydraulic containment of the relevant target capture zones having occurred during the period. Water levels were generally higher than during the previous monitoring period largely as a result of higher than average rainfall throughout the period.

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11 Water levels in the deep aquifer at BIP and PCA were generally within or lower than the range of levels predicted to be required for hydraulic containment by Laase (2005) (approximately between 3.0 and 4.0 mAHD at BIP and between 1.0 and 1.5 mAHD at the PCA).

Achievement of target levels at SCA was more intermittent with averaged water levels higher than the target level of 0.1 m AHD predicted by Laase (2005). The ‘high’ average water levels are likely a result of heavy rainfall, reduced groundwater extraction associated with poor pump performance and the failure of extraction well EWF28D in April 2019 which also reduced groundwater extraction efficiency. A program of installation of new and replacement extractions wells (EWF25D and EWF28D), completed in October 2020 is expected to improve hydraulic containment of the eastern portion of the SCA.

Overall, the observed pattern of groundwater flow in the monitoring period is different to that observed during the baseline monitoring in October 2004 (URS, 2005a), exhibiting greater similarity to that presented in monitoring reports since operation of the full GTP system commenced in 2007, albeit intermittently weaker at SCA as detailed above.

Step 3b – Reverse Gradient Pairs

PCA: An assessment of gradient control pairs for the shallow aquifer is presented in the following table and

shown on Figure A.22 in Appendix A.

Gradient Control Pairs - PCA

Downgradient

Well ID Average SWL (mAHD) PCA Well ID Average SWL (mAHD) Indicative Gradient Flat or Reverse Gradient

MWB15S 2.18 MWB02S 1.68 -0.0198 Yes MWB15S 2.18 MWB03S 2.28 0.0033 No MWB13S 2.40 MWB05S 2.03 -0.0122 Yes MWB11S 1.65 MWB06S 1.71 0.0020 No MWB14S 1.62 MWB07S 1.64 0.0008 No

The assessment shows that an average reverse gradient was achieved in the vicinity of MWB02S and MWB05S in the eastern and central eastern portion of the PCA in the shallow aquifer during the period (Plate B). Near-flat hydraulic gradients were also noted for MWB07/MWB14. Wider analysis of target water levels

suggests that hydraulic containment was also achieved in the intermediate and the deep aquifers of the PCA, with a hydraulic gradient from both the eastern and western portions of the PCA towards the centre (refer to Figure 3.2). As discussed above in Step 3a, limited hydraulic containment in the shallow aquifer at PCA is not expected to affect achievement of the remedy objective.

SCA: The primary assessment of gradient control pairs is presented in the following table. Comparison of

gradient control pairs is further illustrated in hydrographs A.12, A.13 and A.14 presented in Appendix A. Well

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12

Gradient Control Pairs - SCA

Downgradient

Well ID Average SWL (mAHD) SCA Well ID Average SWL (mAHD) Indicative Gradient Flat/Reverse Gradient

MWF17D 0.83 MWF13D 0.77 -0.002 Yes MWF17I 0.79 MWF13I 0.88 0.003 No MWF17S 0.33 MWF13S 0.11 -0.007 Yes MWF17D 0.83 MWF14D 0.94 0.002 No MWF17I 0.79 MWF14I 0.80 0.000 No MWF17S 0.33 MWF14S 0.42 0.002 No MWF15D 0.74 MWF12D 0.84 0.003 No*

MWF15I 0.61 MWF12I 0.52 -0.003 Yes

MWF15S 0.25 MWF12S 0.27 0.001 No MWF15D 0.74 MWF13D 0.77 0.001 No MWF15I 0.61 MWF13I 0.88 0.005 No MWF15S 0.25 MWF13S 0.11 -0.003 Yes MWF15D 0.74 MWF11D 0.65 -0.002 Yes MWF15I 0.61 MWF11I 0.96 0.007 No MWF15S 0.25 MWF11S 0.19 -0.001 Yes MWF18D 0.30 MWF02D 0.58 0.009 No MWF18I 0.52 MWF02I 0.88 0.012 No MWF18S FL MWF02S 0.40 - - MWF19D 0.32 MWF07D 0.43 0.003 No

MWF19I 0.50 MWF07I 0.15 -0.010 Yes

MWF19S 0.33 MWF07S 0.32 0.000 Yes

MWF19D 0.32 MWF08D 0.57 0.006 No

MWF19I 0.50 MWF08I 0.29 -0.005 Yes

MWF19S 0.33 MWF08S 1.43 0.028 No

Notes: *MWF15D is screened in a lower aquifer unit FL = Faulty Logger

This analysis shows that during the monitoring period:



An average reverse gradient was achieved in the shallow aquifer in the eastern, central-eastern and western portions in the vicinity of MWF15S and MWF17S (compared with levels at MWF13S),

MWF15S/MWF11S and MWF19S/MWF07S. The absence of logger data (the data logger at MWF18S was identified to be faulty during the period) in the central portion of SCA limits the assessment of shallow gradient control pairs.



The broader analysis of average shallow water levels provided in Table 3.1 (MWF01, MWF02, MWF06, MWF07, MWF09, MWF10, MWF11, MWF12, MWF13 and MWF14) indicate a flat hydraulic gradient

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13 exists between the eastern, central and western portions of the SCA and the Penrhyn Estuary shoreline, where average levels range between 0.2 and 0.4 m AHD.



An average reverse gradient was achieved in the intermediate aquifer in the central-eastern and western portions of the aquifer in the vicinity of MWF15I/ MWF12I, MWF19I/MWF07I and MWF19I/MWF08I, respectively. Evidence of average reverse gradients was less clear in the central portions of the SCA in the vicinity of MWF17I and MWF18I. The assessment of gradient control pairs and the analysis of target levels in the intermediate aquifer suggest hydraulic containment was achieved, with an expected

hydraulic gradient from the western end of SCA.



Average reverse gradients in the deep aquifer at the SCA were observed in the eastern and central-eastern portion of the SCA in the vicinity of MWF15D and MWF17D. A reverse hydraulic gradient in the central portion of the SCA is also periodically evident in the vicinity of MWF03/MWF18 (refer to

hydrograph A.14 in Appendix A). Hydraulic containment in the western end of the SCA is less clear although it is noted that this area is characterised by relatively low CHC concentrations and falls outside of the SCA Target Capture Zone (refer Step 2).

This analysis of gradient control pairs supports the conclusion that effective hydraulic containment was achieved in the shallow aquifer across the SCA, within the intermediate aquifer in the eastern and western portion and within the deep aquifer in the eastern and central-eastern portion. Hydraulic containment in the deep aquifer in the western end of the SCA is less clear. It is noted that the adopted target levels are considered conservative and have been designed for the long-term operation of the SCA.

Elevated averaged groundwater levels were particularly evident in the eastern portion of the deep aquifer at SCA where the failure of extraction well EWF28D in April 2019 has significantly reduced groundwater extraction.

It is important to highlight that intermediate and deep monitoring wells at SCA are generally screened within the same aquifer unit (except for MWF15D which is screened within a lower unit) and that the downward hydraulic gradient suggests that groundwater in the intermediate aquifer zone will also be drawn towards deeper sections of the SCA containment line.

Springvale Drain Shallow Groundwater – September 2020

During the monitoring period, the groundwater level at MWB03S exceeded the risk review trigger level (refer Figure A.16 in Appendix A) for a cumulative period of 100 days (over three separate intervals) during the six-month monitoring period. The elevated groundwater levels are expected to have primarily resulted from the GTP maintenance shutdown in March 2020, and high rainfall events in June and August 2020. This is discussed further in relation to potential risks to human health in Section 6.3.

3.2.5 Step 4 - Flow and Capture Zone Calculations

As summarised in JBS&G (2019), specific calculations can be performed to provide additional lines of evidence of effective capture:



Simple horizontal analysis, such as estimated flow rate calculations; and



Analytical or numerical modelling to stimulate heads, in conjunction with particle tracking and/or contaminant transport modelling.

The calibrated model developed by Laase (2005) was used to evaluate six design scenarios (Scenarios A to F). Scenario F was the most appropriate model configuration for predictive purposes. The horizontal capture

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14 zone analysis included detailed groundwater modelling (incorporating particle tracking). The modelled

estimate of total extraction flow rate required for hydraulic containment is 6.2 ML/day.

Comparison of Scenario F flow rates to the 2 Year Average (since September 2015) extraction rates indicated lower rates at SCA and PCA. The significantly lower extraction rates at PCA have previously been attributed to the decommissioning of CHC mass removal wells (EWB02D, EWB06D and EWB14D) in March 2011 and redevelopment of Southlands and adjacent areas. The groundwater model was updated in 2017 (Laase, 2017) and concluded:

“When cumulative discharge from the Orica Botany Site extraction well field is 4.67 ML/d or higher, the extraction well field capture zone envelopes the Botany Site and property south of the site stopping further migration of groundwater contamination for all anticipated precipitation conditions”.

The revised modelling indicated that hydraulic containment is achieved at 4.7 ML/d during both drought and high rainfall conditions, periods of time when the GTP planned maintenance or short unplanned shutdowns.

Step 4a - Simple Horizontal Capture Zone Analysis – September 2020

Average extraction flow rates for each containment line are compared against Scenario F (considered the most representative modelling scenario) of the groundwater flow model (Laase, 2005) in the table below. Flow Rates (ML/day)

Containment Line Laase (2005), Scenario F JBS&G (2019), 2 Year Average since September 2015 Current Period* BIP 3.5 3.3 3.51 PCA 1.3 0.6 0.59 SCA 1.4 0.9 0.77 Total 6.2 4.8 4.87

*Period (1 March to 31 August 2020)

Average groundwater extraction rates at the PCA and SCA during the monitoring period were less than the modelled rates for normal climatic conditions, however the cumulative rate was higher than the revised flow rate of 4.7 ML/day (Laase, 2017). Groundwater extraction rates at BIP, PCA and SCA have also been affected by well biofouling, the scheduled GTP maintenance shutdown and the reduced groundwater extraction

required to achieve target levels during extended low rainfall conditions. It is understood that salinity at the SCA is also a limiting factor.

Step 4b - Particle Tracking Zone Review – September 2020

Particle tracking completed as part of the revised numerical model (Laase, 2017) indicated that hydraulic containment was achieved for flows of 4.7 ML/day. The extraction rates have generally been reported to be of a similar order to those modelled.

The September 2020 contours (Figures 3.1 and 3.2) of potentiometric surfaces are similar in pattern to those assessed by JBS&G (2019) and predicted in groundwater modelling (and particle tracking) of Scenario F (Laase, 2005) and updated module (Laase, 2017) to achieve hydraulic containment.

3.2.6 Step 5 - Concentration Trends

Due to the age of the plume(s) and their distribution prior to commencement of groundwater extraction, no sentinel wells are available.

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15 Surface water concentrations at Penrhyn Estuary have decreased dramatically since commencement of groundwater extraction and now satisfy the remedy objective.

Groundwater concentrations and distribution have been characterised by stable or decreasing trends in most CHC concentrations. However, increasing trends are noted at MWF15, MWF17, MWF18 and MWF19 (see Sections 4.0 and 7.0). Whilst noteworthy, these are not yet considered to represent a significant change in overall contaminant distribution Surface water concentrations at Springvale Drain and Penrhyn Estuary reported in the monitoring period (see Sections 4.0 and 5.0) are similarly low compared to those reported historically and continue to satisfy the remedy objective. It should also be noted that the slow migration rates between the SCA and Penrhyn Estuary allow for potential recapture of CHCs that migrate beyond the SCA during periods of poor hydraulic containment.

3.2.7 Step 6 - Compare Actual Capture and Target Capture Zone

Comparison of actual capture to the target capture zones indicates that hydraulic containment is being effectively achieved. Further, assessment of contaminant concentrations indicates that the BGC Project remedy objectives are being achieved.

Further, assessment of contaminant concentrations at Springvale Drain and Penrhyn Estuary (see Sections 4 and 5) indicates that the BGC Project remedy objectives are being achieved.

3.3 Catchment Groundwater Hydraulics

While the focus of the hydraulic monitoring program is assessment of hydraulic containment, an assessment of longer-term water level trends is included for annual and biennial reports.

Long-term hydrographs for selected monitoring wells are presented in Figures A.38 to A.39. The selected wells represent those with continuous long-term data sets and/or those located at significant distances from the containment lines. The hydrographs include a plot of “Rainfall Residual Mass” that shows cumulative deviations from the long-term annual average monthly rainfall. The residual mass plot is interpreted by

assessing the gradient/trend of the line, with a downward trend indicating drier than average conditions and an upward trend indicating relatively wet conditions.

The following general comments are made with respect to regional groundwater flow in the lower GEEA:



Monitoring wells located to the west of the BIP (Figure A.39 - WG231S/D) are influenced by both

groundwater extraction for hydraulic containment and rainfall. Water level changes of approximately 1 m are observed in the deep aquifers in response to extraction whilst the shallow aquifer is predominantly influenced by rainfall events.



For locations immediately adjacent to the BIP containment line (Figure A.38 – WG83S/I and WG123S/D) the commencement of groundwater extraction at BIP in mid-2006 is clearly evident. Variations of

consistent magnitude since this time have occurred in response to changes in groundwater extraction at BIP. Logging ceased at WG83S/I in early 2012 and was substituted by MWG01S/D, which shows a similar response to GTP operation and rainfall trends.



Hydrographs for monitoring wells located around the PCA (Figure A.38) to the east (MWC11S/D) show the commencement of significant groundwater extraction at the PCA in early 2006. Water levels

increased significantly in 2011 following the removal of extraction wells (EWB02, EWB06 and EWB14D) from the PCA system and have subsequently shown a pattern of change influenced by both operation of the PCA and rainfall. Water level trends since then are consistent at well locations to the east of PCA (SL01D) but no significant downward/upward patterns are apparent.

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16



Hydrographs for monitoring wells upgradient of the SCA (Figure A.39 – WG154S/D, WG88S/I and WG23S/WG75I) show the commencement of significant groundwater extraction at SCA in late 2005. Variations in water levels since commencement of groundwater extraction are consistent at all monitoring well locations. Water levels are influenced by both groundwater extraction at the SCA and variable influence of rainfall events.

In summary, an assessment of long-term water levels for monitoring wells located adjacent to, and at significant distances from, the containment lines indicate that no long-term downward trends are evident. Observed drawdowns are similar to those predicted by groundwater modelling (Laase, 2005 and Laase, 2017). The data highlight the relatively localised effects of the hydraulic containment system and its low potential to adversely affect infrastructure and licensed groundwater users.

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17

4.0 CHEMICAL MONITORING

In accordance with the GTP program (see Table 1.1 and Golder, 2017b) the September 2020 sampling program represents an annual monitoring event. As such, chemical sampling was focused on assessment of volatile CHCs concentrations in pore water, groundwater and surface water at, and hydraulically upgradient of, Penrhyn Estuary. Surface water samples were also collected from within Springvale Drain and Floodvale Drain upstream of Penrhyn Estuary. Sampling occurred during September 2020.

Table 4.1 presents field parameters collected at the time of sampling. Tables 4.2, 4.3 and 4.4 present volatile CHC analytical results for Penrhyn Estuary groundwater, pore water and surface water, respectively. Short- and long-term historical trends, detection limit flags and historical maximum concentrations are presented in Tables 4.5 to 4.10 for groundwater, in Tables 5.1 to 5.5 for pore water and in Table 5.6 for surface water. Assessment of historical trends has been undertaken in Section 4.2.

The chemical monitoring locations are presented in Figure 2.2.

Assessment of pore water and surface water analytical results against the relevant criteria (ANZG (2018)) is presented in Sections 5.1 and 5.2.

4.1 Assessment of Groundwater Chemical Monitoring Data

Tables 4.5 to 4.10 present the following parameters:



Locations where a reported contaminant concentration represents an historical maximum (Max Flag);



A Detection Limit Flag (DL Flag) for locations where the reported laboratory detection limit is greater than

the previously reported concentration or detection limit for the previous monitoring round. Such changes in detection limits may result from variable sample dilution during analysis between monitoring rounds, and have occurred for a number of off-site and on-site wells; and



Parametric tests for selected contaminants to identify short-term (4 year) and long-term (all available data) trends. Where increases (>20%) are observed for both short- and long-term tests the result is represented by ‘double red flags’ in the data table. Conversely, decreases (>20%) are represented by ‘double green flags’.

Previous GTP monitoring reports divided groundwater contamination according to plumes derived from DNAPL source zones. Broad descriptions of the plumes are provided below:



Southern Plumes: Comprised of three overlapping plumes (S1, S2 and S3) inferred to be derived from

the former Solvents Plant (CTC, PCE and CFM as a degradation product) and the former TCE Plant (PCE, TCE, 1,1,2,2-TeCA, 1,1,2-TCA and VC as a degradation product). CTC, PCE, TCE, CFM, VC and EDC are the dominant contaminants in terms of concentration and distribution;



Central Plume: The C1 Plume contains a number of volatile CHCs, with EDC being the main

component and accounting for more than 90% of the estimated mass at most locations. PCE and TCE are also present at significant concentrations, albeit several orders of magnitude lower than EDC

concentrations (URS, 2004d). VC is present within the Central Plume with historical concentrations being highly variable. VC may be a product of either biological degradation of TCE or abiotic degradation of EDC and may also be present in the original source material of this plume; and



Northern Plumes: Comprised of several separate plumes derived from a number of potential source

areas in the northern portion of the plant site (BIP). A plume comprised predominantly of CTC is inferred to be derived from the former CTC/PCE storage tanks (Plume N4). Several other plumes are comprised predominantly of EDC and are inferred to be derived from storage of drummed EDC wastes. Previous

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18 works (URS, 2005b/c) have concluded that the Central Plume could have extended significantly further to the north (due to historical groundwater extraction northwest of the BIP) than previously identified and commingled with contamination from the inferred Northern Plumes’ source areas.

While use of the above division of groundwater plume origin was appropriate for interpretation of monitoring data collected during the investigation and early remediation phase, it is less appropriate for the GTP monitoring program (i.e. post hydraulic containment). As a result, the following discussion has been structured such that results are presented in relation the three containment areas: BIP, PCA and SCA (off-site). Where appropriate, the plumes are still referenced within the on-site and off-site groundwater

discussions.

4.2 Groundwater Chemical Monitoring Results

The assessment of changes in the chemical composition of groundwater is presented in this section and a discussion of shallow groundwater quality with reference to human health risk is presented in Section 6.

4.2.1 Historical Maxima

Historical maximum concentrations were reported for:



1,2-dichloroethane (EDC) (50.7 mg/L) at MWF15 (eastern portion of SCA) in the intermediate well. This is greater than the previous historical maximum reported in December 2007 (24 mg/L). The high concentration is likely due to two non-operational extraction wells along SCA (EWF25 and EWF28) which, it is noted, were recently replaced to improve performance. This data is trending towards a notable change in contamination distribution; however, further monitoring and future rounds post commissioning of the replacement extraction wells will determine if the concentrations at this location decrease as expected.



Tetrachloroethene (PCE) (0.189 mg/L) and trichloroethene (TCE) (6.82 mg/L) at MWF18 (Central SCA) in the deep well. These concentrations are greater than, but of a similar order of magnitude to, the previous historical maxima reported in September 2010 for PCE (0.187 mg/L) and in March 2020 for TCE (3.97 mg/L).



EDC (0.208 mg/L), chloroform (CFM) (0.006 mg/L) and PCE (0.001 mg/L) at MWF19 (western portion of the SCA) in the intermediate well. The concentration for EDC is greater than the previous historical maxima reported in September 2010 (0.063 mg/L). There have been no detected concentrations of CFM and PCE historically for this well. These concentrations are similar to those found in nearby extraction well EWF14 in the deep well and are not expected to represent a significant change in the contamination distribution.



EDC (0.002 mg/L) at WG262 (northern perimeter of Southlands) in the shallow well. Historically, there has been no detected concentration of EDC at this well. This is marginally above the limit of detection and is not considered to represent a significant change in contamination distribution.



PCE (0.161 mg/L) and TCE (3.34 mg/L) at BP117 (Penrhyn Estuary) from the 1.5 m port. These concentrations are greater than the previous historical maxima reported in March 2020 for PCE (0.03 mg/L) and in March 2012 for TCE (3.31 mg/L).



CFM (0.001 mg/L) at WG255 (eastern side of Nant Street, Southlands) in the shallow well. Historically there have been no concentrations of CFM detected in this well. This is not expected to represent a significant change in contamination distribution as this concentration is marginally above the limit of detection.

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19 No other historical maximum concentrations for the groundwater wells were reported during the September 2020 monitoring round.

The assessment of data trends for monitoring locations indicates that there have been a number of increases (including historical maxima) in contaminant concentrations. A parametric test will be used to identify

increasing/decreasing trends at sampling locations, major changes to plume and the detailed data assessment will be reported in the August 2021 biennial monitoring report (Golder, 2020b).

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20

5.0 PENRHYN ESTUARY AND SURFACE WATER MONITORING

5.1 Penrhyn Estuary Pore Water Monitoring

There are two bundle piezometers transects in Penrhyn Estuary, installed to monitor pore water quality. Transect A (BP42 and BP43) is located downgradient of the inferred axis of the Southern Plumes (Plumes S2/S3), while Transect B (BP64 and BP65) is located on the western arm of the estuary, downgradient of the Central EDC Plume (C1 Plume). The locations of the piezometers are shown on Figure 2.2.

The bundle piezometers in Transect A and Transect B were sampled in September 2020 at low tide as historical monitoring data have shown that CHC concentrations (when present) are consistently higher at low tide and therefore provide a more conservative assessment of pore-water quality within Penrhyn Estuary. Pore water samples were collected at the discharge interface (0.1 m) and at depths of 0.5 m and 2.0 m below the ground surface of the estuary within the intertidal zone.

The key finding of the baseline survey of the intertidal groundwater discharge zone in Penrhyn Estuary (URS, 2004a) was that concentrations within the terrestrial portion of the aquifer decreased by approximately one to two orders of magnitude at the discharge interface (0.1 m). A general trend of decreasing concentrations at all depths was evident in a seaward direction and concentrations were inferred to decrease towards the

discharge interface due to the presence of a seawater mixing zone. The mixing zone was clearly delineated by the electrical conductivity (EC) data, which also showed that “fresh” groundwater (<10,000 µS/cm) from the terrestrial aquifer did not directly discharge in the intertidal zone at Penrhyn Estuary. The EC of pore water samples at the seepage interface (0.1 m) has been generally greater than 40,000 µS/cm in each monitoring event.

While significant historical data have been collected through the GCP/GTP and surface water variability monitoring programs, conclusions drawn from concentration trends need to carefully consider factors that may influence the contaminant concentrations, including variations in tides and contaminant loads flowing into the estuary from surface water drains. In some instances, the concentration of volatile CHCs at the discharge interface suggest that discharge from Springvale and Floodvale Drains may have a more direct influence on Penrhyn Estuary surface water quality than groundwater discharge through the intertidal zone.

5.1.1 Volatile CHCs

All pore water samples were analysed for volatile CHCs and the results are presented in Table 4.3. Historical concentrations, detection limit variations, historical maxima, short-term (previous 4 years) and long-term trends are presented in Tables 5.1 to 5.5. All available historical data have been used in assessing historical trends, but only data since September 2016 are presented in the tables.

Key contaminant concentrations in samples collected from the discharge interface (0.1 m port) and from shallow pore water in Penrhyn Estuary were assessed against the ANZG (2018) Trigger Values. These data are presented in Table 4.3. Exceedances were recorded for:



VC at BP42 in 0.5 m sample port (0.428 mg/L) and in 2.0 m sample port (1.37 mg/L) compared with the ANZG (2018) Trigger Value of 0.1 mg/L.



TCE at BP42 in 2.0 m sample port (0.434 mg/L) compared with the ANZG (2018) Trigger Value of 0.33 mg/L).

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21

5.1.2 Discharge Interface Pore Water CHC Concentrations

Concentrations of volatile CHCs at the discharge interface (0.1 m port) are considered the most relevant in terms of assessing potential impacts to surface waters within Penrhyn Estuary.

As discussed above, the concentrations of the key contaminants reported in the September 2020 monitoring round are less than the ANZG (2018) Trigger Values for all the samples collected at the discharge interface (0.1 m port).

5.1.3 Comparison with Historical Pore Water Concentrations

In general, the September 2020 data are consistent with previous monitoring rounds with the concentrations of the chemicals of concern generally decreasing with decreasing depth towards the discharge interface. It is noted that CHC concentrations at BP42 have historically been highly variable and the recorded concentrations are lower than historical maximum concentrations reported prior to operation of the SCA.

No historical maximum concentrations for key contaminants were reported during the September 2020 monitoring round.

5.2 Surface Water Monitoring

Surface water samples were collected in Penrhyn Estuary at low tide as historical monitoring data have shown that CHC concentrations (when present) are consistently higher at low tide than at high tide and therefore provide a more conservative assessment of water quality within Penrhyn Estuary. Surface water samples were also collected from locations within Floodvale and Springvale Drains at locations upstream from Penrhyn Estuary.

Table 4.4 presents the volatile CHC analytical results for surface water samples and a comparison against the ANZG (2018) Trigger Values.

Key contaminant concentrations reported in the September 2020 monitoring round were less than the relevant ANZG (2018) Trigger Values at all locations.

5.2.1 Surface Water Variability and Comparison with Historical Data

Historical concentrations, detection limit variations, historical maxima and short-term (previous 1 year) and long-term trends are presented in Table 5.6 for EDC, VC, PCE, TCE, CFM, cis-1,2-DCE and CTC. All known available historical data have been used in assessing historical trends, but only data since March 2017 are presented in the tables.

The concentrations of volatile CHCs collected during the current monitoring round are summarised in Table 5.6 with comparison to historical maximum concentrations and long-term (all available historical data) and short-term (one year) averages. Green shading indicates a decreasing trend compared to the average, yellow shading indicates concentrations remain stable, while red shading indicates an increasing trend compared to the average.

The review of historical surface water monitoring data shows CHC concentrations have historically been highly variable between monitoring events. Despite the variability in reported concentrations, comparison of the September 2020 surface water data with historical data shows CHC concentrations in Springvale Drain and Floodvale Drain have generally been decreasing and have remained low. The decrease in CHC

concentrations within surface water is thought to be attributable to the operation of the hydraulic containment system, reducing groundwater levels and therefore shallow groundwater seepage.

The concentrations of VC at SW029 and SW030, and cis-1,2-DCE at SW029 (both located within Penrhyn Estuary), when compared to the long-term historical and the previous year’s average, have shown an

Groundwater Treatment Plant - September 2020 Annual Groundwater and Surface Water Monitoring Report