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• �� 3164 Gold Camp Drive Deltan Suite 200 Rancho Environmental v 9161638 20 Sava,CA 95670 Consultants,Inc. FAX:9161638-83$5 VIMME$ VICESLTH July 26, 1995 Mr. Mike Infurna Environmental Management Division Public Health Services San Joaquin County 1601 East Hazelton Avenue Stockton, California 95201 Subject: Overpurging of MW-5 Evaluation Exxon Retail Station No. 7-3330 3128 Benjamin Holt Drive Stockton, California Delta Project No. D093-810 . Dear Mr. Infurna: Delta Environmental Consultants, Inc. (Delta), has been authorized by Exxon Company, U.S.A., to perform ground water purging and sampling of monitoring well MW-5 at the above-referenced site. The ground water overpurging and sampling is proposed as a continuous monitoring program and evaluation of concentrations of petroleum hydrocarbons in ground water monitoring well MW-5. This letter presence the results of samples collected during the pumping test conducted on June 29 and 30, 1995, and further request that additional sampling and purging be conducted to evaluate if this process can be used as a means of reducing the concentrations in monitoring well MW-5. On June 29 and 30, 1995, a ground water pumping test was performed on monitoring well MW-5 in accordance to the Delta letter dated June 14, 1995. The letter described the methods and procedures for conducting the pumping test and was approved by San Joaquin County, Environmental Management Division. Monitoring well MW-5 was continuously pumped at a rate of approximately 4 gallons per minute using a submersible pump. After 24 hours of continuous pumping, approximately 5,800 gallons was removed from the well and discharged to an aboveground storage tank. The tank was emptied and removed from the site immediately after the test on June 30, 1995. The water was transported and disposed or recycled at a permitted facility. Ground water samples were collected approximately 30 minutes, 12.5 hours, and 24 hours into the test on June 29 and 30, 1995. Ground water sample analytical results are summarized in Table 1 and copies of the laboratory reports are included in Enclosure A. Ground water samples indicate that the concentrations increased from <0.5 micrograms per liter (µg/L) to 14 µg/L from the beginning of the test to the end of the test, and total petroleum hydrocarbons as gasoline remained below the laboratory's detection limit. Providing a Competitive Edge