2020-02-11_PERMIT FILE - C1981038

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win 9~'~b vo ) v • drainage ditches and haul road culverts. Most of the runoff from the disturbed area will be collected in a sedimentation pond. Construction of this pond at an early stage of excavation and fill operation will prevent increased sediment loading in East Roatcap Creek. Diversion ditches were designed to minimize runoff into the disturbed areas. Small areas on the fill slopes which are not drained into the sedimentation pond will be revegetated and provided with sediment source control measures such as silt traps and hay bales. Design of the inlet and outlet structures on the proposed culvert are based on sound engineering practices which will limit the potential for erosion and help to trap sediment loads carried by the stream. A short construction period in a low flow season will also minimize the impacts of the proposed construction on the local stream. The design of hydraulic structures as presented in this report and the small area of disturbance will practically eliminate potential for impact on local stream quality and quantity. The principal hydraulic structure of the proposed portal bench is an approximately 600 foot long culvert. It will not significantly impede the stream flow for peak flow recurrence intervals up to 500 years. A slight delay of peak f low during an extreme storm event of 500-year recurrence interval or higher may actually be beneficial to the stream flow characteristics during •~, such an event. The sma 11 head probable during peak flow from a ~dC 500-year recurrence interval event would not overtop the fill above the culvert, which could develop a potential for substantial erosion. In addition, after mining is completed the creek fill will be removed, replaced in the cut area at approximate original contours, and revegetated. It can be concluded that the proposed construction will not have any significant impacts or consequences on the local surface water hydrology. 3.0 GROUND WATER HYDROLOGY 3.1 Regional Hydrogeology In the general Colorado Westmoreland, Inc. permit area ground water occurs in alluvial/colluvial sediments along the local drainages and in the bedrock of the Mesaverde Formation. Previous investigation and monitoring indicated that coal seams and some sandstone strata are water bearing in areas where recharge potential is available. Most of the recharge into the bedrock strata is provided at subcrops of these strata beneath the local streams and colluvium. Ground water flows toward the • north and follows the local geologic structure. There are no bedrock ground water supply wells within the permit area. This is due to the low permeability of the water bearing strata, the lenticular character of the sandstone strata and the generally poor quality of water.