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u 45 East Harding Way, Stockton, California July 22, 1992 Chevron U S A Products Company Page 6 36 Groundwater Monitoring On May 19, 1992, the depth to water table in all monitoring wells was gauged to top of casing to determine the static level and thickness of any separate-phase hydrocarbons (SP) The water table level was measured using an ORS Environmental Equipment INTERFACE PROBETM Well Monitoring System, consisting of a dual optical sensor and electrical conductivity probe, that distinguishes between water and petroleum products No SP was present A potentiometric surface map prepared from the monitoring data is presented in Figure 3 3 7 Groundwater Sampling Prior to sampling, the wells were bailed to permit inflow of representative formation water into the well casing The baled water was to be measured for temperature, pH, and conductivity However, due to a technical failure, temperature, pH, and conductivity readings could not be collected, and so a minimum of four well volumes were removed from each well The groundwater samples were collected using a Teflon sampler cleaned with an industrial-strength detergent and distilled water Immediately prior to the collection of the water samples, a distilled water rinsate blank was collected from the Teflon sampler as a quality control check on the cleanliness of the sampler A triptlab blank was also collected for quality control Each sample was acidified, labeled, and placed on ice in an insulated container for delivery to a State-certified laboratory The samples were accompanied by a chain-of-custody manifest during transport and analyzed for TPH-G and BTEX by EPA methods 5030/8020/8015 The analytical results are summarized in Tabel 2, and the laboratory reports are enclosed in Appendix D Purge water generated during the sampling process was stored in a DOT- approved purge water trailer and transported to the Chevron refinery in Richmond, California for recycling The specific procedures used for groundwater monitoring and sampling are described in Groundwater Technology's Standard Operating Procedures (Appendix E) GROUNDWATER TECHNOLOGY I