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. Third Quarter 2005 Thrifty#172 October 25, 2005 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 declined to 65 ug/L and ND<O 63 ug/L, respectively Although the benzene concentration (9 6 ug/L) in well MW-3 also declined, the toluene concentration increased slightly from 71 to 9 2 ug/L 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 is 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+TIE+X ratios based on . the groundwater samples collected dunng 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 8/24/05 MW-3 9 6 92 18 8 ND<0 24 1 2J 144 13.06 Based on the May and August 2005, sampling results, the B+T/E+X ratios for monitoring well MW-3 were 188 and 13 06, respectively Well MW-3 is located downgradfent 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 As of September 27, 2005, a total of 152,894 pounds of hydrocarbons have been removed by the soil vapor extraction (SVE) unit (Table 3) During the current reporting period, the system operated for 2,010 hours and removed 10,487 pounds of hydrocarbon for a removal rate of 5 21