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' Quarterly Groundwater Report i Frontier Transportation ' 0600-091 June 20, 2000 Page 4 ' concentrations of the remaining oxygenates were identified from groundwater sample analysis of all eleven monitoring wells using EPA method 8260 (See Appendix B). 5.0) CONCLUSIONS AND RECOMMENDATIONS Based on groundwater sample analysis results, the dissolved TPH-d, TPH-g, TPH-m, and ' BTEX plumes are spatially stable on-site and confined to the former UST location. No detectable concentrations of dissolved TPH-d, TPH-g, TPH-m, and BTEX were identified in ten of the total ' eleven monitoring wells dedicated to the site. Dissolved TPH-d, TPH-g, TPH-m, and BTEX were identified in monitoring well MW-3 exclusively Iocated just east of former UST location. Attenuation of the above petroleum hydrocarbons has been identified in MW-3 since their ' respective recorded maximums. Previous groundwater testing performed in January 2000 identified dissolved MTBE in three groundwater monitoring wells (MW-1, MW-3, and MW-9), the most wells impacted by MTBE in one monitoring episode since testing began in August 1996. Groundwater testing performed in May 2000 identified dissolved MTBE in only two monitoring wells; MW-3 located near the former UST location and the westernmost well MW-9. Dissolved MTBE concentrations in MW-9 attenuated from 19 pg/L to 7.7 pg/L. Based on the groundwater data, BEII concludes that the dissolved MTBE plume is diminishing in size. However, further groundwater testing is ' required to confirm the diminishing trend. BEII recommends that quarterly groundwater monitoring continue at the site until constant or decreasing dissolved petroleum hydrocarbon concentrations are observed. Groundwater samples will be analyzed for BTEX using EPA method 8020, TPH-d, TPH-g and TPH-m using EPA method 8015m, and oxygenates using EPA method 8260 in all future monitoring episodes as directed by the PHS/EHD. • 1