EPA 1990 Part 2A Enforcement Site
EPA 1990 Part 2A Enforcement Site Photo 1
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EPA 1990 Part 2A Enforcement Site

Mid Devon DC

GEG were commissioned by Mid Devon District Council to undertake an environmental assessment, remediation strategy and full tender remediation specification for an existing residential estate built in Devon in the 1980’s on the site of a former timber works. 

GEG commenced by undertaking a detailed Phase I (Desk Study) to determine the historical extent of the former timber works, the potential areas and types of source contaminants and the various receptors potentially at risk associated with the site. The former timber treatment sector of the site was considered potentially the most highly contaminated in terms of sources. Based on the conceptual site model, a Phase II intrusive investigation was recommended by GEG, providing a broad sampling grid across the entire former timber works site, but providing more targeted sampling in the area of the former wood treatment area.

Limited access drilling techniques were used to investigate residential gardens and recover soil and groundwater samples for chemical analysis.

Arsenic and nickel physiological based extraction tests (PBET) were undertaken to assess potential bioaccessibility to humans.

Plant uptake tests were also carried out for arsenic on a variety of site grown produce to assess soil-plant concentration factors.

The data collated from the site was used in the Contaminated Land Exposure Assessment (CLEA) model v.1.04 to derive site specific assessment criteria for inorganic and selected organic (aliphatic/aromatic TPH and speciated PAH) contaminants of concern. Arsenic, C12-C16 aliphatic TPH and C8-C10 aromatic, naphthalene, dibenzo(a,h)anthracene and benzo(a)pyrene were identified as contaminants of concern with respect to the residents.

Due to current limitations of the CLEA model, the Risk Based Corrective Action (RBCA) Tool Kit v.2.5 made UK compliant by GEG was used to assess risks to the existing residents from volatile and semi volatile organic compounds. 1,1,2,2,-tetrachloroethane was identified as a representing a potential risk to residents, principally via the vapour intrusion pathway.

A deep groundwater investigation was also undertaken to assess risks to Controlled Waters, namely the minor aquifer which provided base flow to local watercourses.

A remedial options appraisal was subsequently undertaken together with a detailed remedial strategy. The resultant preferred remediation technique incorporated the selected removal of shallow soil hotspots and a combination of chemical oxidation and soil vapour extraction for the deeper soil and shallow groundwater organic compounds.

A full remediation specification was produced utilising the Institution of Civil Engineers Minor Works 3rd Edition contract, which was included in a web-based open tender to contractors undertaken on behalf of MDDC (Dec 2009). The remediation, which will overseen by GEG as the Engineer, is expected to commence in March 2010.