Botany Groundwater Strategy Review

Page Content:

• Background
• Improving understanding of the scale of contamination
• Consulting international industry expert
• Outcome of Groundwater Strategy Review
• Dr Kueper's webcast: DNAPL Behaviour new

Background
Since the establishment of the Botany Groundwater Cleanup Project, Orica’s cleanup strategy has been driven by the Notice of Clean Up Action (NCUA) and the Groundwater Cleanup Plan produced by Orica in response to the NCUA.

During late 2007 and 2008 Orica conducted a fundamental review of the cleanup strategy for the project. The review considered the project’s achievements under the NCUA, the status of the Dense Non-Aqueous Phase Liquid (DNAPL) source area investigation and depletion projects, and the need for a revision of the regulatory framework for the project by the Department of Environment and Climate Change* (DECC, now the Department of Environment, Climate Change and Water – DECCW).

Orica conducted laboratory trials and had begun to assess and plan field trials for the shortlisted available and emerging DNAPL remediation technologies in early 2007. At that time it became apparent that there was a need to consider what the potential outcomes of the trials and their subsequent full-scale implementation, if successful, would mean in terms of the duration, costs and scale of the Botany Groundwater Cleanup Project. This required input from leading international experts on DNAPL remediation and the completion of further studies to improve understanding of the groundwater contamination issues at Botany.

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*DECCW reviewed the regulatory framework for the project during late 2008 to early 2009 and decided in July 2009 to regulate it under a Voluntary Management Proposal under the amended Contaminated Land Management Act.

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Improving Understanding of the Scale of Contamination
In order to understand the scale of groundwater contamination issues at Botany, Orica completed the following studies prior to the Botany Groundwater Strategy Review:

• Development of a Conceptual Site Model to consolidate the knowledge of the origins, characteristics, locations and impacts of the contamination associated with historical operations at Botany Industrial Park (BIP)  >> skip to section
• Estimation of contaminant mass in the aquifer >> skip to section
• Prediction of potential cleanup duration under various remediation scenarios >> skip to section

Consolidating Knowledge on the Botany Groundwater Cleanup Issue
A conceptual site model report was compiled to produce a single document that would consolidate the enormous quantity of data, reports and other interpretative information that have been progressively developed for the Botany Groundwater Cleanup Project since 1989. The Conceptual Site Model Report contains information on:

• The area’s geology, hydrology and hydrogeology
• Contaminants in groundwater, soil, sediments, surface water, air and biota
• Risk assessments of human health and the environment
• Current remediation strategies
• Modelling on DNAPL sources, DNAPL release and transport mechanisms (refer to figure below)
• Modelling on transport, transformation and reduction of contaminants

The document will be reviewed periodically to incorporate new findings and developments.

Estimating Contaminant Mass
An estimation of the contaminant mass in all phases (dissolved phase, sorbed phase and free phase [DNAPL]) was conducted using a simplified approach that focused on the most prevalent volatile chlorinated hydrocarbons (CHCs). These are:

• Ethylene dichloride (EDC);
• Vinyl chloride (VC);
• Perchloroethylene (PCE);
• Carbon tetrachloride (CTC);
• Trichloroethene (TCE); and
• Chloroform (CFM).

The total estimated contaminant mass ranged between 9,600 and 19,400 tonnes, with 14,500 tonnes being considered the best approximation of contaminant quantities in each phase.^# The breakdown of the different phases was 1,500 tonnes for dissolved phase, 3,000 tonnes for sorbed phase and 10,000 tonnes for DNAPL, or free-phase. The indicative composition of each of these phases is illustrated below.

The estimated total contaminant mass of 14,500 tonnes amounts to approximately 1.5 two-hundred-litre drums of DNAPL lost daily to the subsurface over the 55 years that the various CHC production facilities operated at the BIP. Hundreds of drums of CHCs were manufactured daily during this period.

The Groundwater Treatment Plant (GTP) has been successfully removing and destroying CHCs from the extracted groundwater since it commenced operating. An updated figure for the mass of CHCs destroyed at the GTP is provided in each quarterly progress report. The mass of contamination removed from the aquifer to date is, however, a small portion of the total, and the rate of contaminant removal will slow down as the concentrations gradually decrease (i.e., it can be expected that, as around 700 tonnes of CHCs were removed and destroyed in the first five years of its operation, that the GTP will have removed and destroyed twenty times the mass of CHCs – about 14,500 tonnes – in twenty times that duration – about 100 years).
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^# It is important to note that the estimated total contaminant mass is only an approximated value to provide a qualitative indication to the scale of the Botany Groundwater Cleanup Project. It cannot be relied on solely without giving consideration to this and other studies done.

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Predicting the Cleanup Duration under Different Remediation Scenarios
A solute transport model assists in understanding how the contaminants behave and move below ground and in groundwater. A numerical (computer-based) model was constructed to predict the aquifer response to different remediation scenarios and to provide insight into the duration of the cleanup under these scenarios. As with estimating the contaminant mass, the model focussed on selected representatives of CHCs (ethylene dichloride [EDC] and carbon tetrachloride [CTC]). The model was calibrated (checked) by modelling the distribution of the contaminants from the time of their release up to the present day. The numerical results were then checked against actual measured groundwater concentration data to verify the assumptions and parameters used in the model.

EDC was selected because it is a CHC that is widespread in the aquifer, has high solubility and is relatively mobile (i.e., it does not tend to sorb, or stick, onto soil particles readily). On the other hand, CTC is also reasonably widespread in the aquifer but has low solubility and is relatively immobile (i.e., it sorbs onto soil particle surfaces readily).

Once the model was verified, it was then used to predict the movement of the contaminants under a number of remediation scenarios. The groundwater remediation scenarios that were considered were:

• Existing ‘pump & treat’ (current project’s situation)
• Existing ‘pump & treat’ + biological barrier on Southlands Block 2
• Existing ‘pump & treat’ + biological barrier + reactive iron barrier on Southlands
• Existing ‘pump & treat’ + additional extraction wells between Southlands and Foreshore Road
• Existing ‘pump & treat’ + biological barrier + reactive iron barrier on Southlands + additional extraction wells between Southlands and Foreshore Road
• Biological barriers + reactive iron barriers on Southlands and Botany Golf Course (no extraction well field)

The model was also used to evaluate the effect of removing all or part of the DNAPL source areas (assuming that there would be treatment technologies that could achieve this).

The DNAPL source treatment scenarios that were considered were:

• No treatment, with an infinite source (i.e., the DNAPL was never depleted, even by slowly dissolving into the groundwater)
• No treatment, with a finite source, which is exhausted by dissolving into passing groundwater (current project’s situation)
• Treatment to reduce initial DNAPL source concentrations by 25%, 50% and 90%
• Treatment to reduce the time it takes for groundwater to completely dissolve DNAPL source by passing through it (or, complete dissolution) by 25%, 50% and 90%

The modelling showed that the EDC source mass is predicted to exhaust itself by 2016 by dissolving into the passing groundwater, or dissolution (i.e. without treatment), and the concentration of EDC anywhere in the aquifer will be 0.1 mg/L by 2055 under all scenarios, including no source treatment (refer to figure below).⁺

On the other hand, even though the model predicted complete dissolution of CTC source mass by 2060 (i.e., without source treatment), it showed it would take at least 300 years for the aquifer to achieve a CTC concentration of 0.1 mg/L everywhere under the existing ‘pump & treat’ scenario, and approximately 200 years under the scenario where highly effective passive barriers (biological and reactive iron barriers) are installed with no groundwater extraction (refer to figure below).⁺

Although not modelled, perchloroethylene (PCE, also known as tetrachloroethene) was determined to potentially be the time-limiting volatile contaminant for the cleanup at the Botany aquifer due to its estimated mass in the aquifer (2.5 times that of CTC), its lower solubility than CTC (by approximately 70%) and its likeliness to sorb to soil (50% more than CTC).

The modelling also showed that although DNAPL source treatment reduces overall CHC concentrations in groundwater plumes, it does not significantly reduce the duration of the overall cleanup.
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⁺ It is important to note that the estimated duration of the overall cleanup is only an indicative figure to provide a qualitative picture of the scale of the Botany Groundwater Cleanup Project. It cannot be relied on solely without giving consideration to this and other studies done.
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Consulting International Industry Experts
A Botany Groundwater Strategy Review Workshop was conducted at Botany on 11 to 13 December 2007 involving ten industry experts. The objectives for the workshop were:

• A comprehensive independent review of the remediation strategy adopted prior to the review
• An improved understanding of the DNAPL source area remediation issues:
• Practical extent of DNAPL source area depletion in the Botany geological and site setting with current likely technologies
• Possible significant new and more cost-effective DNAPL depletion technologies
• Drivers for DNAPL depletion other than reduced cleanup duration and costs
• Whether DNAPL source area depletion makes sense if risks are well managed
• Other remediation technologies or strategies that might better address DNAPL, sorbed mass and dissolved phase mass more cost effectively than the remediation strategy used up until the review
• Produce a shortlist of alternative integrated remediation strategies for further evaluation

Workshop Outcomes

Workshop Follow-Up Action: Full-scale Source Area Remediation Evaluation
One of the outcomes from the workshop was that Orica should conduct an evaluation of full-scale source area remediation with DTT and ISCO treatment methods prior to undertaking any field trials to understand their implications. Relevant case studies of application of both DTT and ISCO were reviewed, and conceptual designs and cost estimates for full-scale applications at Botany were developed considering limitations/advantages of their application in the Botany context.

The evaluation demonstrated that DNAPL source depletion would provide limited benefit for the Botany Groundwater Cleanup Project. Although DTT would be technically viable to remove DNAPL, significant mass would remain in the aquifer (as residual DNAPL, sorbed CHCs and semi-volatile CHCs) after its application at Botany, resulting in limited impact to the duration of GTP operations.

Outcome of Botany Groundwater Strategy Review
The review guided Orica to propose the following modified cleanup strategy for future management of the Botany groundwater contamination. This proposal has been submitted to the DECCW for its consideration.

• Ongoing management of groundwater contamination to ensure risks to human health and environmental receptor areas are acceptable. This would be achieved through extensive ongoing monitoring of the relevant segments of the environment potentially impacted by contaminated groundwater
• Ongoing optimisation of the operation of the hydraulic containment lines and the GTP for protection of critical human health and environmental exposures and for gradual cleanup of the contamination, where containment lines are downgradient of source areas
• Improvements to the hydraulic containment system to further reduce impacts on Springvale Drain and Penrhyn Estuary/Botany Bay. The latter would be achieved by implementing the proposed Groundwater Injection & Recovery (GIR) System as a contingency for a major outage of the GTP
• Ongoing review of developments in remediation technologies and techniques for DNAPL, sorbed mass and dissolved phase treatment and their practical applicability at Botany

Community Workshop on the Botany Groundwater Strategy Review
Following discussion at Community Liaison Committee (CLC) meetings in late 2008, Orica held a community workshop on 31 March 2009 on the Botany Groundwater Strategy Review. A key industry expert, Dr Bernie Kueper from Queen’s University in Canada, who was one of the participants at the Botany Groundwater Strategy Review Workshop in December 2007, provided a presentation to the participants about the characteristics of DNAPL, the development of DNAPL remediation technologies to date, the difficulties associated with remediating DNAPL source areas, and how DNAPL behaves in the Botany aquifer.

Dr Kueper stated that the GTP’s hydraulic containment network is the largest groundwater extraction system in the Southern Hemisphere. He reported that no site contaminated with DNAPL in the world has been remediated to drinking water quality standards, and that no DNAPL source has been fully removed at any site in the world. Dr Kueper’s recommendations to Orica included continuing ‘pump & treat’ and the environmental monitoring program. A webcast of his presentation is available below. Other presentations given at the workshop are available here.

Dr Bernie Kueper - Webcast: DNAPL Behaviour

Disclaimer: This video is based on a presentation that was made to the Botany community at the community workshop held in March 2009. The video may be streamed or downloaded for personal viewing only. No part of this presentation may be reproduced without the prior permission of Dr B. H. Kueper, Queen's University, Kingston, Ontario, Canada (bkueper@cogeco.ca).