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A -zone aquifer is almost always the most highly contaminated. This pattern is most <br />probably due to the presence of strong downward gradients associated with agricul- <br />tural pumpage offpost to the west." <br />SHAD should test its explanation for the occurrence of TCE in the deeper zones by <br />demonstrating the existence of strong downward gradients. <br />13. Pa. 10-3. finding #18. "Seven areas of VOC-contaminated soil have been identified, <br />containing an aggregate of more than 26,000 cubic yards (yd3) of soil contaminated <br />above 100 ppb." <br />See Comment #5. Please identify the .seven areas and explain how this amount was <br />caiculated. <br />14. PR. 10-3, finding #20. "Spatial and frequency distribution patterns of arsenic <br />occurrence in soil and groundwater do not dictate an onsite source." <br />Refer to contaminant contour map for the A zone 'and conclusions based on mapping <br />results in Attachment D? <br />15. Pg. 10-3. finding #22. "Bromacil contamination in soil and groundwater at SHAD is <br />minimal." <br />Lack of a promulgated standard does not prove lack of public health risk. The <br />conclusion that bromacil concentrations are minimal in groundwater and soil should <br />be risk-based. What is considered a significant level of bromacil? <br />The following comments address the first two recommendations made by SHAD in <br />Section 11.0 of the draft RI report. <br />Recommendation #1 Section II.0. In its first recommendation SHAD suggests that <br />further soil sampling should be conducted as proposed in the "Supplementary Soil <br />Investigation Plan for the RI/FS at SHAD" (ESE, 1987x). The regulatory agencies <br />have submitted their comments to SHAD on this document (See also Tetra Tech, <br />1988). However, we are not aware SHAD's response to these comments. Comments <br />7 <br />