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-~ . <br /> <br />3 <br />calculations to support lining selection and construction specifications are normally <br />required. <br />2. The issue of incised impounding capability is often confused. As interpreted in this <br />office, the incised volume must be restrained by massive soil or rock volumes to <br />preclude the remote possibility of overtopping and breaching, underseepage and piping, <br />and slope stability problems. Any combination of native soils and placed embankment <br />material that geometrically appears as a dam is treated as a dam in its entirety. For <br />example, an "incised" pond on an open pit highwall that exhibits a conventional dam <br />shape with aten-foot crest width should be evaluated as a dam. <br />3. When routing the design storm, the normal pool elevation prior to the event should <br />be set at the lowest ungated spillway for calculative purposes. This elevation does not <br />include slot or small holes drilled, cut, or burned into a decant riser below a typical <br />barrel inlet. Further, all typical barrel inlets should be protected with suitable trash <br />retardant structures. Such structures should be sized to minimize velocity into the <br />conduit. <br />Through my examination of the material submitted I have concluded that the facility in <br />question does fall under MSHA jurisdiction with regard to potential impounding <br />capability. I have not assessed hazard potential and some technical aspects of the <br />design. A thorough evaluation will require additional information. <br />Please contact this office if there are any questions about this memorandum or data <br />requirements for a complete submittal. <br />cc: J. Spicer <br />J. Mulhern <br />M. Stanton <br />B. Keffelew <br />Acting Chief, S&HTC <br />