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4.0 RISK-BASED CORRECTIVE!ACTION ASSESSMENT <br /> The purpose of the risk-based corrective action (RBCA) assessment is to determine if residual j <br /> concentrations of constituents of concern (COCs) remaining in site soil and groundwater exceed I <br /> site specific target levels (SSTLs) or,pose a risk to human health and the environment. The soil <br /> " and groundwater analytical data set-usedin the RBCA assessment include the soil samples i <br /> i <br /> E collected from confirmation soil boring CPT-1A in August 2000, and the groundwater samples <br /> collected during the four, 2005 quaiterly,monitoring events. The results of this RBCA <br /> ( i assessment provide a general assessmeEnt of the risks from petroleum hydrocarbons and fuel <br /> oxygenates present in soil and groundwater beneath the site. <br /> 4.1 Methodology <br /> A Tier 2 Risk Assessment was completed with the aid of the software RBCA Tool Kit for <br /> Chemical Releases (version 1.3b) developed by Groundwater Services, Inc. This program <br /> i .{I <br /> evaluates baseline risks and SSTLs for both on-site and off-site receptors based on site-specific <br /> soil and groundwater parameters. <br /> The RBCA assessment evaluated potential risks associated with the following exposure <br /> pathways: <br /> • Dermal contact and ingestion''of affected surficial soils by on-site commercial or <br /> . construction workers, I <br /> -Inhalation of vapor or particulates.by on-site or off-site commercial worker or on-site <br /> construction worker, and <br /> 11 '� • Ingestion of groundwater by an off-site commercial worker. <br /> The RBCA assessment was based on the following.assumptions: <br /> . TPH-as-gasoline, MTBE, and 1,,2-,,DCA are the constituents of concern. <br /> • Each detected TPH-as-gasolihe concentration is assumed to be comprised equally of <br /> i TPH in the C5-C7 and C7-C8''carbon ranges. <br /> . 1 <br /> I <br />[ L) 18 <br /> ;L <br />