EVALUATION OF A NOVEL PASSIVE TREATMENT SYSTEM FOR ACID DEPOSITION AND PH AND ALKALINITY MEASUREMENT CHALLENGES

The headwaters of Buffalo Creek in Union County, Pennsylvania have low pH due to atmospheric acid deposition. A novel passive treatment system, more commonly used to treat acid mine drainage, was installed in Fall 2009. This study examines the system performance and its chemical and biological effects on the receiving stream from 2010 through summer of 2013.

The system diverts a portion of the stream into an aerobic limestone basin and then into a vertical flow compost wetland underlain by limestone before the effluent return to mix with the main stream. Although alkalinity and pH increased in the receiving stream, an algal bloom due to excess nutrient from the compost occurred in the first year, and low biodiversity was observed immediately below the system. By 2012, the algal bloom disappeared, nutrient concentrations decreased dramatically, pH and alkalinity were typical of such a headwater stream, and biodiversity improved dramatically as documented by benthic macroinvertebrate and brook trout population surveys. In addition to examining the system itself, we examined the difficulties of measuring accurate pH and alkalinity values in such low ionic strength systems. The pH values with potassium chloride added to samples to minimize pH electrode junction potential effects gave a more realistic pH value than field pH measurement. For all pH ranges, the US Geological Survey Alkalinity Calculator F1 Gran function and our own spreadsheet F1 Gran calculation provided the most reliable alkalinity values. For pH values above 7, a fixed pH (4.5) endpoint method and an inflection point method in the US Geological Survey Alkalinity Calculator also returned reliable results. The results show that treatment system design and monitoring require more data- and time-intensive alkalinity titrations for such low ionic strength waters.