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19. SHAD should collect <br />offsite (background) <br />soil samples to establish natural <br />levels of <br />arsenic and selenium. <br />In addition, arsenic <br />and bromacil should be sampled <br />onsite at <br />grid points BG57 and <br />BK7. SHAD agreed <br />to do this sampling in their May <br />22, 1987 <br />response to agency comments. <br />20. Underground storage tanks (USTs) for waste chemicals should be investigated as part <br />of the RI/FS. SHAD has included investigation of these SWMUs within its petroleum <br />UST investigation described very briefly in Section 8.0 of the draft RI/FS report. <br />However, investigation of RCRA SWMUs may require additional sampling beyond <br />what has been done or is ongoing for compliance with state UST requirements (e.g., <br />more than leak testing). The results of the investigation of SWMUs should be <br />reported in more detail than was provided in Section 8.0. SHAD should comply with <br />the requirements in Parts 264.90-264.100 and 264.101 'of 40 CFR (U.S. EPA 1987) <br />relating to SWMUs. <br />21. Areas where bromacil was used or stored on the depot should be identified, if known. <br />22. SHAD should investigate and report on the integrity of the storm/ industrial sewer <br />system. SHAD indicated that this would be done in a technical meeting in June, <br />1987. Areas where leaks are detected should be investigated for soil contamination. <br />23. Surface samples should also be collected in areas in which heavy metals. may be <br />among the contaminants (pg. 3-3, paragraph 2). <br />24. Care should be taken to prevent cross -contamination in soil borings that are <br />advanced to the water table. Borings should be advanced to a depth below any <br />visible, or field screening instrument -detectable contamination (pg. 3-3, paragraph 3). <br />25. The depths of the eighteen exploratory borings in the runway ponds were not <br />specified. What criteria will be used to determine the depths of these borings (pg. <br />3-6, paragraph 3)? <br />26. If <br />the <br />ground <br />penetrating <br />radar (GPR) survey <br />is able to <br />clearly define the boundaries <br />of <br />the <br />runway <br />ponds then <br />fewer borings will <br />be needed <br />to confirm the existence of <br />0 <br />