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2004 2" Quarter Groundwater Report i Frontier Transportation I August 9, 2004 Page 5 MW-12 and MW-14 since initial groundwater testing began ich�vell Monitoring wells MW-1 and MW-2 have remained at non detect to trace levels sine at least July of 1999 Monitoring well MW-13 contained 62 µg/L dissolved total BTEX 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 and second quarter groundwater monitoring events Only monitoring wells MW-3 and its replacement MW-3R ' contained dissolved BTEX from every groundwater sampling episode f Detectable concentrations of dissolved BTEX were identified exclusively in monitoring ' wells MW-1 and MW-3R for the groundwater samples collected in June 2004 Groundwater sample results from MW-1 identified dissolved EX only as 1 µg/L and 0 7 µg/L, respectively No dissolved benzene or toluene was identified above laboratory reporting limits (0 3 µglL) 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 to <2 5 µg/L in June 2004 Dissolved benzene was detected at only 0 9 µg/L from MW-3R in June 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 June 2004 from the remaining sixteen (16) monitoring wells using EPA method 8020 See Figure 10 for the recent dissolved BTEX Isoconcentration Map MTBE was identified in three groundwater wells using EPA method 8260 from the second quarter 2004 sampling episode The current California Department of Health Services (CDHS) primary Maximum Contaminant Level (MCL) for MTBE in groundwater is 13 µg/L Monitoring well MW-1 identified dissolved MTBE concentrations at 1,200 µg/L in June 2004, a slight decrease from 1,300 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 inMW-1 overtime) Monitoring well MW-3 identified a maximum dissolved MTBE concentration of 29,400 µg/L in March 199$ This well was abandoned in May 2002 Groundwater analysis for replacement well MW-3R identified a maximum dissolved MTBE concentration of 6,000 µg/l, in December 2003 A significant increase in dissolved MTBE (from I 96 gg/L to 1,000 µg/L) was observed in the June 2004 sampling event compared to the previous quarter(See Figure 12 for MTBE in MW-3R over time) The second quarter 2004 groundwater sampling also identified dissolved MTBE in MW-17 at 130 µg/L No dissolved MTBE was I detected in the deeper monitoring wells The elevated dissolved MTBE concentrations are limited to the shallow monitoring wells only See Figure 13 for the recent shallow well MTBE Iso concentration Map I