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0 0 <br /> James L. Tjosvold, P.E. <br /> August 19, 1996 <br /> Page 16 <br /> diesel concentration detected was 86,000 mg/kg in SB-9-95 at 7.5 feet bgs. (This was <br /> also the sample with the highest PNA concentration.) TPH as diesel was detected at <br /> 22 feet bgs in boring SB-7-95 at a concentration of 9,900 mg/kg. <br /> In SB-8-95, outside of the footprints of the former lampblack pit and gas holder, no <br /> PNAs,VOCs, gasoline, or diesel were detected at either 7.5 or 17.5 feet bgs. <br /> Cyanide was detected in B-17 at 7.0 feet bgs (3.68 mg/kg) and at 17 feet bgs (1.02 <br /> mg/kg). In SB-7-95, cyanide was detected at 7.5 feet bgs (1.03 mg/kg). <br /> In summary, S2 has below-grade structures present at depths of 8 to 25 feet bgs. <br /> These structures appear to provide a lower boundary for soil containing PNAs, <br /> diesel, and gasoline constituents and free liquid. The maximum concentrations of <br /> total PNAs, TPH-gasoline, and TPH-diesel were detected at depths of 8 and 10 feet <br /> bgs. Elevated concentrations of PNAs and TPH as diesel were present in the soil to <br /> 22 feet bgs. <br /> The lateral and vertical extent of S2 is further summarized: <br /> Area covered: 340 sq. yards, outer edges of the former gas holder <br /> Affected depth: 8 to 25 ft bgs <br /> Total depth considered for treatment: 30 ft bgs <br /> Total volume: 3,400 cubic yards <br /> • NORTHEAST: To the northeast, boring B-2 defines the lateral and vertical extent <br /> of MGP residues. No visible MGP residues were observed in the entire boring <br /> and PNAs were not detected at depths of 8 to 13 and 18 to 23 feet bgs. PNAs <br /> were detected at minor amounts (2 mg/kg) between 13 and 18 feet bgs. <br /> • SOUTHWEST: To the southwest, boring SB-8-95 defines the lateral and vertical <br /> extent of MGP residues. PNAs or petroleum hydrocarbons were not detected <br /> between 7.5 and 8 or 17.5 and 18 feet bgs. <br /> • NORTHWEST and SOUTHEAST: The complete absence of MGP residues in <br /> borings B-2 and SB-8-95, which border the footprint of the former gas holder and <br /> lampblack pit, indicate that the lateral extent of the residues are contained <br /> within the footprint of these former structures. <br /> • VERTICAL: The vertical extent of MGP residues in S2 is defined by boring B-25. <br /> Soil samples from 30 feet bgs in B-25 contained no detections of PNAs at 30 feet <br /> bgs and TPH-diesel at only 9.78 mg/kg. SB-7-95 contained elevated <br />