In 2018, RSK Response started an investigation to obtain geoenvironmental data to provide advice regarding hydrocarbon contamination from a damaged transformer bund and a scope of work detailing how to remediate this. The site, an active substation, contained three 275kV supergrid transformers and associated infrastructure. Because of the site’s location, in a residential area with a community centre nearby, it was classified as sensitive.
During the desk-based study to ascertain the nature of the contaminant and possible pathways for it to reach ground- and surface water, our research team identified vertical migration to the primary aquifer and the infiltration of surface and pore water by a free product flow of petroleum hydrocarbons as the most likely contaminant pathways. Upon intrusive ground testing, we discovered evidence of a large volume of oil in the ground and a significant free product layer at the top of the saturated zone. Furthermore, we knew that oil had been migrating into the site’s internal drainage system. RSK Response mobilised its team immediately to isolate the contaminant and to begin the remediation process.
For the past three years, RSK Response’s investigative team has been on-site monthly to conduct the remediation. It has used various in-situ methods over the years; these approaches avoid excessive environmental impacts and the costs associated with excavation, and they can take place on operational sites. Techniques have included replacing absorbents, using bailers to recover the product, using a variety of filters such as activated carbon and installing external sumps that feed into oil–water interceptors. The data collated indicates that we are removing the oil from the ground successfully. By working closely with the client-affiliated engineers, our team has immobilised and removed thousands of litres of oil from the ground below the substation.