Case Study - Remediation of large diesel spill
Background
During the refuelling of a vehicle at a large plant nursery, a site worker noticed that the diesel storage tank was empty. The fuel storage system consisted of two fuel storage tanks which were connected, resulting in an estimated loss of 10,000 litres of red diesel to ground due to corrosion of one of the tanks.
The spillage caused visual impact to near surface soils adjacent to the tanks and contamination of deeper soils and shallow groundwater over a large area. It was identified that the spill posed a risk to a nearby major river given the permeable nature of underlying soils.
Investigation, Mitigation and Remediation
A series of trial pits were initially excavated to enable the plume area to be delineated and a remedial strategy to be devised. It was identified that diesel had impacted soils over an area of 400 square metres. The investigation also identified shallow diesel impacted groundwater.
To prevent the migration of diesel towards the nearby river, a series of interception trenches were excavated and recovery sumps were installed to facilitate diesel recovery using a rapidly deployable mobile pump and treat system comprising a silt separator, oil-water separator and granular activated carbon filters.
Diesel contaminated soils were excavated by our in-house civils team to depths of up to 2 m and a total of 650 tonnes of soils were removed from the site and sent for off-site treatment at a soil treatment facility.
Verification & Reinstatement
The excavation extents were verified by our consultants to ensure sufficient material had been removed to reduce the identified risks, with soil samples submitted to an independent UKAS accredited laboratory.
The groundwater treatment system processed a total of 124,000 litres of diesel contaminated water and prevented any migration towards the nearby river.
The source excavation was reinstated with clean materials and was finished with a topsoil cover to return the site to its original condition.