ESI Ltd - Environment Specialists

Sub-watertable landfill groundwater risk assessment


Courtesy of Courtesy of ESI Ltd - Environment Specialists

Client: Waste Management Industry

Location: Sub-water table landfill site, UK

Services: Data collation and analysis, hydrogeological risk assessment , regulatory liaison and negotiation, Environmental Permit Application support

Issues: Sub-water table landfill site, sensitive receptors (major aquifer), potential risk to controlled waters.

Summary: ESI provided data collation and analysis services, through which a conceptual model for the site was developed and an appropriate risk assessment model constructed. Modelling a range of engineered barriers, in agreement with the regulatory body, allowed the most effective containment of the waste to be determined whilst ensuring adequate protection of the environment.

A major European waste disposal company wished to redevelop the remaining void of a landfill site as part of their first major venture in the UK. Following the cessation of mineral extraction, the void was subsequently operated by several waste disposal companies on the principle of hydraulic containment until the waste management licence was revoked on the grounds of poor operational standards.

The client became the new owner and wished to adopt an engineered containment design extending below the water table. This required a groundwater risk assessment to be undertaken for consideration by the Environment Agency (EA) as part of a Pollution Prevention and Control (PPC) application.

The project involved the collation and analysis of all available data to aid the formulation of a hydrogeological conceptual model. Several potential contaminant receptors were identified which included a major watercourse and a railway drainage system.

A Probabilistic Risk Assessment (Monte Carlo analysis) was carried out, using in-house stochastic modelling techniques which use the advectiondispersion-retardationdecay transport model. This modelling approach was chosen to provide both a robust and transparent assessment of risk using the source-pathway receptor methodology. A number of contaminants were modelled to represent the predicted potential risks
to the identified receptors associated with the proposed landfill.

Regular reporting of the results of the risk assessment kept both the client and EA in agreement with each stage of the assessment. Following meetings with the EA and the client a number of engineering failure scenarios were simulated together with proposed variations of the engineered containment system. Modelling of the various engineered barriers would help constrain the most effective containment of the waste ensuring adequate protection of the environment.

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