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MEMORANDUM CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION 3443 RaRoad Phme: (916) 361-5600 Sa=mentD, CA 95827-3098 ATSS:8-495-5600 TO: TON VORSTER, SR. ENGINEER FROM: DAVE BRENT, PROJECT ENGINEER i DATE: 1 April 1988 SIGNATURE:—C><------ _ �'n' SUBJECT: BECK DEVELOPMENT COMPANY TRACY SITE, SAN JOAQUIN COUNTY The Beck Development Company (BDC) has, by way of their consultant, the American Environmental Management Corp (AEMC) completed the one year quarterly ground water monitoring program implemented in early 1987. The program detected no ground water contamination in the three monitoring wells located around the old oil storage facility. Inconsistencies in the local ground water gradient however, warrant further sampling, increased water level measurements, and possibly additional monitoring wells to ascertain that a water quality problem does not exist. The quarterly monitoring program began in April 1987 and consisted of sampling the three water table monitoring wells for total petroleum hydrocarbons (TPH) and aromatic volatile organics (BTX) . Water level measurements were also taken during each of the four sampling events that have occurred since the program began. All ground water samples collected in each of the four quarterly monitoring events were shown to have no TPH or BTX contamination above the detection limits of 100 ug/1 and 0. 2 ug/1 respectively. One ground water sample collected in November 1986, prior to implementation of the quarterly monitoring program, detected toluene at <1. 0 ug/l and was apparently a result of laboratory error. The quarterly water level measurements indicate that the ground water gradient has shifted about 45 degrees to the north over the last 6 months (see attachment) . This shift has effectively eliminated, for the time being anyway, any truly downgradient monitoring wells. Without knowing if this shift represents a normal yearly fluctuation or if the original gradient was an anomaly, a slight possibility exist that the original downgradient wells are misplaced and contamination downgradient has escaped detection. The possibility of downgradient ground water contamination is mentioned as slight because the extent of soil contamination detected at the site in the original investigation (October 1986) was minimal and no floating or free product was found in the boreholes completed down to the concrete slab below the surface. Furthermore, monitoring wells BD-2 and BD-3 appear to be close enough to the source that mounding effects of a plume should produce