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~~ •• ~• <br />TRAPPER MiNiN61NC. <br />August 24, 1989 <br />CERTIFIED #P175046590 <br />Pfr. Tony Waldron <br />Colorado Mined Land Reclamation Division <br />215 Centennial Bldg. <br />1313 Sherman St. <br />Denver, CO 80203 <br />Dear Tony: <br />Subject: Minor Revision 91. <br />Revise hydrologic model for Coyote sediment structure. <br />The following minor revision to our mining and reclamation permit (C-81-010) <br />is submitted to update the hydrologic model for the Coyote sedimentation <br />structure. The most current rainfall predictions fox 10 and 25-year, 24-hour <br />storm events deCermined by the National Oceanic and Atmospheric Administration <br />(}}OAA) are utilized. Additionally, revised stage storage (Appendix Q, Section <br />III) and spillway discharge (Appendix Q, Section XIV) tables, resulting from <br />newly surveyed spillway elevations, are provided for replacement. <br />Utilization of NOAA Atlas 2, Volume III, hydrologic data reduces the average <br />10-year, 24-hour precipitation event for the Trapper Mine area from 1.7 inc}ies <br />to 1.4 inches of rainfall. The average 25-year, 24-hour event was reduced <br />from 2.1 inches to 1.8 inches. The attached Coyote hydrologic model (Coyote <br />Drainage Hydrology and Sedimen[ology Model 10-year, 24-hour, Precipitation <br />Event) uses NOAA isopluvals and [he revised stage storage and spillway dis- <br />charge tables. All other watershed parameters previously approved remain <br />unchanged. SEDIMOT II software was used to evaluate peak settleable solid <br />concentrations, which again resulted in no significant sediment discharge at <br />the Coyote dam outflow. <br />Data for the Coyote pond as described in Table 4.8-6, "Sediment Pond Summary <br />Information," has changed to reflect the new Coyote dam hydrologic model and <br />is attached (includes 10 and 25-year storm event values). <br />P.O. Box 187 Craig, Colorado 81626 (303) 824 44D1 <br />