Investigation of an active petrol filling station in southern England identified a large area of shallow soil contamination, leaking from a waste oil tank used by the maintenance garage. Drainage issues at the site associated with overflowing surface water drainage were acting as a source of water ingress, leaching the oils through the permeable shallow soils, less than 1m in depth, towards a neighbouring residential property and surface water course adjacent to the site.
In order to be protective to these receptors and to remedy the issue before any environmental harm could occur a treatment programme was put into operation to server the contaminant linkages and remove the residual oils from the ground. This programme combined;
- Source Removal, the excavation of the waste oil tank and all associated grossly contaminated soils to prevent further release of contaminants;
- Delineation and Offsite Disposal of contaminated soil plume in excess of the derived target concentrations, ensuring that this material had not migrated as far as the neighbours property;
- Severing of the Pathway, by replacement of the damaged drainage infrastructure much of the perched water within the shallow soils will be removed, reducing any further migration
- Phased Working, to ensure the site, maintenance garage remained operational and access was available at all times to residential properties throughout the works.
Works were undertaken on the site without shutting down any elements of the commercial operations in order to minimise disruption, and were completed within 2 weeks, backfilling and reinstating the excavated areas with clean imported materials and concrete and tarmac cover hardstanding.
Validation soil sampling, demonstrated that all significantly contaminated soils had been removed from the site and trial pitting ensured that the remediation had occurred in time to prevent the contaminant impact from reaching the neighbours property or the nearby watercourse.