At a train care depot, in the south of England, where trains get cleaned, serviced, and refueled, contamination was discovered in the soils and groundwater under the fuel filling point. An investigation was carried out, and it was found that diesel fuel had been spilled and leaked into the ground over a number of years. This resulted in free-floating fuel on top of the groundwater with a plume of dissolved contamination stretching across the site. This plume had spread to the edge of the site, adjacent to residential properties, where it was deemed to pose a risk to the environment. The aim of the remediation was to remove all floating fuel and reduce the dissolved contamination in the groundwater. This would meet the requirements of environmental regulation and remove any potential of such liabilities.
This is a busy site with an operational depot and mainline station, therefore, the cleanup needed to be completed in the safest and least disruptive manner possible. To meet this requirement, an innovative in situ remediation approach was chosen, so that the contamination would be treated within the subsurface itself, without the need for excavation. This would also minimize the time spent on site by operatives, dramatically reducing health and safety risks posed by the onsite works, and avoid any disruption to the operation of the depot.
The remediation was planned and completed by splitting up the site into two areas based on contamination concentration levels. Several remediation approaches were then integrated to provide the most efficient solution for each level. In the source area, where the floating fuel had been observed, we implemented an enhanced pump-and-treat approach. This comprised the installation of 18 wells to 7 meters below ground level, within 4-foot and 6-foot. Suspended within these wells, special top-loading pumps transported oil and grossly contaminated water along buried or safely retained pipework to an automated treatment system.
The efficiency of the system was dramatically increased through repeated injections of a desorption agent called PetroCleanze to target fuel stuck to the soil, lifting it into the groundwater where the pump could remove it. By using PetroCleanze to enhance oil removal, the required time to operate the system was cut in half, dramatically reducing the length of the remediation program. PetroCleanze is safe to use and doesn’t damage onsite services and infrastructure.
Following the removal of the free product, the dissolved plume was targeted by co-injecting two products into the wells. The first of these was RegenOx, a powerful ISCO agent, which rapidly breaks down high levels of groundwater contamination. ORC Advanced was also injected in order to stimulate and maintain biological degradation of the residual contamination. ORC works by releasing dissolved oxygen into the groundwater over 12 months from a single injection.
The remediation resulted in the successful removal of the free-floating oil within five months, and with the dissolved phase concentrations being reduced across the site as planned. The integration of technologies allowed us to achieve the targets in the safest, most efficient manner. It also provided significant costs and time savings and avoided any disruption to the operation of the depot and station. The success of this environmental solution has been recognized as the project was a finalist at the 2018 UK Rail Industry Awards.