3 Human Health Risk Assessment Preserving the Beauty of California Coastline Soil Contamination Pauses Residential Development Our client approached our team with a desire to redevelop contaminated property situated on the central California coastline. This property was highly desirable for residential development given the sweeping views of the ocean and rolling landscape. Sampling results indicated that there were potential risks to human health due to concentrations of arsenic and to a lesser extent, polycyclic aromatic hydrocarbons, measured in surface and subsurface soils. Arsenic was ubiquitously elevated across the site partially due to the historical use of arsenic as an herbicide. Remediation of these contaminants would have required extensive excavation across the site to achieve the generic residential risk-based screening levels in surface and subsurface soils. This would have been challenging considering the topography and expansive spatial extent of arsenic within soil. In addition, this would have significantly damaged the natural landscape and ecosystem along the coastline. Deploying Tailored Risk-based Approach to Redevelopment Our team developed a risk-based approach that segregated the site based on the level of impacts within soil. Areas with the highest concentrations of arsenic and polycyclic aromatic hydrocarbons were designated for use as natural, recreational areas, such as walking trails. Areas with lower concentrations of these constituents of concern were targeted for residential use and subdivided into estate lots, ranging from one to three acres. Our team tailored the human health risk assessment for these anticipated uses. For example, within those areas designated for recreational use, risk was only considered for surface soils, assuming a short exposure duration. Whereas in areas being considered for residential development, risks for exposure to both surface and subsurface soils were considered, as is typical for residential exposure inputs. Project at a Glance • Highly desirable property along California coastline had high levels of arsenic in soil sample analysis. • Remediation would have required extensive excavation across entire site and changed the landscape and ecosystem • Team developed a risk-based approach that segregated the site based on impact and use. • Worked with redevelopment team to prepare preliminary layouts and required excavation for each lot. • Addressed vapor intrusion pathway by requiring mitigation systems for future residences • Approach saved millions of dollars in redevelopment and preserved coastline.