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Mr Chuck Carmel October 15, 1992 Page 2 Analytical results of groundwater samples are summarized in Table 3 The complete laboratory report for the samplmg event is presented in Exhibit A Figure 4 shows TPH-G and BETX concentrations for the July 1992 sampling event Figure 5 is a benzene isoconcentration map Benzene concentrations ranged from nondetectable in several wells to 150 micrograms per liter (pg/1) in ATR-4 TPH-G concentrations ranged from nondetectable in several wells to 590 pg/l in well ATR-4 The detection limits for the BETX constituents and for TPH-G are 0 5 and 50 pg/l, respectively Approxunately 0 01 feet of free product was detected in ATR-3 Discussion Water level elevations have dropped an average of 0 27 feet across the site since April 1992 The groundwater flow is in a steady north-northeast direction with a 0 002 gradient Depth-to- water ranges from 8 48 feet to 12 90 feet Concentrations of hydrocarbon constituents are nondetectable or nearly nondetectable in on- site monitoring wells ATR-1, ATR-2, and ATR-6 and off-site monitoring wells ATR-9 through ATR-12. BETX and TPH-G concentrations in wells ATR-4,ATR-5, and ATR-8 have not changed measurably since the April 1992 quarterly sampling BETX concentrations in ATR-5 and ATR-8 have decreased, however, ATR-4 showed an increase Well ATR-3 has not been sampled this year due to a trace of free product (thickness approximately 0 01 feet) found each quarterly sampling period If you have any questions about the July 1992 sampling event, please contact me at (916) 444-0123 Smcerely, BROWN/AND CALDWELL CONSULTANTS f/ 6aCC Lucas, R G Project Manager JCL.WL.jrb Enclosures cc: Mr Gordon Boggs, California Regional Water Quality Control Board Mr Harlin Knoll, San Joaquin County Local Health District Brown and Caldwell 673TRF"RTWUL92QTRX1'r Consuitants