Supermarket development, Elgin

Challenge

The site of a former swimming baths required remediation to facilitate the construction of a supermarket.  An ERS site investigation revealed hydrocarbon contamination to be present across the site, concentrated in the groundwater smear zone. Time and cost considerations precluded off-site disposal or treatment options.

The challenge was therefore to remediate smear zone hydrocarbons and prevent them from continued leaching into groundwater.  Remediation work would need to be undertaken whilst construction of the new supermarket was underway. 

Solution

Working closely with the client's development team, ERS engineers designed a bespoke in situ bioremediation system to enable regeneration to begin immediately, whilst also ensuring that remediation could continue post-build without the need for additional intrusive work.

The selected method was bioslurping, a technology that utilises a vacuum pumping system to remove free product and vapour, whilst exerting control over groundwater levels.  By controlled lowering of the local water table the smear zone could be kept exposed, thereby enhancing contaminant volatilisation and biological degradation rates.

The design was implemented using a permanent infrastructure of 36 wells beneath the new building footprint, linked to above ground control plant by underground service runs.  Bioactivity and degradation rates were controlled by in situ respiration monitoring, using equipment installed within pre-placed monitoring wells.

Outcome

• Working closely with the developer's team, ERS engineers designed an in situ groundwater treatment system beneath the development that would ensure ongoing remediation post-build.
• The high-vacuum dual phase system exposes the smear zone, enhancing volatilisation and bioactivity and thereby accelerating remediation.
• The design included a three year remediation schedule, with a detailed monitoring programme throughout.
• The project is on target for completion in 2010.