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Treadwell&Rollo <br /> • <br /> Soil Criteria <br /> 1. USEPA Region 9 Preliminary Remediation Goals (PRGs) (1 October 1999). PRGs are risk <br /> based concentrations used to help evaluate and cleanup contaminated sites. The EPA <br /> Identifies PRGs for soil at residential and industrial sites, ambient air, and tap water. <br /> 2. Site-specific risk assessment findings may define human and ecological exposure, requiring <br /> mitigation to specific limits. <br /> 1.6 Target Cleanup Goals <br /> Cleanup goals must be protective of human health and the environment. Given the generally low <br /> level of estimated excess cancer risk, low total non-cancer risk, and low predicted blood lead <br /> concentration of the current, unremediated situation, it is anticipated that cleanup requirements <br /> will not be difficult to achieve. Target cleanup goals presented in this Feasibility Study are <br /> based on commercial/industrial end-uses of the various properties. However, residential cleanup <br /> • goals could be met, principally by additional soil excavation and removal, if residential <br /> development is desired. It is anticipated that deed restrictions will be used as administrative <br /> controls on certain properties (discussed below)to minimize the potential human health exposure <br /> scenarios. In keeping with the agreement between DTSC and Stockton, we present target <br /> cleanup goals on a site-specific basis. These were derived from the values calculated for and <br /> presented in the 2000 "Risk Assessment,North Shore Parcels, Stockton, California." A Draft <br /> Remedial Action Plan will be issued in October 2000. <br /> Arsenic occurs in soil at each parcel. A statistical analysis of all arsenic data was performed to <br /> determine an acceptable background value. Assuming that the two highest arsenic values are <br /> excavated and removed (88 mg/kg at Area 10 and 110 mg/kg at Area 20), a 95% log normal <br /> upper confidence level (UCL) of 8.76 mg/kg was calculated for the remaining 111 arsenic <br /> samples taken from OU 1 and OU 2, with a geometric mean of 4.72. (Removal of the two high <br /> values was done to not skew the calculated mean and 95%UCL to the high side.) These values <br /> compare to 95%UCLs of 14 mg/kg and 31 mg/kg for colluvium and fill and the Great Valley <br /> • <br /> 13 <br /> 25970318.PGS 15 November 2000 <br />