Long-Term Variability of BDOM and NOM as Precursors in Watershed Sources

All drinking water supplies contain some background NOM. In the early 1970s, NOM became a focus of concern as its central role in the formation of potentially carcinogenic disinfection by-products was recognized. DBPs, including the trihalomethanes (THMs) and haloacetic acids (HAAs), were found to result from the reaction of chlorine with NOM. Starting in the late 1970s, regulations were established by the USEPA with the intention of minimizing DBP exposure. These regulations stimulated the development of in-plant control strategies; however, far less attention has been paid to watershed management for precursor control.


The research objectives of this study were to (1) to investigate the sources, nature, and long-term variability of natural organic matter (NOM) and biodegradable organic matter (BDOM) in source waters, and (2) evaluate their impact on the formation of disinfection by-products (DBPs). Relationship Between NOM and DBP Formation Laboratory experiments were performed on a wide range of raw waters and NOM isolates. Disinfection by-product yields were measured along with some key physico-chemical parameters. These data were blended with literature data and processed using classical power function models.



The final product was a comprehensive assessment of DBP precursor densities in raw waters, and hydrophobic, mesophilic, and hydrophilic NOM fractions. Precursor Generation Laboratory tests were conducted on leachate from plant material and on pure solutions of lignin monomers. Using these data and a lignin degradation/characterization method, assessments were made of the role of lignin in DBP precursors and NOM. Other conclusions were drawn concerning the genesis of soluble precursors in forested watersheds. Modeling Synaptic surveys were conducted in watersheds from across the United States. Export modeling was conducted with the aim of attributing certain land use types or land cover to concentrations of specific DBP precursors.