SITE INFORMATION AND CORRESPONDENCE

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Draft Final Phase I SCR 3 13 July 1994 DDRW, Tracy Ground water at this site must be sampled and analyzed to determine the presence or absence of dioxins. 3. Section 5.2.25, SWMU 30 - Salvage Area: Recommendations have been added in this section for additional samples to characterize the extent of phenols in soils at this site. This section also recommends that these additional soil samples be analyzed for PAHs. Additional soil borings may be necessary to completely define the nature and extent of soil contamination at this site. However, no additional work is proposed for this site in the site- specific recommendations for the Phase II investigation presented in Tables 7-1 and 8-1 of the Draft Final Phase I SCR. A focused soil gas survey must be conducted to further assess the extent of volatile organic constituent (VOC) contamination, and to evaluate this site as a potential source area for TCE and PCE ground water contamination (See comment #5). 4. Section 5.4.4, Area 1 Building 237: This section recommends that no further soil investigation be implemented during the Phase II investigation at this site. We do not concur with this recommendation. This section states that the PCE soil contamination can generally be constrained to the area around the northeast corner of Building 237. However, previous soil sampling in this area was limited to samples taken from one soil boring located to the north of Building 237 where the highest concentrations of PCE were detected in the sample taken from nearest the water table. The vertical and lateral extent of PCE contamination northeast of Building 237 is not defined. A focused soil gas survey should be conducted to further define the extent of contamination and to confirm this site as a potential source area for the OU1 ground water plume (See comment #5). 5. Section 5.4.5, Area 2: A "limited" soil-gas study is proposed to be performed in the southeastern portion of Area 2, which targets depths of 2 to 4 feet below ground surface in the area around soil borings SB-113 and SB-114. Additional soil borings are proposed to be drilled to characterize the vertical extent of contamination in the area, if clearly-defined "hot spots" are identified in the soil-gas results. A more appropriate method to assess the extent of VOC contamination at this site would be expansion of the soil gas survey rather than soil borings because these contaminants can volatilize during soil sampling leading to an underestimation of the concentration and volume of contamination. For sites where VOC contamination is determined to exist in concentrations that threaten or have impacted water quality, then commonly, the unsaturated zone is remediated using vapor extraction. This treatment technology is used to remediate the vapor phase contamination. Therefore, in order to properly assess vapor phase contamination either for purposes of definition of extent or verification of cleanup, a soil gas survey would be more appropriate. The use of additional soil gas survey methods at this site, and other SWMUs contaminated with VOCs, may be critical to completing the RI/FS in an adequate manner. 6. Section 5.4.6, Area 3: No further soil investigation is proposed for the Phase II investigation. A focused soil gas survey must be considered to further define the extent of VOC contamination, and to evaluate this site as a potential source area for OU1 ground water plume (See comment #5).