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• Generic Mud Pit Design <br />OSM personnel have decided that mud pits are temporary impoundments thus <br />mud pits must be designed in accordance with 4.05.9. Mud pits are constructed <br />on drill sites to contain drill cuttings, water and drilling fluids. The size of the mud <br />pits at the Bowie No. 2 Mine are variable, but are considered small, in the order <br />of 500 to 2,000 square feet. <br />The Division may approve a temporary impoundment that relies primarily on <br />storage to control the run-off from the design event specified in 4.05.9(2)(c) when <br />it is demonstrated by the Operator and certified by a qualified registered <br />professional engineer, that the temporary impoundment will safely control the <br />design precipitation event, the water which shall be safely removed in <br />accordance with current prudent engineering practices. Such an impoundment <br />shall be located where failure would not be expected to cause loss of life or <br />serious property damage. <br />The volume of water stored in the mud pits, if released into one of the adjacent <br />perennial streams, would not significantly increase the water level in the stream. <br />Mud pits are typically located in remote areas where a failure would not be <br />expected to cause loss of life for serious property damage. <br />• The design event for the mud pits will be 2.1 inches, the 25 year 24 hour event. <br />The curve number for the drill sites will be 87, disturbed, soil type C. Run-off <br />from drill sites is directed away from the mud pits into silt fences for filtering. <br />Therefore, the drainage area for the mud pits is quite small, in the order of 0.1 <br />acres. A mud pit would need to contain 0.01 acre feet based upon the above run <br />off factors. <br />A 2,000 square foot pond would need to have 0.2 feet of depth to contain the <br />design event. Mud pits may be as small as 500 square feet. A 500 square foot <br />mud pit would be required to have 0.9 feet of depth to contain the design event. <br />Mud pits will be dewatered as necessary to maintain the required depth to <br />contain the design storm event plus 1.0 feet of freeboard. Dewatering will <br />typically be accomplished with a water truck. <br />Mud pits are typically about 4 to 6 feet deep. They are constructed by a dozer or <br />backhoe. They are placed on the edge or end of a drill site and incised in natural <br />ground. In some cases mud pits will be placed in fill material. The inside slope <br />of the pit is usually nearly vertical. The fill material is placed at a slope of about <br />1.5H:1 V. In order to satisfy the requirement for a 5H:1 V combined upstream and <br />downstream side slope of an embankment, the distance between the edge of the <br />pit and the edge of the fill must be 3.5 times the depth of the pond. Construction <br />• of fill slopes will include the removal of topsoil and organic matter. Fills will be <br />TR -V 1 <br />'i m'O vo <br />2130165 <br />Exh-8 -205 - <br />08/05 <br />