A former polystyrene factory site was to be redeveloped for residential purposes.

An initial desk study identified potential historical contamination sources in connection with former factory processes and fuel tanks. The northern part of the site was historically occupied by the Grove Engine Pit and the desk study also highlighted a potential risk from shallow abandoned mining workings.

Terra Firma Wales Limited undertook robust investigation works on the site to ensure that any contamination present could be identified and suitable remedial measures be implemented, and so that the most suitable foundation solution could be recommended for the new development.

The investigation encompassed a series of shallow boreholes and trial pits, as well as deep rotary boreholes into the underlying bedrock to determine the risks from shallow mine workings.

Environmental assessment included sampling and analysis of site soils, groundwater and vapours. In-situ gas monitoring was also performed.

Impact by arsenic was identified in two isolated areas of the site, and petroleum hydrocarbons were found to have made an impact on shallow groundwater in a confined area adjacent to a former diesel tank.

Remediation in the form of soil removal and replacement and groundwater treatment was successfully performed to eliminate the contamination and prepare a safe site for use by future residents.

Deep boreholes confirmed that development area was unaffected by shallow workings and no stabilisation or treatment works were required.

A traditional foundation solution was therefore recommended for the proposed new housing development.

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