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zoos <br />Alluvial deposits along the Purgatoire River are complex. The headwaters of the river are underlain <br />by volcanic rocks and sediments. As it flows to the east, the river cuts its way through many <br />different geologic formations including Pleistocene glacial-fluvial sediments, foothills belt of <br />Paleozoic-Mesozoic strata, terrestrial sediments of the Tertiary, and marine deposits of the Pierre <br />Shale. Channel shape and structure ofthe Purgatoire varywithin each ofthese formations as does the <br />water quality. Alluvial deposits in the area of the mine range from their current location to older <br />terraces of forty to fifty feet above the Purgatoire. Buried channels which are incised into the <br />underlying Raton Formation have also been found. Purgatoire River alluvial deposits support typical <br />hydrophytic vegetation characteristic of floodplains and contain groundwater hydrologically <br />connected to the Purgatoire River. The Picketwire Valley of the Purgatoire River alluvial deposits <br />has been designated as an alluvial valley floor and is classified as a renewable resource. <br />Soils are generally shallow and coarse-grained. They are derived from the underlying sandstones and <br />shales. Bedrock exposures are common and scattered throughout the area. The valley bottoms are <br />characterized by alluvial and colluvial deposits which are also coarse-grained and deeper than soils <br />of the mountain slopes. <br />Vegetation varies from riparian and blue grama complexes in the valley bottoms to pinion-juniper, <br />oak brush, and pine cover on the side slopes. Vegetation cover ranges from 100 percent in the valley <br />bottoms to none on the steeper side slope rock outcrop areas. <br />The nearest weather station to the mine site is located at the Trinidad Airport (elevation 5,746 feet) <br />approximately 30 miles east. Over a recording period from 1961 to 1990, total annual precipitation <br />averaged 13.5 inches. The majority of this precipitation (65 percent) occurs from May to September. <br />July usually has the most rainfall. The mean annual temperature is 51.8°F. January is the coldest <br />month with a mean temperature of 32.9°F, and July is the wannest month, showing a mean of 60.2°F <br />(Owenby and Ezell, 1992). The project area is approximately 1,650 feet higher in elevation than the <br />Trinidad Airport and can be considered to have 5°F lower mean temperatures and higher average <br />precipitation. <br />Surface water availability is directly related to precipitation received in the drainage. The climate <br />summary, as described in the mine permit document, projects a mean annual precipitation near the <br />mine of 16.92 inches. <br />The United States Geological Survey (USGS) monitored the flow of the Middle Fork of the <br />Purgatoire at Stonewall (07124050), approximately four miles upstream from the New Elk Mine, <br />from May 1978 to September 1981. The Purgatoire River at Madrid (07124200), approximately 15 <br />miles downstream of the Golden Eagle Mine, has been monitored since 1972. The size of the <br />drainage area above the Stonewall station is 52.1 square miles (mi2). There are some diversions for <br />imgation above the station. Recorded discharges during the three-and-a-half year period ranged from <br />2.8 cfs to 522 cfs (USGS, Water Resources Division, 1982). The size of the drainage azea above the <br />Madrid station is 505 miZ. There are diversions for imgation for about 6,000 acres upstream of the <br />Madrid station. The average annual discharge between 1972 and 1995 at Madrid was 71.4 cfs and <br />the average annual runoff was 51,740 ac ft (Crowfoot et al, 1996). The annual runoff in the <br />Purgatoire is dominated by snowmelt,with peak flows occumng in May and June. Summer and fall <br />thunderstorms generally produce smaller peaks of short duration. <br />626-Annual Hydrolic Monitoring (Apr.9.02).doc <br />April l7, 2002 <br />