MIGRATION AND NATURAL ATTENUATION OF SULFATE DRAINAGE IN AREA ADJACENT TO ABANDONED COAL MINES IN NORTHEASTERN OHIO

The Middle Kittanning (No. 6) and the Lower Kittanning (No. 5) coals were mined in southeastern Stark County before 1989. The aquifer between these two coals is a major one for domestic uses in the area. The mining and coal washing activities generated acid drainage and contaminated the aquifer from time to time. However, natural attenuation is capable of reducing it to a prevailing lower level, around 400 mg/l, in about 6 years. The sulfate level is 705 mg/l in acid leachate sampled in monitoring well drilled into sulfide rich mine spoil piles. Sulfate level in precipitation diluted acid drainage to 491 mg/l as estimated from ponded water in strip mine pits. Sulfate level in groundwater in the area farther away from the mining activities could be less than 100 mg/l when uncontaminated. Acid drainage was generated and the aquifer polluted when the wash plant refuse piles were disturbed during the reclamation activities from July 1993 to March 1994. The acid drainage formed a new sulfate plume and moved southeastward down piezometric gradient. There are concurrent changes in groundwater pH. The acidity of groundwater appears to affect Ca/Mg ratios. Lower pH favors a higher Ca/Mg ratio but the changes in ratio are delayed in time by a few months. There are also concurrent increases in Ca and Mg concentrations in groundwater as pH is lowered. Reclamation and tire monofill facility construction resulted in added dissolution of Ca and Mg bearing minerals. The distance between two monitoring wells and time it takes for the head to reach the downstream well permit us to estimate the speed of migration of the contamination plume head. The estimated speed at 360 ft/year compares well with 350 ft/year estimated from groundwater modeling.