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r Quarterly Groundwater Report Frontier Transportation r 1199.184 December 2, 1999 Page 3 r (<50 µg/L) concentrations of dissolved TPH-g in MW-2, MW-4, MW-5, MW-6, and MW-7 using EPA method 8015 modified. Groundwater collected from monitoring wells MW-1 and MW-3 identified dissolved TPH-g concentrations as 710 µg/L. and 3,700 4g/L, respectively. TPH-g concentrations increased in MW-1 from 75 µg/L identified in July 1999. Monitoring well MW-3 also observed an increase in dissolved TPH-g concentrations from 100 pg/L identified in July 1999. Please see Figure 4, Figure 5, and Figure 6 for recent TPH-d, TPH-m, and TPH-g isoconcentration maps. No detectable concentrations of dissolved BTEX were identified in groundwater samples collected from monitoring wells MW-2, MW-4, MW-5, MW-6, and MW-7 using EPA method 8020. Groundwater analyzed from wells MW-1 and MW-3 identified total dissolved BTEX as 1.19 pg/L and 496 µg/L, respectively. Total dissolved BTEX concentrations in MW-1 attenuated 43% from 2.08 pg/L in July 1999 and 99% from 302.6 pg/L when initially tested in August 1996. Monitoring well MW-1 contained benzene at 0.47 pg/L and ethylbenzene at 0.72 µg/L r exclusively as the total BTEX concentration identified in November 1999. Total dissolved BTEX concentrations in MW-3 increased from 33.2 µg/L in July 1999, however, BTEX has attenuated � . 96% from the maximum 8,350 µg/L when groundwater rose to its shallowest depth recorded (7.1' bg) in March 1998. Monitoring well MW-3 contained benzene at 140 pg/L, ethylbenzene at 87 pg/L, toluene at 19 µg/L, and xylene at 250 pg/L as the total BTEX concentration identified in November 1999. See Figure 7 for the recent BTEX I soconcent ration Map. MTBE was identified in groundwater from two monitoring wells only. See Figure 8 for the recent MTBE Isoconcentration Map. Groundwater samples collected from monitoring wells MW-1 and MW-3 identified an increase in MTBE concentrations from 530 pg/L to 780 pg/L and from 360 µg/L to 540 pg/L, respectively, since the previous monitoring episode (July 1999) using EPA method 8260. However, MTBE concentrations have attenuated from maximum concentrations of 1,300 µglL identified in MW-1 and 29,400 µg/L in MW-3. No detectable concentrations of the remaining EPA method 8260 analytes were identified from groundwater sample analysis with the exception of 5.9 µg/[, as ethyl t-butyl ether and 740 pg/L as tert-butyl alcohol in MW-3 (See Appendix B). r5,0) CONCLUSIONS AND RECOMMENDATIONS Based on groundwater sample analysis results, the dissolved petroleum hydrocarbons r appear to be migrating laterally to the west from the former UST location in shallow groundwater. Dissolved petroleum hydrocarbon concentrations increased in MW-1 and MW-3 exclusively. Groundwater collected from monitoring wells MW-1, MW-2, MW-4, MW-5, MW- r �, r