Gas Works, Tonbridge, Kent
Investigation and Risk Assessment
Phase 1 - Desk Study and Walkover Survey
The site, which extends to about 1.3Ha, has a history of use as a gas works, plastic manufacturer, car repair yard, and depot. The site is located adjacent to the R. Medway on a Minor Aquifer, at the edge of a Total Catchment Zone SPZ, and is also at risk of flooding. The mapped site geology consists of Alluvium over Upper Tunbridge Wells Sand.
Phase 2 & 3 - Intrusive Investigation, Contamination & Risk Assessment
A phased site investigation, including boreholes, trial pits, groundwater and land gas monitoring, and an asbestos survey was undertaken.
This was followed by geotechnical and contamination testing and analysis, site-specific risk analysis using the CLEA Model, groundwater risk assessment using Environment Agency P20 Method, and environmental modelling using Surfer software.
Analysis indicates the site is heavily contaminated with Arsenic, Cyanides, PAHs, TPH, BTEX compounds and SVOCs, largely correlating with the location of historical gas works structures. Natural soils are shown to be contaminated, although more locally. Slight groundwater contamination has also been identified.
Remedial Design and Proposed Methods
Soils: Ex situ bioremediation (possibly coupled with some form of cement stabilisation).
Groundwater: although not considered necessary at this stage, a combination of in situ DPVE (Dual Phase Vacuum Extraction) and Chemox (Chemical Oxidation) would be suited.
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