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and, when they die, provide adsorption surfaces, along with sites for algal growth- Aeration is best used where the mine drainage pH is about 6.5 or above. Aeration promotes metal precipitation through oxidation processes. Aeration can be accomplished by mechanical means, or simply by channeling the drainage over rough slopes. Mechanical methods require some source of power, which may be generated through wind, solar cells, or hydropower. Aeration methods normally include a settling pond below the aeration component. Mechanical injection of neutralizing agents involves a powered mechanical feeder/dosing system for dispensing neutralizing agents. This type of system requires frequent maintenance, may produce significant quantities of metal sludge, and should be considered "semi-passive." Power for the feeder can come from wind, solar, or hydropower. At the Pennsylvania Mine in Summit County, a turbine running in the adit dischazge stream demonstrated that hydropower is practical in some situations- Mechanical systems are generally considered only where there are no options for truly passive alternatives. Any high pH material can be used in this type of system. Because of cost effectiveness and sludge chazacteristics, the most common neutralizing agent is finely ground limestone. Dilution is often overlooked as a treatment method. It can be a cost effective method of treatment, because the neutralizing agent is simply uncontaminated water. Clean water is mixed with the mine drainage in a settling pond, and the resultant pH increases initiates precipitation of metals. A drawback to this method is that the percentage of metals precipitated is significantly less than other methods. Metal removal is site specific, but generally less than 50'0. This method is most effective in removing iron, aluminum, copper, cadmium, and lead, but has only slight effectiveness for zinc and manganese. Electro-kinetics is a newer semi-passive method to remove metals from mine drainage. There are several forms of this treatment currently being developed. The electro-kinetic method discussed in this report uses slow-maintenance, self- regulating resin to remove metals from mine discharge. Different metals can be separated by using ion specific resins. Electricity is used to strip metals from the resins, producing sludge, and allowing reuse of the resin. Land application is a method designed to use natural metals attenuation processes in soil and subsoil to remove metals. Plant uptake, evaporation and transpiration, and soil exchange capacity act to tie up and remove metals. This method is most effective where mine discharge can be spread over a large area to infiltrate into relatively thick soils or unconsolidated deposits. Drainage should be neutral or neaz neutral to avoid plant toxicity. This alternative is also effective for discharges with high iron and/or aluminum, where pH is approximately 4.5 or above. 10