Geochemistry of an Acid-contaminated Stream in New Lexington, Ohio

Abstract

Rivers draining abandoned and reclaimed coal mining areas are characterized by high concentrations of trace metals and low pH values, and therefore are said to be contaminated by "acid-mine drainage" or AM.. The streams and tributaries in New Lexington of Perry County, Ohio, possess these characteristics due to mining of coal in the area. The pH of the water in Lexington Creek and Rush Creek reaches a low of 2.6. In addition, the water contains the following trace metals listed in order of their highest concentrations: magnesium = 174.0 ppm, calcium = 162.0 ppm, manganese = 44.81 ppm, sodium = 41.2 ppm, iron = 35.03 ppm, potassium = 5.18 ppm, zinc = 1.61 ppm, nickel = 0.776 ppm, cobalt = 0.749 ppm, strontium = 0.647 ppm, yttrium = 0.392 ppm, lead = 0.206 ppm, barium = 0.178 ppm, lanthanum = 0.154 ppm, arsenic = 0.073 ppm, copper = 0.068 ppm, chromium = 0.014 ppm, and molybdenum = 0.01 ppm. The water in Lexington Creek and Rush Creek also has high concentrations of suspended sediment, primarily ferric hydroxide, up to 180 ppm. The suspended sediment is a potential health problem because the ferric hydroxide sorbs anions at low pH and releases them at neutral pH. This metal-rich sediment accumulates on the stream beds within the city of New Lexington. A three-component mixing diagram was used to determine how mixing among the tributaries produced water with a specific chemical composition in Rush Creek. This water contained 108 pprn Ca, 58.4 pprn Mg, 20.6 pprn Na, 4.02 pprn K, and 1.46 pprn Fe. In addition, the water of Lexington Creek was treated as a mixture of three components: ground water, meteoric water, and mine, effluent. The abundances of each component were determined to be: ground water = 65%, meteoric water = 9.6%, and acid-mine drainage reaching a high of 25% at the confluence of Lexington and Rush Creeks. The ferric hydroxide recovered from the sediment of sample 7 consists of many trace elements, some of which are: As = 67,700 ppm; V = 28,000 ppm; Zn = 6260 ppm; Cr = 5750 ppm; Cu = 2320 ppm; and Ba = 1350 ppm. Many of the trace elements found in the ferric hydroxide are toxic and could be released into the water if the pH increases. Therefore, 28 years after mining has stopped, metal rich sediment is being deposited on the streambed channels, and the water of Lexington Creek is significantly contaminated by acid-mine drainage