An applied research program at the Star Fire surface mine in eastern Kentucky, owned and operated by Cypress-AMAX Coal Co., defined spoil characteristics to develop and monitor water resources, which will help identify a reliable water supply for future property development. Water stored in the mine spoil may provide a usable ground-water supply, and the spoil could also be engineered to provide base flow to surfacewater reservoirs.
Ground-water recharge enters the spoil by way of sinking streams, ground-water flow from bedrock in contact with the mine spoil, and a specially designed infiltration basin. Ground water discharges predominantly from springs and seeps along the northwestern outslope of the spoil.
A conceptual model of ground-water flow, based on data from monitoring wells, discharge from springs and ponds, dye tracing, hydraulic gradients, and field reconnaissance, indicates that ground water moves slowly in the spoil interior, where it must flow down into the valley fills before discharging out of the spoil. Two saturated zones have been established: the first in the spoil interior, and the second in the valley fills that surround the main spoil body at lower elevations. The saturated zone in the valley fills contains fresher water than the zone in the spoil interior and exhibits more water-level fluctuation because of efficient recharge pathways along the spoil’s periphery at the spoil-highwall contact. The average saturated thickness of the valley fill areas (30.1 ft) is approximately twice the average saturated thickness found in the spoil’s interior (15.4 ft). Spatial water-quality variations are consistent with those predicted in the proposed flow system.
Based on an estimated average saturated thickness of 21 ft for the entire site, the saturated spoil stores 4,200 acre-ft (1.4 billion gallons) of water. Hydraulic-conductivity (K) values derived from slug tests range from 2.0 × 10-6 to more than 2.9 × 10-5 ft/sec, and are consistent with hydraulic-conductivity data for other spoil areas where similar mining methods are used.
Water samples taken from wells and springs indicate that the ground water is a calcium-magnesium-sulfate type, differing mainly in the total concentration of these constituents at various locations. Mineral saturation indices calculated using the geochemical model PHREEQE indicate that most of the ground water is near equilibrium with gypsum. Nearly all the water samples had pH measurements in a favorable range between 6.0 and 7.0, indicating that the spoil does not produce highly acidic water.
Measurements of vertical displacement around the monitoring-well surface casings indicate that differential settlement is occurring within the mine spoil. The most rapid settlement occurs in the most recently placed spoil near the active mining pit.
Report of Investigations 10
Digital Object Identifier (DOI)
Wunsch, David R.; Dinger, James S.; Taylor, Page B.; Carey, Daniel I.; and Graham, C. Douglas R., "Hydrogeology, Hydrogeochemistry, and Spoil Settlement at a Large Mine-Spoil Area in Eastern Kentucky: Star Fire Tract" (1996). Kentucky Geological Survey Report of Investigations. 50.