ALUMINUM AND pH AT THE ONEIDA#1 MINE DISCHARGE NEAR HAZLETON (LUZERNE COUNTY), PA: HOW EFFECTIVE IS THE PASSIVE LIMESTONE TREATMENT SYSTEM?

Raising pH and lowering dissolved aluminum concentrations is the purpose of an underground passive limestone treatment system on the property of Eagle Rock Resort, Hazleton (Luzerne County), PA. Opened in August 2001, the system treats mine effluent from the Oneida #1 drainage tunnel. Water flows from the mine into an underground tank from where it is gravity fed into three drainage passages filled with limestone. Downstream valves control the flow through the system. When the valves are closed, water is retained in the treatment system long enough for equilibration, raising pH and precipitating aluminum hydroxide (Al(OH)₃). Precipitated Al(OH)₃ is flushed from each drainage passage once every three weeks on a staggered weekly schedule by opening its valve and allowing the water to flow into a settling pond. In October 2008, elevated amounts of dissolved aluminum were found downstream of the settling pond despite low levels of aluminum coming out of the mine and each of the limestone drains, indicating that the settling pond was a potential source of dissolved aluminum to Sugar Loaf Creek. The current study, conducted in September 2009, is to test our hypothesis that low pH water draining out of the central drain (due to a maintenance malfunction) dissolved some of the pond Al(OH)₃ and carried it to the stream. We analyzed pH, specific conductance (TDS) and dissolved oxygen in situ at 14 sites upstream and downstream of the system, including 6 sites within the pond. Large triplicate samples were collected at each site and filtered at a central location. Alkalinity was determined immediately after filtering. Additional filtered subsamples were acidified and kept chilled for later metal analysis of Mg, Ca, and Fe by flame atomic absorption and of Al by colorimetry. A third set of triplicate filtered subsamples was frozen and subsequently analyzed for sulfate, chloride, bromide, fluoride, nitrate, nitrite and phosphate by ion chromatography. The low pH (4.1) in the mine discharge was raised to 6.0 at the pond discharge, indicating mitigation of pH by the treatment system, but the even higher pH (6.4) at the downstream site is most likely attributable to dilution by lake overflow. Dissolved aluminum values were low everywhere (below 0.15 ppm), and in fact were lower in the mine drainage than in the either the pond or the pond discharge.