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C.1.0 INTRODUCTION <br />Hydrologic analyses and designs were prepared for stormwater controls for the reclaimed <br />Tailings Disposal Area (TDA) and the water management ponds in the West Pit area <br />(West Pit Ponds) at the Battle Mountain Resources, Inc. San Luis Project. The San Luis <br />Project is located on the western flank of the Sangre de Cristo Mountains, approximately <br />4 miles northeast of the town of San Luis, in Costilla County, Colorado. The topography <br />of the site is relatively steep and mountainous terrain, with slopes ranging from 7 percent <br />in the valleys to 20 percent along the ridges. The average elevation of the site is 8,600 <br />feet above mean sea level (amsl). Annual average precipitation at the San Luis site is 12 <br />inches (Benson, 1997) and average evaporation is 40 inches (Farnsworth, et al, 1982). <br />The dominant vegetation is greasewood, sagebrush, juniper, and pinon pine near the <br />valley, with spruce fir and ponderosa pine at higher elevations. The Rito Seco is a <br />perennial stream that flows westward across the southern part of the San Luis site <br />(BMRI, 1998; Benson, 1997). <br />C.2.0 TAILINGS DISPOSAL AREA STORMWATER DESIGN <br />C.2.1 Tailings Watershed Analysis <br />In order to design the proposed modifications to the reclaimed TDA, it is necessary to <br />estimate the stormwater response of the upgradient terrain and corresponding data. The <br />stormwater response of areas upgradient of the TDA was estimated using basin <br />characteristics presented in the existing Mine Reclamation Permit (SRK, 1989). <br />Additionally, the subbasins of the watershed were delineated, as shown in Figure 1, to <br />reflect proposed post reclamation configuration shown in Figure 2. The reclamation <br />configuration includes construction of a spillway and final cover of the tailings. The <br />stormwater response of the terrain upgradient of the TDA was modeled using the HEC- <br />HMS hydrologic modeling system (U.S. Army Corps of Engineers, 2006). The subbasin <br />characteristics used in modeling of the TDA watershed are shown in Table 1. To <br />determine lag time for subbasins, the travel time for each flow segment was determined, <br />combined and then multiplied by a factor of 0.6 (Haan, et al, 1994). Sheet flow was