Gasworks points to innovation

IN situ solidification (ISS) demonstrated its potential when used at a former gasworks in Albury, New South Wales, despite its limited application in Australia, writes AECOM’s Paul Carstairs and Clayton Cowper.
Gasworks points to innovation Gasworks points to innovation Gasworks points to innovation Gasworks points to innovation Gasworks points to innovation

Gasworks at Albury, NSW

Staff Reporter

The former operation of the gasworks between 1883 and 1968 resulted in soil and groundwater contamination. The legacy contamination was predominantly caused by storage and handling of coal tar, a byproduct of the former gas manufacturing process.

Coal tar is a dense-non aqueous phase liquid (DNAPL) which will sink below the water table. At the Albury site, where groundwater is present about two to three metres below the site’s surface, coal tar had migrated to a maximum depth of about 11m.

Primarily due to the coal tar acting as a source of groundwater pollution and related risks that it could present, the NSW Environment Protection Authority issued a declaration of remediation site notice in relation to the site, which is now used as a public car park.

Complicating the situation was the fact that the original polluter no longer owned the site, it had been sold to the local council about 25 years earlier.

However, the former owner of the site voluntarily entered into an agreement with EPA to address legacy contamination issues.

Selection of a remediation approach was based upon addressing DNAPL to stop continuing contamination to groundwater.

This approach aimed to improve groundwater quality while reducing potential risks associated with future on-site and surrounding land use, leading to the subsequent withdrawal of the declaration notice.

Further, the remediation method had to take into consideration logistical limitations in addressing contamination at depth, and the site being 500m from the city centre, in an area surrounded by commercial and residential properties. Of particular consideration was a primary school to the east of the site.

Sustainable success

The ISS technology involves the construction of interlocked vertical piles using cement as a base, with the addition of other pozzolanic agents in order to construct a relatively impermeable solidified monolith.

Coal tar and tar-impacted soil are bound up within the solidified monolith, with the objective of reducing ongoing impacts to surrounding groundwater.

While the ISS technology has had very limited application in Australia, it has been used extensively in North America, particularly at former gasworks sites.

The AECOM team was able to call upon US colleagues to provide input into a bench scale trial, which was subsequently scaled up to a successful pilot trial at Albury.

Data from the bench and pilot scale trials was used to detail the ISS approach in a remediation action plan (RAP). Through submission of the RAP and ongoing consultation, AECOM was able to provide the EPA with the confidence it possessed the necessary skills and experience to implement the ISS technology locally.

Implementation of ISS, which involved the construction of about 700 interlocked columns to a maximum depth of 12m, was successfully completed by AECOM at the site in 2013.

Ongoing monitoring since the completion of ISS works has reported reductions of contaminants of concern in both groundwater and soil vapor at the majority of sampling locations, and it is expected that the declaration notice will be removed from the site in 2015.

The ISS technology used by AECOM enabled a sustainable on-site approach when compared to other energy or resource-intensive remedial options. It also enabled greater control of odor and other environmental emissions compared to alternative remedial options, in addition to minimising off-site truck movements.

While a small number of enquiries from the community were made during the project, no formal complaints were received, likely the result of an extensive community and stakeholder consultation program which began a year before the ISS works.

The acceptance of the ISS technology by the NSW EPA and its success to date has created an important precedent in the Australian remediation landscape as many similar projects have not progressed due to the lack of a proven and cost effective remedial solution.

Paul Carstairs is a technical director – environment, working in AECOM’s Melbourne office. Clayton Cowper is a principal – environment, working in AECOM’s Sydney office.

This article was first published in affiliated publication WME Magazine.