Permit applications made to the Office of Surface Mining Reclamation and Enforcement for mining of near-surface coal deposits contain both mining and reclamation plans. These plans must be evaluated by regulatory authorities for compliance with the permanent regulations of the Surface Mining Control and Reclamation Act of 1977. Methodologies for assessment of the effects.jDf mining and reclamation on the hydrologic system are presented for a potential permit area of 640 acres in the Tsosie Swale basin, a small tributary of Escavada Wash in northwestern New Mexico. Escavada Wash is the principal tributary of the upper Chaco River, which is the stream that drains much of the San Juan structural basin. Tsosie Swale represents an arid climatic area and a low relief landscape with a sandy mantle that is moderately vegetated with shrubs and grasses.Premining soils, vegetation, geology, and hydrology of Tsosie Swale are described as a basis for evaluation of changes that may occur. Soil-moisturevegetation relations show that the most grass cover occurs where 1 to 2 feet of sandy surface soils are underlain by fine-textured, less-permeable layers that perch soil moisture.Estimates are made of premining and postraining peak discharges and runoff volumes by the empirical Soil Conservation Service (SCS) method and by a basin-characteristic model. The SCS method was found to be superior because it considers infiltration rates. Postmining peak discharge estimates are 30 to 70 percent of premining estimates, and runoff volumes are 30 to 70 percent of premining values.Methods are demonstrated for estimating soil loss by use of the Universal Soil Loss Equation (USLE) and by simulation of an intense rainstorm on a microwatershed. Estimates of sediment yield from the basin for premining conditions are made using reservoir-sedimentation surveys and a watershedfactor rating method. USLE soil-loss estimates and a sediment delivery ratio is used to estimate postraining sediment yield. Estimated postraining sediment yield is about 50 percent of the premining estimate.Changes in the topography resulting from removal of coalbeds and expansion of the overburden are shown to vary from a lowering of part of the permit area as much as 20 feet, to raising of other parts as much as 20 feet. The primary factors responsible for the reductions in streamflow and sediment yield are the assumptions that the minor areas now consisting of badlands and alluvial plains, from which runoff is high, would be eliminated, and the whole area would be covered with about 2 feet of sandy soil.
Permit applications made to the Office of Surface Mining for mining of near-surface coal deposits contain both mining and reclamation plans. These plans must be evaluated by regulatory authorities for compliance with the permanent regulations of the Surface Mining Control and Reclamation Act of 1977. Methodologies for assessment of the effects of mining and reclamation on the hydrologic system are presented for a potential permit area of about 1,990 acres near the junction of Trail Creek and East Trail Creek, and the adjacent area in the drainage basin of East Trail Creek, about 30 square miles, Big Horn County, Montana. The study area is representative of the hydrologic problems that exist in a semiarid environment of the northern Great Plains. The premining hydrology and geology of the study area are described primarily as a basis for evaluation of potential changes that may occur. Data for soil-moisture relations in seven soil-vegetation types show that differences in void space and surface available for water storage are important factors in planning reclamation. Estimates are also made of runoff volumes and peak discharges for flow magnitudes of specified recurrence intervals using a parametric model developed for the State of Montana. The shallow aquifers and their hydraulic characteristics are described in the study area. Methods for estimating erosion and sediment yield in the study area by means of the Universal Soil Loss Equation (USLE) and reservoir sedimentation surveys are described. Changes in topography that may occur with the removal of coalbeds and replacement of the overburden are shown to be generally minimal. The postmining peak discharges before revegetation may be 2 to 6 times greater than the premining discharges and runoff volumes may be 2 to 3 times greater than premining volumes. However, after vegetation is reestablished, postmininj discharges and volumes may be less than the premining values. Soil loss per acre is estimated to be about 27 percent less after mining and reclamation because of elimination of short steep slopes and the increase in vegetation cover after the fifth year of reclamation. Changes in groundwater levels will be greatest to the east, upgradient from any potential surface mine. However, replacement wells could be completed at greater depths.
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