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Race Against Time

Soil washing is set to divert 75,000m3 of material from landfill on the highly contaminated Athlete’s Village site for the Glasgow Commonwealth Games. But work must be completed in a year. Gemma Goldfingle reports.

With work ticking along nicely on the London 2012 site, attention is turning to Glasgow and the UK’s next Olympic-sized project.

What is now a 32ha industrial area in Dalmarnock in the deprived east end of Glasgow is to be transformed, first into the Athlete’s Village on the site and, post-Games, into a 1,500-strong housing development by the riverside.

The project is one of the biggest urban renewal projects in Glasgow’s history.

Glasgow City Council is committed to delivering a low-carbon Commonwealth Games so sustainability is at the heart of the Athlete’s Village construction.

But with 35 types of contamination on site and only a year to deal with it, this is no mean feat.

Dalmarnock has housed many industrial facilities over the past century, from power stations to water works.

The scars of the site’s industrial past are buried deep within the derelict land that remains.

The council has appointed consultant Grontmij and contractor VHE to heal these scars.

“Metals, arsenic, lead, hydrocarbons, pesticides - we’ve got them all,” says Grontmij principal consultant Iain Hall.

The residue of the power station that used to grace the site made the bulk of the contamination, with a significant level of PAHs (polycyclic aromatic hydrocarbons) and slag material with elevated pH values.

Drawing inspiration from the London 2012 team, Grontmij is using soil washing to reclaim the material.

“We plan to recover as much material as possible. Over 75% of material will be reused on site,” says Hall.

Soil washing is widely used in the US and Europe, but is relatively new in the UK.

“Cleaning up this highly contaminated site will take less than a year, yet will divert 75,000m3 from landfill,”

It works by screening, sorting and cleaning soils, removing a variety of organic and inorganic contaminants.

The technique can reduce the amount of soil going to landfill by up to 90%.

Contamination usually attaches to cohesive material such as clays or silts, which in turn form more granular soils.

The soil washing process filters out granular material leaving only the cohesive material with the contamination.

In light of this, the technique is best suited to soils with a high granular content.

Soil is excavated and transferred to a central processing plant housing a mobile washing plant on the Dalmarnock site.

Separation into grain size is critical to the process so oversized particles are removed during screening.

The remainder is washed with a mix of water and detergents, which adjust pH levels, and vigorously mixed.

The silts and clays which hold the contamination coagulate, making it easy to divide from the more granular sands that can be reused.

Decontaminating the sludge residue would be expensive and extremely time-consuming.

The tight timescales and immovable end date attached to the Athlete’s Village do not allow this, so the clays will be sent to landfill.

A filter press reduces the water content in the sludge leaving a “filter cake”, which can be easily handled and transported to a local landfill site.

“Over 100,000m3 will be excavated and soil washed. Only 25% of that will go to landfill. Cleaning up this highly contaminated site will take less than a year, yet will divert 75,000m3 from landfill,” Hall says.

Work began to excavate the material in December last year and the clean site is due to be handed over in December this year.

Track records

The Athlete’s Village remediation is the first Scottish project to use and gain approval for a scheme using the Scottish Environment Protection Agency’s (SEPA) Assigning Groundwater Assessment Criteria for Pollutant Inputs to compile the water environment quantitative risk assessment (QRA).

SEPA’s new guidance describes how the “prevent and limit” requirements of the EU Water Framework Directive (2000/60/EC) should be applied to assess potentially polluting source inputs to groundwater.

The guidance is not released until later this year, meaning early engagement with the regulators was essential for Grontmij’s pathfinder project.

“The new guidance document is an advantage to the land regeneration industry through providing a more comprehensive method by which water environment matters are more appropriately addressed,” says Hall.

A more detailed method approach is given to elevated background groundwater quality, positioning of pollution assessment points relative to identified contaminant sources, and incorporation of contaminant dilution considerations in surface water bodies.

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