The Mandatory Auditor’s Report (MAR) – Groundwater and Landfill Gas
Background
Prior to the commencement of landfilling on the site, MRC initiated groundwater monitoring activities on a bi-annual basis. This was due to the natural hydrology of the Tamala Park Waste Facility site where the normal movement of groundwater through the site was from east to west, and at a very slow rate.
The construction of MRC’s Tamala Park landfill contains a combination of lined and unlined cells, as approved by the DWER at their respective times of construction. The oldest cell, known as Stage 1, was an unlined cell that was filled with Class II Putrescible waste between 1991 and 2004 and prior to capping, contained approximately 3,151,680 tonnes of waste. MRC suspects this unlined cell to be the primary source of landfill gas and groundwater contamination due to the nature of the cell’s design.
In 2007, elevated concentrations of contaminants of concern were identified in groundwater samples and were subsequently registered with the DWER Contaminated Sites Branch (CSB) in accordance with the Contaminated Sites Act 2003 and the site was reclassified as ‘Possibly Contaminated – Investigation Required’. Since this time, the results of groundwater and landfill gas monitoring have continued to be reported to the CSB on an annual basis
Following this classification, MRC commissioned several additional reports to obtain a better understanding of the movement of groundwater and landfill gas on, and outside, the Tamala Park site. This modelling identified a suspected ‘plume’ of groundwater moving offsite in a northward / north-easterly direction. This represented a material change from the historical westward flow towards the Indian Ocean.
Subsequent updates to these initial reports have continued to monitor and model this plume to account for seasonal variability and patterns over time. This has been assisted by the groundwater monitoring intervals moving from bi-annual to quarterly.
As a consequence of the complexity of the site, the CSB required that a MAR be undertaken to assist in understanding the site and the groundwater plume potential. MRC was required to appoint an accredited contaminated sites auditor approved by the DWER to prepare a MAR by February 2020.
The MAR includes a review of several scientific reports commissioned by MRC dating back to 2014. These reports specifically focus on the impacts on groundwater quality and landfill gas migration, both on and offsite, as they pertain to landfill operations.
As cited in the Report, the overall purpose of the audit is to:
- Confirm that the investigations undertaken adequately characterise the contamination status of the site.
- Confirm the suitability of the site for the current and proposed land uses.
- Confirm whether potentially significant risks to human health, the environment or environmental values exist onsite or offsite.
- Recommend a site classification and/or memorial on Certificates of Title as considered appropriate under the Contaminated Sites Act 2003 (CS Act).
Detail
The MAR was commissioned in March 2019. Significant time was spent over the 2019 year, updating the conceptual site models, and undertaking landfill soil vapour testing and further groundwater investigations to assist in the MAR findings and recommendations.
The report in itself is not an additional scientific report, but rather an independent review by an accredited CSB auditor of 12 independent, third party reports dating back to 2014. These reports commissioned by MRC focus specifically on the impacts on groundwater quality and, to a lesser extent, landfill gas migration, as they pertain to landfill operations, both on and offsite.
Groundwater
The Report notes that groundwater impacts from landfill activities are currently evident in the aquifer immediately beneath the landfill at concentrations above the relevant DWER irrigation or drinking water guidelines.
Further testing and analysis is still required to understand the full extent of the offsite impact on potential groundwater contamination.
MRC has tested, and will continue to test, groundwater abstracted on site in support of operational activities. Based on this testing, that there is no immediate health risk presented to staff or the public under current conditions of groundwater use at Tamala Park, based on the controls in place.
MRC also tests seven groundwater monitoring wells to the north of the Tamala Park site. The presence of ammonia in groundwater, while not of concern itself, is typically a useful marker to identify groundwater movements, based on its solubility in water.
MRC runs a suite of tests on each of these wells to identify potential contaminants, including heavy metals, hydro carbons and emerging contaminants of concern such as the PFAS family.
While some of these potential contaminants are present in some of the test results some of the time, they tend to be at or only marginally above the current drinking water guidelines, and well below the levels set for recreational use or irrigation. Where these contaminants are detected, they are commonly found a depth of greater than 27M below ground level.
Based on the fact that the houses surrounding the Tamala Park site are on scheme water, it is reasonable to expect that there is little to no risk to human health from the consumption of groundwater for drinking water purposes.
Specific observations from the summary of the MAR are shown below.
Tamala Park Site
Groundwater impacts which are evident in the aquifer immediately beneath the landfill and which are elevated at concentrations above the relevant DWER irrigation or drinking water guidelines, comprise: BTEX, TPH, Arsenic and nickel, Nitrogen (as ammonia), and PFAS.
Area to the north
Concentrations of arsenic above DWER drinking water guidelines with concentrations of PFAS detected, including PFHxS, above drinking water guidelines specified in HEPA (2018).
Some of the above such as arsenic, nickel and nitrogen occur naturally in the environment.
In respect of both sites, the key MAR recommendation is that “Further works are required to determine the magnitude and extent of contamination including risks to human health, the environment and environmental values.”
Landfill gas
Landfill gas has also been identified outside of individual landfill cells, however, it is currently contained within the Tamala Park site boundary as required by DWER licence conditions.
MRC maintains a working relationship with the onsite landfill gas power generation contractor, Energy Developments Limited (EDL), in order to ensure adequate landfill gas extraction measures are maintained to prevent offsite gas migration.
Recommendations arising from the MAR and MRC’s response to them
Restrictions
Based on the conclusions above, the following recommendations are made:
Prohibit further encroachment of development surrounding the site, and specifically to the north.
MRC response:
MRC has had ongoing discussions with the CRC over the past number years regarding restricting development in the buffer zone
Groundwater should not be abstracted for drinking purposes without appropriate treatment and testing to confirm its suitability.
MRC response:
MRC is not aware of any domestic abstraction for drinking water either on the Tamala Park site or in the residential development immediately north of the Tamala Park site.
MRC has had ongoing discussion with the Water Corporation over the past number of years regarding the potential impacts on their Q40 abstraction bore to the northeast of the Tamala Park site, and they have been provided with MRC’s testing data and have been provided a copy of the MAR. Water Corporation has undertaken regular testing of Q40 and to date, has not detected PFAS compounds or hydrocarbons (BTEX, TPH). Recent testing in March 2020 of Q40 indicated that all other concentrations of contaminants of concern (ammonia, arsenic, nickel), including PFAS compounds were below the drinking water guidelines. Water Corporation continues to monitor Q40 regularly.
Continue to implement management controls requiring the use of PPE on-site to mitigate exposure to soil and groundwater contamination and landfill gas.
MRC response:
MRC has various controls in place in this regard, which will continue.
Continue monitoring landfill gas and groundwater.
MRC response:
MRC’s testing regime will be continued and enhanced in line with the recommendations of the MAR.
Further works
Based on the conclusions above, the following recommendations are made:
Immediately inform bore users downgradient of the site (including Catalina Development bores and Water Corporation) of the potential for contamination and conduct further assessment to determine if contaminants are present in groundwater as a priority.
MRC response:
MRC is not aware of any domestic abstraction for drinking water either on the Tamala Park site or in the residential development immediately north of the Tamala Park site.
MRC has had ongoing discussion with the Water Corporation over the past number of years about the potential impacts on their Q40 abstraction bore to the northeast of the Tamala Park site, and they have been provided with MRC’s testing data and a copy of the MAR. Water Corporation has undertaken regular testing of Q40 and to date, has not detected PFAS compounds or hydrocarbons (BTEX, TPH). Recent testing in March 2020 of Q40 indicated that all other concentrations of contaminants of concern (ammonia, arsenic, nickel), including PFAS compounds were below the drinking water guidelines. Water Corporation will continue to monitor the water quality within Q40 regularly. Water Corporation undertakes routine monitoring on all its drinking water to verify the quality and safety of drinking water supplied to its customers. Water Corporation is committed to providing safe, high quality drinking water that consistently meets 100 per cent of the water quality health standards set by the Department of Health based on the Australian Drinking Water Guidelines.
MRC has had ongoing discussion with the TPRC over the past number of years about the potential impacts on their three production bores north of the Tamala Park site, and they have been provided with MRC’s testing data and a copy of the MAR.
Prepare a suitable site management (SMP) to monitor and mitigate landfill gas and groundwater migration. The SMP should consider the following:
- A robust sampling and analysis quality plan (SAQP) in accordance with current, relevant guidelines and standards published guidelines
- Establishment of appropriate data quality objectives (DQOs)
- Installation of additional sampling locations on and off-site to vertically and laterally delineate the extent of contamination
- Use of appropriate sampling methodology including incorporation of gas flow and pressure for landfill gas sampling and low flow sampling techniques for purging and sampling groundwater
- Comparison of data to applicable guidelines for risk based decision making
- A community consultation plan
- MRC response:
MRC has engaged a suitable consultant to assist with the preparation of a Site Management Plan, including the Sampling and Analysis Quality Plan. This will outline what further work is required to assist in understanding the impacts.
MRC has also engaged a consultant to assist with the formulation of a community consultation plan.
Once results of further assessment are available, development of Remediation Action Plan (RAP) to mitigate any identified risks and further refinement of the SMP for ongoing assessment.
MRC response:
To be actioned in due course.
Consultation
- MRC has over the past years continued to consult with a primary stakeholder group, including:
- The owners of the Tamala Park site - Briefings have been given to MRC councillors, member council CEOs and the Strategic Working Group
- Catalina Regional Council - The CEO of the CRC has been kept appraised of MRC’s testing results and discussions with other stakeholders
- Contaminated Sites Branch - The CSB has been kept fully appraised of MRC’s testing results and have been supportive of MRC’s approach to dealing with the matter
- Water Corporation - The Water Corporation has been kept fully appraised of MRC’s testing results
Frequently Asked Questions
Is there a public health risk, particularly for households with bores in surrounding suburbs?
There is no health risk to the public as all surrounding suburbs obtain their drinking water directly from the Water Corporation. Based on current test results there is also no health risk to anyone using bore water in the area. Typically household bores draw water from depths above the deeper aquifers where contamination from the landfill may exist.
Is there a public health risk for water extracted at the Neerabup bore?
There is no health risk from water being supplied by the Water Corporation as their water is subject to rigorous testing and monitoring
To what extent have substances leaching from the first stage of landfill contaminated groundwater?
As per the external report, groundwater in the proximity of the first stage of landfill, has a level of contamination present and should not be consumed without it first being tested.
MRC runs a suite of tests on each of its monitoring wells to identify potential contaminants. Where these contaminants are detected, they at concentrations well below the levels set for recreational use or irrigation.
What mitigation has or can be done to reduce contamination or prevent it spreading further?
The recommendation from the external auditor is that further testing be undertaken over the next year, which will better inform what steps – if any – need to be taken. No remediation recommendations were made.
Does MRC test groundwater beyond the landfill site and buffer zone? If not, who is responsible for testing in surrounding areas?
MRC has a number of test wells around its property which extend beyond the landfill itself. In addition, a number of bores in the Tamala Park Regional Council’s buffer zone are monitored, along with a number of other wells in the Catalina Estate. The Water Corporation also conducts its tests on its own wells.
What is the buffer zone?
The buffer zone is a parcel of land that separates the landfill activity from the residential development. MRC uses this land to ensure its impacts are kept within the landfill boundary, hence the monitoring that takes place in this zone. Please note that this buffer zone is not contaminated in any way.
