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G"IogicalTeckmcs14C Page 4 Additional Site Characterization Work Plan Project No 724 2 June 27,2002 Date Benzene Toluene Ethyl Total TPH MTBE ug/L ug/L Benzene Xylenes Gasoline ug/L ug/L ug/L ug/L 12/11/01 138 855 24.7 165 1,140 (ND C 5) 02/27/42 1 1.5 08 16 233 (ND C 5) 06/06/02 NDC 0 3 NDC 0 3 03 5 ND<50 24 MTBE values reported in (parentheses)were performed by EPA method 8260 GTI proposes to install additional monitoring wells at the site to define the vertical & lateral extent of the groundwater plume both on and off site See Figures 2 & 3 for the locations of the proposed wells 2.2 Vertical Definition A single well, MW-301, is proposed for vertical plume definition in the location of the former dispenser island The well will be advanced beyond 155 feet bgs, the maximum depth explored in the investigation to date The well will be constructed in a fashion to minimize the possibility of cross contamination To accomplish this, a conductor casing will be used, as with boring MW-201, which will extend to the depth of the lowest detected contamination (130 feet) The complete well details will be discussed in Section 2 4 3 below 2.3 Lateral Definition The installation of six sets of shallow/intermediate/deep wells will enable the site conceptual model to be refined to show the limits of the plume See Figure 3 for the locations of proposed well sets MW-7/-107/-207, MW-8/-108/-208, MW-9/-109/-209, MW-101-1101-210, MW-11/-1111-211, and MW-12/-112/-212 The installation of these wells will establish the lateral extent of the plume and the need for additional investigation and remediation can be evaluated based on this data The well sets will have screened intervals to define the lateral and vertical profile of the aquifer Three wells per set are chosen because a water table well is necessary to evaluate the current level of groundwater Intermediate wells will be required to monitor the submerged screened levels of existing wells MW-1 through MW-3 These wells were installed when the groundwater levels were approximately thirty feet deeper than today The deep well of each set will be used to define the non-detect point of the bottom of the plume The screened interval of these wells will be installed into course-grained units, refer to Figure 5 & 6 For best results of contaminant evaluation, we plan on the intermediate depth well to be installed in the sandy unit at a depth of approximately 70 feet bgs