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• • PETE WILSON.Gov m <br /> • ,4TE OPCALIFORNIA—ENVIRONMENTAL PROTECTION AGENCY <br /> DEPARTMENT OF TOXIC SUBSTANCES CONTROL <br /> 10151 CROYDON WAY,SUITE 3 <br /> SACRAMENTO,CA 95827-2106 <br /> (916) 255-3737 <br /> February 3, Eq D <br /> F E 0 0 5 11993 <br /> E►wVIRONKr TAL MrA. .TM <br /> Mr. Robert Doss, P.E. PERMIT/SERVICES <br /> Project Manager <br /> Pacific Gas & Electric Company <br /> Environmental Services <br /> 77 Beale Street, Room F-1636 <br /> San Francisco, California 94106 <br /> PACIFIC GAS & ELECTRIC (PG&E) , STOCKTON, REMEDIAL INVESTIGATION <br /> AND RISK ASSESSMENT REPORT <br /> Dear Mr. Doss: <br /> The Department of Toxic Substances Control (Department) has <br /> completed its review of the Remedial Investigation (RI) portion <br /> of the Remedial Investigation and Risk Assessment Report (RI/RA <br /> Report) submitted in November 1992 . Enclosed are the <br /> Department's comments concerning the RI portion. Comments #6 and <br /> #% also concern the general requirements for the Risk Assessment <br /> (RA) . Detailed RA comments will follow after the Department <br /> completes its review. Please address the following comments <br /> within three weeks from receipt of this letter: <br /> 1. Figure 4-8 contains a typographical error. The groundwater <br /> elevation value for Well MW-8 is listed as -34 . 27 . <br /> According to Table 4-2 , the correct value is -35. 27 . <br /> 2 . Paragraph two of Page 5-8 contains a typographical error. <br /> PNA concentrations were detected at borings B-25 and B-26 to <br /> 42 . 5 feet, not 4 . 25 feet. <br /> 3 . The discussion on Pages 5-13 and 5-14 on the use of TTLC and <br /> STLC is incorrect. The correct value to use is 10 times the <br /> STLC, not 20 times the STLC. <br /> 4 . The installation of groundwater monitoring Wells MW-11 and <br /> MW-12 have confirmed that PNA contaminants are migrating off <br /> site to the west and the southeast in the shallow zone. <br /> Installation of additional downgradient wells will be <br /> necessary to characterize the lateral extent of migration in <br /> the shallow zone. The objective of groundwater <br /> characterization includes defining the extent of <br /> contamination to background concentrations. The report must <br /> include a discussion describing the extent of <br /> characterization achieved and the additional work required. <br /> PG&E must evaluate the work necessary to complete <br />