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Fourth Quarter 2005 Thnfty#172 Page 3 Possible New Release or Active Source In the 1st quarter of 2005, Thrifty noted dramatic increases in TPHg (130,000 ug/L) and MTBE (122,000 ug/L) concentrations in well MW-3 that may indicate that a new release occurred or an offsite active source is contributing dissolved hydrocarbons to the area of well MW-3 In the current quarter, TPHg and MTBE concentrations in well MW-3 increased from the previous quarter to 2,550 ug/L and 252 ug/L, respectively The benzene concentration (843 ug/L) in well MW-3 also increased from the previous quarter Further evidence of a recent release is provided by the use of BTEX ratios that are used as a means to compare the relative age of gasoline releases into the subsurface The most common method is the cumulative BTEX ration that 1s described as B+T/E+X Site investigations indicate that values between 1 and 6 or above are supportive of a recent release and that values less than 0 5 usually indicate a release older than about 8 to 10 years (Kaplan et al 1997, "Forensic Environmental Geochemistry Differentiation of Fuel Types, Their Sources and Release Time," Robert D Morrison "Forensic Techniques for Establishing the Origin and Timing of Contaminant Release") The table provided below provides B+T/E+X ratios based on • the groundwater samples collected during sampling events beginning in May 2005 Sampling Well B T B+T E X E+X B+TIE+ Date ID X 5/11/05 MW-3 265 71 2721 72 73 145 1.88 8/24105 MW-3 9 6 92 188 ND<O 24 1 2J 144 13.06 11/9/05 MW-3 843 14 857 49 22 71 12.07 Based on the May, August, and November 2005, sampling results, the B+T/E+X ratios for monitoring well MW-3 were 1 88, 13 06, and 12 07, respectively Well MW-3 is located downgradient of the USTs/piping and dispensers Thus, it is possible that a recent release occurred in the area of well MW-3 Remediation Status Vapor Extraction System On April 26, 2001, a new Baker Furnace Thermal Oxidizer Unit was placed into operation with the hour meter reading at zero Presently, the remediation system is connected to soil vapor extraction wells VW-1, VW-2 (A,B), VW-3, VW-4 (A,B,C), VW-5 (A,B,C), and VW-6 (A,B,C) as shown on Figure 6