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. Gc*ica!?ccrpiW 2= Page 2 Additional site Characterization work Plan Project No.724.2 July 7,2000 investigate the contamination at the site. The directive included several recommendations including: • Installation of additional down gradient monitoring wells east of MW-2 to evaluate r shallow and deep units of the aquifer t • Installation of shallow and deep screened monitoring wells southeast of the source area • Continuing quarterly monitoring 2.0 PROPOSED INVESTIGATION Existing wells MW-2 and MW-4 contain the highest levels of detected contaminants (Figure 2). Well MW4 is located adjacent to the former dispenser island and MW-2 lies approximately 50 feet down gradient of MW-4. During the initial groundwater monitoring event in 1992, groundwater depth was approximately 54 feet bgs at the site. Groundwater depth averaged 31.78 feet bgs during the March 2000 monitoring event and this is an increase of about 22 feet since the 1992 event. Defining the vertical limit of the contamination in the vicinity of MW-4 is warranted since a deeper plume is evident in down gradient well MW-2 [screened at a depth of 44-64 feet bgs(13-33 feet below the current water table)]. In order to investigate the on site vertical extent of soil and groundwater impacted with gasoline range petroleum hydrocarbons, Geological Technics Inc. proposes to advance a L single soil boring near well MW-4 to a maximum of 90 feet below grade and convert it into a discretely screened deep monitoring well. Once the groundwater data from this well is L evaluated, the location, number, and appropriate screened interval of additional, down gradient wells can be determined,and will be submitted in an addendum to this work plan. 2.1 Monitoring Well Installation The boring for the deep well, MW-104, will be drilled using an 8.00 inch outside diameter Lcontinuous flight hollow stem auger owned and operated by V&W Drilling (C57# 720904). Soil cuttings will be placed in 55-gallon steel DOT approved drums and stored on site until L their removal can be arranged. A professional geologist under the supervision of a licensed registered geologist will direct all drilling, sampling, and well construction., L The monitoring well will be constructed using 2.0 inch diameter PVC casing with flush threads. The proposed screened interval will extend from 87.5-90 feet below ground surface based on lithology encountered during drilling. Final construction of the well will be determined in the field. (Rationale: this depth will evaluate groundwater quality at depth below the screened intervals of both MW-2 and MW-0. The well will be constructed as follows: A#12 sand filter pack will surround and extend two feet above the 0.010" screened interval. The filter pack will be surged during placement. A 3 foot retarded hydration weighted bentonite pellet transition seal will be installed and allowed L L