Case Study 2

 

Industry: Filling Station – Redevelopment into Residential Flats

Location: Warwick


Hazrem Environmental was commissioned to conduct both the SI and remediation of a filling station in Warwick. The site was to be redeveloped into 26 residential flats for the elderly.

The comprehensive Site Investigation took the form of a preliminary desk study including a review of the site geology, hydrogeology and past uses to give an impression of possible contaminants, pathways and receptors on the site.

The evidence gathered allowed the development of a conceptual model that clearly indicated the necessity of a Phase II intrusive investigation to quantify define potential risks to both ground waters and human health from potential hydrocarbon contamination released from underground tanks at the site.

An intrusive investigation at the site took the form of taking soil and water samples via the excavation of trial pits and the sinking of boreholes. The samples were sent for further analysis at an UKAS / MCERTs accredited laboratory where they were analysed for a wide range of hydrocarbon contaminants and metals.

Information from the Desk study and intrusive site investigation indicated that a substantial amount of diesel range organics (DRO) had penetrated into the underlying strata consisting of alluvial sands and gravels overlying a mudstone bedrock. Ground water was established to be at 1.75m in depth.

The conceptual model was further refined by integrating this information, following which both human health and ground water modelling was conducted to establish the potential risks to possible receptors and determine targets for remediation.

A remediation strategy was then devised to describe targets for remedial treatments, define volumes for treatment and describe potential remedial treatment options.

Taking into consideration that ground water was the primary receptor, the strategy devised required the removal of any free product remaining on the ground water surface and to remove dissolved phase hydrocarbons. Due to the favourable permeability of the alluvial material, it was proposed that further boreholes would be sunk into the underlying strata and a skimming system installed to remove the presence of free product. Following removal of the free product a mixture of bio-sparging and soil vapour extraction would be employed to reduce levels of dissolved phase hydrocarbons.

Following demolition of the site infrastructure and removal of the UST’s,the above system was employed at the site by Hazrem Environmental technicians. The system was shown to remove free product and reduce dissolved phase hydrocarbons from a 95%UCL of 3000 ppm DRO to beneath the remediation criteria set. This was achieved over an 18 month treatment period.