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t1 <br /> Oxygenates: The highest concentration of MtBE was reported in groundwater samples collected from <br /> upper zone well MW-5 at a concentration of 190 µg/L. MtBE was also reported in lower zone wells <br /> MW-1R and MW-2 at concentrations of 2.5 gg/L, 35 p,g/L, respectively. MtBE was reported below <br /> detection levels inMW-9and MW-10. MW-5 had TAME present at 1.4 pg/L, and TBA present at 14 <br /> Pg/L. IVa <br /> The upper groundwater zone is represented by wells MW-5 and MW-10 only. Well MW-5 was analyzed <br /> for MtBE, TBA and TAME only. MW-10 was analyzed only for MtBE. MW-5 is closest to the original <br /> source and has the highest historical concentrations at the site. Concentration of MtBE has shown a <br /> steady decrease in MW-5 since the peak in March of 2000. TBA in MW-5 has also shown a steady <br /> decrease and is now approaching the detection limit. TAME concentration in MW-5 has been less than 5 <br /> gg/L for the last five quarters. MtBE has been below detection levels in MW-10 for the last four <br /> quarters. <br /> The lower groundwater zone is represented by wells MW-1R, MW-2, MW-4, and MW-9. Well MW-2 is <br /> closest to the original source was analyzed for MtBE,TBA and TAME only. Concentration of MtBE has <br /> decreased by three orders of magnitude from a high of 24,000. TBA in MW-2 has been below detection <br /> levels for the last three quarters. TAME in MW-2 has been below detection levels for the last four <br /> quarters. Well MW-1R is slightly down-gradient from the USTs; it was analyzed for MtBE only and <br /> shows a steady decrease in concentration of MtBE since a peak in May of 2003 and is now nearly at the <br /> detection level. MW4 is the only well analyzed for TPH-g, BTEX and MtBE. TPH-g in MW-4 has <br /> hovered at or below the detection limit(50 µg/L) for the last three quarters. All other analytes except for <br /> toluene are below detection limits for more than a year. Toluene is only present at the site in MW-4. <br /> MW-9 was analyzed only for MtBE which is below the detection limit and has been for the last three <br /> quarters. <br /> Cumulative analytical results of groundwater samples collected from current and past sampling events <br /> ' are presented in Tables 1 and 2. Well construction details and status of screened intervals relative to <br /> current groundwater elevation are provided in Table 3. The two shallow zone wells are the only ones <br /> sampling the top of the water column; all other wells have submerged screens. <br /> r5.0 CONCLUSIONS AND RECOMMENDATIONS <br /> During this sampling episode,ATC employed two different sampling techniques: low-flow sampling and <br /> conventional sampling(described in Appendix C). Results are similar for this one sampling episode, but <br /> we expect that the relative volatility of the analytical data points from quarter to quarter will be less with <br /> the low-flow technique. <br /> Based on the findings derived from the groundwater monitoring and sampling event conducted in August <br /> 2005, ATC recommends this site be considered for closure. ATC will submit a formal closure request in <br /> j the next month. Until the county grants closure, we will continue quarterly monitoring of the remaining <br /> wells. <br /> Quarterly GW Monitoring Report--3rd Qtr 2005 <br /> NVATIC <br /> Quik Stop No. 132 <br /> Quik Stop Markets,Inc. <br /> ATC Project No.75.62503.3206 <br /> September 30,2005 <br /> Page 3 of 4 <br />