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+{ <br /> yi <br /> Ow gp <br /> win <br /> I. <br /> IN <br /> Mr. Cliuck Carmel <br /> Scptem'oer 23. 1991 <br /> Page l? <br /> Discussion <br /> The general groundwater tlow direction and hydraulic gradient ..as not changed signisicrtntly at <br /> this site since rite previous groundwater raonitorini (April 1`91), `Ater levels decreased in all <br /> amprcct ��eus u.'i leeL to u.-la teeL wan an average atecrease of 0.3? feet. <br /> Monitoring well ATR-3 showed a decrease in benzene and an increase in the other BE'T'K <br /> ::,nsutuCMs and T?l1. <br /> Well ATR-4 showed an increase in benzene and a decrease to xylenes and TPH. Well ATR-5 <br /> showed an increase in TPH. The remaining monitoring wells showed no change or insignificant <br /> changes from the April 1991 sampling. <br /> Trichloroethylene (TCE) was detected in the sample from ATR-6 and 1,2-Dichlorethane (DCA) <br /> was detected in samples from ATR-?, -3, -4. and -6. DCA is a degradation product of TCE and <br /> tetrachloroethylene kP('E). TCE was a commonly wed solvent and PCE is a solvent comrnoniv <br /> used by dry cleaners. ARCO is not reported to have used these chemicals. their origin is from <br /> an unknown source. <br /> If you have any questions, please contact me or Ms. Suzanne McNaughwn at (916) -W-',-0123. <br /> Very truly yours, <br /> B WPd AND <br /> r v L <br /> r,o.wl �1 <br /> Projec na <br /> JD:SM.mkw <br /> Enclosures <br /> cc: Mr. Gordon Boggs, California Regional Water Quality Control Board, <br /> Central Valley Region <br /> Mr. Harlin Knoll, San Joaquin County Local Health District <br /> 1-jr. Steve Misner. Brown and Caldv-,ell <br /> Mr. Chris Winsor, ARCO Products Company <br /> orown and caldweil <br />