SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Site-Wide Comprehensive ROD -4- 1 May 1997 DDRW Tracy potential implementation of soil vapor extraction, or other treatment technology, to address VOC contamination (see general comment #8), the selected remedy should include the narrative standard. 8. Selected Remedies Include Field Investigations of VOC Source Areas: The ROD should clarify that contaminant fate and transport modeling was conducted at sites identified as having RI data gaps with respect to characterizing the lateral and vertical extent of vadose zone contamination. Asa result, the selected remedy for these sites, including SWMU 33, SWMU 20/23, Area 1 Building 10, Area 1Building 237, Area 3, and SWMU 1/Area 2, includes additional soil-gas sampling to determine the full extent of VOC vadose zone contamination prior to design of a remedial system. This will be accomplished as a predesign investigation during the RD/RA phase. The ROD should clearly reflect that these activities are part of the selected remedy for these sites. Language should be added to describe conditions that will "trigger" implementation of soil vapor extraction, or other treatment'technology, to address soil vapor contamination as part of each of these selected remedies (also see specific comment Section 9.0). Each remedy should state that the decision to build/expand/operate an SVE system will depend upon the magnitude of the threat to groundwater quality posed by the vadose zone contamination and an analysis of the technical and economic feasibility for SVE technology at the site. The ROD should further specify that each feasibility analysis shall be prepared by DDRW Tracy as a primary document. Text should be added to state that the decision shall be made by the signatory parties to the FFA and shall be based, at a minimum, on the following factors: a. whether the predicted concentration in the leachate at the capillary fringe (using an appropriate vadose zone model that predicts soil gas concentrations) will exceed the groundwater cleanup standards; b. the cost and time associated with installing and continued operation of the SVE system to remove the contamination in the vadose zone to achieve the vadose zone cleanup standards c. the cost and time associated with the predicted additional groundwater remediation if no SVE is implemented; and d. the incremental cost over time of vadose zone remediation compared to the incremental cost of groundwater remediation, on the basis of a common unit (e.g., cost to remove a pound of TCE), provided that the underlying groundwater has not reached aquifer cleanup levels. 9. Soil and Ground Water Remediation SWMUs 2, 3, 33: DDRW Tracy has not conducted the planned soil removal actions developed for the Sewage and Industrial Lagoons (SWMUs 2 & 3) and the Industrial Waste Pipeline (SWMU 33). Based on discussions during past RPM meetings, particularly the meeting on 17 March 1997 held to discuss the design objectives of these planned removal actions, and information presented in the 100% Design Analysis Report, dated January 1997, we understand that these removal actions are designed to excavate soil to meet target concentrations for the CoCs and to be continued beyond the target concentrations to achieve the final cleanup levels, or until the excavations reach a maximum distance of 4 feet above the water table at the time