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C. West Return Ditchl - Flow and Quality <br />• 1. Site SW-N7 <br />Site SW-N7 is located on the West Return Ditch upstream of <br />mining as shown on Exhibit 1. Flow and quality data have routinely <br />been collected from this site since March of 1986; these data are <br />presented in Appendix B and statistically summarized in Table 14. <br />A hydrograph constructed from monthly instantaneous flow <br />measurements is shown in Figure 8. A trilinear plot of the major <br />ions is depicted in Figure 2. <br />Monitoring at this site did not begin until March of 1586 because <br />the need to collect baseline data on the k'est Return Ditch upstream <br />of the triangle area (which lies between SW-N7 and SW-N6) was not <br />apparent until this tirt~e. The triangle area was planned to be <br />mined in early 1987 but this plan has temporarily been abandoned; <br />however, monitoring at this site will continue for the purpose of <br />obtaining baseline data in the case that mining may occur in the <br />future in the triangle area. <br />~J <br />Again, for previously discussed reasons, flow at this site is <br />reflective of the seasonal use of irrigation water. From the <br />record to date, flow was at a low of 0.006 cfs in April rising to a <br />peak of 0.856 cfs in June. <br />Perusal of the data in Table 14 and Figure 2 indicates that the <br />quality of the water at this site can be classified a Ca-HC03-SO4 <br />type. The relatively high percentage of HC03 reflects its origins <br />from the San Miguel River via the Second Park lateral. San Miguel <br />River water as sampled from the West lateral irrigation ditch this <br />spring (1986) shows this water to be a Ca-HC03 type (see Appendix <br />6); Second Park lateral water is assumed to be closely similar to <br />1Note: The drainages referred to as the "West and East Return Ditches" <br />are part of the natural surrounding drainage pattern. Return water from <br />irrigation flows into these drainages because of their location and the <br />rather inefficient method of flood irrigation used upstream. The <br />• "ditches" were never designed as ditches, per se, or for irrigation <br />purposes. <br />41 <br />