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APPENDIX A <br /> DRILLING PROCEDURES FOR UVB 400 <br /> Any drilling operation will change the natural permeability of regolith and rock, at least near the <br /> borehole wall, due to the mechanics and hydraulics of the drilling process To avoid a reduction <br /> of the maximum permeability obtainable along the borehole wall and in the surrounding soils and <br /> to avoid the buildup of a less-permeable mudcake in the immediate vicinity of the well, a drilling <br />' method should be selected, based on the site-specific geology The drilling methods to choose <br /> from are modified bucket auger, hollow stem auger, air rotary, fluid rotary, reverse fluid rotary, <br /> and reverse air rotary with casing driver <br />' The installation of the UVB 400 system will require an open borehole or temporary casing of at <br /> least 24-Inches Inner Diameter <br /> If fluid rotary drilling is chosen, the best solution is to use fresh water as a drilling fluid If <br /> caving or heaving sands occur which require a mud additive to maintain an open borehole, only <br />' biodegradable additives should be used, or reverse rotary drilling should be used MUD <br /> ADDITIVES ARE THE LAST CHOICE FOR FLUID ROTARY DRILLING METHODS If <br /> mud additives are used, the drilling fluid MUST be treated with desanders and desilters before <br /> reentering the well <br /> Before installing the UVB casing stem with the special EA and IEG screens, the borehole will be <br /> cleaned from top to bottom by "water" circulation Only fresh water will stay in the hole <br /> After the UVB casing stem and screens are in the borehole, each screen section will be <br /> developed, using a surge block and pump to remove all introduced additives <br />' After the UVB casing stem is set in place, the remaining annular space will be filled with <br /> bentonite (sealed pellets) gravel, and a Port]and/bentonite grout in the amounts required by the <br /> size of the borehole <br /> 1 <br />' WP61 73942 WP 1096 TX 2 1 <br />