English

Abstract

A pilot biochemical reactor (BCR) with a design flowrate of 3.8 l/m (1 gpm) has been operating at the Standard Mine Superfund Site for over four years, since August, 2007. The pilot system is entirely passive, using solar energy to power sampling equipment and pumping requirements. BCR treatment relies on biological and chemical reactions within an anaerobic reactor comprised of organic and inorganic materials including woodchips, straw, limestone and bacterial inoculum. The BCR pilot has been treating mining influenced wastewater (MIW) since construction was completed in the summer of 2007. Polishing and aeration of BCR effluent is accomplished in an aerobic polishing cell (APC) containing wetland plants in two of the three cells. The Standard Mine BCR is constructed at an elevation of 3,353 meters (11,000 ft ) above MSL with an average annual snowfall of 10.2 m (400 in ). Limited BCR treatment data from reactors operating under harsh alpine conditions was available before this system was constructed. Operation and monitoring of the BCR has been year round since 2007. Due to the inaccessibility of the site during winter months, an automated sampling system was designed incorporating Teledyne ISCO™ (ISCO) samplers, Hydrolab™ sondes, and a satellite transmission system reporting site operational parameters on a daily basis. In addition to automated sampling, grab samples were taken monthly throughout the 2010/2011 winter using backcountry skiing equipment to access the site. Contaminants of concern (COCs) in the MIW include Cd, Cu, Pb, Mn, and Zn. High metals removal has been observed in BCR effluent since the beginning of operation. In 2009, 2010, and 2011 the average percent removal efficiency for cadmium, Cu, Pb, and Zn exceeded 98%. The pilot study is notable for a long operating period and low analytical laboratory detection limits for metals. BCR treatment of cadmium, Cu, and Pb to less than 5 µg/L has been demonstrated indicating that BCR is capable of approaching or meeting stringent aquatic life water quality standards when operated under harsh high alpine conditions. Both metals and nutrient removal are discussed in relation to receiving stream water quality standards. BCR performance is discussed with additional discussion of performance of BCR effluent polishing by aerobic lagoon.