Contaminated land can present a significant risk to controlled waters (groundwater, surface water bodies, or public supply reservoirs). Groundwater risk assessments range from direct comparison of groundwater concentrations against screening values, to complex modelling to predict the transport of contaminants as they migrate from their source.
If the conceptual model has identified a controlled water receptor is at potential risk from contamination, then groundwater sampling and testing is required to assess any impact. If significant contamination is identified within the groundwater, a hydrogeological detailed quantitative risk assessment (DQRA), frequently known as a P20, may be required. This assessment will consider in more detail the predicted impact at an agreed downstream receptor, like a river or water abstraction.
The purpose of a DQRA for groundwater is to determine acceptable concentrations of contaminants that could be present without suffering a detrimental impact to a defined receptor. The calculated remedial target concentrations from a DQRA must be agreed with the Environment Agency prior to implementation within a remedial strategy for a site.
The Environment Agency provides guidance and methodologies for the assessment of groundwater with the aim of protecting controlled waters from pollution. The Environment Agency has powers to protect, monitor and enforce remediation of contaminated groundwater as set out within several legislative documents including the Environmental Protection Act 1990.