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STATE OF C.1.1-1 FORNIA—ENVIRONMENTAL PROTECTION AGENCY PETE WILSON.Gov„r <br /> CALIF(_,)R,NIA REGIONAL WA- I OUALITY CONTROL B.OARD— <br /> C_.>'NTRAL VALLEY REGION <br /> 3443 ROUTIER ROAD. SUITE A <br /> SACRAMENTO,CA 95827-3098 <br /> PHONE: (916)255-3000 z:77. .7717-: <br /> FAk (916)255-3015 <br /> 19 December 1994 <br /> "114N, HEALIH <br /> Mr DOLICI Ohland NVUUNNIr <br /> PERMIT/SERVICES <br /> Southwest Hide Companv <br /> P.O. Box 795 <br /> Modesto CA 95353 <br /> CLOSURE OF CLASS 11 SURFACE IMPOUNDMENTS, SOUTHWEST HIDE <br /> COINIPANY, 11651 PALM LANE, MANTECA, SAN JOAQUIN COUNTY (Case <br /> X <br /> No. 2664) <br /> Regional Board staff have reviewed your request for Closure of the Class H surface impoundments <br /> at your facility in Manteca. We concur with Your request to complete closure, although, as <br /> discussed below, we do not agree with your use of the Threshold Limit Value for determination of <br /> background in this context. Our principal concern is with the mitigation of the ground water <br /> impacts at this site, and we regard cleanup Of contaminated soils and closure of the impoundments <br /> as important steps in the site remediation process.: herefore, subject to the concerns and <br /> limitations expressed in this letter, YOU may proceed to backfill the impoundment arca with clean <br /> soil. <br /> 1. REVIEW OF ANALYTICAL RESULTS .AND DETERMINATION OF <br /> IMPOUNDMENT LEAKAGE: <br /> In reviewing the analvtical results of the ten samples from the impoundment subliner and berm <br /> soils, we noted a significant range of values in the concentrations of TDS and chlorides <br /> (i.e.,chlorides ranged from not detected to 12,000 ppm and TDS from 540 ppm to 11,000 ppm). <br /> Sample SLB-4, taken from the north berm of the eastern impoundment, was the highest (TDS <br /> 11,000 ppm, chlorides = 12,000 ppm). Five other samples (three from berms, two from subliner <br /> soils) contained significant TDS (1900 to 5300 ppm). The remaining four samples contained TDS <br /> concentrations in the range of several hundred ppm. This uneven "clustering" of analytical results <br /> 1.) t7 <br /> is also evident in soil samples from other portions of the Southwest Hide site, although the highest <br /> concentrations from other areas are many times higher than any obtained from the impoundments <br /> area. <br /> Regarding the entire Southwest Hide site, the sample location maps show that high concentrations <br /> Of TDS and chlorides OCCLIr in "hot spots", vdille some other areas exhibit very low concentrations. <br /> These results cannot be attributed to variation in soil properties: In a June 1994 site visit, staff <br /> observed that the soils are dominantly fine sands and silts. Therefore. our review of the soil <br /> samplino, results and site conditions Supports the suggestion that historical site practices contributed <br /> significantly to soil contamination. Because the berms around the impoundment. - <br /> were C011SILI'LICLCLI. <br /> Of on-site soils, some contamination in the berms is expected. Because the impoundments were <br />