Addressing Nutrient Impairment in Illinois Watersheds: Challenges for Watershed-based Permitting

Excess nutrients from point sources (e.g., wastewater treatment plants and municipal separate storm sewer systems [MS4s]) and nonpoint sources (e.g., stormwater runoff, agricultural runoff) have impaired many water bodies around the United States. Nutrient-related impairments, including harmful algal blooms (HABs), threaten freshwater and marine ecosystems, recreation in surface waters, and public drinking water supplies. Since 2000, EPA has been working with states, US territories, and tribes to address nutrient-related impairments. For example, in 2018, the Illinois EPA, the Illinois Association of Wastewater Agencies, and environmental nongovernmental organizations negotiated the Nutrient Assessment Reduction Plan (NARP) special conditions for National Pollutant Discharge Elimination System (NPDES) permits for major publicly owned treatment works (POTWs). The NARP conditions allow POTWs to understand the relative contribution of sources and the benefits (or lack of benefits) of reducing point sources, nonpoint sources, and other measures (such as dam removals). Illinois EPA allows the POTWs to develop a stand-alone NARP or adopt a watershed-based approach by working with other POTWs and local stakeholders to address the phosphorus-related impairments. Joining a watershed group enhances stakeholder engagement and provides cost savings but may require a longer timeline to complete the NARP. While the NARP requirements allow POTWs to understand the system and determine an effluent phosphorus limit based on site-specific conditions, it can be a significant undertaking for smaller municipalities discharging to large rivers like the Mississippi and Illinois rivers. Furthermore, regional agencies might be better suited to lead the assessment of nutrientrelated impairments on larger rivers often impacted by nutrient loads from multiple states. Lessons learned from addressing nutrient impairment at a watershed-based level can be applied to other impaired waters around the United States.