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Mr. Trapp <br /> April 2 , 1996 <br /> Page 3 <br /> sewer lines and are not on the City's sewer map. In addition to <br /> mapping, video survey of these sewer lines and the sewer lines <br /> downgradient of the LCN facility to Sacramento Street until Louie <br /> Avenue should be conducted. This information will provide WZI <br /> with a better indication of the contaminant migration pathway. <br /> 4 . WZI proposes to conduct additional soil gas sampling after <br /> completing the sewer investigation. A statistically significant <br /> number of soil gas data points (approximately 15 to 20) around <br /> the Site using Geoprobe system or eYsivalert will c--ller!*.ed. <br /> The following information is needed pertaining to the <br /> proposed soil gas sampling task: <br /> a. Copies of the QA/QC soil gas sampling procedures. DTSC <br /> is attaching a partial list of soil gas consultants in <br /> Attachment A for your review and consideration. This list <br /> was compiled by the Los Angeles Regional Water Quality <br /> Control Board (LARWQCB) in March 1994 . You may contact the <br /> LARWQCB for an update of the list; <br /> b. The name of the mobile laboratory to be used and the <br /> laboratory QA/QC control manual ; <br /> C. Rationales to be used for the determination of soil gas <br /> sampling locations, and the depth intervals to be sampled. <br /> The proposed sampling depth ranging from 10 to 50 feet below <br /> ground surface at each of the sampling points, and the term <br /> "statistical significant" must to be defined for determining <br /> sampling locations and sampling intervals. <br /> d. The analytical method identified on page 4 should <br /> specif, detection limit to be achieved for all VOCs <br /> analyzed. The VOC compounds identified on page 5 should <br /> include all breakdown products of tetrachloroethene (PCE) <br /> and trichloroethene (TCE) . <br /> 5. WZI proposes to collect at least three groundwater samples. <br /> DTSC requires that a QA/QC groundwater sampling plan <br /> including decontamination procedures, analytical laboratory, <br /> analytical method to be used for analysis, and rationales to be <br /> used to determine groundwater sampling locations be submitted for <br /> review and approval by DTSC. <br /> 6. WZI proposes to use four wells in the vapor extraction <br /> system (VES) pilot study. WZI stated that "DTSC staff comments <br /> that were pertinent to the previously submitted workplan have <br /> been evaluated and used to develop the VES Pilot Study in this <br />