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 cleanup criteria and removal of primary sources. This was followed by remedial technology pilot testing, and 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 piezometry have been obtained for the sparge system. Naphthalene degradative activities have been assessed through the application of Filters for the Recovery of Organisms from Groundwater Samples (FROGS). Integration and interpretation of the data is undertaken using a biogeochemical groundwater model. Significant reductions in dissolved phase hydrocarbons are being achieved within and downgradient of the aeration zone. Integration of laboratory challenge tests for hydrocarbon mineralisation 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.