0022b ESA & Remedation

LAND & PROPERTY Environmental Site Assessment and Hydrocarbon Impacted Soil and Groundwater Former Petrol Filling Station and Garage, UK

Remediation

of

Project Summary

Environmental Site Assessment and Remediation of Hydrocarbon Impacted Soil and Groundwater Former Petrol Filling Station and Garage

Key Project Elements • Phase I ESA • Phase II ESA • Asbestos Survey • Contamination Delineation

CRA was commissioned to complete a Phase I Environmental Site Assessment (ESA) for a former petrol filling station and car servicing garage. The Phase I ESA identified the need for a targeted Phase II ESA in areas of underground fuel storage tanks and fuel pipelines. An asbestos survey was also required prior to any redevelopment of the site.

The Phase II ESA works focused on the collection of soil and groundwater samples, and ground gas monitoring in order to facilitate the planning requirements for the site’s redevelopment. An asbestos survey was undertaken that identified asbestos containing materials requiring removal during the redevelopment of the site.

• Ground Gas Monitoring • Remediation of Hydrocarbon Impacted Soil • Abstraction of Hydrocarbon Impacted Groundwater • Regulatory Liaison

Elevated concentrations of hydrocarbons were identified in both the soil and groundwater, resulting from historical storage of fuels on site. A Conceptual Site Model was developed that identified the potential sources, pathways and receptors relating to the site. This highlighted pollutant linkages presenting a potential risk to controlled waters. A ground gas risk assessment was also undertaken in order to inform the design of gas protection measures. CRA liaised with the Environment Agency and Local Authority with regard to the potential risks to formulate a remedial strategy that would address the requirements of the regulators and planning condition. The remedial strategy involved source removal works consisting of decommissioning the underground fuel storage tanks, contaminated soil excavation and disposal, and a contaminated groundwater pumping system.

On completion of the soil excavation works, verification samples were obtained to ensure that the excavation had been extended sufficiently (vertically and laterally). The soils were disposed of off-site due to the short redevelopment timeframe and lack of space at the site for ex-situ remediation. Abstraction wells were installed in the location of two groundwater hotspots for groundwater source removal. The unobtrusive groundwater abstraction works were able to continue during the redevelopment works and once the site was operational. At one location, oxygen release compounds (ORCs) were also installed to encourage the degradation of hydrocarbons in the groundwater. Continual groundwater sampling was undertaken to show the reduction in hydrocarbon concentrations. CRA ensured that the Environment Agency was informed of progress and ultimately the remedial works were able to cease as the groundwater condition beneath the site improved.

Ref: PS0022b