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Pacific Gas and Electric mpany Environmental Services <br /> `QSo/ 3VE LTfi <br /> 415/973- <br /> 91012/$73-A"12: 01 ial12/$7 <br /> dg A"J2: 0 1 <br /> August 19, 1996 <br /> James L. Tjosvold, P.E. <br /> Chief, Site Mitigation Branch <br /> California Environmental Protection Agency <br /> Department of Toxic Substances Control <br /> 10151 Croydon Way, Suite 3 <br /> Sacramento, CA 95827 <br /> Attention: Mr. Fernando Amador <br /> Dear Mr. Tjosvold: <br /> Subject Docket#HSA 90/91-08 -Stockton Former Manufactured Gas Plant <br /> Site -Responses to Comments on Draft Soil OUFS <br /> Enclosed are PG&E's responses to DTSC and RWQCB (the agencies) comments on <br /> the Draft Soil Operable Unit Feasibility Study (OUFS) report for the Stockton former <br /> manufactured gas plant(MGP) site. The soil OUFS report was submitted to the <br /> agencies on November 8, 1995. DTSCs comments were dated December 26, 1995 <br /> and the RWQCB comments (dated December 14, 1995) were included with DTSC's <br /> comments. It was agreed in the meeting held on November 30, 1995 that PG&E <br /> would address the comments concerning soil source area definition and conduct a <br /> solidification treatability study prior to submitting the final soil OUFS report. A <br /> conceptual model was developed and transport modeling was employed to <br /> evaluate chemicals of potential concern(COPC) migration from soil to groundwater. <br /> The modeling was documented in the Evaluation of Potential Groundwater Impacts <br /> from Residues in Soil report submitted in March 1996. It had been decided that once <br /> the delineation of the source areas was agreed upon by the agencies, the final OUFS <br /> would incorporate the remaining agency comments. <br /> A PG&E/agency meeting was held on May 22, 1996 for the purpose of agreeing on <br /> groundwater objectives and goals, reviewing results of the transport modeling, and <br /> discussing the results of the solidification treatability study. During this meeting, <br /> DTSC suggested that PG&E recombine the soil and groundwater feasibility studies. <br /> In PG&E's June 6, 1996 letter to DTSC, an approach is outlined and a schedule is <br /> presented for developing a combined groundwater and soil FS. The following <br /> responses to comments pertain to the draft soil OUFS; however where appropriate, <br />