Laserfiche WebLink
Rimrock Mine Sediment Pond Certification <br />The site inspection was conducted on September 21, 2002. It was a sunny warm <br />afternoon of approximately 70 degree temperature. The pond contained considerable <br />water and it was evident that a fairly large storm had occurred within the past 24 hours <br />since there were still puddles in Engleville Gulch. The pond itself was free of any type <br />of problem with stability or erosion, in spite of the large storm. The pond is to be left <br />as a permanent impoundment for use in the grazing operation. The staff gage in the <br />pond showed 3.7 feet and since the bottom of the sediment level is 2.0 feet, the water <br />level was 1.7 feet high. <br />The following items were checked to see if they coincided with the design shown in the <br />mine permit application. I, Greg Lewicki, did the pond design in March of 1990. <br />1) Constructed Elevations: The elevations listed below were checked with a precision <br />level and stadia rod: <br />-Dewatering pipe inlet <br />-Dewatering pipe outlet <br />-Top of Dam <br />-Bottom of Emergency Spillway <br />-Toe of Dam (outside and inside) <br />-Bottom of Pond <br />-A number of points within the pond <br />All elevations were found to be acceptable. The inlet to the principal spillway was <br />placed at a slightly higher elevation to allow more sediment storage. The 10 year - 24 <br />hour runoff storage was still present above the principal spillway. <br />2) Width of Emergencv Spillway Design: 12 feet. Measured: 12.2 feet. <br />3) Depth of Emer encX S iln iwav Design: 1.55 feet. Measured: 1.60 feet. The spillway <br />showed no evidence of flow or any signs of erosion or other instability. <br />4) Width of toQof Dam Design: 10 ft. Measured: 10.2 ft - 10.6 feet. <br />5) Principal Spillway Design: 4.0" pipe placed in compacted embankment. Measured: 4" <br />steel pipe placed in compacted embankment. Extensions on this pipe were added to <br />both sides so that the embankment could be widened. Some black plastic hose was also <br />present near the spillway at the time of the inspection but was not functional. The <br />principal spillway pipe was completely free of debris and was functional during the site <br />visit. <br />