Performance assessment of the phased remediation of a former gas manufacturing plant.

The remediation of a former manufactured gas plant (MGP) in the north of England is the subject of both a commercial remediation project and an ongoing collaborative research programme. A risk-based remediation strategy has been adopted, which involved an initial risk assessment to identify appropriate clean up criteria and removal of primary sources. This was followed by the installation and monitoring of a full-scale in situ air sparging system. This system is currently operational. Periodic measurements of dissolved organic and inorganic components, and highly detailed time series of temperature, Eh, pH, dissolved oxygen and piezometric measurements have been obtained for the sparge system. Naphthalene degradation activities have been assessed through the application of filters for the recovery of organisms from groundwater samples (FROGS). Significant reductions in dissolved phase hydrocarbons are being achieved within and downgradient of the aeration zone. Integration of laboratory challenge tests for hydrocarbon mineralization rates with in situ measurements from the sparge system have demonstrated the response of the subsurface environment to the changes in redox conditions following the introduction of the sparge barrier. These results also provide guidance on the long-term effectiveness of the sparge barrier.