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' Updated Site Conceptual Model and Third Quarter 2003 Monitormg and Remediation Report <br /> Cleanup and Abatement_Order No_ 5-00-707_ ___ EAI Prosect No-I <br />' 2.0 <br /> 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 /> 1 EAl 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 (Figure 3 and Table 2) The approximate depth intervals corresponding to <br /> the hydro-stratigraphic units are as follows <br /> Hydro-Strati ra hic Unit Depth 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 /> N 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 />' lower than the May 2003 testing results The two exceptions are wells MW-11 and MW-12, <br /> which indicated higher hydrocarbon concentrations in ground water <br /> BHM WORD 1232RO351 -4- <br />