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5t• REVISIONS -May 1995 <br />This report is the same as the May 1994 report by the same name with the following <br />revisions. <br />1) All peak discharges, volumes, pipe sizes, ditch sizes and other hydraulic structures <br />have been updated to reflect changes in the rainfall depths for the design storm events <br />requested by the State of Colorado Division of Mines and Geology. <br />on final revised <br />10yr-24hr 2.30 in 2.20 in <br />25yr-24hr 2.90 in 2.60 in <br />100yr-24hr 3.25 in 3.20 in <br />2) A natural hillside area of 3.49 acres south and east of the office which previously <br />drained into the mine yard and into the west pond has been rerouted into the eastside <br />ditch and will not contribute to the required pond volume. <br />3) The east pond and west pond are connected by a culvert to allow the excess volume <br />in the east pond to be used by the west pond. <br />4) The elevation of the low level outlet for the west pond has been raised to allow for <br />more room for sedimentation and maintenance purposes. A combination of the reduction <br />in rainfall.depths, item 1, diversion of-area, item 2, and the linkage of the east pond with <br />the west pond, item 3, compensates for this change. <br />• REVISION 1 -July 1997 <br />This report is the same as the May 1995 report by the same name with the following <br />revisions. <br />1) The design of the swale crossing the entrance road (reach 12), between the <br />sedimentation ponds, has been modified to reflect the current, constructed conditions. <br />The required 100-yr capacity is 0.5 cfs. The minimum design channel is a trapezoidal <br />channel with 15:1 side slopes, 1 % bed slope, 1 ft bottom width and depth of 0.3 ft. This <br />results in a flow capacity of 2.2 cfs. The swale as currently constructed is much larger <br />and has a maximum capacity of over 30 cfs. <br />Changes were made to section 5.3, page 7, Reach 12- open channel .... ;and the table <br />entitled DESIGN CHARACTERISTICS FOR PIPES AND CHANNELS, on the same <br />page, reach 12 ... <br />REVISION 2 -July 1997 <br />Changes to the drainage system which reflect the enlargement and reconfiguration of <br />the mine waste pile in#o a valley fill (approx. 1 million cu. yds., see Waste Bank Design, <br />July 1997 updated report) have been made to this report. <br />1) The hydrology for the site has been redone to include changes caused by the <br />enlarged waste pile. Updated pond volumes and ditch and pipe discharges were <br />January 1998 <br />