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<br />As mentioned earlier, the Hydrology Map shows proposed open 'channel <br />and pond construction. Undisturbed water percolates naturally into the 'meadow, <br />and disturbed water is diverted into the sedimentation pond. There should be <br />no effect on water quality in Hay Gulch attributable to the Blue Flatne Coal <br />Mine, because the pond collects all disturbed water. The quality of this water <br />will be monitored. Samples taken at the emergency discharge end of the pond <br />will determine any change in the quality of runoff. Water contained in the <br />pond will not be discharged, but allowed to evaporate. The pond will be a <br />square structure of 50' x 50' at the top and 46' x 46' at the bottom. This <br />design includes an emergency spillway but does not anticipate the need for a <br />principal spillway. It is planned to pump out water to leave significant <br />storage to accommodate runoff from a ten year, 24 hour storm event. This <br />emergency spillway provides a non-clogging conduit avenue to remove water <br />storage resultiny from inflow. This conduit will be located on the West end of <br />the sediment pond and will be located at a higher level than the maximum sedi- <br />ment storage level. As recommended by Peter O'Connor, a staff gauge will be <br />installed to determine the 608 sediment cleanout level. <br />• Sediment Pond Size <br />The pond is 50 feet wide, 50 feet long, and has a normal depth of <br />about 4 feet. See attached letter from Anne Bald rigs. <br />Calculation of Surface Runoff <br />PEAK WATER RUNOFF AND SEDIMENT POND SIZE: <br />By regulation, the ponds mast handle precipitation from an expected 10 <br />year, 29 hour storm event. <br />Referencing: Natural Oceanic and Atmospheric Precipitation Frequency <br />Atlas and Soil Conservation Service's Technical Release Peak Flows in <br />Colorado. Precipitation data is listed. 2.5 inches is the predicted precipi- <br />tation. <br />• <br />