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<br />00225'1 <br /> <br />Durango Pumoin~ Plant - Stage] <br /> <br />-113, and -119 through -122 penetrated between 65 and 90 percent <br />siltstone, 10 to 25 percent sandstone, and 0 to 10 percent shale. Drill hole <br />DH-l08 encountered siltstone and sandstone in approximate equal <br />proportions. The siltstone is moderately hard to moderately soft and the <br />sandstone is moderately hard. The shale was encountered in drill holes <br />DH-l07, -108, -Ill, and -112 and occurs as interbeds to about 0.3 feet <br />within interbedded siltstone and sandstone intervals. The shale constitutes <br />less than 10 percent of these intervals and is moderately soft to soft. <br /> <br />c. Bedrock encountered in drill holes was intensely weathered to an average <br />depth of about 3 feet with a maximum of 9 feet below the rock surface in <br />drill hole DH-lll. The remainder of rock encountered during drilling was <br />predominantly slightly weathered to fresh. <br /> <br />d. Drill core generally shows a decrease in fracture densities with depth. <br />Intense or moderate to intense fracturing occurs from the rock surface and <br />decreases to slightly fractured near excavation grade. The intensely <br />fractured zone averages about 5 feet below the rock surface and reaches a <br />maximum of9.9 feet in drill hole DH-Ill. Joints are predominantly tight <br />to slightly open. Significant open jointing was encountered at grade in <br />drill hole DH-l07 and slightly below grade in drill hole DH-lll. <br />Associated permeabilities in these locations are 478 feet per year in drill <br />hole DH-107, and range from 193 to 785 feet per year in DH-I11. <br />Permeability tests within a fracture zone encountered in drill hole DH -112 <br />from 16.5 to 35.0 feet in depth were unsuccessful due to the inability to <br />seat the packer to obtain appropriate pump pressures. <br /> <br />e. The top of bedrock surface within the river channel was surveyed in <br />January, 2002 to provide additional information for intake channel design. <br />The bedrock consists primarily of siltstone of the Cretaceous Point <br />Lookout Sandstone. The bedrock surface averages between approximate <br />elevation 6438 and 6439. The survey points and their corresponding <br />elevations are shown on drawing No. 69-529-5. <br /> <br />1.07 GEOLOGY OF AIR CHAMBER AREA <br /> <br />A. The Air Chamber is located immediately south of the Durango Pumping Plant. No <br />specific explorations were performed at this location however, drill hole DH-112, was <br />drilled approximately 55 feet south and east of the center of the air chamber. The Point <br />Lookout Sandstone was encountered at elevation 6465.9 feet in DH-112. The rock <br />consists of siltstone interbedded with sandstone and shale. The upper ten feet of the <br />bedrock is moderately to slightly fractured, becoming slightly fractured with depth. The <br />rock is intensely weathered from the top of bedrock at elevation 6465.9 to elevation <br />6463,1, moderately weathered to 6461.0, becoming slightly weathered to fresh with <br />depth. <br /> <br />B. Groundwater is anticipated to be encountered near the top of bedrock surface at the air <br />chamber location. <br /> <br />Geology <br />00320 - 18 <br />