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r Ms. Marla Guensler Exxon Company, U.S.A. �S October 16, 1995 Page 2 Ground Water Sampling and Analytical Re u�lt.. Ground water samples were collected from the monitoring wells using the field procedures described in Enclosure A. An additional ground water sample was collected from monitoring well MW-5 on July 27, 1995, prior to and following the overpurging approximately of 250 gallons of water from the well. Quarterly ground water monitoring sampling was performed on August 31, 1995, from monitoring wells MW-4, MW-5, and MW-6. Monitoring well MW-5 was overpurged on August 31, 1995, prior to quarterly sampling with a centrifugal pump. Approximately 240 gallons of water was removed. A ground water sample could not be collected from monitoring well MW-3 on August 31, 1995, because the well had been paved over. Following removal of the pavement, a ground water sample was collected from monitoring well MW-3 on September 11, 1995. All ground water samples collected from the site visits in July, August, and September 1995 were submitted to Sequoia Analytical (a California-certified laboratory) for analysis of benzene, toluene, ethylbenzene, total xylenes (BTEX), and total petroleum hydrocarbons (TPH) as gasoline. Cumulative analytical test results are summarized in Table 2. Ground water samples collected from monitoring wells MW-3 through MW-6 did not contain detectable concentrations of petroleum hydrocarbons during the third quarter quarterly monitoring event performed on August 31 and September 11, 1995, however, the ground water samples collected from monitoring well MW-5 on !` July 27, 1995, reported benzene concentrations of 0.62 and 1.2 micrograms per liter (µg/L) prior to, and following overpurging of the well, respectively. Copies of the laboratory's analytical reports and chain of custody documentation for this sampling event are presented in Enclosure B. Discussion Delta proposes to conduct a soil vapor extraction test using MW-5 to evaluate the concentration of petroleum hydrocarbon vapors in the vicinity of this well. Future Work The next quarterly monitoring event for this site is scheduled for November 1995. Remarks/Signatures The interpretations contained in this report represent our professional opinions, and are based in part, on information supplied by the client. These opinions are based on currently available information and are arrived at in accordance with currently accepted hydrogeologic and engineering practices at this time and location. Other than this, no warranty is implied or intended. Delta recommends that copies of this report be forwarded to the following agencies: Mr. Mike Infurna Ms. EIizabeth Thayer Environmental Management Division California Regional Water Quality Control Board, Public Health Services Central Valley Region San Joaquin County 3443 Routier Road Post Office Box 2009 Sacramento, California 95827-3098 Stockton, California 95201