Thirteen acid mine drainage seeps emanating from waste rock dumps and associated sediment ponds were monitored at Stockton Coal Mine near Westport, New Zealand to identify and quantify metal loads and delineate their spatial and temporal variability. Dissolved metal concentrations ranged from 0.05Á1430 mg/L Fe, 0.200Á627 mg/L Al, 0.0024Á0.594 mg/L Cu, 0.0052Á4.21 mg/L Ni, 0.019Á18.8 mg/L Zn, B0.00005Á0.0232 mg/L Cd, 0.0007Á0.0028 mg/L Pb, B0.001Á0.154 mg/L As and 0.103Á29.3 mg/L Mn and the pH ranged from 2.04Á4.31. Currently this acid mine drainage is treated further downstream by a number of water treatment plants employing a combination of ultra fine limestone and Ca(OH) 2 . However, in the interest of assessing more cost-effective technologies, biogeochemical reactors were assessed in the laboratory as potential cost-effective passive treatment options. Results of mesocosm-scale treatability tests showed that biogeochemical reactors incorporating mussel shells, pine bark, wood fragments (post peel) and compost increased pH to 6.7 and sequestered ]98.2% of the metal load from the Manchester Seep located within the Mangatini Catchment. Laboratory results demonstrated that the maximum loading rate was 0.8 mol total metals/m 3 substrate, and an average of 20.0 kg/day (7.30 tonnes/year) of metals could be removed by appropriately sized biogeochemical reactors.