SEASONAL AND CHEMICAL VARIABILITY OF AMD DISCHARGE IN A PASSIVE WETLAND TREATMENT SYSTEM

Moraine State Park, located north of Pittsburgh, PA, was once mined for oil, gas and coal. Through the 1960’s and 70’s, underground bituminous coal mines were sealed; however some seals failed and are currently the principle source of acid mine drainage (AMD) entering Lake Arthur, a large reservoir located within the park. A three pond passive wetland remediation system is treating AMD entering Lake Arthur. The ponds have outlived their proposed life span and their current efficacy is in question. Based on historical data, multiple discharges are thought to be in Pond 1, a settling pond. However, the number of discharge points seems to vary with changes in both flow and season. Monitoring the seasonal variations in chemistry, and thus, flow, will help in determining the number of discharge points. Mean concentrations of iron species as well as pH, temperature and conductivity are indicators of AMD. Identification of specific discharge points will focus future remediation efforts.

Data is collected using a float strung across Pond 1. A multi-probe is attached and submerged 1.5 ft below the surface. This meter is used to contour the pond at 5-foot intervals. During each sampling event, thirty-five measurements are recorded on the center, left and right sides of the 171-foot pond. Point-specific changes in pH, temperature and specific conductivity show two AMD discharge points, one located at approximately 60 feet and another at 120 feet. Temperature varied ±1-1.5^οC over a 15 foot span at these locations. pH decreased up to 0.5 within 5 feet of these points. Seasonal contouring demonstrated that surface run-off from a limestone channel also affected this pond, allowing for a mixing effect to appear near this location.