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Remedial Investigation Report -10- 8 March 1991 <br /> DDRW, Sharpe <br /> rainfall record as shown begins in October 1987 and the first year of drought <br /> began the previous year (Winter 1986 to 1987) . The precipitation record begins <br /> in the drought period and therefore, does not show a reduction in the rainfall <br /> over time. The hydrographs should be revised using wells with the longest <br /> historical record and with an equivalent period for the record of precipitation <br /> to support the finding. <br /> FINDING <br /> 27. A small area of very highly contaminated ground water (12,000 µg/L TCE) has been <br /> identified in Plume 6. <br /> RESPONSE <br /> 27. I concur with this finding. The highest concentrations of TCE have been detected <br /> in Plume 6. The October to December 1990 Quarterly Ground Water Monitoring Report <br /> Monitor reported a concentration of 13,200 Mg/l for the sample from monitor well <br /> 455-B. <br /> FINDING <br /> 28. Over 300,000,000 gal of contaminated ground water have been extracted and treated <br /> by the South Balloon Groundwater Treatment System, removing over 400 lb of TCE. <br /> RESPONSE <br /> 28. Finding is noted. <br /> FINDING <br /> 29. A thorough investigation of the potential discharge of hazardous and/or toxic <br /> materials from the combined industrial waste/storm sewer system at SHAD <br /> demonstrated no evidence of contamination. <br /> RESPONSE <br /> 29. Finding is noted. The investigation of the sewer system used soils gas surveys <br /> in the areas of the worst breaks in the lines which was based on a television <br /> survey of the lines. Only five soils borings were installed with three samples <br /> collected per boring. This seems like a minimal number of soils samples to the <br /> number of observed cracks in the lines. In addition, soils-gas surveys indicate <br /> the relative concentrations of the vapor phase of contamination, whereas soil <br /> samples indicate concentrations of the dissolved phase. <br /> FINDING <br /> 30. Although more than eight different laboratories have analyzed samples as part of <br /> this study, the quality of the data, as evidenced by the agreement between <br /> laboratories, is generally very good. <br /> RESPONSE <br /> 30. Finding is noted. <br />