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YAMPA MINING CO. Page 2, LTP-5 (904) Mr. Dan Mathews June 26, 1985 and Ms. Beattie. Specific areas of topsoil received a higher priority for removal over other areas to be stripped, but at no time did any mining activity take priority over construction of water control measures. The diversion ditch was staked and ready for construction prior to your in- spection. The second shift crew began stripping in the area the evening prior to your inspection. A misunderstanding by second shift personnel resulted in the disturbance prior to construction of the ditch. The ditch was completed the day following your inspection with no precipitation prior to completion of the ditch. Therefore no environmental consequences result- ed from this activity. A third NOV (C-85-064) was issued far failing to maintain an emergency spillway on Pond HG-8. Cross-sections and profiles have been developed from survey data to illustrate that an emergency spillway is present (Exhibit 1). The spillway is wide with nearly flat side slopes due to the haul road which was constructed across the top of the dam (as identified in the permit application). A hydrologic evaluation was conducted to determine if the existing emergency spillway would pass the 100-year, 24-hour rainfall event (221 cfs) and maintain one foot of freeboard. Table I illustrates a spillway discharge curve for the emergency spillway. TABLE I HAYDEN GULCH MINE SPILLWAY DISCHARGE CURVE Elevation Depth L Q 7391.70 0 0 0 1391.95 .25 53 17.4 7392.20 .50 100 93.0 7392.45 .75 145 247.7 7392.70 1.00 195 512.9 7392.95 1.25 225 827.0 Reference: Handbook of Hydraulics, E.F. Baxter & H.W. King A flow of 221 cfs passes over the emergency spillway at an elevation of 7392.45 feet. The top of the dam is 7394.5 feet, providing one foot of freeboard. Based on the information provided, YMC requests the Division vacate NOV #C-85-064.