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Frontier Transportation, Inc. Well Installation Work Plan July 30, 2008 Page 4 generally in a western direction beneath the site. See Figure 3 , Groundwater Gradient Map. Historic first subsurface groundwater data identified a west or southwest flow beneath the site. 4.0) PROPOSED SCOPE OF WORK The extent of the MTBE contaminant plume is not clearly defined to the western edge of the current defined contaminant plume. Based on current data, BEA proposes the installation of one ( 1 ) additional well, which will be monitoring well MW-27. The location of the well will be approximately 50-feet due west of the westernmost well (MW-24). See Figure 2 for proposed well location. The well will be advanced to a total depth of 20' below grade surface (bgs) with the screen interval between 5 ' bgs and 20 ' bgs . See Figure 4 for the well construction diagram. The analytical data from the soil and groundwater samples at the new shallow well will aid in defining the boundary of the contaminant plume. 5.0) GROUNDWATER WELL INSTALLATION A hollow stem auger drill rig will be used to provide the soil borings for well installation. Drillers will hold a California State C-57 contractor's license. Typical auger size for the well installation described below is 8-inch outside diameter and 4.25-inch inside diameter. The boring for the well installation will be advanced to 20 ' bgs. The monitoring well will consist of a central section composed of riser and screen. The riser and screen will be constructed of 2-inch inside diameter, schedule 40 polyvinyl chloride (PVC) pipe. The proposed shallow well will consist of slotted PVC (screen) extending from approximately 20 ' bgs to 5 ' bgs and it will contain three 5-foot rows of 0. 010-inch slots. The annular space around the screen will be filled with an appropriate grain size of clean sand from 20 ' bgs to 4. 5 ' bgs to form a filter pack. This will be overlain with a F seal of bentonite pellets, then grouted to near ground surface with a 5% bentonite mixture with cement and water (See Figure 4) . Ends of the screen and riser sections will be constructed with flush-joining threaded fittings to ` ensure leak-proof unions. A filter pack of sand will be placed around the screen to retain the finer grained fractions of formation material and to create a zone of high permeability that allows free entry of water in the well. The pack will consist of clean sand (#2/ 16) . The bentonite and annular seals are necessary to prevent the annulus from serving as a vertical conduit for potential contaminants.