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October 2012 Page 1 -2 <br />The geologic setting is an important factor when analyzing hydrology of an area. <br />Stratigraphy in the region of the mine ranges in age from Pre - Cambrian to Quaternary. <br />However, only portions of the Raton Formation (see Figure 1 -1) and recent alluvial deposits are <br />exposed in the area of the mine. Most of the formation consists of very fine- to medium - grained <br />sandstone interbedded with siltstone and shale. Coal that was mined at the New Elk Mine is <br />located near the middle of the Raton Formation. The outcrop of the formation in the area may be <br />characterized as stream deposits including channel -point bar facies, floodplain deposits and <br />swamp deposits. <br />Alluvial deposits along the Purgatoire River are complex. The headwaters of the river <br />are 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 Tertiary, and marine <br />deposits of the Pierre Shale. Channel shape and structure of the Purgatoire vary within each of <br />these formations as does water quality. Alluvial deposits in the area of the mine range from their <br />current location to older terraces of forty to fifty feet above the Purgatoire. Buried channels <br />which are incised into the underlying Raton Formation have also been found. Purgatoire River <br />alluvial deposits support typical hydrophilic vegetation characteristic of floodplains and contain <br />groundwater hydrologically connected to the Purgatoire River. <br />Soils are generally shallow and coarse - grained. They are derived from the underlying <br />sandstones and shales. Bedrock exposures are common and scattered throughout the area. The <br />valley bottoms are characterized by alluvial and colluvial deposits which are also coarse - grained <br />and deeper than solids of the mountain slopes. <br />Vegetation varies from riparian and blue grama complexes in the valley bottoms to <br />pinion juniper, oak brush, and pine cover on the side slopes. Vegetative cover ranges from <br />100 percent ( %) in the valley 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 <br />5,746 feet [ft]) approximately 30 miles east. Over a recording period from 1961 to 1990, total <br />annual precipitation averages 13.5 inches. The majority of this precipitation (65 %) occurs from <br />May to September. July usually has the most rainfall. The mean annual temperature is 51.8 <br />degrees Fahrenheit ( °F). January is the coldest month with a mean temperature of 32.9 °F, and <br />July is the warmest month, showing a mean of 60.2 °F (Owenby and Ezell 1992). The project <br />area is approximately 1,650 ft higher in elevation than the Trinidad Airport and can be <br />considered to have 5 °F lower mean temperatures and higher average precipitation. <br />Surface water availability is directly related to precipitation received in the drainage. The <br />climate summary, as described in the mine permit document, projects a mean annual <br />precipitation near the mine of 16.92 inches. <br />The United States Geological Survey (USGS) monitored the flow of the Middle Fork of <br />the Purgatoire at Stonewall (07124050) approximately four miles upstream from the New Elk <br />Mine, from May 1978 to September 1981. The Purgatoire River at Madrid (07124200), <br />approximately 18 miles downstream from the New Elk Mine, has been monitored since 1972. <br />The size of the drainage area above the Stonewall station is 52.1 square miles (mi2). There are <br />