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LORENCITO CANYON MINE <br />ANNUAL HYDROLOGIC MONITORING REPORT - 2004 <br /> <br />SECTION 1 -INTRODUCTION <br />To fulfill the requirements of the Regulations of the Colorado Mined Land Reclamation <br />Boazd, the following report has been assembled in compliance with Rule 2.04.7. Since the <br />beginning of 1996, substantial work has been performed at the Lorencito Canyon Mine site <br />to interpret the hydrology of the area. Specific methodologies employed for this work are <br />described below. Field work accomplished during the baseline period has included the <br />installation and testing of 12 alluvial wells, 16 consolidated aquifer wells, along with the <br />monitoring of 11 surface water sites, 1 I springs and seeps, and 19 pond sites in the azea. <br />From the field data collected, insight has been gained into the recharge and discharge <br />characteristics of aquifers, hydraulic properties, potentiometric and water table surfaces, and <br />water quality for each of the hydrologic units. The program was reduced following issuance <br />of the permit in August 1997, resulting in a reduction of monitoring stations, frequency of <br />monitoring, and water quality pazameter analyses. A revision to the program was also <br />approved in early 1999 to reduce the frequency of monitoring during the premining period <br />until disturbance activities begin. <br />• In early 2001, a Permit Revision was submitted for approval of mining operations in the <br />surface mining area. As a result, the monitoring program was adjusted to use only those <br />stations that would detect potential impacts of these operations .These stations and water <br />quality parameters are listed on Tables 1-1 and 1-2. This revision eliminated all deep aquifer <br />wells from the monitoring program. This report presents the results of monitoring for <br />operations in 2004 and a summary of data from previous monitoring periods. <br />SECTION 2 -METHODOLOGY <br />Groundwater <br />To determine the presence of alluvial aquifers, wells were installed in the alluvium of major <br />canyons within the permit azea. Four wells were installed in Lorencito Canyon, and two <br />wells in Cow Canyon, with the other canyons having one well installed near the canyon <br />mouth. A total of 12 wells were installed. Most wells were installed with ten feet of screen <br />and generally do not exceed thirty feet in depth. Alluvial wells were assigned names based <br />upon location. Each well was designated with an MW prefix, followed by a two or three <br />letter code for the canyon the well was located in, and a number to designate the location <br />with the numbers increasing up the canyon. The location of monitoring wells is depicted on <br />Map 2.04.7-1. <br />• <br />1 <br />