SULFATE CONCENTRATION VARIATIONS IN GROUNDWATER AT A LIGNITE MINE

Sulfate concentrations in the groundwater at the TXU Monticello lignite mine in northeast Texas are variable with time and space. Some monitoring wells show steady, cyclic variations in sulfate concentration; others show sharp short term increases or decreases, long term changes in sulfate concentration trends (both increasing and decreasing), and concentrations that first increase then decrease. The monitoring wells in the reclaimed section of the mine have the highest sulfate concentrations and the widest range in sulfate concentration; one reclaim well ranges from 141 ppm to 2450 ppm sulfate. The monitoring wells placed in undisturbed overburden and underburden have both lower concentrations and narrower ranges. These fluctuations are related to several processes. Seasonal changes in precipitation correlate with concentration in some wells. Other wells are affected by proximity to surface water bodies, including newly constructed ponds. Finally, spoil heterogeneity is an important factor. The investigative program includes water sampling, test wells, and statistical analysis.