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water table would be equivalent with the top of the Upper <br /> Horizon. The piezometric level would not rise 11 feet above <br /> the aquifer under unconfined conditions. The hydrogeologic <br /> definition at SWMU No. 3 needs to be clarified. <br /> 32 . Page 3-17, Section 3.2.1.5.1.1 <br /> The metals beryllium, cadmium and mercury (among many other <br /> metals) are present in the sludge samples from both ponds, <br /> at levels that could be of significant risk to human health <br /> and/or the environment. These metals may have CVs <br /> significantly greater than 100%. (See also General Comment <br /> No. 14 . ) Also, background values for all metals and <br /> pesticides have yet to be determined at DDRW-Tracy. For <br /> both of these reasons, the assumptions going into the <br /> calculations may be faulty for SWMU No. 3 and for the entire <br /> IWPL. Revise calculations accordingly. <br /> 33 . Page 3-17, Sections 3.2 .1.5. 1.2 and 3.2 . 1.5.1.3 <br /> Figure 3 . 0-17 shows one slant boring into each of the IWPs. <br /> This does not meet even the criteria of three, which the <br /> above comment suggests may be insufficient. An alternate <br /> suggestion would be to dig trenches alongside each IWP, into <br /> which any number of horizontal borings could be drilled at <br /> the desired depths. The EPA reviewers believe it important <br /> to retrieve soil samples from immediately beneath the six- <br /> foot deep, lined ponds in order to adequately judge the <br /> potential for migration of these hazardous constituents. <br /> (See also General Comment No. 11. ) Propose appropriate <br /> sampling. <br /> 34 . Page 3-18, Section 3.2 . 1.5.4.2 <br /> The 1990 RFA concluded probable releases to the air. <br /> Propose appropriate air sampling. <br /> 35. Page 3-25, Section 3.2 .3.2.4 <br /> The text does not state if there are any cracks in the paved <br /> area where SWMU No. 6 was located. Explain if this is so. <br /> 36. Page 3-31, Section 3.2 .4.2 <br /> Any unpaved areas that are not sealed to the surface <br /> elements could help provide pathways for migrating fluids. <br /> Likewise, any cracks in the pavement or in the floors and <br /> foundations of Buildings 19 and 21 could provide pathways <br /> for upward migration of gases and possibly of particulates <br /> to onsite workers, and for downward migration of <br /> contaminants to the water table. All possible hazardous <br /> constituents used or stored at DDRW-Tracy may exist in this <br /> Burn Pit No. 1, as well as in Burn Pit No. 2 (SWMU No. 8) , <br /> and, possibly in SWMU Nos. 16 and 22 . Propose appropriate <br /> investigative work. <br /> 37 . Page 3-33, Section 3.2 . 4.5. 1 <br /> I-13 <br />