South Mine Pit

Two surface mines were developed in the lower portion of the North Potato Creek Watershed - the North Mine Pit and the South Mine Pit. After completion of mining, the North Mine Pit was filled with spoil from the South Mine Pit. Today what remains of the the South Mine Pit is an 8.1 hectare (20 acre) impoundment that is approximately 60 meters (200 feet) deep and contains approximately 20 million hectoliters (550 million gallons) of water. North Potato Creek was diverted into the South Mine Pit in 1991 to act as a sediment trap. The water quality in the South Mine Pit and in North Potato Creek as it enters and exits from the Pit is degraded.

The agreement with the EPA required GSHI to conduct a study to determine the appropriate remedial action to alleviate contaminant discharge from North Potato Creek into the Ocoee River. As part of the study, a streamlined risk assessment based upon human health risk based screening values determined that current conditions posed no human health risk. Consequently, ecological impacts were the principal focus of the study and chronic and acute ecological screening values were used to determine that aluminum, cadmium, cobalt, copper, iron, manganese, lead, and zinc were the contaminants of potential ecological concern. Bench and field scale treatability studies determined that removal efficiencies for these metals averaged 95 percent, and the generated sludge would settle to the bottom of the pit through its strongly stratified layers.

A year-long limnology and surface water study, including bench tests and a full-scale pilot study, determined that a lime/aeration treatment plant that drew anaerobic, highly mineralized water from the bottom of the pit (which is permanently stratified thermally and chemically mixed with the flow from North Potato Creek would settle its precipitates in the pit before discharging from the pit to the Ocoee River.

Acid neutralization and metals precipitation through conventional lime treatment was selected as the appropriate remedial action, and the plant, went online in Jan. 2005, and is capable of treating the 10-year, 24-hour storm in the 4,000 hectare (10,000 acre) watershed of North Potato Creek. This capacity of 27,000 lps (972 cfs or 436,000 gpm) makes this arguable the largest acid mine damage (AMD) treatment facility in the world. The plant is projected to remove 240,000 lbs/yr of metals and 1.8 million lbs. of acid from North Potato  Creek.

By treating water at this plant and the Cantrell Flats wastewater treatment plant in Davis Mill Creek, more than 98 percent of the metals that previously flowed into the Ocoee River have been eliminated.

-top-