A PRACTICAL MEASURE OF ACIDITY LOADING IN COAL-MINED WATERSHEDS

A measure is proposed to characterize acidity loading behavior of streams impacted by mine drainage. This metric, the acidity loading at mean daily discharge, can be estimated from USGS NWIS data, acidity measured under high- and low-flow conditions and corresponding stream discharges and does not require continuous sampling. The assumed power-law relationship between acidity and discharge is supported by test cases from the Appalachian Plateau and indicates that the dominant physical model is partial flushing in which acidity loading is greater at low flow. A decrease in the acidity loading at mean discharge in response to remediation can be taken as an indicator of a decrease in mean acidity loading provided the discharge variance is within typical ranges. The proposed measure provides public managers with a relatively easy and inexpensive method to assess and report the effectiveness of source control, passive and active treatments in alleviating acidity loads and establishes a basis for comparing the cost-effectiveness of remediation alternatives.