MAJOR-ION CHEMISTRY OF SURFACE WATER AND IDENTIFICATION OF HYDROGEOCHEMCIAL PROCESSES IN A RECOVERING SURFACE-MINED WATERSHED, THE WILDS, SOUTHEASTERN OHIO

Major-ion chemistry of surface water at The Wilds was determined by ICP analysis in an attempt to resolve hydrogeochemical processes in the recovering watershed. Today surface water, exclusive of springs, can be divided into three geographic regions based on characteristic levels of total dissolved solids (TDS). The northern region typically has TDS values between 1200 to 1400 mg/L. TDS values in the middle region range between 800 to 1100 mg/L and in the southern region range between 100 to 500 mg/L. The pH values of surface water at The Wilds vary between 6.5 and 9.0 and appear to be primarily controlled by the limestone-rich spoil. There is a characteristic type of lake in each region that reflects changes in the reclamation practices in the watershed. Northern region lakes are fed by surface runoff/groundwater or a combination of surface runoff/groundwater and springs, have very small drainage basins and are flow-through lakes. Lakes in the middle region are fed by a combination of surface runoff/groundwater and springs, have large drainage basins and are flow-through lakes. Most of the southern region lakes are fed by surface runoff only, have small drainage basins and are not flow-through lakes. Southern region lakes based on TDS values appear to be above the regional groundwater table. Additionally, each region is drained by a stream. Final reclamation in the watershed occurred in 1984.

Analysis of ICP results indicates several hydrogeochemical processes, including the oxidation of pyrite, and the possible deposition of calcite. Mg and Ca values are significantly less than sulfate indicating that pyrite oxidation remains a significant process in the watershed. Also Mg is approximately equal to Ca indicating either the main carbonate in the area is dolomite or that Ca is being removed by the deposition of calcite. Mixing models were attempted to determine if the isolated lakes in the southern area could be mixed with the spring water (proxy for groundwater). The results of the modeling were mixed. The best results were for the southern region where a flow-through lake was modeled by mixing the isolated lake and the spring in equal amounts. Results of the mixing model for the central and northern regions were poor indicating either a change in the groundwater composition or additional hydrogeochemical processes in these lakes.