SEDIMENT AND WATER ANALYSIS OF A VEGETATION POND IN A PASSIVE WETLAND AMD TREATMENT SYSTEM

Moraine State Park, located thirty six miles north of Pittsburgh, was at one time extensively mined with both underground and strip coal mines. A total of sixty nine mine entrances were sealed in the early 1970’s, but assessment of these seals in the 80’s determined that a number of these have failed. A passive wetland acid mine drainage (AMD) treatment system was installed in 1996 to combat a few of these failing seals, the exact number is unknown. The passive wetland treatment systems consist of three ponds, the first is the settling pond, the second is the vegetation pond, and the third is the finishing pond. Of the three ponds that make up the treatment system pond two, the vegetation pond, is demonstrating signs of stress and possibly close to failure. The ponds were predicted to last twelve years with no required maintenance and are currently on their fourteenth year. There are shallow water levels in pond two, which is believed to be attributed to the sediment build up over the years. Initially, hay bales were installed in pond two to direct flow and give the iron-laden water the proper residence time for natural attenuation. Water samples were taken at the inflow, outflow, and at the midpoint of each side of pond two. The sides of the pond were registering little to no iron content, while the both the inflow and outflow measured about 1.5 mg/L. Chemistry suggests that sediments have overcome these guides and water is not attaining the proper residence time to settle out iron hydroxide precipitates, among other AMD contaminants. A preliminary sediment sample was taken at the inflow and was colloidal in form. Upon settling, the samples total length was 47 cm, of this 30.5 cm was iron precipitate, and 16.5 cm was clear water, for a precipitate to water ratio of 1.85:1. Additional water and sediment samples will be taken around pond two to determine sediment thickness, along with chemical parameters such as temperature, pH, conductivity, iron, and alkalinity. Water and sediment sample collection and analysis through the winter, when the pond is free of active vegetation and reduced microbial activity, will provide clearer results to the chemical controls, flow patterns, and precipitation rates of pond 2.