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0 <br /> James L. Tjosvold, P.E. <br /> August 19, 1996 <br /> Page 21 <br /> detected, respectively. Elevated PNA and TPH as diesel concentrations are <br /> present at 20 and 24 feet bgs in borings SB-14-95 and SB-15-95, respectively. <br /> Treatment is recommended down to 25 feet bgs over S4. <br /> Comment: <br /> 13. Page 4-12, Section 4.2.1.5, Borings Outside of Source Areas <br /> a. Northern Third <br /> The bulk of the contamination in other areas was found at approximately 25 feet bgs. <br /> However, the deepest sample from the former gas holder was taken only at about 13 feet bgs. <br /> On the other hand, MW-17 was sampled only at 100 feet bgs. The FS did not explain why B- <br /> 5, MW-2, and SB-4 were not tested for TPHd/g. A sample should be taken in the storage <br /> building and at each of the former purifiers. If PG&E proposes not to sample these former <br /> facilities, the FS should provide the justification for not sampling. <br /> Response: <br /> The borings in the northern third of the site are MW-2, MW-17, B-5, B-21, and SB-4. <br /> Only samples from B-21 contained any detectable levels of PNAs or TPH-diesel. No <br /> TPH-gasoline or BTEX were detected in B-21. In B-21, the near-surface soil sample <br /> (1.0 to 1.3 feet bgs) contained PNAs at 121.9 mg/kg and 99.8 mg/kg of diesel. In <br /> deeper samples from this boring, levels of PNAs and TPH-diesel were either not <br /> detected or detected at levels close to the detection limits. Attached Table 4-6 <br /> summarizes this soil data and the soil data from the other borings outside the source <br /> areas. <br /> Comment: b. Middle Third <br /> The lateral contamination extent of SB-1-95, B-16, SB-1B, SB-21-95, B-14, and B- <br /> 26 should be defined. Vertical definition is necessary at B-16, SB-1A, and B-14. A <br /> sample should be taken in the former lampblack separator and oil tank. The data for <br /> B-1 and MW-5 are not included in Table 4-6. The FS did not explain why SB-IA, <br /> SB-IB, unnamed boring location (28-33 feet bgs), MW-4, and B-2 were not tested for <br /> TPHd/g. <br /> Response: <br /> The eleven borings in the middle third of the site that are not included in a source <br /> area are: SB-1-95, B-16, SB-lA, SB-1B, B-1, SB-21-95, SB-22-95, B-14, MW-4, B-26, and <br /> B-2. (No soil samples were collected from MW-5 or MW-13.) <br />