A review of the processing of contaminated land in highway earthworks was undertaken by TRL for the Highways Agency. The traditional approach to contaminated land in highway construction has been to excavate, remove to landfill and replace with acceptable material. However, a number of techniques are now available whereby the contaminated land can be remediated and utilised in the construction works. This is more environmentally friendly than the `dig and dump' approach, but there has been relatively little utilisation of these techniques to date. With the implementation of the Contaminated Land Regulations and Statutory Guidance on 1 April 2000, greater use of remediation techniques is anticipated in the future. A guide to the current legislation on contaminated land as it relates to highways is given, and changes are proposed to the definition of contaminated land in the Manual of Contract Documents for Highway Works. A review of available techniques for the remediation of contaminated land and their advantages and limitations for highway works was undertaken and case studies of various methods are presented. Technologies, which have potential for use in highway schemes, include stabilisation/solidification, ex-situ bioremediation, soil washing, mechanical sorting, soil-vapour extraction and hydraulic control of groundwater (pump-and-treat). Detailed work on the durability of lime-stabilised contaminated material is described, comprising laboratory trials, long-term leaching tests, a pilot scale test bed and sampling of lime-modified material which had been utilised in a highway scheme. The results indicate that the treated material retains its strength in the medium term and does not release significant amounts of contaminants to groundwater. Recommendations are given for the use of remedial measures for contaminated land in highway earthworks. (Author/publisher).
Abstract