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STATE OF CALIFORNIA-Environmental 1rotection7'gency PETE WILSON, Govemoi <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD <br /> CENTRAL VALLEY REGION <br /> 3443 Routier Road,Suite A <br /> Sacramento,CA 95827-3098 <br /> PHONE: (916)255-3000 <br /> FAX:(916)255-3015 <br /> 15 May 1996 <br /> Mr. Nathan Esformes <br /> Triple E Produce <br /> P.O. Box 239 <br /> Tracy, CA 95378 <br /> DOMESTIC WELL SURVEY NORTH OF MW-7, TRIPLE E PRODUCE FACILITY, <br /> TRACY, SAN JOAQUIN COUNTY <br /> I have reviewed the 3 January 1996 letter from Tom Guido regarding the Board's required <br /> domestic well survey north of MW-7 for the Triple E facility in Tracy. As noted by Mr. Guido, <br /> Triple E has already conducted a domestic well survey in this area. All domestic wells between <br /> MW-7 and Maurland Manor have been identified and the depth and screened interval of the <br /> wells have been determined, but these wells have not been sampled on a regular basis and have <br /> not been sampled in the past five years. Most of the wells have only been sampled twice, first in <br /> 1988 and again in 1991. Board staff sampled one of the wells in 1987. <br /> The increase in chloroform in MW-7 since it was installed in 1992 indicates that chloroform <br /> concentrations in the domestic wells north of MW-7 also may have increased. It is necessary to <br /> determine what concentrations of chloroform are present in the ground water for the protection <br /> of the residents who use the ground water for drinking. <br /> My responses to Trini_e E's additional comments are in reference to the noted sections of the <br /> letter. <br /> Northern Fringe of Chloroform Plume <br /> The northern fringe of the chloroform plume does not likely remain in the vicinity of Fair Oaks <br /> Road. The fringe of the plume is defined as nondetectable concentrations of chloroform. <br /> Chloroform has increased in MW-7, which is immediately south of Fair Oaks Road, from <br /> approximately 9 µg/1 when it was first installed in October 1992 to as high as 43 µg/1 in <br /> December 1994. In January 1996 the chloroform concentration was 19 µg/1. This exceeds the <br /> Proposition 65 regulatory level of 10 µg/l. As noted above, it is very likely that chloroform <br /> concentrations also have increased in the domestic wells downgradient of MW-7 since 1992. <br /> Although the capture zone predicted by the numerical model extends 200 feet or more north of <br /> Fair Oaks Road, it cannot be determined if the extraction well XW-1 will capture all of the <br /> chloroform plume since the actual extent of the chloroform plume north of Fair Oaks Road is not <br />