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I n a GEOMA"Mix SUMMARY OF SOIL AND GROUNDWATER INVESTIGATION Fi' AND RECOMMENDATION FOR SITE CLOSURE Highiet/Monterosso Parcel .r Tracy, California FEXECUTWE SUMMARY This report was prepared by Geomatrix Consultants, Inc. on behalf of Chevron Pipe Line Company to Fpresent the results of previous assessments and recent groundwater monitoring performed at the Highiet/Monterosso parcel and to recommend appropriate further action, if any. The Highiet/Mon- terosso parcel (assessor's parcel number [APN] 238-040-02) is being developed for residential use and F is located at the southwest corner of the intersection of Corral Hollow and West Byron roads in Tracy, California. Two former pipeline systems that carried crude oil and Bunker C oil from the 1900s to F1950s were located parallel to West Byron Road; environmental assessments at the parcel have focused on the presence of petroleum hydrocarbons in subsurface soil. Soil and groundwater analytical results collected b Geomatrix and others demonstrate that etroleum Y p hydrocarbons in soil are limited in extent and have not impacted groundwater at the site. No further characterization appears necessary. Fingerprint characterization of the petroleum hydrocarbon at the Highiet/Monterosso parcel indicates it is similar to the petroleum hydrocarbon at the nearby Dividend FF property (degraded crude oil/Bunker C); therefore, comparison to the Dividend property regarding the potential health risk posed by the residual petroleum is appropriate. The Screening Health Risk As- sessment conducted for the Dividend property demonstrated that the residual petroleum poses no sig- nificant risk to future on-site residents. Accordingly, because the concentrations of petroleum in soil at the Highiet/Monterosso parcel are significantly less than those at the Dividend property (1,100 mg/kg vs. 7,500 mg/kg), we conclude that the residual petroleum at the site poses no significant risk to future on-site residents. FBecause the residual petroleum does not pose an environmental or human health risk, we recommend that the Highiet/Monterosso parcel be closed by'the San Joaquin County Environmental Health De- Fpartment (SJCEHD) and that development of the parcel proceed. We recommend that the four on-site monitoring wells be destroyed in accordance with SJCEHD requirements. F h F ii 6i