Two coal mine drainage sites in eastern Ohio were characterized. The mine near Leetonia, OH is covered by glacial till with carbonate minerals that impart alkalinity to the shallow groundwater. Water is brought to the mine via subsidence fractures that cause a quick increase in discharge from the mine in response to runoff events on the surface once the mine pool has filled. A dilution effect on dissolved ions due to new recharge water is minor compared to changes in discharge and indicates that the majority of the water entering the mine has a sufficiently long time to reach chemical equilibrium. The alkaline water buffers the acidity produced by pyrite oxidation keeping the pH inside the mine circumneutral. Maintaining a circumneutral pH reduces ferric iron solubility and prevents further pyrite oxidation, essentially shutting down this positive feedback mechanism that would drive the pH down and contaminant concentrations up. Therefore without glacial deposits above the mine the drainage could be more harmful to the environment.
The other mine located near Hammondsville, OH within the unglaciated region has no flowing discharge at the surface as the result of a sealing of the mine entry. Without new mine discharge, the water chemistry was controlled by variation in seasonal climate with dissolution of minerals during the wet season and precipitation of minerals during the dry season.