The Economic and Environmental Significance of Nonpoint Source Abatement in Large Watersheds

摘要

Throughout the United States, nonpoint source pollution from stormwater runoff,failing septic tanks and other diverse sources is a significant, often dominant, cause ofnoncompliance with water quality standards in large watersheds. Even with thisknowledge, considerable economic resources are spent on reduction of conventionalpoint source pollution (e.g., wastewater discharges and combined sewer overflows)with little more than a casual understanding of the nonpoint source pollution sourceswithin a large watershed, or of the potential value of dollars spent, as measured byimprovements in receiving water quality or designated use attainability. This workshows that quantification of nonpoint sources and their influence on regulatorycompliance should be at the forefront of watershed management efforts, not as areplacement for point source abatement, but as a factor worthy of equivalentscientific and economic attention. With this guiding principle, this work illustrateshow abatement costs and resulting environmental improvements for both point andnonpoint source controls must be clearly understood and managed together if thefundamental precepts and objectives of the Clean Water Act are to be addresseddecisively.In 2002, the U.S. Army Corps of Engineers initiated the Merrimack River WatershedAssessment Study to address water quality impairments on the Merrimack River. As aresult of combined sewer overflows (CSOs) and other point and nonpoint sources,many reaches of the river have been placed on the New Hampshire andMassachusetts 303(d) lists for violations of bacteria water quality standards. The goalof the study was to quantify the relative impacts of point sources and nonpointsources on water quality, and to compare the economic and environmental value ofalternative management strategies. The study blended comprehensive fieldmonitoring with detailed simulation modeling that compared alternative managementstrategies for watershed-wide pollution abatement. The management strategy whichresulted in the greatest value of abatement dollars was a combination of modesttreatment upgrades and partial combined sewer separation with modest nonpointsource reduction throughout the watershed. This balanced approach showed morevalue than scenarios focusing only on long-term CSO control plans and full combinedsewer separation, emphasizing the need for a more comprehensive approach tomanaging sources of pollution as well as the need for more attention on the economicvalue of nonpoint source abatement alternatives for large watersheds.