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Former Discovery Chevrolet March 20, 1998 <br /> Tracy.CaliforniaProblem Assessment Report <br /> during drilling of the monitoring wells. Subsequent to the development of wells MW-4 and <br /> MW-5, groundwater samples were collected from all five site wells and analyzed for TPHg, <br /> BTEX and bio-parameters (historical Horizon Table 2 and Table 3 in Appendix C). The <br /> groundwater samples collected and analyzed from wells MW-1 and MW-2, located within <br /> the dissolved hydrocarbon plume, indicated lower concentrations of nitrate, sulfate, and <br /> ferric iron than the concentrations detected in perimeter wells MW-3 through MW-5. The <br /> bio-parameters demonstrated that intrinsic bioremediation is a viable and active method of <br /> remediation at the site. The overall historical trend has been a reduction in hydrocarbon <br /> concentrations in the groundwater beneath the site. <br /> Hand borings SA through SK were drilled around and in the former UST excavation by <br /> Horizon personnel to a depth of approximately 8 feet bsg on April 3, 1997. Selected soil <br /> samples collected from the hand borings were analyzed and reported concentrations of <br /> gasoline hydrocarbons with the highest concentrations in hand borings SB and SK in the <br /> vicinity of the former product lines adjacent to the southwest corner of the former UST <br /> excavation. The TPHg/Benzene results in boring SB at 8 feet bsg were 4,370/16.5 ppm. <br /> Boring SK was analyzed at 5 feet (6,110115.7 ppm) and 8 feet (6,290118.5 ppm) bsg (see <br /> historical Horizon Table 1 and Figure 3 - Work Area in Appendix C). Results of this <br /> investigation were summarized in Report of Additional Subsurface Investigation (Horizon, <br /> June 6, 1997). <br /> 4.0 FIELDWORK <br /> The field work was accomplished as outlined in Horizon's Work Plan No. 3001-13, dated <br /> January 27, 1998 and letter Addendum to Work Plan, dated February 10, 1998. The work <br /> plan and addendum were submitted to the SJC DHS/EHD and the California Regional Water <br /> Quality Control Board-Central Valley Region (CRWQCB-CVR). The SJC DHSIEHD <br /> approved the work plan and addendum in February 1998. <br /> 3001-12.par 4 HORIZON ENVIRONMENTAL INC. <br />