Hydrology of the North Fork of the Right Fork of Miller Creek, Carbon County, Utah, before, during, and after underground coal mining

Abstract

From 1988-92 the U.S. Geological Survey, in cooperation with the Utah Division of Oil, Gas, and Mining, studied the effects of underground coal mining and the resulting subsidence on the hydrologic system near the North Fork of the Right Fork of Miller Creek, Carbon County, Utah. The subsidence caused open fractures at land surface, debris slides, and rockfalls in the canyon above the mined area. Land surface subsided and moved several feet horizontally. The perennial stream and a tributary upstream from the mined area were diverted into the ground by surface fractures where the overburden thickness above the Wattis coal seam is about 300 to 500 feet. The reach downstream was dry but flow resumed where the channel traversed the Star Point Sandstone, which forms the aquifer below the coal seams where groundwater discharge provides new base flow. Concentrations of dissolved constituents in the stream water sampled just downstream of the mined area increased from about 300 mg/L to more than 1,500 mg/L, and the water changed from primarily a magnesium calcium bicarbonate to primarily a magnesium sulfate type. Monitored water levels in two wells completed in the perched aquifer(s) above the mine indicate that fractures from subsidence-related deformation drained the perched aquifer in the Blackhawk Formation. The deformation also could have contributed to the decrease in discharge of three springs above the mined area, but discharge from other springs in the area did not change substantially; thus, the relation between subsidence and spring discharge, if any, is not clear. No significant changes in the chemical characteristics of water discharging from springs were detected, but the dissolved-solids concentration in water collected from a perched sandstone aquifer overlying the mined coal seams increased during mining activity.