Developing Numeric Nutrient Criteria: Influence of TMDLs

In 1998, the United States Environmental Protection Agency (USEPA) released the “National Strategy for Development of Regional Nutrient Criteria,” which called for states and authorized tribes to establish numeric criteria for nutrients (nitrogen and phosphorus) in their water quality standards. Currently, most states are in the process of developing numeric criteria. However, until such criteria is established, a wastewater discharge permit writer or person developing a total maximum daily load (TMDL) is responsible for assembling site-specific data and developing appropriate permit limits for nutrients on a site-by-site basis. Several recent nutrient and dissolved oxygen TMDLs have been used to set discharge permit limits on phosphorus and nitrogen. This presentation focuses on the Androscoggin River TMDL (Maine), TMDL for Nutrients in the Lower St. Johns River (LSJR) (Florida), and Draft TMDL and Managed Implementation Plan (MIP) for Spokane River and Long Lake (Washington) as concrete examples of setting site-specific numeric nutrient criteria. Comparison of the methods used in each of these TMDLs and MIP to determine nutrient criteria to existing and proposed state and federal methods is presented. In many cases, states will be looking to federal guidance, recent and existing TMDLs, and watershed management plans to guide the development state-wide numeric nutrient criteria. Active participation by water resource managers and other stakeholders in state level work groups addressing nutrient TMDLs and nutrient criteria is critical for development of water quality standards that are achievable and protective of the water body.