SITE INFORMATION AND CORRESPONDENCE 1995-2004

Home Browse Search

0 0 James L. Tjosvold, P.E. August 19, 1996 Page 19 had 2.4 mg/kg of total PNAs, but it was only sampled at four feet bgs. To the southeast, SB- 14-95 was sampled only at 20 feet bgs and had high concentrations of total PNAs and TPHd and detections of total VOCs and TPHg. Therefore,further lateral and vertical definition is needed in the southern section of S4. Response: 12. Source Area 4 (S4) extends from the location of a former underground diesel storage tank near MW-10 to the location of a former oil tank and gas/oil sump near MW-8. Source area 4 has not been defined to the north and west as discussed in the general response to comments 9 through 13. Depending on the type of remedial action chosen for soil, this source area may be further refined during or before remediation. The lateral and vertical extent of Source Area 4 was determined by data from the following 11 borings: MW-10, MW-6, MW-8, MW-18, B-9, B-11, SB-11-95, SB-13-95, SB-14-95, SB-15-95, and SB-16-95. During the drilling of boring MW-6, concrete was encountered from 6 to 7 feet bgs and oily soil was noted at 20 feet bgs. The concrete was likely the foundation of a former MGP structure (see Figure 4-1). No samples were collected from MW-6 for analysis. Chemical data for S4 are summarized in attached Table 4-5. In MW-10, MW-8, and B-9, PNA concentrations generally decreased with depth; in SB-15-95, PNA concentrations increased with depth. The highest PNA concentration (4,640 mg/kg) was found in B-11 between 3 and 8 feet bgs. The deepest PNA detection was in SB-15-95 with 528 mg/kg total PNAs at 24 feet bgs. The highest TPH as gasoline concentrations were found in MW-8 (394 mg/kg at 41 feet bgs) and SB-15-95 (220 mg/kg at 17.5 feet bgs). The sample from 41 feet bgs in MW-8 was taken from below the water table, so this result may due to TPH as gasoline constituents at the water table and may not represent TPH-gasoline constituents in soil at that depth. The maximum TPH as diesel concentrations were found in MW-8, SB-14-95 and SB- 15-95. The maximum depth of detection was at 24 feet bgs in SB-15-95. Cyanide was detected in one soil sample from MW-10 (1.29 mg/kg at 7.1 feet bgs) and one soil sample from MW-8 (1.15 mg/kg at 2.6 feet bgs). 'In summary, S4 consists of soil containing elevated levels of PNAs and fuel hydrocarbons (gasoline and diesel). PNAs, diesel, and gasoline were detected at a wide range of concentrations at various depths from near the surface to about 25 feet bgs in most parts of this area. The highest concentrations detected are: PNAs at