The use of passive treatment alternatives for the mitigation of acidic drainage at the Williams Brother mine, California: Bench-scale study Erin J. Clyde a , Pascale Champagne b, * , Heather E. Jamieson a a Department of Geological Sciences and Geological Engineering, Queen’s University, Kingston ON, Canada K7L 3N6 b Department of Civil Engineering, Queen’s University, Kingston ON, Canada K7L 3N6 article info Article history: Received 19 August 2009 Accepted 7 April 2010 Available online 11 April 2010 Editorial handling by LeeAnn Munk abstract The aim of the study was to evaluate passive treatment system alternatives to mitigate acid mine drain- age (AMD) characterized by low SO 2À 4 and metal concentrations associated with adit drainage at the Williams Brothers Mine located in the Sierra National Forest, California. Surface water from the site drains into the San Joaquin River Basin and a goal of this study was to mitigate AMD to meet water qual- ity objectives for the San Joaquin River Basin. Effluent sampling from the opening of the lowermost adit identified (AMD) characterized by a pH of 3.90, average SO 2À 4 concentration of 101 mg/L and relatively low average metal concentrations of 4.60, 0.074, 0.047 and 0.133 mg/L for Fe, Cu, Ni and Zn, respectively. The bench-scale study involved the testing of three passive treatment systems: (1) a peat biofilter fol- lowed by an anoxic limestone drain (ALD); (2) a SO 2À 4 -reducing bacteria (SRB) bioreactor followed by an ALD; and (3) a single SRB bioreactor. Synthetic AMD was produced to represent the AMD character- istics observed at the site. The peat–ALD system efficiently increased the pH of the effluent to an average of 6.95. Metals were reduced to average concentrations of 0.06, 0.008, 0.013 and 0.057 mg/L, respectively, for Fe, Cu, Ni and Zn. The SRB–ALD system increased the effluent pH to an average of 6.47, decreased SO 2À 4 concentrations to an average of 11.6 mg/L and decreased the concentrations of Fe, Cu, Ni and Zn to aver- ages of 1.04, 0.004, 0.016 and 0.025 mg/L, respectively. The SRB system efficiently increased the pH to an average of 6.56 and decreased SO 2À 4 concentrations to an average of 18.8 mg/L. Metal concentrations for Fe, Cu, Ni and Zn were reduced to 0.63, 0.006, 0.010 and 0.027 mg/L, respectively. The peat–ALD and SRB systems were capable of increasing the pH of the AMD to 6.5 to meet water quality objectives. The peat– ALD system was capable of removing Fe and Cu to below water quality objectives, however, removal of other metals was insufficient. The SRB containing systems were incapable of removing Fe to water quality objectives, while sufficient removal of Cu, Ni and Zn was attained. From these results, the most effective treatment system would incorporate a peat biofilter, for Fe and Cu removal and a SRB bioreactor for Cu, Ni and Zn removal. The results of this study demonstrate that passive treatment mitigation of AMD can best be accomplished via the use of a combined treatment system that incorporates a peat biofilter, SRB bio- reactor and anoxic limestone drain, thereby accomplishing targeted removal of constituents in individual system components. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Due to the remoteness and inaccessibility of some mine sites, active treatment of acid mine drainage (AMD) is often not feasible. Therefore, passive treatment systems may provide a more viable option. One type of treatment option that has proven to be useful in the treatment of AMD is the use of a peat biofilter (Champagne et al., 2005). Peat moss has been shown to remove metals, such as Cd, Cu, Fe, Mn, Ni and Zn, from solution (Champagne et al., 2005, 2008; Henrot and Weider, 1990; Bonnett and Cousins, 1987; Twardowska and Kyziol, 1996; Ringqvist et al., 2002; Ringqvist and Öborn, 2002; Gosset et al., 1986). Metals are removed from solution in peat biofilters by sorption mechanisms such as chela- tion and cation exchange (Couillard, 1994). During a column study by Champagne et al. (2005) a peat bio- filter was used to remove metals from AMD and after approxi- mately 50 days breakthrough of Cd, Mn, Ni and Zn began to occur, while no breakthrough of Cu and Fe was observed. Cham- pagne et al. (2008) attributed this to competitive adsorption, where dissolved metals in solution compete for sorption sites in the peat, causing ions with tighter bonds to be favoured. As a re- sult, the less favoured metals were released back into solution and became mobile throughout the peat biofilter. Furthermore, peat tends to have an acidic nature; as such, the pH of the effluent from peat biofilters is often acidic, as the natural 0883-2927/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.apgeochem.2010.04.004 * Corresponding author. Tel.: +1 613 533 3053; fax: +1 613 533 2128. E-mail address: champagne@civil.queensu.ca (P. Champagne). Applied Geochemistry 25 (2010) 958–971 Contents lists available at ScienceDirect Applied Geochemistry journal homepage: www.elsevier.com/locate/apgeochem