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3.0 MONITORING RESULTS <br /> The geologic setting is an important factor when analyzing hydrology of an area. <br /> Stratigraphy in the region ranges in age from Pre-Cambrian to Quarternary. However, <br /> only the Raton Formation and Quarternary (alluvial) deposits are exposed in the area of <br /> the mines. The Raton Formation constitutes the bedrock of the area having a total <br /> thickness of 1200 to 1600 feet. Most of the formation consists of very fine to medium <br /> grained sandstone interbedded with siltstone and shale. Coal to be mined at the New Elk <br /> and Golden Eagle is located near the middle of the Raton Formation. The outcrop of the <br /> formation in the area may be characterized as stream deposits including channel-point bar <br /> facies, floodplain deposits and swamp deposits. <br /> Alluvial deposits along the Purgatoire River are complex. The headwaters of the <br /> river are underlain by volcanic rocks and sediments. As it flows to the east, the river cuts <br /> its way through many different geologic formations including Pleistocene glacial-fluvial <br /> sediments, foothills belt of Paleozoic-Mesozoic strata, terrestrial sediments of the <br /> Tertiary, and marine deposits of the Pierre Shale. Channel shape and structure of the <br /> Purgatoire also vary within each of these formations as does the water quality. A natural <br /> deterioration of water quality can be expected as the stream flows out of the igneous <br /> terrains, through sodic sediments, and into marine sediments. Alluvial deposits in the <br /> area of the mines range from their current location to older terraces of forty to fifty feet <br /> above the Purgatoire. Buried channels filled with alluvium incised into the underlying <br /> Raton Formation have also been found. These alluvial deposits support typical <br /> hydrophytic vegetation characteristic of floodplains and contain ground water <br /> hydrologically connected to the Purgatoire River. <br /> 3.1 Surface Water <br /> Surface water availability is directly related to precipitation received in the <br /> drainage. The climate summary, as described in the 1981 mine permit application, <br /> indicates total calculated precipitation for the mines should be 16.92 inches. As <br /> previously mentioned, above average precipitation was recorded at the mine weather <br /> stations and above average snowfall was recorded in the upper elevations of the <br /> Purgatoire drainage which indicates that 1984 was an above average year for runoff and <br /> stream flow. <br /> -8- <br />