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i Based on historic soil analytical results, it appears the lateral and vertical extent of TPHg, BTEX, and MTBE impact to soil beneath the site and site vicinity was minimal in nature and has been 1 adequately characterized. 3.3.2 Groundwater For more than nine years (thirty-four quarters), quarterly groundwater samples have been collected and analyzed from the well array to evaluate the presence and distribution of fuel- related hydrocarbons and oxygenates in groundwater in Sands A, B, and C beneath the site and site vicinity. Historical analytical results indicate that the COCs in groundwater historically were TPHd, TPHg, MTBE, and TBA. Groundwater has also been tested for BTEX, TAME, ETBE, DIPE, EDB, 1,2-DCA, McOH and EtOH but little to no detectable concentrations of these chemicals were reported in historical groundwater samples. In addition, analytical results of groundwater samples collected over the past two years indicate the only COC in groundwater is now MTBE (though low level sporadic TPHg and/or TPHd concentrations are intermittently present in some wells). Sands A and B: Analytical results of samples collected during the most recent quarterly groundwater monitoring and sampling event (June 2, 2009) indicate the only COC in Sands A and B wells is MTBE. No concentrations of BTEX were reported in any of the wells; only low concentrations GRO and/or (laboratory-flagged) DRO concentrations were reported in three F , Sand A wells (MW-13A/B, MW-14A, and MW-4) and two Sand B wells (MW-8 and MWO-1 x) 1 The current approximated extent of MTBE in Sand A wells is illustrated on Figure 7. The current approximated extent of MTBE in Sand B wells is illustrated.on Figure 8. Currently, the dissolved-phase MTBE plumes in Sand A and Sand B (exceeding the secondary maximum contaminant :level [MCL] of 5.0 µg/1) extend from source area near the former/existing'northem USTs (MW-2, MW-7, MWO-1 x) toward the northeast to the vicinity of wells MW-9, MWO-2, MWO-3, and MW-8 and to the north-northwest to the vicinity of(cross- screened) well MW-13A/B. The maximum concentration of MTBE (120 pg/1) was reported in (cross-screened) well MW-13A/B. Historical analytical results clearly demonstrate the natural attenuation of the MTBE plume over time in all Sand A and Sand B wells, with the exception of (cross-screened) well MW-13A/B (in which insufficient data has been gathered). Graphs illustrating MTBE concentrations over time in Sand A wells MW-2, MW-3, MWO-2, MW-7, MW-9; and MWO-3 are presented as Figures 9 through 14, respectively. Graphs illustrating MTBE concentrations over time in Sand B wells MW-8 and MWO-lx and Sand A/B well MW-13A/B are presented as Figures 15 through 17,respectively. The MTBE plume in Sands A and B appears adequately assessed to the secondary MCL in all directions in both zones, with the exception of to the northwest of well MW-13A/B in which the presence of Interstate 5 precludes additional assessment (see section 5.0 of this document for further discussion regarding the predicted extent of the MTBE plumes in this direction). Sand C: Analytical results of samples collected during the most recent quarterly groundwater monitoring and sampling event (June 2, 2009) indicates no concentrations of GRO, BTEX, or l�Jl Page 14 $TKATUr✓'