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Current landfill design drawings (pending EMCON design report) indi- cate development of initial fill in the northwest corner of the facil- ity. An outline of the completed landfill is shown on Figure 5. As the ground -water elevation map in Figure 4 shows, ground water in the site vicinity is apparently mounded, with local flow directions potentially different than the southwest gradient observed regionally. EMCON believes the gradient is influenced by pumpage from nearby domestic and irrigation wells. Water -level measurements from the initial three landfill monitoring wells along with the domestic on- site well will provide data over the next few years regarding these anticipated fluctuations in flow directions. Wells G-1, G-2, and G-3 should be operational prior to initiating waste disposal of the facility. Other wells may be added as filling progresses across the site. 10 B. DRILLING AND WELL CONSTRUCTION METHODS EMCON recommends that the proposed- borings for monitoring wells be drilled using air -rotary drilling equipment with a casing advance system. It has been EMCON's experience that the semi consolidated nature of the sediments in the subsurface can make drilling and well installation very difficult if conventional air -rotary or mud -rotary methods are used. The use of a casing advancer will: I. Prevent the caving of sidewall material by advancing casing as the hole is drilled. 2. Improve stratigraphic control by preventing the caving, slough- ing, or other infiltration of material from above. 3. Minimize potential well completion problems by enabling construc- tion of the well inside the casing, then extracting the casing as PJ9 9390207.00D 11