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1 <br />Even though these changes have occurred, the direction of the composite hydraulic gradient <br />has retrained quite similar to that observed during pre-mining. However, the potentiometric <br />' surface is approximately 50 feet lower than the pre-mining condition. <br />' 2.3.2 Surface Water Hydrology <br />' The mine area is located entirely within the drainage basin of Rito Seco, a stream that <br />originates in the Sangre de Cristo Mountains to the east and flows in a genetal east-to-west <br />' direction towards its confluence with Culebra Creek. Through the mine area, Rito Seco <br />transitions from a mountainous stream that is relatively straight and has a channel bed <br />comprised principally of cobbles, to an earthen channel bed that is very sinuous in nature and <br />contains mostly sands, silts, and clays. <br />During the pre-mining monitoring period, Rito Seco experienced very few gains or losses in <br />the channel through the mine area. Flows at RS-1, in the mountainous portion of the Rito Seco <br />' channel above the mine activities ranged from 4.0 to 8.8 cubic feet per second (cfs), with an <br />average annual flow of 6.1 cfs. Station RS-2, located downgradient of the milting activities, <br />' had flows during the pre-mining period that ranged from 2.6 to 9.9 cfs, with an average <br />annual flow of 5.8 cfs. The furthest downgradient station on Rito Seco (R5-5), located near <br />the western boundary of the lease area, had flows during the pre-mining period that ranged <br />from 5.0 to 7.7 cfs, with an average annual flow of 6.0 cfs. The channel had several beaver <br />ponds in the reach between RS-2 and RS-5. <br />During the course of mining, the only hydrologic change in the flow regime in Rito Seco was <br />' the establishment of larger beaver ponds throughout the reach between RS-2 and RS-5. In fact, <br />the inundation of the original RS-5 station by a beaver pond resulted in the need to move this <br />' station to afree-flowing reach of Rito Seco. Pit dewatering activities and highwall inflows <br />from the south wall yielded minimal water and no measurable impact on stream flows. <br />' At the completion of mining, Rito Seco continues to have several beaver ponds on the main <br />channel that interrupt the free Flow of surface water. However, the flows measured at the <br />i surface water gaging stations on the main stem (RS-1, RS-2, and RS-5) contipue to exhibit <br />flows in a range consistent with the pre-mining surface flows. <br />7 <br />1 <br />