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segment of the West Lateral. The ditch channel bottom in this reach is largely fractured and <br />weathered sandstone, and likely results in relatively large amounts of seepage. This seepage, in <br />combination with localized intensive "flood -type" irrigation, travels laterally through the shallow <br />soils and fractured sandstone eventually flowing back into the West Lateral slightly downstream. <br />The combination of fractured, weathered sandstone channel bottoms in the ditch and localized <br />"flood -type" irrigation along these two gaining reaches likely resulted in the measured gains in <br />flow. <br />Flows in Calamity Draw, which is roughly parallel to the southern boundary of NHM, generally <br />reflect local irrigation practices. Water from the West Lateral Ditch's return irrigation flow is its <br />primary source. Very little supplemental flow is derived from precipitation and snowmelt runoff. <br />In 1987, measured flow rates in Calamity Draw varied from 0.605 cfs in April to 13.4 cfs in July. <br />Flow in Calamity Draw varied from 1.04 to 2.06 cfs during the non -irrigation period. Shallow <br />ground water alluvial sources provide a large portion of this low flow period's water. This ground <br />water flow is related to local irrigation practices but is consolidated into a more uniform and regular <br />flow by the permeability of these near surface alluvial deposits. Sediment Pond 007 will contribute <br />water to the Calamity Draw system. The drainage system at the NHM site has been designed to <br />provide adequate capacity and storage times to completely control a 10 -year 24-hour precipitation <br />event. This system will collect all runoff from the mine site and should actually lower present <br />total suspended solids (TSS) contribution from this area over the life of the mine. Increased TDS <br />levels in this water from mining disturbances are expected, but are projected to be within <br />acceptable discharge levels and will be mitigated by dilution. Regular monitoring of these flow <br />rates and water quality will give adequate control of this current water source to protect water <br />quality in Calamity Draw. The discharges from the mine enter Calamity Draw at a point about 2.5 <br />miles above the confluence of Calamity Draw and the San Miguel River. <br />The above-mentioned parks consist of recent undifferentiated aeolian silts and sands overlaying <br />the Dakota and Burro Canyon Formations. The perennial flow nature of both Tuttle and Calamity <br />Draws is largely due to the local irrigation practices. Over the years, this more or less constant <br />source of water in these drainage systems has encouraged the growth of vegetation. This has <br />resulted in the channels becoming more erosionally stable but more incised. <br />Surface water monitoring practices and frequencies are described within the permit application. <br />Also see Findings Section B, Item II E, of this document for a summary of surface and ground <br />water monitoring practices to which ERMR has committed. <br />D. Ground Water <br />The NHM lies in a ground water basin defined by the Nucla Syncline. This broad northwest <br />trending syncline is recharged along the Uncompahgre uplift to the northeast and discharges <br />southwest toward the major rivers flowing through the area. <br />Near surface ground water in the Nucla area is partially recharged by irrigation return flow through <br />Quaternary aeolian and alluvial deposits. The lower Dakota and underlying Morrison Formations <br />are regional aquifers, although water from the Dakota Formation is not heavily utilized due to its <br />high salinity. The Morrison Formation water is widely used for stock and domestic wells. <br />12 <br />