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2004 1" Quarter Groundwater Report . Frontier Transportation May 20, 2004 Page 5 4I MW-13,and MW-14 since initial groundwater testing began in each well Momtonng wells MW-1 and MW-2 have remained non detect to trace levels since at least July of 1999 Monitoring well MW-13 contained dissolved total BTEX as 62 gg/L in June 2002 but has remained non-detect since then Newly installed monitoring wells MW-15 through MW-18 identified no detectable concentrations of dissolved total BTEX during the 2004 first quarter groundwater monitoring event Only monitoring wells MW-3 and its replacement MW-3R contained dissolved BTEX from every groundwater sampling episode Detectable concentrations of dissolved BTEX were identified exclusively in monitoring wells MW-1 and MW-3R for the groundwater samples collected in March 2004 Groundwater sample results from MW-1 identified dissolved TEX only as 1 jig/L, 0 9 µg/L and LWig/L, respectively No dissolved benzene was identified above laboratory reporting limits (0 3 µg/L) See Figure 8 for dissolved benzene in MW-1 overtime Analytical results from MW-3R demonstrated a significant decrease in total dissolved BTEX from 2216 µg/L in December 2003 r to <2 7 µg/L in March 2004 Dissolved benzene was detected at only 0 5 µg/L from MW-3R in March 2004, a decrease from the maximum of 494 µg/l, identified in October 2002 (See Figure 9 for dissolved benzene over time in MW-3R) No detectable concentrations of dissolved BTEX were identified in the groundwater samples collected in March 2004 from the remaining sixteen ' • (16) monitoring wells using EPA method 8020 See Figure 10 for the recent dissolved BTEX Isoconcentration Map ' MTBE was the only oxygenate identified in groundwater using EPA method 8260 from the first quarter 2004 sampling episode The current California Department of Health Services ' (CDHS) primary Maximum Contaminant Level (MCL) for MTBE in groundwater is 13 gg/L Monitonng well MW-1 identified dissolved MTBE concentrations at 1,300 µg/L, a large increase from 75 µg/L identified from the previous sampling episode Dissolved MTBE in MW-1 was ' identified in October 2002 at a maximum of 5,800 µg/L (See Figure 11 for MTBE in MW-1 over time) Monitoring well MW-3 identified a maximum dissolved MTBE concentration of 29,400 µg/]L in March 1998 This well was abandoned in May 2002 Groundwater analysis for Ireplacement well MW-3R identified a maximum dissolved MTBE concentration of 6,000 µg/L in December 2003 A significant decrease in dissolved MTBE (96 }ig/L) was observed in the first quarter March 2004 sampling event compared to the previous quarter in December 2003 ' (See Figure 12 for MTBE in MW-3R over time) The first quarter 2004 groundwater sampling also identified dissolved MTBE in MW-9, MW-14, MW-15 and MW-17 at 1 2 µg/L, 0 81 µg/L, ' 0 54 µg/L and 99 gg/L, respectively Dissolved MTBE in the deeper monitoring wells was detected at a maximum of only 0 81 µg/L The elevated dissolved MTBE concentrations are limited to the shallow monitoring wells only See Figure 13 for the recent shallow well MTBE ' Isoconcentration Map I 1