Homebush Bay shows degraded sites can be cleaned up

Homebush Bay, situated in the middle of Sydney opposite the site of the 2000 Sydney Olympic Games precinct, has been left heavily contaminated by decades of industrial activity, to an extent that there are bans on eating fish caught there and in nearby waterways because of the potential health risks.
However, a lengthy and ongoing remediation process is significantly improving the ecology in the Bay and making the area safe for human use again, according to Thiess Services’ manager of technical services John Hunt.
Homebush Bay and the adjacent prime residential land on the Rhodes Peninsula, were contaminated over several decades with a cocktail of organic contaminants, including persistent organic pollutants (POPs), such as DDT and dioxins. Over time the POPs have built up in the food chain so that fish caught in Homebush Bay are unsafe for human consumption and a fin-fishing ban is in place for the area.
Development stymied
“There has been a great desire to redevelop the former industrial site into a high value harbour side residential precinct. However cleaning up dioxins and pesticides in soil and sediment is a complex process and remediation of the land and the bay was considered too difficult for a decade or more,’’ Hunt said.
“In the early 1990s, everyone in the remediation industry, myself included, said it couldn’t be done. A decade later thermal soil treatment technologies had been developed to the point where we were able to tell people that it now could be done.”
Several remediation strategies were considered to clean up the POPs in the bay, including monitored natural attenuation, capping, and removal followed by either land filling or treatment. Removal and treatment was eventually selected given the persistent nature of the contaminants and their ability to migrate by natural processes in the marine environment.
The remediation method used by Thiess Services involves dredging the top half a metre of sediment from the bay and either thermally treating the sediment (removing the POPs entirely) or placing it, untreated, at a depth onshore, depending on contamination levels. A clean shale cap is then placed into the dredged area.
Dredging footprint
The dredging footprint is located parallel to the shoreline of the former Union Carbide and adjoining Allied Feeds sites. It was initially designed to ensure the reduction of POPs was sufficient enough to reduce contaminant transmission to a level where fish from the area would be safe to eat and new housing developments had a clean common area in front of them. “Following consultation with local residents it was later extended to remove additional contaminant hotspots further into the bay,” Hunt said.
Although it will require a period of monitoring before the fin fishing ban is removed, the bay will be safe for human contact and development of the neighbouring land has begun, Hunt said. The success of the remediation shows that polluted sites around Australia, that have previously been in the too hard basket, could be cleaned up with new technology, according to Hunt.
“This project has succeeded because the timing was right, the technology was ready and there was a large collaborative effort and will to succeed, involving environmental groups, the NSW government, residents and industry,” he said.
Clean up, recycle
“As Australia emphasises its focus on sustainability in the future, it will be important to remediate these sorts of contaminated sites in prime locations, as it’s better to clean up and recycle what we have, rather than further expand the footprint of our cities.
“The lesson from the successful restoration, is that polluted areas once deemed ‘unusable,’ should be re-examined as new technology evolves. This is the first significant remediation effort in Sydney harbour, and the works are already greatly benefiting the city. This shows that sites that have been badly contaminated in the past are not necessarily worthless.”
The CleanUp 09 conference was hosted by the CRC for Contamination Assessment and Remediation of the Environment in Adelaide from September 28 to 30.
More information: John Hunt, Thiess Services, 0419 617 148, Peter Martin, CRC CARE communication, 0429 779 228, Peter.martin@crccare.com