ENV-08-013 A Practical Methodology for Determining Trading Ratio from TMDL Allocation Matrix in Support of Watershed-based Permitting

Description:

This paper presents a practical methodology for estimating “equivalent trading ratio” (ETR) and links uncertainty analysis with trading ratio determination from a TMDL allocation matrix. Determination of ETR can provide a good initial evaluation of “tradeoffs” between various combinations of point and nonpoint source control strategies on ambient water quality improvement. In summary, a greater portion of nonpoint load reduction in overall TMDL load reduction generally correlates with greater uncertainty and thus requires a larger trading ratio. The rigorous quantification of the trading ratio will enhance the scientific basis in water quality trading and allow for more informed decisions for a successful watershed-based permitting program.