Modeling Framework for Establishing Water Quality Trading Units near Pacific, Missouri

The Environmental Protection Agency (EPA) has promulgated a water quality trading policy. (WQT). The discharge of pollutants may be traded within/between locations in a watershed as long as nowhere along the applicable stream are water quality criteria exceeded. The tradable discharges may be of a point or a nonpoint nature. While the trading of point source pollutants has progressed, nonpoint source pollution (NPS) trading has not made as much progress. As the EPA stated in the policy statement, the development of appropriate trading units will be a considerable difficulty for nonpoint trades. The specification of trading units for nonpoint source trading may be difficult because of uncertainty for a number of reasons. The first of these is that trading must be initiated and executed legally in the present in order to trade with/for pollutants generated in the future. Nonpoint source pollutants, by their nature, can be generated by a number of different sources in different locations; the greater the number of sources and locations, the greater the uncertainty in their quantification. In addition, the generation of nonpoint source pollutants is driven, in part, by precipitation. Even as precipitation patterns are understood, there is considerable variability in the precipitation intensity and total volumes at specific locations at specific times. To meet these challenges, a research effort has been undertaken. As a start, a modeling system has been set up/established in a rapidly developing location southwest of St. Louis, Missouri. The test location is the Brush Creek watershed, where the area of the outlet of the watershed intersects the community in and around Pacific, Missouri. Because of its location 30 miles southwest of St. Louis, Missouri, the Pacific region expects to see considerable development that could increase the generation of nonpoint source pollutants. In addition, because Pacific is located in the lower portion of the watershed, nonpoint source pollution expected to be generated in the city could be traded with upstream locations and not cause decreases in water quality anywhere along Brush Creek. Because of the uncertainties associated with NPS trading, it can only be addressed via modeling. For this initial effort, the modeling is being limited to discharges and the generation of sediment. U.S. Geological Survey data for discharges and sediment concentrations in the Meramec River have been used to calibrate EPA's HSPF model for the Brush Creek watershed. Alternative development scenarios have been developed to represent potential conditions in the upstream and downstream locations that may be associated with a trade. Multiple precipitation patterns allow the modeling to represent the variability that may occur in the precipitation that drives the generation of sediment loads. Altogether, the modeling framework is appropriate to investigate and offer insights into the development of NPS trading units. Because Brush Creek is not currently impaired, and is not associated with any regulatory actions, it is an excellent location within which to test the modeling framework.