Rail/road hub buries railways’ soil contamination sins

Containment on site is being achieved because of the expense and logistical challenges of moving the mostly arsenic contaminated soil elsewhere.
The site has been Victorian railways owned land almost since railways began in Victoria about a century and a half ago. So it is suspected that the contamination was caused by arsenic stored there, and used to kill weeds on rail lines around the state. Also, there are polycyclic aromatic hydrocarbons (PAH) in the soil on the site, as a result of decades of steam engine ash being dumped there too.
$5m operation
But the operation to have the soil rendered safe and ensconced out of harms way – there was no economic way of removing the arsenic - has been a massive and detailed $5m operation for EnviroPacific Services and its subcontractors.
The company, 40% owned by Newcastle, NSW based Daracon, won the tender from four or five short listed tenderers in March. Then EnviroPacific’s chemists, spent several months devising a chemical mix that would render the arsenic and PAH contaminated soil safe, despite it being totally contained.
Environmental engineer and Victoria/Tasmania manager for EnviroPacific Fred Lunsmann, told Earthmover the company had to verify the chemical mix would do the job of making the arsenic inactive. In turn it had to convince the EPA, the chemical fixation recipe, would for ever render the arsenic insoluble as iron arsenate, he said.
Controlled pH
At the same time the treated soil had to fall within a 6.5 to 8pH band, so it would not risk degrading the quite substantial layers of geofabrics, between the earth and the soil at the bottom of the bunker. But with eight layers of various geofabrics isolating the contaminated soil from the water table, there would seem to be little risk of the treated arsenic migrating.
EnviroPacific started work on the site in May by removing old sleepers, various huts and other debris, as well as about 1m of fill that had accumulated largely from deposited steam engine firebox ash.
Then it removed about 2m of Western Plains clay, and dug down to the basalt bedrock to gain enough clay to initially seal the bunker base, Lunsmann said.
In fact they only gained about 50% of the clay fill they needed and had to import the rest. It was compacted using hired Coates rollers before pre cast concrete panels were installed and propped around the perimeter. Then extra clay was laid to form an internal wall against the concrete on which the bunker’s protective layers could be installed.
Six week’s lining work
Starting at the northern end, the first of the eight layers was laid. Overall subcontractor V Lining Victoria, estimated it needed six weeks just to install the eight layers. The first is an 8mm thick geosynthetic clay liner (GCL) geotextile sandwiching a bentonite mixture and offers equivalency to very thick layers of compacted clay. Lunsmann said if a Star picket was driven through it and removed, it had the ability to “self heal”, thanks to the bentonite.
The next layer is a 2mm thick HDPE followed by a 5mm thick geonet drainage mesh. They are topped by another GCL, another 2mm thick high density polyethylene (HDPE) layer and another geonet layer.
At every stage, Golder Associates p/l, Hawthorn, has been observing and testing EnviroPacific’s work. All HDPE layers have been welded twice. Then to test the welds, air is pumped between the welds and leaks looked for. As well, welded sections are periodically cut out and tested offsite.
Once the eight layers are in place across the site, Golder Associates and the EPA will spend two weeks auditing their installation before earth is carefully placed within the bunker’s retaining walls.
Then soil will be compacted to the level of the retaining walls to end EnviroPacfic’s contract about next February. Above that will be 200mm of concrete tied to the concrete retaining walls, to form the floor of the warehouse.

Dumping not an option
Because the arsenic in the Spotswood soil measured about 5000mg/kg, it was close to the EPA’s category B limit which meant it had to be cleaned up or sent to landfill.
The trouble was that there were only two landfill sites available and they could not handle that volume of contaminated material. If they could, they would have charged $600 to $1000 a cubic metre, depending on the amount of arsenic.
At the same time, according to EnviroPacific’s Fred Lunsmann, there is a push by the EPA to have contaminated soil treated and retained safely on site. And by 2020, the EPA aims to have no hazardous waste going to landfill.
The machine used to treat the soil with the custom made chemicals was a portable, tracked Hitachi pug mill. Easily trucked and moved under its own power on site, it was moved to the soil on the 3ha site rather than have the soil brought to it.
Five air monitors around the site keep tabs on air quality. They operate at predetermined times and periodically their filters are extracted and taken off site to be examined for content. But Lunsmann says base levels of air contaminants are fairly high in the area anyway and excursions due to EnviroPacific’s activities have not been evident.