Human Health Risk Assessment 2 Establishing Background Concentrations Using Historical Data Risk Assessment Calls for Site-Specific Background Concentrations for Metals Our client wanted to establish site-specific background concentrations as part of the human health and ecological risk assessment for surface and subsurface soils at a remote project site underlain by fractured bedrock. At the time that this work was completed, the state regulatory agency had only established background concentrations for arsenic, based on a limited data set and relied on nationwide studies such as the frequently cited Shackeltte and Boerngen (1984) for evaluating background concentrations for other naturally occurring metals. Conducting an independent background study can be expensive and complicated, often including negotiations with third-party property owners. Historical Remedial Investigation Data Provides Answers Our team identified that a substantial data set for metals collected from both surface and subsurface soil was collected as part of historical remedial investigation activities. We were able to negotiate the use of the existing data to establish site-specific background concentrations with the regulatory agency. A grid pattern had been established across the 300-acre site with higher density sampling conducted within former process areas and lower density sampling occurring in undisturbed areas. The background data was selected by segregating sampling locations in impacted or potentially impacted areas based on four criteria. 1. We eliminated all the samples that were collected in redeveloped areas as there was a potential for non-native backfill to have been used during construction. 2. Samples with lead concentrations that exceeded the site-specific screening criteria (including direct exposure as well as migration to groundwater) were eliminated. The site has been used to process leaded gasoline and as such lead was one considered one of the primary risk drivers. 3. We eliminated any samples collected in former tank berms, due to the potential for historical releases from bulk storage tanks. 4. Any remaining outliers were eliminated using Rosner’s algorithm implemented in ProUCL version 4.0. Stepwise Approach Reduces Costs and Expedites Redevelopment The resulting data set was comprised of 25 samples that were used to calculate background concentrations of naturally occurring metals using ProUCL version 4.0. This stepwise approach for establish background concentrations using existing historical data resulted in a significant cost savings and expedited redevelopment of portions of the site that had not previously been used for historical refining and bulk storage activities Project at a Glance • Client wanted to establish site-specific background concentrations for naturally occurring metals. • Team used historical remedial data to establish background concentrations • Stepwise approach leads to significant cost savings and expedited redevelopment of 300-acre site.