1986-12-31_REPORT - C1981008 (3)

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will commit to sampling for these parameters in the future. If not, PCC's variance request will be pursued. B. Tuttle Draw - Flow and Quality 1. Site SW-N1 Site SW-N1 is located on Tuttle Draw upstream from the Nucla Mine as shown on Exhibit 1. Flow and quality data have been routinely collected from this site since April 1980; these data are presented in Appendix B and statistically summarized in Table 6. A hydrograph constructed from monthly instantaneous flows is shown in Figure 1. A trilinear plot (piper diagram) of the distribution of major ions is depicted in Figure 2. As is characteristic of all of the surface water sites at the Nucla Mine, the flow regime at site SW-N1 is artificially controlled by irrigation practices for most of the year. From mid-April through mid-October, the Second Park lateral irrigation - ditch (managed by the Colorado Cooperative Ditch Company) is in continuous operation. During this time, the ditch is primarily used for irrigating farmland and secondarily for maintaining water levels in stockponds and domestic cisterns. Between mid-October and mid-April , the ditch is turned on occasionally in order to maintain levels in stockponds and domestic cisterns. As a consequence of the operation of this ditch, the majority of flow in Tuttle Draw is irrigation return flow except for occasional supplemental flow from precipitation (see Table 1) and snowmelt runoff events. The hydrograph depicted in Figure 1 reveals that flow during the summer months is generally between 1.0 and 2.0 cfs; during the winter when the ditch is often dry, flow is generally less than 0.4 cfs. Upon perusal of the data in Appendix B and Figure 2, the quality of the water at this site can be classified as a calcium-magnesium-sulfate (Ca-Mg-SO4), type with essentially equal percentage milliequivalents of Ca and Mg. Seasonal changes in quality with respect to total dissolved solids (TDS) 16