ARCHIVED REPORTS XR0000648 - Laserfiche WebLink

Home Browse Search

irY ■� 29 July 2005 AGE-NC Project No 96-0232 Page 6 of 9 3.0. SUMMARY OF FINDINGS FROM QUARTERLY ACTIVITIES Previous soil characteristics data obtained by a CPT investigation enabled AGE to define five informal hydrogeologic units (Final Remediation Plan, dated 31 August 2000) The informal hydrogeologic units were defined as First Zone (10-35 feet bsg), Second Zone (40-60 feet bsg), Rocky's Upper Zone (65-75 feet bsg), Secondary Aquifer Zone (85-105 feet bsg), and Primary Aquifer Zone (130-150 feet bsg) The Rocky's Upper Zone was the shallowest ground water zone screened in the destroyed Rocky's domestic drinking water well Between November 2000 and 17 August 2004, a total volume of 27,086,201 gallons of MTBE- Impacted water was treated at the site utilizing pump-treat and carbon filtration remediation technology,due to the lack of cost effectiveness for the clean-up of MTBE-impacted ground water, pump-and-treat operations were suspended on 17 August 2004 The results from the ground water monitoring and sampling events performed in June 2005 are as follows • Generally, depth to ground water at the site varied between 9 and 13 feet bsg, ground water elevations ranged between 0 51 feet(MW-14) and 1 84 feet(MW-13B-C) above mean sea level (Table 2) • Net ground water flow direction in all informal hydrogeologic units was generally inferred to be east-northeast to southeast at the Flag City Chevron site and the Three B's Truck Plaza site, hydraulic gradients were calculated to be approximately 0 001 ft/ft or less Due to the low ground water gradient at the site, small variations in ground water measurements or changes of recharge/discharge of the local ground water could greatly modify the inferred ground water flow direction(Figures 4 through 7) • The most intense on-site Flag City Chevron MTBE concentrations were detected from Second Zone well MW-8A at 610 µg/1 (Figure 9) Significant concentrations of First Zone MTBE were detected from on-site wells MW-2(220µg/1),EW-7(110µg/1),EW-9(46µg/1) and EW-10 (100 µg/1 ), for the third consecutive quarter, a significant MTBE increase was reported at well MW-2 (Figures 8, Table 3) • The most intense off-site MTBE concentrations were detected north of the site from First Zone wells MW-19A and MW-20A, at concentrations as high as 460 4g/1, and west of the site from First Zone well MW-8A (Three B's Truck Plaza) at a concentration of 120 µg/1 Low to moderate MTBE concentrations were also detected in First Zone wells west of the site at Three B's Truck Plaza wells MW-1,MW-2,MW-4,MW-5,MW-l0A and at Rocky's Restaurant from wells MW-7 and MW-16 (Figure 8) Between the June 2004 and the June 2005 quarterly monitoring events,a significant MTBE decrease was reported at northeastern- most well MW-19A, from 4,800 µg/l to 1,300 µg/1 to 900 µg11 to 240 µg/1 to 100 µg/l Advanced GeoEnv►ronmental,Inc