Trap efficiency of a sediment-control pond below a block-cut coal mine in Fayette County, Pennsylvania

The U. S. Geological Survey determined the efficiency of a pond constructed to control sediment from a surface coal mine site by measuring runoff and sediment loads at the inlet to and discharge from the pond during storms. The pond is below a 17.9-acre block-cut coal mine in Fayette County, Pennsylvania and has a permanent pool capacity of 60,000 cu ft. The capacity at the principal spillway and the emergency spillway are 128,900 and 175,500 cu ft, respectively. The pond is equipped with a 3-inch flow control valve, used by the mine operator to regulate the pond stage between the permanent pool and the principal spillway. Data were collected during five moderate storms when the 3-inch control valve was intentionally opened. The ration between the quantity of water in the pond at the start of the storm and the quantity to runoff to the pond was calculated for each storm. The ratios were 3.6, 2.5, 8.6, 2.9, and 1.5 for the five storms. The measured trap efficiencies were 98.1, 92.8, 99.6, 99.1, and 98.2%, for the five storms. (USGS)