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<br />00224:) <br /> <br />Durango Pomoing Plant - Stage I <br /> <br />~ <br /> <br />d. <br /> <br />b. <br /> <br />Within the site area, the trend of the fault is variable from N25E to N45E, <br />dipping 52 to 59 degrees southeast. <br /> <br />Fault F-l is characterized by 0.5 to 1.0 feet of gray, soft to firm, silty to <br />clayey gouge with 35 to 85 percent angular to platy fragments of siltstone <br />and sandstone up to about JI,-inch size. Slickensides observed in outcrop <br />have a rake of 67 degrees south indicating a normal, left-lateral slip <br />displacement. The horizontal component of displacement is unknown and <br />vertical component is estimated to be 150 to 200 feet based on general <br />lithologic correlations. Previous studies estimated displacements of up to <br />300 feet (Zapp, 1949) and greater than 140 feet (Kearl, Ludlam, and <br />Johnson, 1983), <br /> <br />Variablypropylitized andesite dikes are associated with the fault and were <br />encountered within IO feet of the fault plane in drill holes DH-I05, DH- <br />110, and DH-118. In drill hole DH-109, dikes were encountered 15.4 <br />above and 8.8 feet below the fault. Andesite dikes were observed in <br />outcrop to have orientations ofN22E to N45E and dip 52 to 75 degrees to <br />the southeast. Thickness of the dikes range from 0.3 to 3.3 feet in surface <br />outcrops and from 0.5 to 8.2 feet in drill holes. <br /> <br />Permeabilities determined by packer tests within the fault zone range from <br />o in drill hole DH-118 to 2,543 feet per year in drill hole DH-1 05. The <br />fault is believed to carry a substantial percentage of the groundwater at the <br />site. <br /> <br />c. <br /> <br />1.05 GROUNDWATER <br /> <br />A. Groundwater occurs at the site in bedrock and within the fault zone. It occurs locally in <br />surficial deposits where the groundwater surface rises above the bedrock surface. <br />Groundwater enters the area from the west and southwest. Groundwater flow is mostly <br />through secondary penneability consisting of open bedding planes and joints. Drill core <br />indicates dominant flow paths are open bedding planes in the Point Lookout Sandstone <br />and open joints and coal beds in the Menefee Formation, Fault F-I has significantly <br />higher permeabilities than the surrounding rock and, therefore, is believed to transmit a <br />significant quantity of groundwater. <br /> <br />B. Groundwater flow at the site is northward and eastward toward the Animas River. The <br />groundwater surface ranges from approximate elevation 6472 in DH-114 to elevation <br />6442 in DH-113 near the river and averages between elevation 6455 and 6460 through <br />the center of the area to be affected by excavation and construction. A groundwater <br />contour map using data from August 2001 is shown on drawing _ (69-529-1O). The 2001 <br />data represents a dry year. Fluctuations of up to about 10 feet should be anticipated. <br />Table 00320C is included which updates groundwater elevations in the monitoring wells <br />to August 2001 (see Appendix B). The groundwater regime at the site is discussed in the <br />Reclamation report Durango Pumping Plant - Animas-La Plata Project- <br />Hydrogeochemical Site Characterization - dated November 1990. Addendums to <br />Reclamation's report were published in September 1992, April 1996, and April 2002, <br /> <br />Geology <br />00320 - 13 <br />