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Updated Site Conceptual Model and Fourth Quarter 2002 Momtormg and Remediation Report <br /> Cleanup and Abatement Order No 5-00-707 EAI Project No 1232 <br /> 2.0 SITE CONCEPTUAL MODEL UPDATE <br /> In a letter dated February 8, 2002, the RWQCB requested completion of an updated Site <br /> Conceptual Model (SCM) for this site The initial SCM was submitted to the RWQCB in an <br /> EAI report titled "Supplemental Investigation Report, Problem Assessment Report, and Work <br /> Plan, Cleanup and Abatement Order No 5-00-707, Montgomery Ward Auto Service Center <br /> and Former Unocal Site, 5400 and 5606 Pacific Avenue, Stockton, California," dated October <br /> 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-stratigraphic 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 /> H dro-Strati ra hic Unit De th Interval feet b s <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-11 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 Hydrocarbons observed in ground water during this quarter were generally <br /> similar to, or lower than, the September 2002 testing results Possible exceptions were ground <br /> water samples obtained from wells MW-3, MW-4 MW-6, MW-23S, MW-23D, and AS-26 In <br /> general, these wells had slightly higher testing results <br /> r13HM WORD 1232Ra2D1 -4- EAWRONMENTAL AUDIT, INC <br />