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} <br /> Mr Chuck Carmel <br /> August 11 1992 <br /> Page 2 <br /> Figure 4 presents the TPH-G and BETX concentrations for the April 1992 sampling event <br /> Figure 5 presents a benzene isoconcentration map <br /> Benzene concentrations ranged from nondetectable in several wells to 150 micrograms per <br /> liter (pg/1) in ATR-4 TPH-G concentrations ranged from nondetectable in several wells to <br /> 560 pg/l in well ATR-4 The detection limits for the BETX constituents and for TPH-G are <br /> 0 5 and 50 ug/l, respectively Approximately 0 01 feet of free product was detected in ATR-3 <br /> Discussion <br /> The northeasterly groundwater flow direction and a 0 003 hydraulic gradient is common for <br /> flus site Groundwater flow directions and hydraulic gradient for the past two years of <br /> groundwater monitoring range from north to northeast and 0 001 to 0 003,respectively Water <br /> level elevations increased an average of 0 10 feet since the January 1992 water level <br /> measurements ATR-10 showed a slight decrease in water elevation from the previous <br /> sampling period The average depth-to-water is 10 56 feet <br /> BETX and TPH-G concentrations continue to be nondetectable in four off-site wells (ATR-9 <br /> through ATR-12) and three on-site wells (ATR-1,ATR-2, and ATR-6) BETX concentrations <br /> in wells ATR-4 and ATR-5 have decreased or are nearly the same since the January 1992 <br /> quarterly sampling Well ATR-4 shows a decrease in TPH-G concentration, however, the <br /> same constituent in ATR-5 has increased All constituents analyzed in well ATR-8 have <br /> increased since January 1992 Well ATR-3 contained a trace of free product (thickness less <br /> than 0 01 feet) Well ATR-3 has contained traces of free product previously <br /> If you have any questions about this April 1992 sampling event, please contact me at <br /> (916) 444-0123 <br /> Sincerely, <br /> BROWN AND CALDWELL CONSULTANTS <br /> 7 4&m <br /> j', <br /> Lucas, R G <br /> Project Manager <br /> JCL WL mkw <br /> Enclosures <br /> cc Mr Gordon Boggs, California Regional Water Quality Control Board <br /> Mr Harlin Knoll, San Joaquin County Local Health District <br />.' Mr Chris Wmsor, ARCO Products Company <br /> Brown and Caldwell 6732TREPORTSI. P QTRAYr <br /> Consultants <br />