Investigation and risk assessment of a diesel leak: confidential

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Courtesy of ESI Ltd - Environment Specialists

Project: Emergency Investigation of a Fuel Leak

Client: Confidential infrastructure management company

Services: Rapid site characterisation and risk assessment

Summary: Detailed risk assessment was used to quantify the environment risks pose by a fuel leak and avoid unnecessary remediation

ESI was commissioned to manage the emergency response to a diesel fuel leak at a secure engineering facility in the West Midlands. Following the isolation of the leak, ESI undertook a detailed quantitative risk assessment in order to inform the ongoing leak management and assess the requirements for land remediation.

The fuel leak first became apparent when free product was observed on the surface of a balancing pond at the edge of site. A rapid site visit and desk study investigation indicated that a ruptured underground fuel line had caused red diesel to enter the on-site storm water drainage system, resulting in contaminated discharges to the balancing pond. The initial ground model also identified the potential for vertical migration to the underlying major Sandstone aquifer.

Emergency response actions included the isolation of two 140,000 litre fuel tanks, clean-up of the balancing pond, the hand excavation of buried pipe work in order to confirm the leak location, and pumping of residual fuel.

Exploratory drilling was undertaken in and around the location of the fuel leak in order to improve the characterisation of both the leak extent and the likely contaminant fate and transport. Soil and water samples were also taken.

The revised conceptual site model suggested that the petroleum hydrocarbon source was constrained to a relatively small area around the site of the leak due to the presence of stiff clays close to ground surface and the absence of any appreciable shallow groundwater. The subsequent human health risk assessment (performed using the Environment Agency’s CLEA methodology) concluded that health risks were low due to the limited contaminant extent, the low levels of occupation of the site area and the relatively low vapour potential associated with diesel fuel.

A controlled waters risk assessment was undertaken, using ESI’s Risk Assessment Model (RAM), in order to predict the extent of petroleum hydrocarbon migration to the underlying Sandstone aquifer. Based on conservative modelling assumptions, no appreciable breakthrough of diesel was modelled within the thousand year simulation period.

The final risk assessment report concluded that no significant environmental risks were present at the site and hence no land remediation was necessary. However, recommendations were made for improved inspection and maintenance of all oil interceptors associated with the storm water drainage network and CCTV surveying of selected drain sections, plus any associated drain repair works.

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