ARCHIVED REPORTS XR0003978 - Laserfiche WebLink

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1 The analytical results implied that gasoline migration through the soil was primarily ' downward until the groundwater interface was reached, followed by lateral migration in the capillary fringe. Initially, the groundwater gradient was east-northeast, probably in response to drawdown in Lodi Municipal Well #1, which was located approximately 350 feet east of ' the site; this may explain the high concentration of hydrocarbons initially in the water sample from MW-3. The regional hydraulic gradient is to the southwest, which probably accounts for the petroleum hydrocarbons detected in MW-2. Lodi Municipal Well #1 was ' abandoned in 1991. t23 Initial Monitoring It is our understanding that no further work was performed at the site until November 1991. In November of 1991, Earth Systems Environmental (ESE) attempted to measure the t groundwater depths and collect water samples from wells MW-1 through MW-3. ESE reported that water levels had dropped below the screened intervals in MW-2 and MW-3 ' and the wells were dry. Floating product was present in MW-1 and no sample was collected. However, the product thickness in MW-1 was not reported by ESE. The depth to water in MW-1 in 1991 was 60.12 feet. No further monitoring occurred in 1991. ' 2.4 Installation of Monitoring Welts MW-4 and MW-5 ' In January 1992, PHS/EHD required replacement of MW-2 and MW-3. Monitoring wells MW-4 and -MW-5 were installed in June 1992. GeoAudit supervised the drilling and collected the samples. No petroleum hydrocarbons were detected in any of the soil samples from MW-4 or MW-5. Low to moderate concentrations of hydrocarbons were detected in water samples from both ' MW-4 and MW-5. Due to low water levels, none of the other wells could be sampled in June 1992. Measurement of the depth to groundwater in MW-1, MW-4, and MW-5 indicated that the groundwater gradient had rotated to the southwest, in accord with the ' regional gradient. Based on these results, GeoAudit recommended that two additional wells be installed to tdefine the limits of the petroleum hydrocarbon plume in groundwater. Subsequently, PHS/EHD required three additional wells, all located north and east of MW-1. ' 2.5 Installation of Monitoring Wells MW-6, MW-7 and MW-8 Monitoring wells MW-6, MW-7, and MW-8 were installed in April 1993. Two soil samples were analyzed from each well: one from the existing groundwater interface (55 feet) and one from the former groundwater interface (45 feet). Each sample was analyzed for TPH as ' gasoline and volatile aromatics (BTE&X). No petroleum hydrocarbons were detected in any of the samples analyzed. Oeok6aal Audi)Se M.&Inc. A M A Ar&t.OPMO-W-1.47 `F 1 1