USING CHEMICAL PARAMETERS TO LOCATE AMD DISCHARGE POINTS IN A PASSIVE WETLAND TREATMENT SYSTEM

Moraine State Park, located north of Pittsburgh, Pennsylvania, was once mined for oil, gas and coal. In the late 1960’s and early 1970’s underground bituminous coal mines were sealed; however, some seals failed and are now the principle source of acid mine drainage (AMD) entering Lake Arthur, a large reservoir. Abandoned mines like the ones in Moraine State Park produce high levels of metals which contaminates ground and surface waterways. Mean concentrations of iron species as well as pH, temperature and conductivity are indicators of AMD discharge in these waterways. Testing for these parameters at seasonal intervals may indicate discrete flows of AMD discharge. A three pond passive wetland remediation system is treating an unknown number of failed mine seals into Lake Arthur. Pond 1 is a settling pond that collects the AMD discharge and uses residence time to remove dissolved iron and other contaminates through oxidation and precipitation. Pond 2 is a vegetation pond and pond 3 is a polishing pond, conditioning the water before discharge. Historical flow data through the system has suggested that water flux is not dependent on precipitation, and hence is directly dependent on mine discharge. Understanding the number of mine discharge points is crucial in predicting the lifespan of the system. However, this system has outlived its proposed 12 year life span, currently in its 14th year, and its efficacy is in question. Monitoring seasonal variations in chemistry will help in determining the nature of discharge into pond 1. Data is collected using a multi-probe meter attached to a float and submerged 1.5 feet to avoid contact with the sediment bed. Scaling by 5 feet intervals, 35 separate measurements are recorded across 3 transects of the 171 foot pond. Initial results collected in October and December of 2010 indicates varying discharge. The October data demonstrated two distinct negative spikes in both temperature (2°C decrease) and pH (1 unit decrease) at 55 and 95 feet. However, in December, three negative spikes are seen in pH, but a 2°C gradual change in temperature occurs over 50 feet with no distinct spike. The pH spikes occur again at the 55 and 95 foot markers, with an additional spike at 145 feet. Further testing through the winter and into the spring should allow for better characterization of the AMD inflows into Pond 1.