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%1r Chuck Cannel February i o 1993 Page Anah Tical results Tit groundwater samples are summarized in Table 3 The complete laborater-v report for the sampling event is presented in Exhibit A Figure 4 ,hows TPH-G and BETX concentrations for the October 1992 sampling e%ent Figure 5 is a benzene isoconcentration neap Benzene concentrations rangedfrom nondetectable in several wells to 240 micrograms per liter (ug/1) in ATR-4 TPH-G concentrations ranged from nondetectable in several wells to 1,200 ug/1 in well ATR-4 The detection limits for the BETX constituents and for TPH-G are 0 5 and 50 ug/l, respectively Approximately 0 01 feet of free product was measured in 4TR-3 ug Discussion Water level elevations have dropped an average of 0 15 feet across the site since July 1992 The groundwater flow is in a steady north-northeast direction with a 0 002 gradient Depth-to- water ranges from 8 69 feet to 13 09 feet Concentrations of hydrocarbon constituents are nondetectable or lust above detection Innits in on-site monitoring wells ATR-1, ATR-6, and ATR-7 and off-site monitonng wells ATR-9 through ATR-12 BETX and TPH-G concentrations in wells ATR-4 and ATR-8 have increased since the July 1992 quarterly sampling Benzene and TPH-G concentration increased slightly in well ATR-2 while ethylbenzene and TPH-G concentrations decreased m well ATR-5 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 Remediation at this site is expected to begin in the spnng of 1993 If you have any questions about the October 1992 sampling event, please contact me at (916) 444-0123. Sincerely, BROWN AND CALDWELL CONSULTANTS ay Lucas, R G Project Manager .TCL WL mrp Enclosures Mr Gordon Boggs, California Regional Water Quality Control Board �Ir Harlin Knoll San Joaquin County Local Health District Brown and Caldwell 67 2WEPORT510Ci' 0TRRPI' Cc su of i�