COMPLIANCE INFO_FILE 3 - Laserfiche WebLink

Home Browse Search

June 27—Soil samples 2, 5, and 6 consisted of a sample from each end of the tank excavation at a depth of 2 ft beneath the tank excavation floor and a sample from the north wall of the tank excavation at 2 ft beneath the piping. Of the two soil samples that were collected from beneath the tank excavation floor, the east end sample (5) was below the TEPH-Diesel detection limit and the west end (6) sample yielded a concentration of 65 ppm TEPH-Diesel. • July 10 — Soil sample 7 was collected from the floor of the piping excavation at approximately 3 ft below the depth of the piping. Neither of the soil samples (2 or 7) collected from beneath the piping exceeded the detection limit for TEPH-Diesel. As shown on Figure 4, none of the six soil samples yielded detectable concentrations of benzene, toluene, xylenes, or ethylbenzene (BTE or X). The proposed soil sample specified in the Closure Pan as 1 was not collected because the SJCPHS-EHD representative said it was unnecessary. Sample 1 would have been collected 1 ft above sample 2. Leaching Potential Analysis All diesel-stained soil was removed from the piping excavation. The non-detectable (ND) concentrations of TEPH-Diesel and BTE and X in sample 7 support this fact. The diesel-stained soil from above the tank was excavated before the tank was removed from the excavation. As mentioned earlier, this soil was sampled twice and yielded TEPH-Diesel concentrations of 2,300 and 4,400 ppm. These concentrations are probably the result of diesel fuel spillage from fueling operations while the tank was in service. No diesel-stained soil was evident in the floor or walls of the tank excavation. However, due to the depth of the tank excavation and the proximity of numerous utilities the removal of all soil with detectable concentrations of diesel from the floor of the tank excavation was not possible. Since soil sample 6 from the west end of the tank excavation yielded a TEPH-Diesel concentration of 65 ppm, this soil had to be evaluated to determine if it could be left in place. To do that, a Leaching Potential Analysis was performed. The analysis is excerpted from the Leaking Underground Fuel Tank (LUFT) Manual as Appendix G of this report. It estimates the concentrations of petroleum hydrocarbons that can be left in place without threatening ground water. See Table 1 for the site characteristics and scores based on their potential influence for increasing the vertical migration of fluids in the vicinity of the tank excavation (McIlvride et al., 1990). 6