The OMEX site once housed a waste oil recovery facility. Years of deposition of waste product into unlined surface ponds lead to significant migration of a range of heavy metal and hydrocarbon pollutants into the sub-surface formations. After extensive investigations it was decided to remove the worst of the polluted near surface material to secure land fill. A precursor to this operation was to install a low permeability barrier around the site to have a two-fold application:
- To limit ingress of ground water to the excavation as the removal and backfilling took place.
- To limit the ongoing migration of pollutants away from the site.
The barrier was created by the installation of a slurry trench cut-off installed to depths in excess of 25 m to penetrate into a low permeability stiff clay layer. This paper describes the techniques applied and presents some details of the quality control and compliance testing measures adopted