SITE INFORMATION AND CORRESPONDENCE 1995-2004

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James L. Tjosvold, P.E. August 19, 1996 Page 18 the tar pit as determined by boring B-15 contains elevated levels of TPH-gasoline to about 20 feet bgs, TPH-diesel to about 8 feet bgs, and elevated levels of PNAs to about 7.5 feet bgs. Two other soil borings, SB-19-95 and SB-20-95, located immediately adjacent to the tar pit contained very low levels of PNAs and petroleum fuel constituents. Soil samples from B-13 and MW-3, borings in the general vicinity of S3, contained low to moderate levels of PNAs, TPH-diesel, TPH- gasoline, and BTEX, but do not appear to be affected by residues from the tar pit and sump. The lateral and vertical extent of S3 is further summarized: Area covered: 48 sq. yards, areas encompassed by former tar pit and tar sump Affected depth: 17 ft bgs Total depth considered for treatment: 17 ft bgs Total volume: 272 cubic yards: • NORTH and EAST: SB-20-95 and SB-19-95 define the northern and eastern extent of S3, respectively. Both borings contained minor amounts of PNAs and petroleum hydrocarbons at maximum depths of 16 and 24 feet bgs, respectively. Results from boring B-15 and SB-19-95 indicated that the MGP residues are limited to the shallow soil above 17 feet bgs. Results from 17 and 24 feet bgs in B-15 from 16 feet bgs in SB-19-95 indicated minor amounts of PNAs at those depths. TPH-gasoline was detected at 398 mg/kg at 21 feet bgs in B-15, but was not detected at 26 feet bgs. Thus vertical extent of PNAs in S3 is 17 feet bgs and the vertical extent of TPH as gasoline is 26 feet bgs. • WEST and SOUTHWEST: Tar was not observed in borings SB-21-95, SB-22-95, and B-14, located to the west and southwest of the former tar pit. The elevated PNA concentrations in the shallow soil samples from these borings are due to the presence of lampblack and cannot be linked to the tar pits. Comment: 12. Page 4-12, Section 4.2.1.4, Potential Source Area 4 (S4) The FS states that borings MW-10, MW-6,MW-8, MW-18, B-9, B-11, SB-13-95, SB-14- 95, and SB-13-95 characterize S4. MW-10 is the northernmost sample location. Due to the high concentrations of total PNAs and TPHd at seven feet bgs,further lateral definition is needed in this area and also to the northwest where no data are available. SB-16-95 should be used to approximate the lateral and vertical limit of contamination to the east, instead of estimating the limit as being between SB-15-95 and SB-16-95. To the southwest, SB-13-95