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i to 37 feet in July of 1993, fell to 40 feet in October of 1993, rose to 38 feet in February 1994 and rose to 37 feet in May 1994. These fluctuations are due to seasonal effects and are common in San Joaquin County. The groundwater gradient 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. Very low levels of benzene have been detected in samples from MW-1 and MW-4. Toluene was detected in the initial sample from MW-1 and the May 1994 sample 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 I ' Low residual concentrations of toluene and xylene were detected in three soil samples 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 do not pose a significant risk to groundwater.. 3.0 PROCEDURES 3.1 Monitoring Well Purge Procedures On September 14, 1994, a Solinst water level meter was used to measure the depth to rgroundwater in the five monitoring wells. After water levels were measured, a purge pump was used to remove approximately 5 to 7 gallons of water from monitoring wells MW-1, MW-4 and MW-5.Temperature, pH and conductivity were measured at one-gallon intervals using an ICM water analyzer. The purge water was placed in DOT-approved drums and stored on-site. Field data sheets are included in Appendix A. Ceebpal Aode Serviora,!ac- C Wntem lift QA5A69V-L.10 5