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2.5.1 Groundwater Depth and Gradient <br /> The depth to groundwater at the site rose from approximately 42 feet in November of 1992 <br /> to 37 feet in July of 1993, fell to 40 feet in October of 1993, then rose to 38 feet in February <br /> 1994.These fluctuations are due to seasonal effects and are common in San Joaquin County. <br /> The groundwater gradient at the site has varied from northwest in November of 1992 to <br /> northeast in February of 1994. <br /> 2.5.2 Petroleum Hydrocarbon Impacted Groundwater <br /> ' TPH as gasoline and diesel were detected in the initial sample collected from MW-1 in June <br /> of 1992 (260 ppb and 310 ppb, respectively). However, TPH as diesel has not been detected <br /> at the site since the initial sampling. <br /> ' Very low levels of benzene have been detected in samples from MW-1 and MW-4. Toluene <br /> was detected only in the initial sample from MW-1. No contamination has been detected <br /> ' in samples from MW-2, MW-3 or MW-5. Analytical results of groundwater samples are <br /> summarized in Table 2. <br /> 3.0 PROCEDURES <br /> 3.1 Monitoring Well Purge Procedures <br /> On May 31, 1994, a Solinst water level meter was-used to measure the depth to groundwater <br /> ' in the five monitoring wells, After water levels were measured, a 2-stage purge pump was <br /> used to purge approximately 7 to 9 gallons of water from monitoring wells MW-1, MW-4 <br /> ' and MW-5. Temperature, pH and conductivity were measured at one-gallon intervals and <br /> recorded. The purge water was placed in DOT-approved drums and stored on-site. Field <br /> data sheets are included in Appendix A. <br /> 3.2 Groundwater Sample Collection <br /> ' Water samples were collected from MW-1, MW-4, and MW-5 using new disposable plastic <br /> bailers. Three 40-m1 EPA vials and one 1-liter amber bottle of water were collected from <br /> each well and transported in a chilled container to Alpha Analytical Laboratories in Ukiah. <br /> . ' Each sample was analyzed for TPH as gasoline and diesel, and BTE&X in accordance with <br /> EPA methods 5030, 8015m and 602, respectively. <br /> ' 3.3 Soil Boring Installation <br /> Since petroleum hydrocarbons were detected in soil samples from MW-1, an assessment of <br /> the remaining impacted soil is required. Therefore, one additional soil boring was drilled to <br /> Oenbp 1 A.diSrrvin r— C <br /> W. .lift ORO-W4.10 J <br /> 1 <br />