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LORENCITO CANYON MINE ANNUAL HYDROLOGIC MONITORING REPORT - 2006 I• SECTION 1 -INTRODUCTION To fulfill the requirements of the Regulations of the Colorado Mined Land Reclamation Boazd, 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 azea. Specific methodologies employed for this work aze described below. Field work accomplished during the baseline period has included the installation and testing of 12 alluvial wells, 16 consolidated aquifer wells, along with the monitoring of 11 surface water sites, 11 springs and seeps, and 19 pond sites in the azea. From the field data collected, insight has been gained into the rechazge and dischazge characteristics of aquifers, hydraulic properties, potentiometric and water table surfaces, and water quality for each of the hydrologic units. The program was reduced following issuance of the permit in August 1997, resulting in a reduction of monitoring stations, frequency of monitoring, and water quality pazameter analyses. A revision to the program was also approved in eazly 1999 to reduce the frequency of monitoring during the pre-mining period until disturbance activities begin. In early 2001, a Permit Revision was submitted for approval of mining operations in the • surface mining azea. As a result, the monitoring program was adjusted to use only those stations that would detect potential impacts of these operations .These stations and water quality pazameters aze listed on Tables 1-1 and 1-2. This revision eliminated all deep aquifer wells from the monitoring program. 1n 2002, alluvial monitoring wells MWLO-E and MWLO-W were completed to monitor potential impacts from the coal loadout area. In 2005, quarry operations conducted by the surface owner destroyed MWLO-W. This report presents the results of monitoring for operations in 2006 and a summary of data from previous monitoring periods. SECTION 2 -METHODOLOGY Groundwater To determine the presence of alluvial aquifers, wells were installed in the alluvium of major canyons within the permit azea. Four wells were installed in Lorencito Canyon, and two wells in Cow Canyon, with the other canyons having one well installed neaz the canyon mouth. A total of 12 wells were installed. Most wells were installed with ten feet of screen and generally do not exceed thirty feet in depth. Alluvial wells were assigned names based upon location. Each well was designated with an MW prefix, followed by a two or three • letter code for the canyon the well was located in, and a number to designate the location with the numbers increasing up the canyon. The location of monitoring wells is depictod on Map 2.04.7-1. 1