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Draft Final Phase I SCR 2 13 July 1994 DDRW, Tracy Section 4.3.0.0.3. The appropriate factors must be determined using the vertical distance from the pollutants, or constituents of concern, in the vadose zone soils (the location of the constituents for which the analysis is performed) to the water table, instead of the distance from the ground surface to the water table. For example, in areas where the water table is found less than 30 feet from the location of the constituents of concern, an attenuation factor of 10 may be used for most constituents and a factor of 100 may be used for the less mobile constituents (copper, lead, and zinc). The generic attenuation factors, as described in Section 4.3.0.0.3, must be revised to incorporate this criterion in relation to the depth to water table. The results and significance of the new information compiled in accordance with these factors must be presented in the appropriate tables and discussed in Section 5.2. DETAILED COMMENTS 1. Section 5.2.7, SWMU 7 - Burn Pit No. 1: No additional investigation is proposed for the Phase II investigation. We do not concur with this recommendation. Although Buildings 16 and 19 cover most of the original site, further investigation of the nature and extent of contamination at this site is appropriate for Phase II investigation activities. The two borings drilled to characterize this site did not show any evidence of past activities. Therefore, the samples collected were not representative of locations where past activites occurred. Results from analysis of these samples may underestimate the nature of the contamination associated with these activities and their threat to ground water. Additional borings must be drilled to completely characterize areas of potential highest contamination. In addition, ground water samples from LM095A must be analyzed for dioxins to determine if ground water contamination has resulted from these contaminants present in soils at this site. Concentrations of 25 and 33 pg/g octachlorodibenzo-p-dioxin were detected in soil samples taken at the approximate depth of the water table in both soil borings SB161 and SB162, respectively. Although the results of ground water sampling discussed in Section 5.2.7.4.2 states that dioxins were not present at levels above the reporting limits of the analyses, Table 5-15 indicates that ground water samples taken from monitoring well LM095A were not analyzed for dioxins. 2. Section 5.2.8, SWMU 8 - Burn Pit No. 2: No additional investigation is proposed for the Phase 11 investigation. We do not concur with this recommendation. This section states that no ground water contamination appears to have resulted from disposal activities at this site. However, the nearest downgradient monitoring well (LM019A) is located approximately 400 feet to the north-northeast of SWMU 8. Dioxins were detected in concentrations of up to 220 pg/g in the soil samples collected from borings at this site. Although lower concentrations of dioxins, 10 to 19 pg/g, were detected in samples collected from nearest the water table, the presence or absence of dioxins in ground water should be determined. At least one soil boring, located at the downgradient boundary of SWMU 8, must be extended to the water table where a ground water sample will be collected to determine if ground water has been impacted by the contaminants present in soils at this site. The methods used during the Phase I investigation to analyze for constituents of concern from samples collected from monitoring well LM019A are acceptable. However, Table 5-17 indicates that ground water samples collected from monitoring well LM019A were not analyzed for dioxins.