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Mr Chuck Carmel March 26, 1993 Page 2 Benzene concentrations ranged from nondetectable in several wells to 240 micrograms per liter (pg/1) in ATR-4 TPH-G concentrations ranged from nondetectable in several wells to 1,200 pg/1 in well ATR4 The detection lunnts for the BETX constituents and for TPH-G are 0 5 and 50 pg/l, respectively Approximately 0 01 feet of free product was measured in ATR-3 Discussion Water level elevations have increased an average of 105 feet across the site since October 1992 The groundwater flow direction was to the west-northwest for the first time since monitoring began in 1987, the flow direction has historically been measured to range from north to east The hydraulic gradient (0 004) is slightly greater than previously measured, it has ranged from 0 001 to 0 003 in the past Depth-to-water ranges from 7 09 feet to 11 33 feet. Concentrations of hydrocarbon constituents are nondetectable or ,lust above detection limits in on-site monitoring wells ATR-6 and ATR-7, and off-site monitoring wells ATR-9 through ATR-12. BETX and TPH-G concentrations in wells ATR4, ATR-5, and ATR-8 are within the range of previously reported values Well ATR-3 has not been sampled since the fourth quarter of 1991 due to a trace of free product (thickness approximately 0.01 feet) found each quarterly samplmg period • Remediation at thrs site is expected to begin in the spring of 1993 If you have any questions about the January 1993 sampling event, please contact me at (916) 444-0123 Sincerely, BROWN AND CALDWELL CONSULTANTS C.3-2�7 Jay 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 0 Brown and Caldwell 740MUIPMTSV M3QrItAFr Consultants