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residual discharge of shallow ground water from the irrigated fields above the site • contributes some flow up through even January. During the irrigation period, measured flow ranged from .088 cfs (October) to 2.18 cfs (August). During periods of no irrigation, flow observations made at SW-N2 ranged from zero (February, March and early April) up to .031 cfs (January). SW-N107 is located about a mile and a half below SW-N101 on Calamity Draw (see Exhibit 7-1). Flow measurements have only periodically been collected at this site since July of 1986. A crest-stage gage has been installed at this site for the purpose of recording high water marks of large runoff events (rainfall or spring snowmelt runoff). These high water marks are used to determine the peak discharge of large runoff events using indirect discharge measurement techniques (see Tab 15, Hydrologic Monitoring Program). Since monitoring began (July, 1986), only four events have been calculated using indirect techniques: 1) 39 cfs, 11/11/86; 2) 35 cfs, 5/20/87; 3) 34 cfs, 6/22!87; and 4) 96 cfs, 8/27/87. The listed dates represent the respective visit dates that high water marks were measured at the crest gage. All events likely resulted from unusually intense summer thunderstorms, although no information of those particular storms was collected. • Finally, Site SW-N103 is located downstream of SW-N107 on Calamity Draw (see Exhibit 7-1). Discharge has been measured at this site on a monthly basis since Jwly of 1986 (see Appendix 7-S). As at the other sites established along Calamity, flow at SW-N103 is artifically controlled by irrigation, and to a lesser extent, by contributions from rainfall and snowmelt runoff, and even shallow ground water discharge. As shown in Table 7-42, measured discharge ranges from 3.36 cfs to 24.4 cfs during the irrigation season. For periods of no irrigation, flow measurements vary from 1.7 cfs up to 5.7 cfs. The highest discharge measured during the irrigation period was 14.4 cfs in July, and the lowest occurred in October (3,36 cfs). Streams - Water Quality. The following sections present discussions of water quality data collected at surface water monitoring sites established at both the Nucla Mine and Nucla East mining area. As in the previous section, discussions are grouped according to the drainage in which the sites have been located. All historic data (prior to January, 1988) for each site have been compiled and are presented as water quality reports in Appendix 7-7 and Appendix 7-9. Appendix 7-8 contains trilinear plots (Piper diagrams) of the . distribution of major ions from all samples collected at each surface water site for both the irrigation and non irrigation periods. The reader should refer to Exhibit 7-1 for locating surface water monitoring sites mentioned in the following sections. 7-122 Revised 04/11/88