SITE INFORMATION AND CORRESPONDENCE

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Pre-Design Technical Su• -2- • 19 December 1996 DDRW-Sharpe The seven remaining VOC sites required further characterization to determine if they are a source areas for VOC in the ground water and warrant in-situ volatilization (ISV). Two additional sites were added to this characterization effort after a data review indicated that they may be degrading ground water. Information collected from the additional field work was to be used to determine if these areas required ISV or if they were in compliance with the ISV cleanup standard. The ISV standard as stated in Section 9.2.2 of the OU2 ROD, states that VOC contaminated soils will be remediated to be; 1) (a) protective of human health and the environment, and (b) not cause or threaten to cause concentrations in the ground water to exceed aquifer cleanup levels. All Parties agreed in the Sharpe ROD that a WE soil gas concentration at or below 350 ppbv would be considered to satisfy the ISV standard. However for those sites in which the soil gas concentrations in the vadose zone exceed 350 ppbv TCE, an interpretation of soil gas data is needed to evaluate what concentrations of VOCs will potentially reach the ground water at each VOC site. The technical and economic analysis presented in the Pre-Design Technical Summary is relevant only for areas where ISV has been operated and the VOC concentrations are below the ISV cleanup standard and Sharpe wants to proceed with remedial action. Therefore, the technical and economic analysis presented in section 5.2.2 is not appropriate at this time. This section should be replaced with an analysis to evaluate if concentrations of VOCs in the vadose zone could impact water quality and to determine if the standard under Section 9.2.2 has been met. 2. Based on 1987 data, Sites P-ID and P-5A (see Table 1)were targeted for ISV treatment because they were believed to be source areas for groundwater contamination found in plume 1 and plume 5. Omission of the areas from taking actions as required in the OU2 ROD will require preparation of a primary document that will provide greater detail and explanation into why the field results from this effort do not reflect the data collected in 1987. 3. It appears that the Pre-Design investigation was not conducted in some of the areas which showed the highest concentrations of VOCs. Soil gas investigations of VOC contaminated soil identified in the Pre-Design Technical Summary do not consistently match up with the areas of high concentration VOCs identified in the 1987 data. Specifically, sites P-113, P-4C and P5A identified during the 1987 investigation do not appear to have been adequately investigated during the Pre-Design field effort. Please incorporate the 1987 data into the VOC-contaminated site maps presented in the Technical Summary. Discrepancies between any locations of 1987 "hot spots" and the areas investigated in the Pre-Design Technical Summary, need to be explained. 4. The assumption in the ROD, that elevated levels of lead and chromium existed within 2 feet of the ground surface at locations where levels of chromium and lead exceeded the cleanup standard at depth, was not proven correct. Seven areas were reported to exceed the action levels in the South Balloon Area in the OU2- ROD on pages 28, 33 and 44. Soil samples collected as part of the RDFS detected the following concentrations.