Project: Former Engineering Works, Grafton Works, Bedford
Client: Major House Builder
Contract Value: £80,000

A site investigation of the former engineering works identified elevated concentration of hydrocarbons within the soil and groundwater beneath the location of an above ground storage tank. The hydrocarbon plume covered an area of approximately 480 square metres and contained TPH concentrations of 6000 milligrams per kilogram in the soil and 8000 micrograms per litre in the groundwater.

Knight Environmental Limited was commissioned to remediate the contaminated area. The Developer imposed time constraints on the project so remediation occurred alongside the development works.

The methodology adopted to remove the principal source area within the soil was excavation and disposal to a licensed landfill due to the time constraints.

A review of the geological and hydrogeological conditions indicated that the optimum remediation option for the treatment of groundwater was the use of air sparging and soil vapour extraction. To enhance the degradation of the hydrocarbons ozone was also injected.

A series of injection wells were installed across the remediation area and linked to Knight Environmental Limited’s C-Sparge unit. The C-Sparge unit is able to inject a combined flow of air and ozone to a maximum of 30 sparge points. Hydrocarbon contaminated air was extracted, treated and discharged to the atmosphere.

During the 6-month treatment programme the TPH concentrations in soils and groundwater were reduced to less that 2000 milligrams per kilogram and 3000 micrograms per litre respectively.