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q 19 June 2000 AGE-NC Project No 96-0232 Page 16 of 35 from Flag City Chevron shallow well MW-12A , at concentrations ranging from 95 µg/l to 3,300 µg/l The estimated extent of dissolved TPH-g in shallow ground water(5 to 30 feet) is depicted in Figure 38 Based on ground water analytical data collected in the area bound by P17, MW-13, and Three B's Truck Plaza wells MW-1, MW-2, MW-3 and MW-6, AGE suspects that ground water has been impacted by at least one other plume of dissolved fuel components that has not been sourced by the Flag City Chevron plume(see Figures 36, 38,39 and 40) The area bound by Three B's Truck Plaza shallow wells MW-1, MW-2, MW-3 and MW-6 (screened 5 to 25 feet) has yielded ground water samples containing TPH-g at concentrations as high as 44,000 µg/1, TPH-d as high as 6,400 µg/1, BTEX compounds as high as 8,100 µg/l, MTBE as high as 57 µg/l and TBA as high as 66 µg/1 Ground water at depths greater than 25 feet bsg on the Three B's site has not been investigated Laboratory analysis of ground water samples collected from MW-13 at the far west side of the monitoring well network detected a substantial concentration of MTBE at 460 µg/l, TPH-d at a concentration of 74 µg/1,benzene at a concentration of 1 6 µg/1 and TAME at a concentration of 15 µg/1, these results cannot be reasonably modeled to be part of the Flag City Chevron plume at this time Additional horizontal and vertical investigation is warranted at the Three B's Truck plaza to better define the plumes of impacted groundwater between Flag City Chevron wells MW-7,MW-13 and Three B's Truck Plaza wells MW-1 through MW-6 Figures 9, 10, 21, 22 and 23 depict general lithology and the approximate extent of petroleum- impacted ground water beneath the site in cross sectional view,Figures 25, 26, 27 and 36 depict the estimated concentration distribution and extent of dissolved petroleum hydrocarbons in plan view These figures show wells MW-1,MW-2,MW-4,MW-6,MW-7,MW-9A and MW-11 (A,B,C and D)and CPT soil borings P 14,P 16 and P 17 to be located within the dissolved petroleum hydrocarbon ground water plume associated with the Flag City Chevron site Based on geologic model depicted in the cross sections and on the results of laboratory analysis of ground water samples, the vertical extent of impacted ground water on-site appears to lie between 10 feet bsg(estimated depth to ground water)and 50 to 60 feet bsg in the area of P 1,P 14,MW-1 and MW-9 (Figures 21 and 23) Impacted ground water in the area at 40 to 50 feet bsg in MW-9 is underlain by two thin fine-grained units that appear to have retarded the downward migration of the MTBE as evidenced by the non-detectable concentrations in samples from P 14 at 59 to 62 feet bsg Two thicker fine-grained units, each more than 10 feet thick,occur below 60 feet bsg The latter two fine-grained units definitely appear to effectively retard the downward migration of MTBE as evidenced by the non-detectable concentrations in samples from P 14 at 73 to 76 feet bsg and 85 to 88 feet bsg and at 100 feet bsg in MW-9 bsg in the area Going off-site toward the west,the plume may extend to as much as 70 feet bsg approaching the area . of P 16 and MW-11,near Rocky's Restaurant domestic well(RDW-1)as the underlying fine-grained Advanced GeoEmironmental,Inc