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Mr. Stephen Muir <br /> September 6, 1996 <br /> Page 2 <br /> 2 . SVE System Stabilization Criteria. <br /> This criteria has been changed three times since <br /> December 15, 1995 . The criteria was 112%" in the <br /> December 15 , 1996 version, and then changed to 1120%" in <br /> the May 6 , 1996 version. Now in the August 1996 the <br /> criteria is listed as 1110%" (Page 5, section 4 . 3) . <br /> DTSC specified in the April 4, 1996 letter and <br /> reiterated in the June 5, 1996 letter that, the mass <br /> removal rates and the VOC concentrations in the <br /> extracted vapor shall not vary by more than two percent <br /> (2%) during four consecutive weekly monitoring events. <br /> 3 . Samples Collection and Analysis. <br /> Methods for analyzing soil gas samples were not <br /> discussed in the first proposal . In the second <br /> proposal, the use of a laboratory to analyze all soil <br /> gas samples was implied in the statement to justify the <br /> change of proposed stabilization criteria from 29. to <br /> 20% (The second paragraph of page 5) . <br /> After realizing the consultants' intent of sending <br /> all soil gas samples to a laboratory for complete VOC <br /> analysis, DTSC responded in the June 5, 1996 letter <br /> that (1) it was not necessary to run complete VOC <br /> analysis on all samples collected; lot of the samples <br /> for VOC analysis is adequate; and (2) the field <br /> instrument Flame Ionization Detector (FID) can be used <br /> in lieu of a laboratory; and (3) the total VOC <br /> concentrations (TOC) measured by the FID can be used to <br /> determine whether the system has reached the asymptotic <br /> level ra'Eher than waiting for the VOC analytical <br /> results from the laboratory. <br /> Following DTSC' s recommendations would save the <br /> RPS considerable sampling and operational <br /> costs in the <br /> compared to the consultants' proposal . <br /> August proposal, the consultants now propose 115%" of <br /> soil gas certifiedsamples be laboratorycforeated and completenVOCzanalstate <br /> ysis <br /> 4 . Soil Gas Confirmation Test. <br /> DTSC repeatedly stated that soil gas confirmation <br /> sampling is required at the closure fthe HowevSVE estethe <br /> even after it meets DTSC' s cleanup goals . <br /> proposal continues to indicate that "Clean closure <br />