SITE INFORMATION AND CORRESPONDENCE

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G ACTON • MICKELSON + van DAM, INC. Consulting Scientists, Engineers, and Geologists 5090 Robert J. Mathews Parkway, #4 (916) 939-7550 El Dorado Hills, California 95762 Fax (916) 939-7570 May 21, 1993 Mr. Larry Williams Department of Municipal Utilities City of Stockton 2500 Navy Drive Stockton, California 95206 19005.05 Subject: Limited Discharge of Ground Water From Closed Beacon Station #494 2185 East Fremont Street, Stockton, California Dear Mr. Williams: Acton s Mickelson o van Dam, Inc. (AMV), is`proposing to perform an aquifer pumping test at the subject location (Figure 1). The pumping test will provide information necessary for final design of a treatment system to remediate ground water containing dissolved petroleum hydrocarbons derived from gasoline. The pumping test will be conducted over a 2-week period, during which time an estimated 10,000 gallons of ground water will be extracted from beneath F. the site. This letter constitutes a formal request to discharge this water to the sanitary sewer system. In the proposed pumping test, ground water extracted from monitoring well MW-3 (Figure 2) will flow directly into a sewer line on site. Flow is expected to be continuous for the first 2 i days of the test, and intermittent thereafter. Maximum instantaneous- flow rate should be no higher than 1.5 gallons per minute (gpm), and the time averaged flow rate over the 2-week period should be about 0.5 gpm. An in-line flow totalizer will measure discharge flow during- the uringthe test. Table 1 summarizes analytical results for ground water samples collected from site monitoring wells since 1992. The three results for monitoring well MW-3 range from 0.83 parts per million (ppm) to 4.2 ppm for total petroleum hydrocarbons as gasoline (TPHg). Additional samples from monitoring well MM'-3 were collected on April 25, 1993, and analyzed for total toxic organics (TTO) by U.S. Environmental Protection Agency (EPA) Methods 624 and 625. The analytical results (Enclosure A) show the total TTO detected to be 2.0 ppm. Note, however, that 75 percent of the TTO was the 1.5 ppm benzene detected.in the 624 analysis.