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ENCLOSUREI <br /> Department of Toxic Substances Control 's <br /> Comments on the <br /> Pre-Design Data Report <br /> Operable Unit 1 <br /> Defense Distribution Region West, Tracy <br /> Defense Distribution Region West (DDRW) Tracy has produced <br /> a Pre-Design Data Report (PDDR) for the Operable Unit (OU) 1 <br /> groundwater remedial design. The PDDR is composed of three basic <br /> parts: 1) groundwater data collected for the OU-1 Remedial <br /> Investigation/Feasibility Study (RI/FS) , 2) presentation of the <br /> 3-D groundwater model, and 3) potential remediation scenarios. <br /> The Department of Toxic Substances Control's (DTSC) comments are <br /> as follows and the Regional Water Quality Control Board's <br /> comments are provided in Enclosure 2 . <br /> GENERAL COMMENTS <br /> 1. Groundwater data presented in PDDR is consistent with <br /> groundwater monitoring reports generated for the OU-1 <br /> RI/FS. DTSC accepts the data as the best possible factual <br /> representation of conditions for OU-1. <br /> 2 . The 3-D groundwater model components selected were MODFLOW <br /> and MT3D, both components were previously approved by all <br /> parties. DDRW Tracy has been diligent in updating the <br /> agencies on the model's development throughout the OU-1 <br /> RI/FS process. DTSC accepts the model as sufficient for <br /> developing the remediation scenarios presented in the PDDR. <br /> We recommend that the model undergo further refinement as <br /> additional hard data is obtained from the expanded interim <br /> groundwater treatment system. <br /> 3 . The preferred remedial action scenario in the PDDR was one <br /> that provided plume containment and capture with an <br /> extraction network placed entirely on DDRW Tracy owned <br /> property. Based on our evaluation of the PDDR and <br /> subsequent discussions during the March 22 and 23, 1995 <br /> project managers meeting, DTSC is supportive of this <br /> approach. To obtain plume capture in the most economical <br /> mode, DTSC recommends that DDRW Tracy move forward with the <br /> remedial design as rapidly as possible. The possibility of <br /> implementing a remedial action that is more aggressive then <br /> the PDDR the preferred remedial action scenario (while still <br /> staying on DDRW property) was discussed at the project <br /> manager's meeting. DTSC would recommend that the more <br /> aggressive approach be implemented, if feasible. <br />