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• s � <br /> Sierra-Pacific Groundwater Consultants, Inc. Y Y <br /> Geologists, Engineers, and Compliance Specialists <br /> July 14, 1997 97 JUL 15 AM [k 22 <br /> Mr. W.T.Nickerson, Project Manager <br /> Unocal-DBG/AMG <br /> 2000 Crow Canyon Place, Suite 470 <br /> San Ramon, California 94583-0973 <br /> Subject: Response to Comments from Central Valley Region,Regional Water Quality Control Board, <br /> on Sierra-Pacific's Report Entitled "Evaluation of Alternatives for Remediation of 1,2- <br /> Dichloropropane in Ground Water, Former PureGroBrea Ag-Chem Facility, 1905 North <br /> Broadway Avenue,Stockton, California'; dated August 14, 1996, Sierra-Pacific Project No. <br /> 94-055.03 <br /> Dear Mr.Nickerson: <br /> As discussed in our April 16, 1997 meeting with Central Valley Region,Regional Water Quality Control Board <br /> (the Board), we have prepared this response to review comments issued by the Board for the above-referenced <br /> report. A copy of the review comments, dated March 5, 1997, is attached. <br /> The review comments included three general comments and a number of specific comments pertaining to <br /> various sections of the report. The general comments present regulatory policy, or regulatory decisions with <br /> respect to this site. We have no disagreement with any of the general comments. The following responses <br /> relate to the specific comments on the report sections cited. The reviewers comments are in quotation marks. <br /> Our responses, in italics, follow each comment. <br /> Executive Summary: <br /> 11 <br /> 1. The document states that the shallow groundwater contains up to 44 µg/l 1,2-DCP. Actually, two <br /> significantly higher concentrations have been detected: in 1993, MW-2 had 160 µg/l, while in 1995, <br /> MW-6 had 88 µg/U' <br /> The reviewer is correct, the highest concentration cited for 1,2-DCP was in error. <br /> "2. The"basic risk analysis"was not conducted per the Board's guidance for health risk assessments. A <br /> copy of the guidance memo is attached. In addition, there appears to be a basic misunderstanding of <br /> the Board's policy regarding sources of drinking water. As stated in the Basin Plan, except under <br /> specific circumstances, all groundwaters are to be protected as existing or potential sources of <br /> municipal or domestic water supply." <br /> We understand the Board's policy. <br /> (916)933-1468 <br /> 4911 Windplay Drive,Suite 4 EI Dorado Hills,California 95762 (916)933-3197 FAX <br />