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One main, perennial spring has been identified on the Idaho Mine site at an elevation of <br /> approximately 8,778 feet, located within the Entrada Formation. <br /> 7.2 GROUNDWATER <br /> Groundwater in the area is characterized as low flow through porous media and along fractures <br /> and faults. Fracturing of the local formations locally increases the secondary permeability; as a <br /> result, the transmissivity (flow) also is increased locally. Offsets due to faulting create <br /> discontinuous hydrologic blocks which tend to prevent or impede porous flow. <br /> Generally, recharge to the groundwater system is from: <br /> o Precipitation and snow melt on outcrops; and <br /> o Stream channel loss to the formations as streams cross outcrops or <br /> fractures <br /> Generally, discharges to the groundwater system are from springs and seeps in topographically <br /> lower parts of the outcrop. <br /> In general, the underlying porous media(Table 2) would have the following relative <br /> hydrogeologic properties based on the composition of the formations and limited laboratory tests <br /> by Trautner Geotechnical Consultants (Appendix B). <br /> When examining the recharge potential for the site, it would appear to be extremely low as the <br /> underlying geologic formations are generally low permeability layered material which would <br /> inhibit water recharge from the slopes to the underlying formations. In addition to the low <br /> permeability material, onsite observations indicate that the alluvial/fluvial cover on the hillsides <br /> is extremely thin and the hillsides are relatively steep gradient (30%). These two factors will tend <br /> to reduce the time of concentration of any overland flow from precipitation or snow melt events <br /> thus minimizing the amount of recharge that could enter the ground water system. Additionally, <br /> the faulting in the area has caused offsets of geologic formations that place units of differing <br /> permeability and porosity in contact with each other thus effectively limiting the flow of <br /> potential recharge water from areas of high potential to lower potential. Frequently, if geologic <br /> formations of differing permeability are in contact on slopes where recharge is occurring, the <br /> near surface recharge is forced back to the surface and either perched springs or enhanced <br /> vegetation such as aspen, can be found along these zones. Finally, this same faulting has created <br /> small, isolated areas for potential recharge to infiltrate the bedrock in the local vicinity (within <br /> the upgradient watershed areas). For recharge to be effective in the environment presented by <br /> Southern Colorado, large areas of exposure are needed to collect runoff and snowmelt for <br /> effective recharge. <br /> It has been noted that where the La Plata River and Little Deadwood Gulch flow across more <br /> permeable formations, such as the Entrada sandstone, the streams are losing streams in that flow <br /> May Day Idaho Mine Complex <br /> M-1981-185 <br /> January 19, 2017 <br /> Page I - 10- <br />