USING MULTI-METHOD, MULTI-SCALE METHODOLOGY FOR CHARACTERIZING GROUNDWATER/SURFACE-WATER INTERACTIONS TO IMPROVE USEPA DECISION MAKING AT A RCRA CORRECTIVE ACTION CONTAMINATION SITE

At RCRA sites, the site owner is responsible for the investigation and remediation of site contamination and USEPA’s role is primarily to enforce the environmental regulations and review and approve work done by the owner. One of the main challenges for USEPA is to negotiate and ensure enough work is done by the site owner to reduce uncertainties to reasonable levels and to protect human health and the environment. For site owners, one of the primary goals is to achieve regulatory compliance at the least cost. The result is often a difference in opinion regarding how much work is necessary to characterize the site and what requires remediation. An underlying problem that both parties must contend with is that contaminated sites are often quite complex spatially and temporally with respect to: contaminant distribution; geology; groundwater flow; geochemical conditions; and, especially, groundwater/surface water interactions. Hence the need for economical site assessment approaches that can adequately characterize the variability at the site, significantly reduce uncertainty, and support science-based decision making for plumes passing though the groundwater/surface-water interface. A case study is presented for a RCRA site where a benzene groundwater plume flows toward Lake Michigan. USEPA funded a study to obtain a preliminary understanding of the site to demonstrate that further investigations by the site owner were needed. A cost-effective multi-scale, multi-technique, characterization approach was developed that applied large-scale reconnaissance techniques to quickly assess large areas and use progressively smaller-scale, higher sensitivity techniques to identify key discharge areas for strategic sampling. The approach provided a considerable amount of semi-quantitative information on groundwater discharge and water quality that quickly enabled targeted sampling rather than relying on random out-of-context grid sampling. The approach identified high levels of contamination in locations one might not have normally investigated and resulted in a reassessment of the existing remedial system. The site owner adopted some of these investigative techniques which resulted in a better defined contamination footprint of the discharging plume in the lakebed and more targeted remedial actions.