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Frontier Transportation, Inc. Well Installation Work Plan r j November 14, 2006 Page 4 MW-5, MW- 10 and MW- 11 identified no detectable MTBE along the south of the property. Monitoring wells MW-6 and MW-7 demonstrate that the MTBE plume has not migrated to the east. The recent laboratory analytical results presented in Table 1 and in Appendix A. f ij However, there are currently no wells along the northern or western edges of the plume to delineate the extent of the MTBE plume. Currently the westernmost wells (MW-9, MW-20 and MW-4) demonstrate dissolved MTBE between 377 ug/L and 928 ug/L.- The northernmost wells (MW-2 and MW-8) identified dissolved MTBE at 1 ,380 ug/L and 2, 150 ug/L, respectively: It is, therefore, proposed that additional shallow wells be installed; one well (MW-24) should be placed proximately 50 feet west of MW-9 and another well (MW-25) should be placed 50 feet north�o 4W4. The proposed locations of these two wells are based upon elevated concentrations of MTBE in the westernmost wells at the site. Groundwater samples from these two locations will provide information regarding MTBE plume migration. See Figure 2 for proposed well locations. It may also be beneficial to install a third monitoring well north of MW-2 so that the northeastern edge of the plume can be monitored. The location of proposed monitoring well 41 MW-26 is approximately 70' north of MW-2. Sampling at this location would provide further MTBE plume delineation. j Each 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 2 for proposed well location). The analytical data from the soil and groundwater samples at the new shallow wells will be C I significant in determining 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 84nch outside diameter and 6-inch inside diameter. The borings for shallow well installation will be advanced to 20' bgs. i` Each well will consist of a central section composed of riser and screen. The riser and screen will be constructed of two-inch inside diameter, schedule 40 polyvinyl chloride (PVC) pipe. The proposed shallow wells will consist of slotted PVCextendfrom approximately 20 ' bgs to 5' bgs and it will contain three rows of 0 . 010-inch slots. The annular space around the screen will be filled with an appropriate grain size of sand from, 20' bgs to 4.5' bgs to form a filter pack. This will be overlain with a 1' seal of bentonite pellets, then grouted to near ground j surface with a 5% bentonite mixture with cement and water. Ends of the screen and riser I, I