Protecting communities from contamination
Lubrication oil and diesel spillages from trains over a prolonged period led to light non-aqueous phase liquid (LNAPL) contamination in groundwater at a train depot in Hampshire, UK. The contamination had begun to migrate off-site and contaminate site protection wells belonging to neighbouring properties. The 6-ha depot is alongside the railway lines.
RemedX, an RSK company, designed a remediation strategy that would not disrupt ongoing depot operations or require track possessions of the main line. The apparent LNAPL thickness in a well can indicate hydrogeological conditions that inform the remediation strategy.
The strategy targeted LNAPL removal through pumping followed by in-situ surfactant flushing, in which surface active agents (surfactants) act as detergents to lower the surface tension between the contaminant and water. This technique requires a 5% surfactant solution to be injected into the wells, which had a measurable thickness of LNAPL.
The contaminated groundwater and injected surfactant are then pumped out from the accessible wells and into tanks to be treated. RemedX reduced the LNAPL levels with three surfactant enhanced removals. Groundwater gauging and sampling determined the water table depth and tested for hydrocarbons after the first and second surfactant events. After the third surfactant injection, the LNAPL concentrations were reduced to a point at which the Environment Agency agreed to monitored natural attenuation, a method that enables contaminants to reach safe levels through natural processes such as volatilisation, degradation or dispersion without deliberate human intervention.
Owing to the site’s proximity to the railway lines, RemedX staff needed to be personal track safety trained to minimise the risks on-site and enable the team to use a flatbed railway vehicle to move equipment between locations across the site. Equipment could then be transported close to existing boreholes.