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' Updated Site Conceptual Model and Second Quarter 2002 Monitoring and Remediation Report <br /> Cleanup and Abatement Order No 5-00-707 EAl Project No 1232 <br /> . 2.0 SITE CONCEPTUAL MODEL UPDATE <br /> iIn a letter dated February 8, 2002, the RWQCB requested completion of an Updated SCM for <br /> this matter The initial SCM was submitted to the RWQCB in an EAI report titled <br />' "Supplemental Investigation Report, Problem Assessment Report, and Work Plan, Cleanup and <br /> Abatement Order No 5-00-707, Montgomery Ward Auto Service Center and Former Unocal <br /> Site, 5400 and 5606 Pacific Avenue, Stockton, California," dated October 13, 2000 <br /> Site stratigraphy is segregated into four hydro-stratigraphic units that generally correspond to <br /> screened intervals on ground water monitoring wells The shallowest wells are screened in the <br /> hydro-strati graphic unit designated as Unit A and the deepest wells are screened across hydro- <br /> stratigraphic Unit D (see Figure 3 and Table 2) The approximate depth intervals <br /> corresponding to the hydro-stratigraphic units are as follows <br /> Hydro-Stratigraphic Unit Depth Interval (feet bgs) <br /> A 30-50 <br /> B 50-70 <br /> C 85-90 <br /> D 98-103 <br />' Figures 4 through 7 present a "Trend Analysis" for ground water monitoring wells MW-2, <br /> MW-3, MW-1l and MW-12, respectively The trend analysis indicated a general decline in <br /> hydrocarbon concentration in ground water with slightly higher concentrations observed during <br /> winter months <br /> 6HM 1232RO231 -4- <br /> ENVIRONMENTAL AUDIT, INC <br /> 1 <br />