THE CHALLENGE OF ATMOSPHERIC DEPOSITION TMDLs

Section 303(d) of the Clean Water Act, known as the Total Maximum Daily Load (TMDL) program, establishes pollutant budgets and management plans for watersheds containing impaired waters. In a TMDL, pollutants are identified and recommended reductions are allocated among identified sources. In this paper we present the results of a nationwide review of TMDLs, focusing specifically on TMDLs that address pollutant loadings from atmospheric deposition. The paper reviews the unique technical challenges posed by atmospheric deposition TMDLs and identifies specific research needs for better implementation of these TMDLs. With future improvements in methods for quantifying the contributions from atmospheric sources, TMDL implementation plans will likely be required to identify more specifically the sources of pollutants from atmospheric deposition, and to more precisely estimate the expected reductions in pollutant loadings from atmospheric deposition.