2009-12-02_PERMIT FILE - C1981008A (2)

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monitoring began (July, 1986), only four events were 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. Monitoring of this site has been discontinued. Finally, Site SW-N103 was located downstream of SW-N107 on Calamity Draw. Discharge was measured at this site on a monthly basis since July of 1986 (see Attachment 2.04.7-8 (Peabody Appendix 7-5). As at the other sites established along Calamity, flow at SW-N103 was artificially controlled by irrigation, and to a lesser extent, by contributions from rainfall and snowmelt runoff, and even shallow ground water discharge. Measured discharge ranged from 3.36 cfs to 24.4 cfs during the irrigation season. For periods of no irrigation, flow measurements varied from 1.7 cfs up to 5.7 cfs. The highest discharge measured during the irrigation period was 24.4 cfs in July, and the lowest occurred in October (3.36 cfs). Monitoring of this site was discontinued prior to mining, but will be reactivated as the downstream sample point of Calamity Draw, as of August of 2009. Tuttle Draw. As is characteristic of all of the surface water sites at both the Nucla Mine and the Nucla East mining area, the flow regime in Tuttle Draw is artificially controlled by irrigation practices for most of the year. From about mi d-April through mid-October, the Second Park lateral irrigation ditch (managed by the Colorado Cooperative Company) is in continuous operation. However, exact dates for turning the ditch on and off vary from year to year. During this period, water from the ditch is primarily used for irrigation and secondarily for maintaining water levels in stock ponds and domestic cisterns. Between mid-October and mid-April, the ditch is turned on occasionally in order to maintain levels in stock ponds and 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 and snow melt runoff events. Surface water monitoring Site SW-N 1 is located in Tuttle Draw upstream of the Nucla Mine permit boundary. SW-N1 has been monitored for flow routinely since April of 1980. Table 7-40, from the New Horizon #1 Mine permit filed by Peabody on the following pages, presents means and ranges of monitored instantaneous discharge at both Sites SW-N1 and SW-N3. Table 7-40 also shows that flow measured at SW-N1 varies from zero up to 11.6 cfs. During the irrigation season (approximately mid-April through mid-October), the means of measured discharge range between 0.149 and 2.94 cfs, with high flows measured from 0.275 in April up to 11.6 cfs in September. During the non-irrigation season, (mid-October through 2.04.7-33