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flow is its primary source. Very little supplemental flow is derived from <br />precipitation and snowmelt runoff. In 1987, measured flow rates in Calamity <br />Draw varied from 0.605 cfs in April to 13.4 cfs in July. Flow in Calamity <br />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 <br />period's water. This ground water flow is related to local irrigation <br />practices but is consolidated into a more uniform and regular flow by the <br />permeabilities of these near surface alluvial deposits. Proposed Sediment <br />Pond 007 for the Nucla East mining site will contribute water to the Calamity <br />Draw system. The proposed drainaoe system at the Nuc1a East Site has been <br />designed to provide adequate capacity and storage times to completely contain <br />a 10-year 24-hour precipitation event. This svstem will collect all runoff <br />from the mine site and should actually lower present total suspended solids <br />(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 <br />to be within acceptable discharge levels and will be mitigated by dilution. <br />Regular monitoring of these flow rates and water quality will give adequate <br />control of this current water source to protect water quality in Calamity Draw <br />Surface water monitoring practices and frequencies are described the permit <br />revision application, Tab 15, pages 15-1-1 to 15-1-5 for the Nucla and Nucla <br />East Areas. Also see Section B.I.B. of this document for a summary of surface <br />and ground water monitoring practices that Peabody has committed to. <br />Ground Water <br />The Nucla Mines lie in a ground water basin defined by the Nucla Syncline. <br />This broad northwest trending syncline is recharged along the Uncompahgre <br />uplift to the northeast and discharges southwest toward the major rivers <br />flowing through the area. <br />Near surface ground water in the Nucla area is partially recharged by <br />irrigation return flow through Quaternary aeolian and alluvial deposits. The <br />lower Dakota and underlying Morrison Formations are regional aquifers, <br />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 <br />domestic wells. <br />Very little hydrologic documentation is available regarding the alluvium found <br />along the small tributaries draining the area. Peabody drilled one well in <br />the alluvium of Calamity Draw in mid-1986. The well appears to have been <br />completed in a clay lens. The alluvial water table fluctuates seasonally <br />within 5'-10' of the surface with highest water levels in August and lowest <br />water levels in January. Recharge is primarily derived from irrigation return <br />flow and secondarily from flow in Calamity Draw. Transmissivit.y varies from <br />6.6 to 10.1 ft2/day. The hydraulic conductivity varies from 0.4 to 0.6 <br />ft/day. The water is characterized as a saline, hard, neutral pH, calcium <br />sulfate water with average TDS of 3291 mg/1. <br />-10- <br />