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4-1 <br />4.0 DAM GROUTING <br />4.1 GENERAL <br />Grouting was performed within the pervious rock and alluvial soils beneath the <br />lower tailings dam to assess the potential for reducing seepage beneath the <br />dam. The locations of the grout holes were initially selected in the area <br />believed to be carrying the majority of the seepage. Alternate locations were <br />chosen as grouting progressed and more information was obtained. An initial <br />program consisted of six holes, G-1 through G-6, from stations 7+00 to 5+30, <br />respectively. A second phase of additional holes, G-7 through G-9, both split <br />the previously grouted holes and extended the grout line to station 5400. The <br />locations of all grout holes are presented in Figures 2 and 5. <br />Grouting began by advancing a hole with a Mobile 5-80 drill rig using HQ <br />casing and a retractable casing advancer roller bit. HQ casing was advanced <br />until rock (Creede Formation) was reached. At this point, NX wireline with a <br />diamond rock coring bit was used to advance the hole into the rock. In some <br />borings, the casing was advanced into the rock to prevent caving. <br />After each approximate 10 foot interval of rock coring, a packer (water <br />pressure) test was performed on the rock to measure rock mass permeability and <br />the potential for grout take. A Reading double packer was lowered down to the <br />bottom of the NX drill rods after the core barrel was retracted. The upper <br />packer was seated in the bottom of the drill rods and the lower packer was <br />inflated against the rock just below the NX rods. The packers were inflated <br />with nitrogen gas to an average of 150 pounds per square inch (psi). Water <br />was then forced under pressure through the drill rods and packer out into the <br />rock formation. The amount of water injected into the formation per time <br />period was recorded and converted to a permeability as shown in Table 1. The <br />drilling and pressure testing was continued until rock was encountered that <br />showed very little signs of weathering and was measured to be relatively <br />impervious. Water pressure at the hole collar was kept below 40 psi at all <br />times. <br />