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TreadweIEMIO <br /> • <br /> 2. Installation of a permanent cap with deed restrictions and maintenance <br /> 3. Focused excavation and off-site removal of soil where contamination exceeds acceptable risk <br /> concentrations <br /> 4. Focused excavation and on-site capping of soil where contamination exceeds acceptable risk <br /> concentrations <br /> 3.3 Operable Unit 2 <br /> OU 2 is comprised of areas 15, 16, and 21. Area 16 is the site of an operating soil venting and <br /> air sparging system installed to remediate soil and groundwater contamination with petroleum <br /> hydrocarbons from a leaking UST that has been removed. Area 15 has had eight USTs removed, <br /> and several episodes of contaminated soil excavation, and has residual groundwater <br /> contamination with dissolved-phase fuel and halogenated hydrocarbons. A minimal amount of <br /> residual soil contamination with petroleum hydrocarbons is present. Area 21 has had a leaking <br /> UST removed and is currently being evaluated for soil vapor extraction as a remedial measure <br /> for residual groundwater contamination due to petroleum hydrocarbons. The UST remediation <br /> activities at each of the sites in OU 2 are under the regulatory oversight of the San Joaquin <br /> County Department of Public Health. <br /> The current total excess cancer risk for Areas 15, 16, and 21 range from 2E-03 (Area 21 resident) <br /> to 4E-06 (Area 15 construction worker). Predicted blood lead concentrations do not exceed <br /> 10 ug/dl at any of the Areas. <br /> Cancer risk-based concentrations in soil at both Areas 15 and 16 are driven solely by the <br /> presence of arsenic,where the calculated background arsenic concentration of 8.76 is exceeded <br /> only once, at 1513-2-6.0 where 41.0 mg/kg of arsenic was detected. <br /> Non-cancer hazard-based target concentrations for soil at Areas 15 and 16 are present for <br /> residents only. At Area 15, arsenic and total xylene drive the risks, and at Area 16, arsenic and <br /> potentially barium drive the risk. <br /> 19 <br /> 25970318.PGS 15 November 2000 <br />