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0 0 <br /> James L. Tjosvold, P.E. <br /> August 19, 1996 <br /> Page 20 <br /> 4,540 mg/kg from 3 to 8 feet bgs in B-11; TPH-gasoline at 394 mg/kg at 41 feet bgs <br /> in MW-8; and TPH-diesel at 2,823 mg/kg at 6.6 feet bgs in MW-10. <br /> The lateral and vertical extent of S-4 is further summarized below: <br /> Area covered: 422 sq. yards, extent of fuel tank, oil tank, and gas/oil sump. <br /> Affected depth: 0 to 25 feet with TPH-gasoline in MW-8 at 40 feet <br /> Total depth considered for treatment: 25 ft bgs <br /> Total volume: 3,516 cubic yards <br /> • EAST: The eastern limit of S4 is defined by soil boring SB-16-95 which had <br /> minimal detections of PNAs and petroleum hydrocarbons between 12 and 24 <br /> bags. <br /> • SOUTH: The southern extent of S4 is defined by SB-13-93 and SB-11-95. SB-13-95 <br /> had only minor concentrations of total PNAs (2.35 mg/kg) at 4 feet bgs. No <br /> other samples were obtained for laboratory analysis from this boring. The <br /> boring log indicates sheen down to 12 feet bgs, and apparently clean soil below <br /> 12 feet bgs. Soil samples from SB-11-95 indicate only minor concentrations of <br /> PNAs and TPH at 20 and 24 feet bgs. <br /> • NORTH: MW-10 defines the northern extent of S4. Fill and MGP residues are <br /> present in MW-10 but are limited to the soil above 8 feet bgs. Elevated <br /> concentrations of PNAs and TPH as diesel are present at 7 feet bgs, but are not <br /> detected or are at very low levels below 7 feet bgs. Thus any MGP residues in <br /> this area appear to be limited to the shallow soil, and are not considered to be a <br /> threat to groundwater. <br /> • NORTHWEST: No data are available to define the northwestern extent of S4. <br /> Since no gas plant gas manufacturing activities took place in this area of the site, <br /> any MGP residues in this area will likely be limited to the shallow soil, and <br /> should not pose a threat to groundwater. <br /> • WEST: No data are available to define the western extent of S4, but the assumed <br /> western limit should be sufficient since it encompasses the area around the <br /> former oil tank. <br /> • VERTICAL: Borings B-9 and B-11 both indicate that the vertical extent of PNAs <br /> is limited to the soil above 23 feet bgs. The soil samples from 18 to 23 feet bgs <br /> from these borings had total PNA concentrations of 0.68 mg/kg and none <br />