Connecting the Science and Economics of Watershed Pollution Abatement

Nonpoint source (diffuse) pollution from stormwater runoff, failing septic tanks, and other diverse sources is a significant, and often dominant, cause of noncompliance with bacteria water quality standards in large watersheds throughout the United States. However, regulatory emphasis and economic resources have traditionally been directed primarily at reducing conventional point source pollution (e.g., wastewater discharges and combined sewer overflows) with little more than a casual understanding of the nonpoint source pollution sources within a large watershed. This work shows that quantification of nonpoint sources (including urban stormwater) and their influence on regulatory compliance should be at the forefront of watershed management efforts, not as a replacement for point source abatement, but as a factor worthy of equivalent scientific and economic attention. By comparing the value of dollars spent on point source abatement and nonpoint source abatement, as measured by improvements in receiving water quality or designated use attainability, this study shows that greater environmental value is possible by redirecting attention and dollars toward nonpoint source abatement. The work uses the Merrimack River Basin in New England as a case study, funded by the United States Army Corps of Engineers. The basin's 5,000 square mile size, interstate coverage, and mixed land use ranging from large tracts of forested areas to densely populated urban cities render it an ideal representation of dozens of large watersheds throughout the country. Watershed hydrology and mainstem hydraulics were characterized in detail using calibrated simulation models, which established a necessary and credible platform for evaluating dynamic water quality. Upon this platform, alternative management plans were formulated to blend point and nonpoint source abatement in various degrees. The outcome clearly illustrates how abatement costs and resulting effects on instream water quality for both point and nonpoint source controls must be clearly understood and managed together if the fundamental precepts and objectives of the Clean Water Act are to be addressed efficiently and cost-effectively. In fact, after a certain point, dollars spent on nonpoint source abatement in the subject watershed are shown to return more than four times the benefit of continued expenditures on point source abatement, which are currently mandated.