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SOIL CONTAMINATION ASSESSMENT Lockeford Mini Hart NCA Project No, 10-90-104 Page 7 Comparison of the soil analytical data shown in Table 2 with the suggested maximum allowable BTXE and TPH concentrations shown in Table 3 for sites with a score of 48 points (the score assigned to this site) demonstrates that 12 of the 13 soil samples taken at the site have BTXE and TPH concentrations appreciably less than suggested allowable concentrations. The only soil sample that -- contained BTXE and TPH concentrations higher than those shown on Table 3 (for a site with a total score of 48) was sample T3N. Of constituents analyzed in this sample, only xylenes and TPH (2.1 and 390 ppm respectively) were detected at concentrations higher than the suggested concentrations (1 and 100 ppm respectively) . The score of 48 points assigned to this site is at the upper limit of the range of scores designated on Table 3 for allowable BTXE and TPH concentrations of .3, .3,1,1 and 100 ppm. Examination of Table 3 shows that the next category (with total scores of 49 or more) has allowable BTXE and TPH concentrations of 1,50,50,50, and 1000 ppm. These concentrations range from 3 to 166 times greater than the suggested concentrations for sites with 41.-48 points. In comparison to suggested allowable concentrations of BTXE and TPH for the bordering category (sites with a score of 49 or more) the concentrations of xylenes and TPH found in sample T3N are low. To better evaluate the potential threat (if any) to ground water posed by native soils in the vicinity of the tank basin it is instructive to examine ground-water analytical data (Appendix A) from monitoring wells MW-1 and MW-3, located adjacent to the tank basin (Figure 2) . Examination of this data shows that BTEX and TPH concentrations in these swells has historically been very low and has shown a marked decline since commencement of quarterly sampling at the site in June, 1987, Data from the August, 1989 sampling event shows no detected hydrocarbons in well MW--3 and no BTEX constituents detected in well MW--1. TPH was detected in well MW- 1 at a concentration of 25 ppb during the August, 1989 sampling event. 5.0 CONCLUSIONS RECOMMEIFAA�'}ONS Based on the low concentrations of petroleum constituents detected in soil samples from beneath the removed USTs and along product lines as well as the negligible concentrations of hydrocarbons detected in ground-water samples from monitoring wells MW-1 and MW-3 (located adjacent to the tank basin) it is our professional opinion that hydrocarbons remaining in site soils pose Little threat to ground water beneath the site. Based onthis,opinion,_-- - - ---we--believe-that--operation-of-the soil-venting system installed in the base of the tank excavation is not warranted at this time.