REP35277 - Laserfiche WebLink

Home Browse Search

sorted underdrain under the remainder of the fill. The proposed underdrain will be extended to the head of the fill to meet the requirements of Rule 4.09.2(2). It is important to note that in the opinion of CTL/Thompson, the extension of the subdrain will serve to meet a regulatory requirement, but will not provide for a substantial improvement in mass stability. Taking into consideration CTL/Thompson's site investigation, proposed designs and construction plans with modifications resulting from joint OSMRE/MLRD/Colowyo discussions and review, Colowyo will commit to the following design and construction plan. CONSTRUCTION PLAN All available topsoil will be removed and either stockpiled for later use or direct haul replaced to a reclaimed area. Colowyo will follow the CTL/Thompson recommendation for excavation of clay materials in the valley bottom to bedrock or a depth of at least 20 feet (which ever is less) about 700 feet upstream of the toe of the fill. A buttress fill comprised of these excavated materials in accordance with the CTL/Thompson recommendations will also be constructed. A controlled underdrain in accordance with the CTL/Thompson recommendations will be placed in the natural drainage bottom from the head to the top of the fill. The harder, available sandstones obtained from the mining operation will be selectively handled and placed in at least a 24 foot wide by 8 foot high configuration to serve as the underdrain before covered by spoil material. The natural spoil sorting which will occur by utilizing the thicker lifts recommended by CTL/Thompson will be sufficient to protect the drain from clogging. CTL/Thompson also believes that it is desirable to create a permeable fill to reduce the risk of developing free water levels within the fill. Lift thicknesses up to 100 feet thick is acceptable and will be utilized to construct the fill. This method of spoil placement also enhances the construction of a free- draining layer of spoil material at the base of the fill. Experience at Colowyo provides evidence that the natural sorting process which occurs while dumping in higher lifts is sufficient to create this drain. Inspection and documentation of this natural sorting is recommended and will be conducted by Colowyo. See the Inspection Plan section for additional details. RECLAMATION PLAN The final configuration of the fill is designed to minimize erosion. The final configuration takes into account a number of the components of the Streeter Fill reclamation which have proven successful. The final outslope will not exceed 3h:ly. Drainage benches of at least a 12 foot width will be constructed at approximately 100 foot vertical increments. These drainage benches