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Water chemistry was monitored monthly for ten months from an acid mine drainage (AMD) seep emanating at Stockton Coal Mine within the Mangatini watershed in New Zealand. Metal concentrations of the seep water were Fe (4.31-146 mg/L), Al (7.43-76.7 mg/L), Cu (0.0201-0.0669 mg/L), Ni (0.0629-0.261 mg/L), Zn (0.380-1.39 mg/L), Cd (0.000540-0.00134 mg/L) and Pb (0.0049-0.0056 mg/L), pH was 2.49-3.34 and total acidity (pH 8.3) was 78.5-626 mg/L as CaCO 3. Water chemistry signature prompted laboratory mesocosm studies measuring the effectiveness of sulfate-reducing bioreactors (SRBRs) for generating alkalinity and sequestering metals. Alkaline materials utilized in the SRBRs included industrial waste products such as mussel shells, nodulated stack dust (NSD) derived from the cement industry, and limestone. Organic substrate materials included post peel, a by-product from fence post manufacture, Pinus radiata bark and compost. Seven SRBRs comprised of varying substrate mixes received aerated AMD for nearly four months. AMD was sourced from the pond that collected the seep water. The SRBR containing NSD successfully removed all metals, but effluent was caustic with pH>9. Bioreactors consisting of 20-30% mussel shells were most successful at immobilizing metals and generating circumneutral effluent. Systems containing mussel shells sequestered more than 0.8 moles of metals/m 3 of substrate/day at stable operating conditions and yielded effluent concentrations (removal efficiencies) of 0.120-3.46 mg/L Fe (96.5-99.8%), 0.0170-0.277 mg/L Al (99.5-99.9%), <0.0005-<0.001 mg/L Cu (>99.7->99.9%), <0.0005-0.0020 mg/L Ni (99.3->99.7%), <0.001-0.005 mg/L Zn (99.7-99.9%), < 0.00005 Cd (>98.3->98.9%) and <0.0001-0.0001 Pb (99.5-<99.7%). The system consisting of limestone as the only alkalinity generating material was less effective (15.4-64.3 mg/L Fe). Results from duplicate systems but different reactor shapes indicated reactor dimensions influence flow characteristics and therefore treatment efficacy.

Abstract. Coal mining in New Zealand has caused perturbation of water resources and biodiversity. Contaminants impairing local waterbodies include acidity, iron, aluminum, arsenic, manganese, nickel, zinc, copper, sulfate and suspended solids. Exposure of sulfur containing rocks, such as pyrite, to atmospheric oxygen during mining operations produces acid mine drainage (AMD). Sulfuric acid and metal acidity are generated and can accentuate metal mobilization and bioavailability. Metals favor the dissolved state in acidic environments but form less toxic precipitates when exposed to adequate alkalinity. Metal toxicity effects are synergistic dependent on metals speciation and their concentrations.New Zealand is in the initial stages of acid mine drainage mitigation and has yet to develop proven treatment technologies. Implementation of passive treatment methods, such as engineered wetlands, have successfully reduced acid mine drainage impacts worldwide. Design criteria for these systems are improving while their limitations are well documented. We are currently collecting water quality and flow data from selected AMD-impacted sites. We are in the process of designing pilot-scale engineered wetland systems to ameliorate acid mine drainage in New Zealand. Sequential-treatment trains will be constructed and their performance evaluated in order to optimize design effectiveness.New Zealand acid mine drainage characteristics and complex topography offer unique challenges for implementing treatment systems. The AMD typically contains very high aluminum concentrations (commonly exceeding 50 g/m 3 ) and has an aluminum to iron concentration ratio of three to one. Abundant steep topography can be exploited to create adequate driving head for implementing systems such as SCOOFI reactors while reducing and alkalinity producing systems can also be employed. Precipitation of up to six meters per year contributes to dynamic hydraulic characteristics and will offer unique design and treatment challenges. Additional

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