A contaminated land assessment, site-specific risk assessment, and remediation options appraisal was completed for a residential site heavily contaminated with chlorinated solvents in soil and groundwater. The risk assessment included the calculation of sitespecific assessment criteria based on human exposure pathways, including migration of vapours to indoor air of homes.

The Major Aquifer in the region is the Lincolnshire Limestone Formation, which comprises shelly, oolitic and sandy limestone, and is around 10m thick in the Crowland area. The Lincolnshire Formation however, is overlain by the Oxford Clay, generally considered a non-aquifer and to be of low mass and material permeability. The Oxford Clay is estimated to be approximately 27 metres thick in the vicinity of the site. The Oxford Clay acts as a confining layer, effectively precluding vertical contaminant migration to the Major Aquifer.

The feasible media-specific options identified in were assembled into possible alternatives to accomplish the remedial objectives identified for the Site.These are given below.

Alternative 1: Large Scale Soil Excavation and Removal:
Excavation and off-site disposal of soil exceeding thresholds across the Site. Groundwater remediation following active soil remediation activities would occur through monitored natural attenuation. Costs for implementation of this alternative would be exceedingly high, estimated at GBP 684,000 to GBP 927,000 with contingencies. Therefore, this option was not considered viable on a commercial basis.

Alternative 2: Localised excavation of soil, natural attenuation and Restrictive Covenants:
Localised excavation of soil exhibiting the highest contaminant concentrations and restrictive covenants requiring vapour barriers for any future structures at the Site intended for human occupancy. Costs for this alternative are estimated as ranging from GBP 126,000 to GBP 182,000. However, there would be issues with remaining source materials, which could act as a continuing source for contamination to groundwater.

Alternative 3: Phytoremediation of soil and groundwater:
Soil and groundwater remediation through phytoremediation (trees) to achieve compliance with standards for contaminants in groundwater. This alternative would rely on the transfer of contamination from the soil to the groundwater matrix and phytoremediation to ultimately mitigate the soils as an ongoing source of contamination. Although innovative, this technology appeared likely to represent an effective technology for remediating the contamination in soil and groundwater such that they no longer represent a risk to future on-site residents in the long term. However, this option would not effectively result in short term reduction of source concentrations. Therefore, it is likely that phytoremediation coupled with focussed source removal would be a more effective measure, which was recommended. Costs for this alternative were estimated as ranging from GBP 126,000 to GBP 200,000.