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Updated Site Conceptual Model and Third Quarter 2002 Monitoring and Remediation Report <br /> Cleanup and Abatement Order No 5-00-707_ EAI Pr_ject No 1232 <br /> 2.0 SITE CONCEPTUAL MODEL UPDATE <br /> In 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-strati graphic 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 />' H dro-Strati ra hrc 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 /> 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 dunng <br /> winter months Slightly elevated TPH-G concentrations were observed in monitoring well <br /> MW-11 during this sampling event This may be the result of the air sparging system Iiberating <br /> hydrocarbons that have been entrained in soils below the top of the water table <br /> i <br /> BHM WORD 123280291 -4- ENVIRONMENTAL AUDIT,INC p <br />