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February 10, 1997 <br />Page 3 <br />example, a range of+/- 30 percent would not be unexpected. Especially poor measwements <br />would be anticipated during higher flows. If a staff gage is installed, it would be necessary <br />to develop a stage (water depth) versus discharge relationship for the gage. During high <br />flows, there will be no practical way to measure the depth of flow and corresponding flow <br />velocities at multiple locations across the channel using a current meter as it would be <br />unsafe to have a person in the river under these conditions. Without a control section, the <br />nature of the stage versus discharge curve at the staff gage location will change on a year- <br />to-yeaz basis and a new curve will need to be developed. If installed, the staff gage does not <br />allow for a reliable comparison of the upstream and downstream flow, as continuous flow <br />data is collected on the upstream gage and instantaneous flow measurements would be <br />collected on a downstream gage. <br />MCC believes that an analysis of whether the West Elk Mine is significantly affecting the <br />quantity and quality of the North Fork of the Gunnison River can be made by using data that <br />is currently collected, including NPDES discharge records and North Fork diversion <br />records. In the Division's CHIA, impacts have been measured using a mass balance <br />approach, which would ignore the non-MCC related effects on the North Fork and focus on <br />the mine's impacts, and would be a more conservative approach. <br />8. The Probable Hydrologic Consequences (PHC) section of the permit is currently being <br />updated. MCC expects to submit this revision to the Division by February 21, 1997. <br />Please call if you have any questions. <br />Christine E. <br />Permitting' <br />cc: Phil Schmidt <br />Kathy Welt <br />nya«*w.aa <br />