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f 1 ASSOCIATES I N C . f - clean pea gravel. Additionally, Class A/B subbase was imported to complete the backfilling of the diesel tank excavation and pipeline trench. Laboratory analysis of a soil sample collected from beneath the former diesel UST locations indicated the presence of total petroleum hydrocarbons as diesel (TPHd) at a concentration of 6,150 parts per million (ppm). Of the,seventeen soil samples collected from the pipeline trench, only one sample, located near the fill end, contained TPHd above the laboratory reporting limits at a concentration of 1,550 ppm. Because the original backfill material removed from the trench contained TPHd at concentrations less than the 100-ppm threshold for acceptable backfill material, the soil removed from the + pipeline trench was used to backfill the trench. i I On February 16, 1999, ATC supervised the advancement of two soil borings (SB 1 and SB2) in the vicinity of the former remote fill pipeline's fill-end. Drilling was performed by employing Geoprobe® method of direct push technology (DPT). Soil Borings SBI and SB2 were completed at depths of 20 feet bgs. Soil boring SBI was advanced at an approximate angle of 30 degrees from vertical and boring SB2 was a vertical boring. Soil boring locations are shown on Figure"3. On February 23, 1999, ATC supervised the advancement of three soil borings (SB3, SB4, and SB5) in the vicinity of the former diesel USTs. Drilling was conducted utilizing a hollow stem auger drill rig. Soil borings SB3 through SBS were advanced and sampled to 36.5 feet bgs. The laboratory reported that none of the soil samples collected from borings SBI through SB5 in the vicinity of the former diesel USTs or the remote fill pipeline contained aromatic petroleum fi hydrocarbon constituents, benzene, toluene, ethylbenzene, and xylenes (BTEX), above laboratory detection limits. Soil samples collected from borings SBI, SB2, and SB3 did contain detectable concentrations of TPHd. SBI and SB2 contained concentrations of TPHd ranging from <1.0 to 7.5 ppm, however the chromatogram pattern indicated the presence of an unidentified hydrocarbon (C9-C24) and discrete peaks (@C20, C24). TPHd was observed above laboratory detection limits in soil samples collected from SB3. TPHd concentrations ranged from 16,700 ppm at 15.5 feet bgs to < 5.0 ppm at 35.5 feet bgs suggesting that TPHd attenuates rapidly relative to depth. No analytes were detected above laboratory detection limits in soil samples analyzed from borings SB4 or SB5. A summary of analytical data of soil samples collected in February 1999 is included as Table 1. a Gasoline Tanks In January 1997, two gasoline USTs were removed from the northwest portion of the property and soil samples were subsequently collected from the open excavation (see Figure 2). Only one sample was reported to have contained TPH as gasoline (TPHg) above.laboratory detection w:1172921reporU\SuPpl lnvesidoc 2