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1 <br />' 2002 1" Quarter Groundwater Report <br /> . Frontier Transportation <br />' 0502-163 <br /> May 6, 2002 <br /> Page 4 <br /> t Historically no detectable concentrations of dissolved BTEX were identified in <br /> monitoring wells MW-5, MW-6, MW-7, MW-8, MW-9, MW-10, and MW-11 since initial <br /> groundwater testing began in each well. Monitoring wells MW-1, MW-2, and MW-4 have <br /> remained non detect since at least January of 2000. Only monitoring well MW-3 has contained <br /> dissolved BTEX from every groundwater sampling episode. <br /> No detectable concentrations of dissolved BTEX were identified in groundwater samples <br /> collected in April 2002 from monitoring wells MWA, MW-2, MW-4, MW-5, MW-6, MW-7, <br /> MW-8, MW-9, MW-10, and MW-1 I using EPA method 8020. Monitoring well MW-3 <br />' exclusively identified total dissolved BTEX at a concentration of 2,873.7 gg/L, an increase from <br /> 53.3 pg/L identified in November 2001. However, total dissolved BTEX concentrations in MW- <br /> 3 have attenuated by 66% since the maximum was identified as 8,350 p.g/L in March 1998 when <br />' groundwater rose to its shallowest depth recorded (7.1' bg). See Figure 5 for the recent <br /> dissolved BTEX Isoconcentration Map. <br />' MTBE was the only oxygenate identified in groundwater using EPA method 8260 from <br /> the April 2002 sampling episode. Monitoring well MW-3 exclusively identified dissolved <br />' MTBE concentrations from 370 pg/L, an increase from 110 gg/L during the previous monitoring <br /> episode (November 2002). However, MTBE concentrations have attenuated by 99% from the <br /> maximum concentration of 29,400 µg/L identified in MW-3 during March 1998. No detectable <br />' concentrations of other oxygenates were identified from groundwater sample analysis of all <br /> eleven monitoring wells using EPA method 8260 (See Appendix B). See Figure 6 for the recent <br /> MTBE Iso concentration Map. <br />' 5.0) CONCLUSIONS AND RECOMMENDATIONS <br />' Based on groundwater sample analysis results, the dissolved TPH-g, BTEX, and MTBE <br /> plumes are spatially stable on-site and confined to the former UST location. No detectable <br /> concentrations of dissolved TPH-d, TPH-g, BTEX, and MTBE were identified in ten of the <br />' eleven monitoring wells dedicated to the site. Dissolved TPH-g, BTEX, and MTBE were <br /> identified in monitoring well MW-3 exclusively located just east of former UST location. <br /> Attenuation of the above petroleum hydrocarbons has been identified in MW-3 since their <br />' respective recorded maximums identified in March 1998. <br /> BEII recommends that quarterly groundwater monitoring continue at the site until <br />' constant or decreasing dissolved petroleum hydrocarbon concentrations are observed. <br /> Groundwater samples will be analyzed for BTEX using EPA method 8020, TPH-d and TPH-g <br /> using EPA method 8015m, and oxygenates using EPA method 8260 in all future monitoring <br />' episodes as directed by the PHS/EHD. <br /> • <br />