2021-04-14_PERMIT FILE - C1996084 (8)

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• Surface Water Surface water flow within the permit area is limited and occurs in conjunction with storm events or snowmelt. Flow within Lorencito and Cow Canyons is discontinuous along the channel length due to communication between the colluvial materials and the stream (see discussion in Exhibit 8). The watersheds are small in lateral extent, with the exception of Lorencito Canyon, which receives over half of its flow from watersheds upstream of the area. The baseline reconnaissance suggests that springs contribute an insignificant flow to the annual yields from the watersheds. Consequently, there is little surface water flow to be impacted during mining. The probable hydrologic consequences of mining on surface water in the Lorencito Canyon permit area will vary depending upon the type of disturbance, and the period of time under discussion. There will be three types ofpotential disturbance at the site: facilities area disturbance; disturbance associated with surface mining; and affected area disturbance associated with subsidence from undermining. Disturbances will vazy from the operational phase to the post-mining or reclamation phase. Impacts are typically classified into changes in flow or changes in water quality. Quantitative impacts to surface waters which are derived from disturbances during operations will consist of increases in peak discharges and runoff volumes associated with the reduction of vegetative cover. Most of the runoff from disturbances associated with the operation will be treated • by sediment ponds, which will discharge storm waters for several days following a storm event. This will temporarily modify the stream's original runoff hydrograph by extending the period of flow. Elevated peak discharges from the disturbed areas will occur across limited areas, as ponds will be located as close to disturbances as possible. Water will be required for potable water, bath house use, and water within the mine. Water consumption requirements will range from 15 acre-feet in 2003 to 75 acre-feet in 2012. Water consumption is not expected to increase for the duration of the life-of--mine (Table 2.05.2-1A). It is anticipated that long-term, there will be low flow springs discharging from the surface mine on the north facing slopes of Jeff Canyon and Cow Canyon following snowmelt and precipitation events. The springs will exhibit flows from March through June, as a consequence of snowmelt, and may flow again in August and September if precipitation from late summer thunderstorms is considerable. Typically there will be a two-to-four week delay between the period of high infiltration and the subsequent discharge from the aquifer. Spoil spring discharges may contribute to the Purgatoire River during the spring, if water is running in the streams. It is unlikely that the fall discharges will travel to the Purgatoire, due to their limited flow rates and the high infiltration which will occur in the dry canyon bottoms. Qualitative changes to surface waters which are derived from disturbances during operations will consist oftemporary increases in total suspended solids (TSS) and total dissolved solids (TDS). The increases in suspended solids will be restricted to the disturbance areas, as sediment ponds and other • ass-rem,¢ rev (Nuv.4-o2).wpe 2.05-100 (Revised 10/31/02)