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I ' 2003 4`' Quarter Groundwater Report SFrontier Transportation ' February 11, 2004 Page 3 ; First subsurface water was encountered at depths from to 1,2' bg during tank removal ' and monitoring well installation at this site in 1995 and 1996 Since then, shallow subsurface water has been encountered beneath the site between 6' and 10' bg Data collected in December of 2003 identified the flow of groundwater in a generally western direction beneath the site (See Figure 3, Groundwater Gradient Map) Monitoring well MW-3R was installed within the excavation backfill material, which was coarser than the native soil The permeability difference ' between the backfill material and native soil can cause groundwater to accumulate within the backfill material as it flows in the downgradient western direction Historic groundwater data identified a west or southwest flow beneath the site ' 4.0) QUARTERLY GROUNDWATER SAMPLE RESULTS ' On December 30, 2003, BEH contracted Del-Tech to collect groundwater samples from �,� monitoring wells MW-1 through MW-14 for laboratory analysis Groundwater parameters (pH, 1 temperature, and conductivity) were measured before, during, and after well purging (See ,dos l0):� ' Appendix A for Monitoring Well Field Logs) Groundwater samples were analyzed for TPH-d, 5A ;Ao TPH-g, TPH-m, BTEX, and MTBE using EPA methods 8015 modified for diesel, 8015 modified 0%�V, 'e,��Q�` for gasoline, 8015 modified for motor oil, 8020 for BTEX, and 8260 for MTBE, respectively ,� �1y9 tLaboratory analysis results for all monitoring episodes are presented in Table 1 Recent analytical reports are included as Appendix B A Historical groundwater data has identified dissolved TPH-m in monitoring well MW-3 'off v� exclusively Maximum concentrations of dissolved TPH-m were identified in MW-3 as 33,000 �o° µg/L in January 2000 using EPA method 8015 modified In January 2000, the well cover for MW-3 was destroyed allowing oily surface water to infiltrate the well BEI[ concludes that the damaged well cover caused the increase in TPH-m in MW-3 from November 1999 to May 2000 Dissolved TPH-m concentrations have remained non-detect at the site since September 2000, when the well cover was repaired BEII, therefore, has discontinued groundwater sample analysis for TPH-m at the site ' Laboratory analysis identified dissolved TPH-d in monitoring well MW-3 at a maximum concentration of 33,000 µg/L in January 2000 However, the groundwater results were reported ' as TPH-d and TPH-m combined Since then, dissolved TPH-d concentrations in MW-3 have attenuated to non-detect in April, August, and November of 2001 Groundwater analysis results from April 2002 identified dissolved TPH-d exclusively from MW-3 as 14,200 µg/L The groundwater level in MW-3 dropped to its lowest recorded depth (10 72') in April 2002 Monitoring well MW-3 was abandoned in May 2002 Replacement well MW-3R identified no detectable concentrations of dissolved TPH-d No other detectable concentrations of dissolved ' TPH-d were identified from laboratory analysis in any of the wells sampled since then, which