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the area ntay be characterized as strcmn deposits including channel-point bar lades. <br />floodplain deposits and swamp deposits. <br />Alluvial deposits along the Purgatoire River are complex. 7~he headwaters of the river arc <br />underlain by volcanic rocks and sediments. As it flows to the east, the river cuts its way <br />through many different geologic formations including Pleistocene glacial-fluvial sediments. <br />foothills belt of Paleozoic-Mesozoic strata, terrestrial sediments of the 'I'erliary, and marine <br />deposits of the Pierre Shale. Clramrel shape and structure of the Purgatoire vary within each <br />of these formations as does water quality. Alluvial deposits in the area of the mine range <br />from their current location to older terraces of forty to Gfty feet above the Purgatoire. Buried <br />channels which are incised into the underlying Raton Formation have also been found. <br />Purgatoire River alluvial deposits support typical hydrophilic vegetation characlerislic of <br />floodplains and contain groundwater hydrologically connected to the Purgatoire River. <br />Soils are generally shallow and coarse-grained. 'They arc derived Isom the underlying <br />sandstones and shales. Bedrock exposures are common and scattered throughout the area. <br />The valley bottoms are characterized by alluvial and colluvial deposits which are also coarse- <br />grained and deeper than soils of the mountain slopes. <br />Vegetation varies from riparian and blue grama complexes in the valley bottoms to pinion- <br />juniper, oak brush, and pine cover on the side slopes. Vegetation cover ranges from IOU <br />percent in the valley bottoms to none ou the sleeper side slope rock outcrop areas. <br />The nearest weather station to the mine site is located at lhe'friuidad Airport (elevation 5,74E <br />feet) approximately 30 miles east. Over a recording period from 1961 to 1990, total annual <br />precipitation averaged 13.5 inches. 'fhe majority of this precipitation (GS percent) occurs <br />from May to September. July usually has the most rainfall. 7~hc mean annual temperature is <br />51.8°F. January is the coldest month with a mean temperature of 32.9°P. and .luly is the <br />warmest month, showing a mean of 60.2°I~ (Owenby and Izcll, 1992). "I~he project area is <br />approximately 1,650 feet higher in elevation than the ~IYinidad Airport and can be considered <br />to have 5°F lower mean temperatures and higher average precipitation. <br />Surface water availability is directly related to precipitation received in the drainage. 'I'hc <br />climate summary, as described in the mine permit document, projects a menu annual <br />precipitation near the mine of 16.92 inches. <br />The United States Geological Survey (USGS) monitored the (low of the Middle Fork of the <br />Purgatoire at Stonewall (07124050), approximately lour miles upstream from the New 131k <br />Mine, from May 1978 to September 1981. "Fhe Purgatoire River at Madrid (07124200), <br />approximately 18 miles downstream from the New I~Ik Mine, has been monitored since <br />1972. The size of the drainage area above the Stonewall station is 52.] square miles (mi2). <br />There are some diversions for irrigation above the station. Recorded discharges during the <br />three-and-a-half year period range from 2.8 cfs to 522 cfs (USGS, Water Resow~ces Division, <br />1982). The size of the drainage above the Madrid station is 505 miz . "There are diversions for <br />irrigation for about 6,000 acres upstream of the Madrid station. The average annual <br />discharge between 1972 and ] 995 at Madrid was 71.4 cfs and the average annual runoff was <br />3 <br />