Methodology for hydrologic evaluation of a potential surface mine: East Trail Creek Basin, Big Horn County, Montana

Abstract

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.

The Erosional Response of Natural and Reclaimed Hillslopes at the Glenrock Coal Company

“…Collier et al (1970) and Ringen et al (19.19) measured sediment yields from small mined and unm.ined watersheds in Kentucky and Wyoming, respectively. Shown et al (1982), Frickel et al (1981), and Hadley et al (1981) used the Universal Soil Loss Equation to estimate soil loss from natural, act"ively-mined, and reclaimed lands in Alabama, Wyoming, and ~Montana, respectively. Lusby and Toy ( 1.977), Gifford (1983), Gilley et al (1977), and Hofmann et al (1983) employed different tYpes of rainfall simulation apparatus to generate erosion data from pl9ts of different _dimensions in Wyoming and North Dakota.…”

An assessment of surface‐mine reclamation based upon sheetwash erosion rates at the Glenrock coal company, Glenrock, Wyoming

“…Several provide sufficient data for a comparison of rates on natural and reclaimed areas (Collier et al, 1970Curtis, 1971Shown et al, 1982;Mitchell et al, 1983;Lusby and Toy, 1976;Gilley et al, 1977;Ringen et al, 1979;Gifford, 1983;Frickel et al, 1981;Hadley et al, 1981;Hofmann et al, 1983). The results of these comparisons are tabulated in Toy and Hadley (1987) and show that erosion rates are usually higher on unreclaimed and reclaimed lands than on nearby undisturbed areas.…”