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3 <br />t <br />• INTRODUCTION <br />~ This report presents the results of a surface and subsurface hydro- <br />1 logic investigation in the immediate vicinity of CF&I Steel Corporation's <br />Maxwell and Allen Mines in Las Animas County in southern Colorado. Both <br />mines are underground coal mines with entries located in the Picketwire <br />j Valley along the Purgatoire River about 30 miles west of Trinidad and im- <br />! mediately west of Weston, Colorado. The Allen Mine is upstream of the <br />Maxwell Mine approximately 3.5 miles. The Allen Mine has been in production <br />i <br />for about 30 years and is in its declining years of production. The Maxwell <br />Mine has more recently been put into production and coal extraction is <br />~ planned far many years. <br />The purposesof the investigations reported herein were to gather and <br />~ analyze the hydrologic, water quality, and selected geologic data pertinent <br />to the application for a mining permit. Because of the expected phase out, <br />the~item of major concern at the Allen Mine is the effect of the active <br />waste dump upon the quality of waters in the adjacent Purgatoire River, <br />• . and this concern is analyzed in detail. The study at the Maxwell Mine in- <br />cluded characterization of the bedrock and alluvial deposits relative to <br />t hydraulic and water quality parameters. These data were used to assist the <br />I estimation of mine inflows; degree, extent and persistence of the disturbance <br />of the piezometric surface; and potential influence of mining on the hydro- <br />logic balance with respect to both quantity and quality of waters. <br />GEOLOGIC SETTING <br />1 The study area is situated in the Park Plateau, a subidivision of the <br />Great P loins physiographic province which is applied to dissected highlands <br />that separate the High Plains to the east from the Rocky Mountains to the <br />' west. The Purgatoire River flows through the study area and is one of the <br />master streams that drains the region. It heads in the Sangre de Cristo <br />Range south of the Spanish Peaks and has three major headwater tributaries, <br />the north, middle and south forks that unite near the study area. The study <br />area is located slightly above 7000 feet in elevation. Cottonwood is common <br />on the floodplain of the Purgatoire, whereas pinyon, juniper, scrub oak and <br />~ mountain mahogany are common to Slopes above the river. <br />