Abstract
A surface lignite mine in central Texas began operating in Eocene deltaic sediments in 1982. By 1986, reclamation and monitoring of ground-water recovery had begun in two mine blocks. Analysis of the ground water at that time revealed high concentrations of many ions, and correlations could not be made with the age of the spoil. However, examination of the geochemical evolution of spoil water, a decade after mining, revealed the development of a number of trends. Ground-water recovery reached equilibrium within 7 to 8 years after reclamation began. Recovery was not influenced by the lithology of the spoil. However, spoil lithology did affect the concentrations of ions in the ground water. Mine blocks containing a greater percentage of overburden sand had increased ion concentrations for most parameters due to either limited oxidation of reduced sediments or better mixing between ground water and spoil. Another important factor in the geochemical development of the ground water was the rate of ground-water recovery. Most ion concentrations exhibited an increasing trend until ground-water recovery was complete. At that time, flushing of the ground water began to dominate and concentrations decreased. Important processes occurring in the spoil include the oxidation of pyrite, cation exchange reactions, the dissolution of carbonates, and the precipitation of gypsum.
