AN investigation into the use of toxic firefighting foams at the Gingin satellite airfield recommends further assessment of the use by site personnel of water from one bore.
The investigation also recommends consideration of the risk to the Gnangara underground water pollution control area from off-site migration of PFAS in groundwater.
The Gnangara groundwater areas cover about 2200sqkm in the northern part of Perth.
The area covers the groundwater resources of the Yanchep, Gnangara, Wanneroo, Swan, Mirrabooka, Gwelup and Perth groundwater areas and includes a portion of the Gingin groundwater area.
According to the Department of Water and Environmental Regulation the Gnangara groundwater areas consist of three main aquifers – the unconfined Superficial aquifer (commonly known as the Gnangara Mound), the deep, partly confined Leederville aquifer and the deep, mostly confined Yarragadee aquifer.
Minor aquifers include the Mirrabooka and Fractured Rock.
The Gnangara Mound includes part of the Gingin Brook and the Moore River in the Shire of Gingin and part of the Ellen Brook in the City of Swan.
A report presented to Gingin residents on July 25 said a human health risk assessment (HHRA) was recommended in order to further assess risks identified during the detailed site investigation (DSI) carried out by Jacobs Group for the Department of Defence.
The report said the HHRA should focus specifically on the use of groundwater from abstraction bore 2 by site personnel and should additionally consider the risk to the Gnangara underground water pollution control area from off-site migration of PFAS in groundwater.
Additional sampling may be required to assess the risk to human health through the national environment protection measures (NEPMs) NEPC, 2013 compliant HHRA process.
NEPMs are a special set of national objectives designed to assist in protecting or managing particular aspects of the environment provided for under the National Environment Protection Acts (NEPC Acts).
NEPMs can be made about a variety of environmental matters such as ambient air quality, ambient marine, estuarine and fresh water quality, general guidelines for the assessment of site contamination and the environmental impacts associated with hazardous wastes.
The report recommended an immediate commencement of the HHRA.
“A PFAS management area plan (PMAP) will be developed as part of this project and will outline options for managing any unacceptable risks that may be identified as part of the HHRA in relation to the use of shallow groundwater at the site,’’ the report said.
“The PMAP forms part of the scope of this project and will be completed within three months of this DSI being published and after the HHRA has been completed.
“In addition, the PMAP should also include a requirement that a specific assessment of risks to construction and maintenance workers should be undertaken prior to commencement of any future works in identified PFAS source areas.
“This assessment should also consider measures to ensure appropriate storage, handling and disposal of any PFAS impacted materials that may be encountered.’’
The report said the PMAP should include an ongoing monitoring plan in order to assess PFAS concentrations trends over time.
“The sampling will confirm the results of this DSI and assess variability inherent in laboratory methods, drilling methods, sampling processes or seasonal variability in groundwater conditions. “Groundwater sampling conducted to date has been limited to summer (low rainfall) conditions.
“Given that detectable concentrations of PFAS have been recorded at the site boundary (albeit below the investigation criteria) further sampling as part of an ongoing monitoring plan is considered prudent.
It also recommended relevant site management requirements, such as, the restriction of growing fruit and vegetables onsite and other maintenance requirements.
“For example, the integrity of the interceptor trap in the wash down bay should be assessed and the trap cleared to minimise the risk of sediment in the trap acting as on ongoing source of PFAS to surface soils/groundwater.
The report said concentrations of PFAS in the samples collected were compared to investigation criteria.
“These criteria were adopted from guideline values presented in the PFAS NEMP (HEPA, 2018).
“Where concentrations exceed these criteria, further assessment is required to understand whether there is an unacceptable risk to human health or the environment.
“PFAS concentrations in soil in the source areas do not present a human health risk to site personnel.
“However, the concentrations exceed the commercial-industrial (indirect exposure) investigation criteria for ecological protection.
“On this basis, risks to terrestrial ecology on site required further assessment.
“PFAS concentrations in the water supply to the site (derived from the central on-site abstraction bore) exceed the human health criteria for drinking water and recreational water use.’’
The DSI identified four primary sources of PFAS contamination at the site.
“This contamination is migrating in groundwater away from these source areas in a west south-west direction.
“The extent of contamination in groundwater wells exceeding the investigation criteria for drinking water is largely limited to the shallow aquifer in the central area of the site, in the vicinity of the former fuel farm, fire house, power house and firefighting equipment testing area.
“However, an abstraction bore is located in this area that is used to provide the site water supply.
“Samples collected from this bore, as well as taps located across the site contain concentrations of PFAS above the drinking water criteria.
“Some samples also reported concentrations above the criteria for the recreational use of water.
“While this water supply is not currently used for drinking, it is used for laundry, bathing, irrigation and other uses that may result in incidental ingestion by individuals that work at the site.
“Further away from the central area of the site, significant dilution-dispersion of PFAS in groundwater is apparent, one exceedance of the investigation criteria was reported – one shallow well on the southern boundary of the site.
“Additionally, detections for PFAS below investigation criteria were noted in three monitoring wells.
“Samples were collected from existing off-site monitoring wells to the west of the Site – no PFAS was detected in these samples.
“Based on the current understanding of PFAS concentrations in groundwater at the site, the existing groundwater monitoring network is considered adequate to delineate the extent of the potential on and off-site plume at concentrations exceeding drinking water guidelines.’’