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and chemical concentrations will allow for a worst case analysis, Tables 17-19, 17-20A, <br />• and 17-20B are presented to show the impact assessment computations for the combined Nucla <br />and Nucla East spoil discharges into the San Miguel, Nucla East spoil discharges into <br />Calamity Draw, and Nucla spoil discharges into Tuttle Draw, respectively. Assumptions <br />that were necessary in performing the computations are explained in Table 17-21. The <br />results of the water quality impact computations are: 1) The combined impact from the <br />Nucla and Nucla East spoil discharges on the San Miguel water quality is only a 3 percent <br />increase in mean annual TDS; 2) The impact of Nucla East spoil discharges on Calamity Draw <br />water quality is a 12 percent increase in TDS from 2,254 mg/1 to 2,533 mg/1; and 3) The <br />impact of the Nucla spoil discharges on Tuttle Draw is a 70 percent increase in TDS from <br />1,213 mg/1 to 2,061 mg/1. <br />The affects of the spoil discharges on the surface water quality in Calamity Draw and <br />Tuttle Draw appears to be significant only when taken in the context of percent TDS <br />increase over background. Concentrations of Fe, Mn, 504 as well as pH render the <br />background surface water in both of these draws unsuitable for use as domestic drinking <br />water. Concentrations of Mn and pH levels also render the water unsuitable for use as <br />• irrigation water. The significance of the TDS increases to 2,500 and 2,100 mg/1 in terms <br />of water use is very minimal as the changes will not affect the present and potential use <br />of the water which is livestock drinking water. Mining impacts on the San Miguel water <br />quality are very minimal (3 percent TDS increase) and will in no way ip reclude any of the <br />present or potential uses of this water. <br />G.-Gene Wete.. <br />Effects of Mining on the Local Geomorphology. Mining impacts to the local geomorphology <br />in the vicinity of the Nucla Mine and Nucla East mining area can be grouped under two <br />categories: 1) Impacts to stream channels; and 2) Impacts to drainage basins. Surface <br />mining affects streams channels by disrupting natural stream courses and reestablishing <br />(via reclamation) different stream lengths and gradients. Drainage basin impacts may <br />include changes in such basin parameters as watershed area, slopes and slope lengths. <br />The West Return Ditch (see Exhibit 7-1, Tab 7) is the only prominent stream channel <br />impacted (geomorphical ly) in the vicinity of the Nucla Mine. Impacts to this channel are <br />• limited to the reach from the 001 pond to a point about 250 yards upstream of Site SW-N6. <br />Mining activities altered this channel reach beginning in the mid-1970's, and reclamation <br />17-68 Revised 04/11/88 <br />