2010-02-09_PERMIT FILE - C1982056A (6)

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It is difficult to estimate the magnitude of ground water contributions to baseflow between the upstream and downstream stations although it appears that most if not all of the baseflow originates from upstream of Station 1001. Calculations given in the ground water information section indicates a contribution of about 0.02 cfs from the Wadge overburden aquifer and about 0.5 cfs from the Twentymile Sandstone aquifer. These contributions constitute about 16.5 percent of the average low flow in Fish Creek. Most of the annual streamflow originates from surface runoff and shallow ground water contributions between the upstream station 1001 and site 1003 near the mouth. About 75% of the runoff from the upstream station 1002 occurs during the months of April through June while over 90% of the runoff at the downstream station 1003 occurs during this same period. The USGS maintained stream gauging station number 09244100 on Fish Creek at the same location as TCC Station 1001 upstream of the mine. The period of record for the USGS Station is from October 1955 through September 1973. The seven day, ten year flow calculated for this data record is 0.64 cfs. The highest average annual discharge of 25 cfs occurred during water year 1958. The lowest average annual discharge of 5 cfs occurred in water year 1964. A Log-Pearson Type III flood frequency analysis of floods on Fish Creek at Station 09244100 indicate a 10-year peak flow of 299 cfs and a 100 year peak flow of about 444 cfs. One of the minor tributaries to Fish Creek is the Cow Camp Creek drainage, which intersects Fish Creek between TCC surface sites SW-14 and SW-15. This is an ephemeral stream that may only flow during spring runoff periods (flows are typically less than 0.1 cfs throughout much of the year). As part of their DMG permit, the Seneca II Mine currently monitors above the confluence of Cow Camp Creek with Fish Creek at their surface site SSC10. Irt addition, Seneca monitors Fish Creek upstream and downstream of this confluence at surface sites SSF11 and SSF13. The three sites are monitored for field parameters and water quality on a monthly basis from May through September. Their 2002 AHR indicated that there was no flow at site SSC10 for that water year due to stream channel infiltration, evapotranspiration, and the absence of lateral inflow from tributaries to Cow Camp Creek. Trout Creek is a perennial stream along the entire reach adjacent to Twentymile Park. Variation in streamflow at Station 69 on Trout Creek above Fish Creek are shown in Figure 5-h. These data indicate baseflow conditions on Trout Creek of about 5 to 10 cfs during the monitoring period. Comparison of average monthly flows at this station with average monthly flows on Trout Creek upstream near the Edna Mine, show lower baseflow conditions at the downstream station (Table 10, Surface Water Data). The differences could be the result of streamflow depletions for irrigation but could also be due to differences in the selected monitoring periods. The average monthly flow data summarized in Table 10 for Trout Creek near Edna Mine was taken from "Cumulative Hydrologic Assessment: Effects of Coal Mining on the Yampa River Basin, Moffat and Routt Counties, Colorado" prepared by Kaman Tempo, January 29, 1982. The location of sampling shown in Figure 3 of that report is just downstream of the Edna Mine and approximately 3 miles above the confluence with Middle Creek. The data as indicated in Table 6 are pre-mining data taken from the mine plan. On the other hand, the text on page 26 of the Kaman Tempo report indicates that the Trout Creek data wee taken from the report, "Surface and Subsurface Water Quality Hydrology in Surface Mined Watersheds" prepared by McWhorter and others, 1979. Reference to this report indicates that the data were collected over the period from October, 1973 to November 1975. On the other hand, the average monthly flow data summarized in Table 10 for Trout Creek above Fish Creek were taken from station 69 on Trout Creek. These data are included in Table 10 and cover the period from March, 1979 through September, 1983. The location of Station 69 is shown on Map 13, Twentymile Park Hydrology. Since the monitoring periods are different it is not possible to attribute differences in flow to basin conditions as differences could be the result of climatic differences between monitoring periods. Data from both stations indicate that about 70% of the annual streamflow occurs during the months of May, June and July. PR 03-06 2.04-33 03/02/04