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139 South Center Street, Stockton, California <br />Chevron U.S.A. Products Company <br />3.8 Groundwater Monitoring <br />January 25, 1993 <br />Page 5 <br />On November 10, 1992, the water table in all five monitoring wells was gauged to grade to determine <br />the static level and thickness of any separate -phase hydrocarbons (SP). The water table level was <br />measured using an ORS Environmental Equipment INTERFACE PROBETm Well Monitoring System, <br />consisting of a dual optical sensor and electrical conductivity probe, that distinguishes between water <br />and petroleum products. No SP was present in any of the wells. The data revealed a southeast <br />groundwater flow direction at a gradient of between 0.0033 and 0.002 (Figure 3). <br />3.9 Groundwater Sampling <br />Prior to sampling, the wells were purged of a minimum of four well casing volumes. Temperature, <br />conductivity and pH were also measured during purging. The groundwater samples were collected <br />using a Teflon sampler cleaned with an industrial -strength detergent and distilled water. Immediately <br />prior to the collection of the water samples, a distilled water rinsate blank was collected from the <br />Teflon sampler as a quality control check on the cleanliness of the sampler. A trip/lab blank was <br />also collected for quality control. Each sample was acidified, labeled, and placed on ice in an <br />insulated container for delivery to a State -certified laboratory. The samples were accompanied by a <br />chain -of -custody manifest during transport and analyzed for TPH-G and BTEX by EPA methods <br />5030/8020/8015. Purge water generated during the sampling process was stored in a DOT - <br />approved purge water trailer and transported to the Chevron refinery in Richmond, California for <br />recycling. SOP's for groundwater sampling are listed in Appendix F. <br />GROUNDWATER <br />TECHNOLOGY <br />