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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 Nuc la 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 TDSp 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 ~a nd 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 preclude any of the <br />present or potential uses of this water. <br />At the request of MLR (9/22/88 letter from Catherine Begej to Ted Smith) additional salt <br />loading projections have been performed and are included as Appendix 17-2 to this tab. <br />The additional analyses utilize only the 07-10 low flow value for the San Miguel and <br />include combined during mining impacts from Nucla and Nucla East. <br />According to Irons et al., 1965, page 131, the 0 flow value of 6.48 cfs at Na turita <br />7-10 <br />has a probability of being exceeded 99.9 percent of the time. Peabody questions the <br /> relevance of using such a low flow value for PHC purposes, particularly considering the <br /> fact that some of the input parameters may have significant (in terms of the magnitude of <br /> the flan values being used) amounts of error associated with them. Any conclusions <br /> derived from this additional analysis should be carefully qualified. <br /> <br />17-68 Revised 10/07/86 <br />