2012-10-01_REVISION - M1977310 (10)

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JD -6 Mine Environmental Protection Plan 37 9.2.2 Regional Aquifer Recharge Recharge to the upper Mesozoic aquifer occurs as infiltration of runoff and direct precipitation. In the Dolores River basin, this runoff occurs primarily from spring snowmelt at higher elevations. In the summer and fall, additional runoff occurs from rainstorms that are sometimes intense and usually limited in extent (Weir et al., 1983). Although direct precipitation infiltration may recharge the aquifers on mesas and at higher elevations, little or no recharge to the upper Mesozoic aquifer occurs from direct precipitation or infiltration of snowmelt in the Paradox Valley. As reported by Golder (2009a), studies have shown that diffuse recharge (rain and snowmelt over the valley area) to basin aquifers in arid areas like Paradox Valley is limited or absent due to low precipitation rates, large vadose zones, and the water- scavenging vegetation found in dry areas (Wilson and Guan, 2004; Foster and Smith - Carrington, 1980). Recharge to the lower Paleozoic aquifer occurs outside of the Paradox Basin (Weir, et al., 1983). The Leadville Limestone outcrops north of Durango, and receives recharge at the outcrop from runoff and snowmelt from the San Juan Mountains. 9.2.3 Regional Flow Direction and Aquifer Discharge Regionally, groundwater flows to the west - northwest, discharging to the Dolores River (Weir, et al., 1983, Topper, et al., 2003). Flow direction in the lower Paleozoic carbonate aquifer is shown in Figure 9. The flow regime in the lower aquifer does not appear to be affected by the overlying Mesozoic aquifer, surface topography, or surface water flow, as it is essentially isolated by the confining evaporites (salt layers). Flow directions in the upper Mesozoic aquifer are variable on a local and regional scale, and are affected by geologic structure and areas of recharge and discharge. The overall general flow direction is west toward the Dolores River. As reported by Weir, et al., (1983), "where the Dolores River is deeply incised, water from the Mesozoic sandstone aquifers discharges directly to the Dolores River." However, local flow directions may deviate from this overall regional trend. 9.3 Local Groundwater System The JD -6 Mine has been developed in the Salt Wash Member of the Morrison Formation. This unit is variably saturated in the vicinity of the JD -6 Mine. Where saturated, the Morrison Formation has been referred to as the "M" aquifer (Avery, 1986) and is generally perched on the underlying low - permeability Summerville Formation. 9.3.1 Local Stratigraphic Units The principal stratigraphic units at the JD -6 Mine are as follows: • Colluvium - Unsaturated • Dakota Formation — Unsaturated • Mancos Shale Formation — Unsaturated • Brushy Basin Member of the Morrison Formation — Unsaturated • Salt Wash Member of the Morrison Formation — Variably Saturated (where saturated, referred to as "M" Aquifer) • Summerville Formation — Lower Confining Unit • Entrada Formation — Sandstone, commonly water - bearing 9.3.2 Local Groundwater System near the JD - 6 Underground Workings Groundwater in the vicinity of the JD -6 Mine is strongly controlled by geologic structure. The alluvium and landslide deposits are typically unsaturated, based on data compiled from exploration drill holes and 4148A.120927 Whetstone Associates •