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LORENCITO CANYON MINE GROUNDWATER TECHNICAL REPORT SECTION 1 -INTRODUCTION To fulfill the requirements of the Regulations of the Colorado Mined Land Reclamation Board, the following report has been assembled in compliance with Rule 2.04.7. Since the beginning of 1996, substantial work has been performed at the Lorencito Canyon Mine site to interpret the hydrology of the area. Specific methodologies employed for this work are described in Section 2 of this document. Further background materials were obtained from a study of the Raton Basin published in 1982. The study "The Hydrogeology of the Raton Basin" (Howard, 1982) is utilized in conjunction with the site-specific materials to provide a comprehensive view of the hydrogeology of the site area. Field work accomplished during the baseline year has included the installation and testing of 10 alluvial wells, 16 consolidated aquifer wells, along with the monitoring of springs and seeps in the site area. From the field data collected, insight has been gained into the recharge and discharge characteristics of aquifers, hydraulic properties, potentiometric and water table surfaces, and water quality for each of the hydrologic units. On the basis of the previous study and the baseline data, both conceptual and mathematical hydrologic models have been developed to show the relationships between the various units. • SECTION 2 -METHODOLOGY Determinations of Aquifer Extents and Depths To determine the site-specific aquifer and potential water-bearing zone extensive field studies and existing data reviews were performed. Existing data and field studies show both Primero and Ciruela coal outcrop at the surface at the site. Elevations for these two coal seams are approximately 6800 and 7200 feet AMSL, respectively. These values were combined with contour maps developed during the baseline data period to approximate the location of the coal outcrops at the site. Outcrops were assumed as downgradient extents for these coals. The downgradient extent for the target coals are found on the north side of the site. Following the initial review of [he coal elevations and preliminary mine plans, a baseline characterization plan was developed based upon proposed mining areas. For alluvial groundwater, monitoring wells were emplaced above and below proposed disturbances and in tributary drainage areas (Table GW-1 and Map 2.04.7-1). These placements allow for monitoring of effects within all drainages at the site. Consolidated rock monitoring wells were emplaced to provide up and downgradient of the proposed mine layouts. Sites MW-1 and MW-3 were placed to determine the potential upgradient effects from proposed R-1 through R-4 mines. Site MW-2 was placed for determination of the potential effects from these same mines in the downgradient direction. Well sites MW-4 and MW-6 were placed to determine the downsteam effects from the P-1 and P-2 GmwAuarer.g75\Deccmber 9. 1996