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Risk Based Corrective Action

Risk-based corrective action (RBCA) is the process that allows for the assessment of existing and potential risks to human health and the environment as a tool to determine the extent of corrective action required/recommended at a site with soil or groundwater contamination. This concept is formalized in the American Society for Testing and Materials (ASTM) Standard Guide for Risk-Based Corrective Action Applied at Petroleum Release Sites (E1739-95), and ASTM Standard Provisional Guide for Risk Based Corrective Action (PS-104).

Contaminant concentrations in soil vapor are compared to commercial property ESLs identified in Screening for Environmental Concerns at Sites with Contaminated Soil and Groundwater (RWQCB, November 2007). If concentrations are below ESLs, the potential risk from exposure is low and site closure can be requested. If concentrations are significantly higher than ESLs, the chemical data are used to develop Site Specific Toxicity Levels (SSTLs) for soil and groundwater. The SSTLs then become the cleanup target concentrations.

In contrast to the concept of cleaning up to the background levels, the RBCA approach considers the environmental fate of the chemical, the exposure pathways for the chemical to come in contact with human or environmental receptors, and known toxicological properties of the chemical. The consideration of these factors allows use of one of the most fundamental concepts of risk assessment, i.e., Risk = Exposure x Toxicity. By considering both exposure and toxicity, risk can be estimated. RBCA allows for either estimates of risk based on known toxicity and exposure, or estimations of clean-up levels based on a pre-determined and acceptable level of risk. Clean-up level estimation is one of the strengths of the RBCA approach, providing a rational way to answer the question, "How clean is clean enough?"