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<br />that of the West Lateral. Mean TDS concentration for tiie period of • <br />record is 973 mg/1 ranging from 488 to 1732 mg/1, <br />2. Site SW-N6 <br />Site SW-N6 is located on the West Return Ditch immediately <br />downstream of County Road 124 as shown on Exhibit 1. 'f his site is <br />a]so downstream of mining activity which has taken place north of <br />this east-west road. Flow and quality data have routinely been <br />collected from this site since August of 1980; these data are <br />presented in Appendix B and statistically summarized in Table 15. <br />A hydrograph constructed from monthly instantaneous flow <br />measurements is shown in Figure 9. A trilinear• plot of the major <br />ions is depicted in Figure 2. <br />As previously discussed, flow at this site is reflective of the <br />seasonal use of irrigation water. For the period of record <br />depicted in Figure 9, flow general]y ranges between 0.0 and 1.25 <br />cfs. This reach of the West Return Ditch is routinely dry from • <br />November to April. <br />The statistical]y summarized water quality data from Table 15 used <br />to construct Figure Z indicate that this water is a Ca-Mg-SO4 type; <br />mean TDS concentration for the period of record 'is 815 mg/1, <br />ranging from 405 to 1550 mg/1. Because of the limited upstream <br />data collected to date at site SW-N7, it is difficult to assess any <br />changes in flow or quality to the West Return DitcFi water as it <br />crosses mine spoils immediately north of County Road 124. However, <br />from the data illustrated in Figure 5, it appears that the flow and <br />quality of the water sampled at the two sites during the summer of <br />this year (1986) are very similar showing little to no detectable <br />change. <br />3. Site NPDES OOI <br />NPDES discharge point 001 (Permit No. CO-0(100213; see Appendix <br />7-6) is located on the 41est Return Ditch at the southernmost , <br />edge of mining disturbance as shown on Exhibit 1. Flow and quality <br />data have routinely been collected from this site since 1975. Data <br />44 <br />