Project: Emergency Fuel Leak at an Operational Petrol Station
Client: Franchised petrol station operator
Services: Emergency response/leak management, regulator negotiation, site investigation, remediation and verification
Summary: Responsive, pragmatic advice and robust regulator negotiations aided rapid characterisation of a fuel leak and timely remediation
A public sewer located in front of an ageing petrol filling station was discovered to contain petrol and diesel fuels. ESI were commissioned to investigate the source of the fuel ingress, to assess the risks posed by the sub surface contamination and to develop a strategy for managing the contamination, including all identified risks associated with free phase, sorbed phase, dissolved phase and vapour phase petroleum hydrocarbons.
The emergency actions undertaken in response to the leak discovery, included
- Air quality monitoring within nearby residential properties and along the public sewer system in order to assess both explosive risks and possible acute toxic health effects.
- Removal of residual fuel from all underground fuel storage tanks.
- Pressure testing of all fuel tanks and transmission pipes.
- Consultation with the Environment Agency and Local Authority, plus the utility provider responsible for maintaining public sewerage.
- Characterisation of the sub surface in order to establish likely contaminant pathways and receptors.
- Trial pitting within the forecourt area of the filling station in order to characterise the soil type and depth to groundwater and to establish the nature and extent of ground contamination.
The site setting presented a number of distinct challenges for effective site characterisation and spill management, not least the suspected advancement of free phase material beneath a public highway and also onto a residential property, ongoing commercial activities at the filling station, the presence of numerous buried services directly surrounding the suspected leak location and the unknown point(s) of ingress to the public sewer.
In order to better define the problem additional site characterisation works comprised:
- Off site drilling, soil logging and borehole installation including locations within residential gardens and also within the pavement associated with the public highway.
- Soil, water, soil gas, free product and air quality sampling and testing.
- Aquifer testing.
- Continuous air quality measurements (PID readings at a five minute frequency).
Due to ongoing vapour risks within the adjacent property, nuisance odours within the town centre (associated with fuel contamination entering and migrating through the public sewer) and the presence of free phase petroleum hydrocarbons on the shallow groundwater surface a remediation strategy was devised for the site.
Key aspects of the strategy included:
- Agreeing remediation objectives and measureable targets with the relevant regulators.
- Identifying a suitable remediation contractor on behalf of the client.
- Third party consultations, including agreeing access to residential areas for drilling and allied infrastructure works.
- Working under CDM to ensure a safe and controlled approach to all intrusive investigations, remediation techniques and associated monitoring activities.
- Dual phase abstraction from a network of some 15 large diameter boreholes and subsequent on-site effluent treatment.
- Soil vapour extraction and on-site treatment.
- Regular performance monitoring and environmental monitoring to measure the remediation success and the need for ongoing/modified remedial treatment.
- Verification monitoring/sampling on completion of the remediation treatment activities.
- Production of a verification report.
- Regulator liaison and remediation sign-off.