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