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T&T Trucking Subsurface Investigation Results and Site Conceptual Model ' Page 4-7 Groundwater samples from wells MW-1 through MW-4 have been collected on a quarterly basis ' since January 2000 The on-site private supply wells have been sampled on a quarterly basis since November 2002 Quarterly groundwater quality samples are analyzed for BTEX, TPH-g, and MtBE The other fuel oxygenates have been analyzed since May, 2003 The analytical ' groundwater data are presented in Appendix B The results of the water quality analysis show that shallow groundwater has been impacted by ' petroleum hydrocarbons, primarily the fuel oxygenate MTBE MtBE has been detected in all four monitoring wells but has not been detected in. the private supply well Concentrations of MtBE have historically been, and continue to be, highest in samples from MW-1, located within the source area Concentrations of BTEX constituents are not consistently detected in any monitoring well BTEX concentrations have not been detected in well MW-2 since April 1999 or in MW-4 since January 2001 Low concentrations of benzene are consistently detected In MW-3 and appear to be ' decreasing 4 3 1 Soil Analytical Results Based on investigation results from previous and the current CPT subsurface investigation,impacted soil is localized below the area of the former UST and extends from the bottom of the former UST excavation to the water table The CPT investigation analytical results for soil indicate two (25- and 35-ft bgs) of the five soil samples collected from CPT-1 had detections of TPH-g above the reporting limit All five soil samples from CPT-1 had detections of MtBE and ranged from 14 to ' 27 g/kg The highest concentration of MtBE (27 mg/kg) in soil from CPT-1 was from 35-ft bgs In addition to TPH-g and MtBE, concentrations of benzene, toluene, ethylbenzene, total xylenes, and tert-butanol were detected in soil samples as presented in Table 3-1 Figures 4-1 through 4-3 ' show soil analytical results from CPT-1 4 3 2 Groundwater Analytical Results MtBE MtBE is the primary constituent of concern at the site Of the 22 groundwater samples collected MtBE was only detected in samples collected from 80-, 95-, and 108-ft bgs at location CPT-1, as shown on Figure 4-5 The MtBE results from CPT-1 ranged from 750 µg/l from the sample collected at 108-ft bgs to 16,000 µg/l from the sample collected at 80-ft bgs BTEX BTEX constituent concentrations were detected in only the groundwater sample from ' CPT-1 Benzene concentrations exceeded its drinking water maximum contaminant level (MCL) of 1 µg/L in the sample from 108-ft bgs at a concentration of 54 µg/L However, due to elevated reporting himits for the samples collected at 80- and 95-ft bgs, benzene may exist in lower ' concentrations All other constituents were detected in very low concentrations and far below . their respective drinking water MCLS 1 ' P\23000\23954 I`1 trucking\(-PT Summary Report\1 iNAL i&T ]"rucking DOC