Acidity Loading Analysis (9/16/04 version)

To assess AMD reclamation project performance, an acidity loading analysis will be conducted annually to compare loading changes upstream and downstream of each major project. The performance indicator will be the mean annual acidity load. This indicator is meaningful for assessing and reporting the effectiveness of source control, passive treatment and active treatment in alleviating acidity loads, and also provides a basis for comparing cost-effectiveness of alternatives. (The method is not a substitute for biocriteria in measuring attainment of aquatic life uses.)

The mean annual load is a representative indicator of water quality because it integrates all probable daily loads over a typical year. The proposed method requires measuring the contributing drainage area, acidity and discharge, for high- and low-flow conditions, before and after treatment. Acidity load (acidity x discharge) is graphed against normalized discharge (normalized to mean annual discharge) in log space using Excel. Linear regressions are performed separately on pre-treatment and post-treatment data. The difference between the two regressions at normalized mean annual discharge is the change in the mean annual acidity load.

Mean annual discharge can be estimated with high confidence from drainage area, for southeast Ohio basins with record lengths exceeding 25 years. For historic data, acidity often was not measured. In those cases, acidity will be estimated from pH and dissolved metal concentrations, which account for the hydrogen acidity and the mineral acidity.