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PFAS Investigation &
Management Program

RAAF Base Williamtown

Lake Cochran Water Treatment Plant

Defence is undertaking a range of management activities across the country. Visist the management activities page to see our other initiatives.

Background

Figure 1: Treatment Process - Lake Cochran Water Treatment Plant (click to expand)

Lake Cochran has been identified as containing elevated concentrations of per- and poly-fluoroalkyl substances (PFAS). These elevated concentrations are consistent with Lake Cochran being a collection point for contaminated surface water from across the RAAF Base Williamtown. Defence’s objective is to reduce PFAS contamination where possible, including within Lake Cochran.

The Lake Cochran Water Treatment Plant (WTP) was developed by Synergy Resource Management. The WTP is an interim measure to treat water leaving Lake Cochran. It will operate for up to 12 months while Defence continues to identify and investigate long-term management options for Lake Cochran.

The WTP is treating the water leaving Lake Cochran to ensure that PFAS concentrations are below the limits of the relevant adopted drinking water screening criteria.

The WTP consists of two separate systems that run in parallel. This provides the ability to process flow rates ranging from 15 to 70 litres per second and allows uninterrupted operation during maintenance activities.

The WTP combines various water treatment techniques consecutively to create a multi-barrier treatment process. Each of these techniques have been individually proven to reduce PFAS concentrations. However by combining the techniques, the Lake Cochran WTP is able to reduce PFAS concentrations to below the levels of the adopted screening criteria.



The Treatment Process

Phase One

Is designed to remove a significant amount of PFAS from the water prior to moving to phase two. Phase one consists of three stages:

Stage 1: A proprietary Powdered Activated Carbon (PAC) is added as a pre-treatment, removing PFAS from the untreated water through a process called adsorption. This means the PAC gathers the PFAS on its surface in a condensed layer. The PAC also removes organic matter and, reduces turbidity.

Stage 2: This stage includes the addition of three reagents , coagulation, flocculation and pH adjustment. A reagent is a substance added to a system to cause a chemical reaction. These reagents are used in combination to increase the effectiveness of the treatment process and to assist in the removal of contaminated particles.

Stage 3: During this settlement stage, the PFAS (which has been adsorbed by the PAC particles) reacts with the recently added coagulants and flocculants to bond together to form larger/heavier particles that drop out of suspension under certain pH conditions. The settled particles form a waste product called sludge that collects at the bottom of the settlement tanks.
To minimise volumes of waste sludge, it is periodically removed from the tanks and de-watered. The waste water is reprocessed into the WTP. The remaining solids are sampled and classified in accordance with NSW Environment Protection Authority waste classification guidelines for offsite disposal to an appropriately licenced facility, where possible. If the solids do not meet the relevant criteria for offsite disposal, they are retained onsite for further treatment in the future.

Phase Two

Consists of a series of deep-bed media filters where further particulates are removed from the water via mechanical filtration. Phase two consists of four stages:

Stage 1: Water is passed through a series of deep-bed media filters containing a proprietary gravel medium blend.

Stage 2: Water is passed though a series of deep-bed media filters containing a proprietary sand media blend.

Stage 3: Water is passed though a series of deep-bed media filters containing a proprietary Anion Exchange Resin (AIX). The AIX used has a unique PFAS holding capacity and has been manufactured and activated specifically to remove a variety of PFAS. The PFAS-saturated AIX is regenerated, enabling its re-use in the WTP.

Stage 4: The final stage is a precautionary measure to capture any remaining PFAS which may have passed through the previous stages due to adverse conditions. The water is passed through a series of deep-bed media filters containing a proprietary Granulated Activated Carbon (GAC) blend.
Throughout the filtration phase, the pH levels are adjusted to ensure the water is within an optimum pH range for each media type. Prior to the fully treated water being either discharged to Dawsons Drain or returned back to Lake Cochran, the pH level is again adjusted to suit the receiving environment.

Water Sampling Summaries

The Water Sampling Summaries track the PFAS concentrations against the limits defined by the relevant adopted drinking water screening criteria. They include results for perfluorooctanoic acid (PFOA), 6:2 fluorotelomer sulfonic acid (6:2 FTS) and the sum of perfluorooctane sulfonic acid (PFOS) and perfluorohexane sulfonic acid (PFHxS).

The water quality data is drawn from water samples on both untreated and treated water from Lake Cochran. The summaries of water sampling results can be downloaded below.


The initial report was a summary of the results from 30 November 2016 until 9 March 2017.