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.I 3) During the most recent groundwater _sampling= event (January 23 , 1996) , only downgradient well MW-13 contained detectable concentrations of dissolved BTEX compounds (MW-13 : B = 11 ppb, T = ND, E = 1. 1 ppb, X = ND) (see attached Cumulative Table of Well and Analytical Results) . It should be noted that wells MW-3, -4 and -5, all of which formerly contained elevated concentrations of dissolved hydrocarbons, have not been sampled due to insufficient water since September 1989. The relatively low concentrations of dissolved hydrocarbons in MW-9 from late 1992 to the present, may be an artifact of sampling groundwater from a submerged well screen, rather than representing a genuine improvement in water quality. The screen interval of MW-9 is 53 to 58 feet BGL, with a measured range in water depth varying in the well from 41. 1 to 56 .88 feet BGL (see attached Installation Log- MW-9) . The sampling events characterized by relatively low dissolved TPH-G concentrations generally correspond to a submerged screen interval (see attached Dissolved TPH-G/DTW/Screen Interval - Figure A) . The decline in the concentrations of dissolved hydrocarbons noted in MW-11 apparently represents a genuine reduction in the hydrocarbon mass in the surrounding formation, even though the screen was submerged during the three most recent sampling events (water table shallower than 43 feet BGL during the July 1995, October 1995 and January 1996 events) (see attached Installation Log - MW-11, and Dissolved TPH-G/DTW/Screen Interval - Figure B) . The top of the well screen in MW-11 is 43 feet BGL. Nondetectable to minimal concentrations of dissolved hydrocarbons also characterize water samples from the well from July 1993 to April 1995, when the local water table was below the top of the well screen. 4) As stated in the October 21, 1994 memo, the formerly operating soil vapor extraction system (November 1990 to November 1992) was apparently effective in addressing the residual hydrocarbons present in the vadose zone. Approximately 12 , 000 pounds of volatile hydrocarbons (measured as TPH) are calculated to have been removed by the VES, with an asymptotic decline in recovery noted during the last several sampling events (see attached Cumulative Hydrocarbon Recovery - Figure C) . The analytical results of confirmation soil boring samples indicated that concentrations of residual phase hydrocarbons were reduced within the presumed source area, which was addressed by the VES. 2 w