EFFICACY OF THE ONEIDA #3 PASSIVE LIMESTONE TREATMENT SYSTEM (LUZERNE COUNTY, PA) DURING NORMAL MINE DISCHARGE CONDITIONS

The Oneida #3 mine is located near Sheppton, PA, and used to flow directly into Little Tomhicken Creek. This mine drainage historically exhibited high aluminum levels and low pH. The Eastern Pennsylvania Coalition for Abandoned Mine Reclamation (EPCAMR) installed a passive limestone treatment system for the drainage, completed in December 2009. The system has the capacity to treat from 50 to 100% of the mine outflow depending on flow conditions. On July 17, 2010, we conducted a field study on the Oneida #3 mine drainage and Little Tomhicken Creek to test the effectiveness of the treatment system in lowering aluminum levels and raising pH and alkalinity. As part of the study, we collected additional samples for analysis for anions and metals. Nine samples were collected from Little Tomhicken Creek upstream and downstream of the confluence of stream and mine drainage, at the mine outflow, and within the treatment system. The pH, dissolved oxygen, and conductance were assessed in situ at all sites. Large volume samples were collected and filtered on site (glass fiber filter, 0.7 µm effective pore size). Upon filtration, subsamples were analyzed for acidity, alkalinity, and hardness. Triplicate non-filtered and filtered subsamples were collected, acidified, and chilled for later metal analysis by furnace and flame atomic absorption. An additional triplicate set of filtered subsamples were collected, put on ice, and frozen on return to the laboratory for later analysis of several anions by ion chromatography. The system increased pH from 4.98 in the tunnel to 6.88 at the treatment discharge. The treatment system also increased the alkalinity (0 to 19.1 mg/L as CaCO₃ from the tunnel to the outflow, respectively). We have several concerns regarding the aluminum results. Analyses for aluminum concentrations were problematical in that the numbers were unreasonably high. An additional concern is that colloidal aluminum might be passing through our filters leading to higher “dissolved” aluminum numbers than would be expected at the individual sample pH’s. It is also possible that some colloidal aluminum hydroxide precipitated in the treatment system is being carried all the way through the system back to Tomhicken Creek.