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Ms. Laurie Cotulla <br /> December 5, 1988 <br /> Page 3 <br /> Groundwater Flow <br /> Groundwater levels at'the site are being measured in each well on a quarterly basis. The <br /> levels are measured with an. electronic water level indicator to determine groundwater <br /> elevations relative to top of casing elevations. Since late June 1988, the groundwater flow <br /> direction has remained constant and approximately due north. <br /> Conclusions <br /> The groundwater, samples collected during September 1988 show :that BETX concentrations <br /> have increased: in wells ATR-3, and ATR-4- Monitoring 'well ATR-1. has not shown <br /> significant levels of benzene since December 1987 (5.9p arts per billion)- ATR-2 has had <br /> nondetectable BETX concentrations since this investigation began in April 1987. <br /> Recommendations <br /> Because of the relatively high, BETX concentrations Brown and Caldwell recommends a <br /> continued monitoring and sampling program for the four monitoring wells at this site. This <br /> -sampling should ,be done on a quarterly basis. <br /> If you .have any questions or comments regarding this report, please .call -me or Steve <br /> Misner at (916).444-0123. <br /> Very truly yours, }� <br /> BROWN AND CALDWELL <br /> arry P fillips <br /> Projec Manager <br /> LEP:SDM:mkw <br /> -Enclosure <br /> cc: Mr. Kyle Christie, ARCO Products-Company. , ;San Mateo F <br /> cc/enc: Mr. Gordon Boggs,'California Regional Water Quality -Control Board, <br /> Central Valley Region, Sacramento <br /> i <br /> BROWN AND CALDWELL <br /> 723 S STREET SACRAMENTO,CALIFORNIA 95814-7092.(916)444-0123 jl <br />