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E: 2.2 Monitoring Wells MW-1 Through MW-3 The initial assessment was performed by Weiss Associates. Three groundwater monitoring ' wells were drilled in July 1987. Wells MW-1, MW-2, and MW-3 were completed with 4-inch diameter slotted PVC casing to depths of 65, 60, and 59 feet, respectively. Soil samples were ?' collected at 5-foot intervals during drilling;five samples were selected for laboratory analysis. After the wells bad stabilized, water depths were measured to determine the groundwater gradient, and groundwater samples were collected for analysis. The limited sampling performed in this phase indicated that soil contamination was limited to the vicinity of the former tank. No contamination was present in MW-2 and MW-3, but high concentrations of hydrocarbons were present in MW-1 (Table 1). Groundwater was contaminated in all three wells, with a maximum benzene concentration of 2,800 µg11 in MW-3 (Table 2). These results imply that gasoline migration through the soil was primarily downward until the groundwater interface was reached, followed by lateral migration in the capillary fringe. The groundwater gradient at that time was to the east-northeast, probably in response to drawdown in Lodi municipal well #1, which was located approximately 350 feet east of the site. This explains the high concentrations of hydrocarbons in the water sample from MW-3. The regional hydraulic gradient is to the southwest, which probably i' accounts for the contamination detected in MW-2. 2.3 Initial Monitoring According to information presently available to GeoAudit, no further work was performed at this site until November 1991, when Earth Systems Environmental (ESE) attempted to collect water samples and measure the depth to groundwater in wells MW-1 through MW-3. ESE reported that water levels had dropped to below the screened intervals in MW-2 and MW-3 and the wells were dry. Both water and floating product were present in MW-1, but no sample was collected. The depth to water in MW-1 was 60.12 feet. No further monitoring occurred in 1991. 2.4 Monitoring Wells MW-4 and MW-5 In January 1992, PHS/EHD required replacement of MW-2 and MW-3. Monitoring wells j' MW-4 and MW-5 were drilled to a depth of 75 feet in June 1992 and completed with 25 feet of 2-inch diameter slotted PVC casing. GeoAudit supervised the drilling and collected the samples. Seven soil samples and two water samples were analyzed during this phase of investigation. ' No hydrocarbon contamination was detected in any of the soil samples (Table 1). Low to moderate concentrations of hydrocarbons were detected in water samples from both MW-4 I� �y.:. Ar cmwS=t nada s<w�1 4