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eto 37 feet in July of 1993, fell to 40 feet in October of 1993, rose to 37 feet in May 1994 and • dropped to 41 feet in September 1994. These fluctuations are due to seasonal effects and are common in San Joaquin County. The group gradient radient at the site has varied from northwest in November of 1992 to northeast in February of 1994. 2.5.2 Petroleum Hydrocarbon Impacted Groundwater ' TPH as gasoline and diesel were detected in the initial sample collected from MW-1 in June of 1992 (260 ppb and 310 ppb, respectively). TPH as gasoline and diesel were detected in MW-1 during the May 1994 monitoring event at concentrations of 100 ppb and 58 ppb, ' respectively. TPH as gasoline was detected in MW-1 at a concentration of 170 ppb during the September 1994 monitoring event. No TPH as diesel was detected during the September 1994 monitoring. Low concentrations of benzene have been detected in samples from MW-1 and MW-4. ' Toluene was detected in the initial sample from MW-1, the September 1994 sample from MW-4 and the May and September 1994 samples from MW-5. No contamination has been' detected in samples from MW-2 or MW-3. Analytical results of groundwater samples are summarized in Table 2. 2.6 Soil Boring Installation Low residual concentrations of toluene and leve were detected in three soil samples Lo r xylene collected from MW-1 in 1992. An assessment of the remaining impacted soil was ' subsequently required by the PHS/EHD. On July 13, 1994, one soil boring was drilled approximately 7 feet north of monitoring well MW-1 and advanced to a depth of 45 feet. Three samples, from depths of 35, 40 and 45 feet, were analyzed for TPH as gasoline and ' diesel and BTE&X. No petroleum hydrocarbons were detected in any of these samples. Therefore, it is likely that petroleum hydrocarbons detected in samples from MW-1 in 1992 are no longer present at the site or of very limited extent, and do not pose a significant risk to groundwater. 3.0 PROCEDURES ' 3.1 Limited Groundwater Extraction On December 7, 1994, the groundwater depth was measured in each monitoring well relative to the top of the casing using a Solinst water level meter (Table 1). An extended purge was then performed on MW-1 in an attempt to remove impacted groundwater at the site. A submersible pump was used to purge MW-1. Approximately 400 gallons of water were removed in 4.5 hours. Purge water was stored on-site in an above-ground 'Baker" tank. Q.obpn3 Au&Servwn,[.c. C We.eem C.ih QR6n7-9v1,10 J I