2009-05-22_PERMIT FILE - C1981044A (7)

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SURFACE WATER RESOURCES The EC permit area is within the Yampa River drainage basin. Portions of the permit area drain directly into the Yampa River while others drain into the Williams Fork River. The Williams Fork River is a tributary to [he Yampa River and joins the Yampa River within the permit area, There are no other significant streams or surface water bodies within the permit or adjacent area. However, there are two (2) natural springs in the permit area which are monitored, neither of which is significant. The total average spring flow is less than 10 gpm. Surface Water Quantity Flow data for the Yampa and Williams Fork Rivers in the mine vicinity has historically been recorded at four-(4) United Stales Geological Survey (USGS) gauging stations. Two (2) gauging stations are located on the Yampa River. These are 1) below diversion near Hayden, Colorado and 2) near Maybell, Colorado. The remaining two (2) gauging stations are located on the Williams Fork River. These are l) near Hamilton, Colorado and 2) at the EC mine site. The location the gauging station at EC is shown on the Hydrologic Monitoring Program Location Map, (Map 11). Recently, EC and the USGS have begun monitoring flows of the Yampa and Williams Fork Rivers with staff gauges. One (1) staff gauge is located on the Yampa River, downstream of the confluence with [he Williams Fork River, and one (1) staff gauge is located on the Williams Fork River upstream of the No. 6 Mine. In addition, a recorder has been installedjust below the Craig Power Plant Diversion on the Yampa River. A summary of flows for the four-(4) USGS gauging stations is presented in Table 21, Mean Monthly Flows for the Yampa and Williams Fork Rivers. The Yampa River gauging station below [he Diversion, near Hayden, Colorado (USGS Station No. 09244410) is located approximately 35 miles upstream of the EC Site. The drainage area at this station is 1,410 square miles and the recording period is from 1966 to present. The average mean monthly flows range from a low of 236 cfs during September to 6,028 cfs during May. Refer to Table 22, Extreme Flows for Yampa and Williams Fork Rivers, for historical extreme flows for the Yampa and Williams Fork Rivers. Monthly flows during the winter months range from between one (1) to two (2) percent of the total annual discharge. The peak flow of record is 17,900 cfs recorded on May 19, 1971. A minimum flow of 2.0 cfs was recorded on July 17-19, 1934. The 7-day/10-year low flow was calculated by the USGS to be 37.6 cfs. Flow data from the USGS stations on the Yampa River were used to derive estimated flows for the Yampa River at the EC mine site. Establishing a correlation between the drainage area and discharge at the Yampa River station and then extending the relationship to the Yampa River at the mine site derived the estimated flows. Results indicate that the average mean monthly flow at the mine site range from approximately 180 cfs in September to approximately 4,700 cfs during June. The 7-day/10-year low flow was estimated to be approximately 32 cfs. The Williams Fork River, a ]eft bank tributary to the Yampa River, has a drainage area of approximately 376 square miles. Flow records are available for the Williams Fork River from a discontinued USGS station at Hamilton, Colorado (USGS Station No. 2495). This station was operated during water years 1905 to 1906 and 1910 to 1927. Average monthly means for the recording period range from 920 cfs in May to 51.2 in December. (Refer to Table 21, Mean Monthly Flows for the Yampa and Williams Fork River). Tha peak discharge recorded at this station was 3,400 cfs in June 1917. The 7-day/10-year low flow is 20.5 cfs. The station was located approximately six (6) miles upstream from the mouth of the Williams Fork River and has a drainage basin of 341 square miles. Data from the Williams Fork River gauging station reveal that the flow of the Williams Fork River is more dependent on snowmelt than the flow of the Yampa River and that there is less ground water discharge [o sustain the flows of the river during low flow periods. Because there is less ground water discharge during the low flow season, the range of the flows of the Williams Fork River is higher than the range recorded at stations on the Yampa River. EC installed a stream gauge on the Williams Fork River at the Haul Road Bridge, approximately 2,300 feet Permit Revision 04-34 2.04-20 Revised 7/2/04