SURFACE WATER RISK-BASED CRITERIA FOR GROUNDWATER REMEDIATION SYSTEMS: PROCESS AND APPLICATION

When groundwater combines with surface water, the characteristics of each are blended and new gradients are established. Any contaminants contained within the groundwater discharge can affect the quality of the surface water. When the potential exists for groundwater to impact surface water, groundwater cleanup goals are developed to protect potentially exposed human and ecological receptors. Typically, performance based criteria for a groundwater treatment system are based on meeting groundwater cleanup goals such as maximum contaminant levels (MCLs) and ambient water quality criteria (AWQC) at a downgradient well that represents groundwater prior to discharge to a surface water body. Using this approach, low levels of contaminants can persist, even with expensive cleanup technologies in place, and the resulting cost and technological limitations can make this approach unsustainable. Alternatively, a process can be used to develop groundwater cleanup goals from potential exposure points in adjacent surface waters. When there are no direct exposures to the groundwater, such as via an active drinking water source, a better approach is to take into account the fate and transport processes that occur within the groundwater to surface water interface (GSI) and within the mixing zone of the surface water body. This approach will minimize the unnecessary expenditure of resources due to compliance with groundwater cleanup goals that are not representative of the relevant surface water exposure point for human and ecological receptors. The significance of the potential exposure point (groundwater verse surface water) is the key cost-benefit factor for determining the level of effort required for any groundwater treatment system. When groundwater-to-surface water is identified as the primary complete exposure pathway for a site that requires a groundwater treatment system, the remedial objective for the site is to develop site-specific groundwater remedial criteria that are protective to potentially exposed human and ecological receptors in surface waters downgradient of the site.