Nutrient Assessment and Reduction Plan
The Lower Des Plaines Watershed Group is coordinating the Nutrient Assessment and Reduction Plan (NARP) on behalf of member wastewater treatment plants in the watershed. With the size and complexity of the Lower Des Plaines Watershed, the differences between the mainstem Des Plaines River, which is considered a nonwadeable stream, and the 17 tributaries, that are wadeable streams, the approach to the NARP is separated as such, recommendations for the Des Plaines River and recommendations for the tributary subwatersheds.
For the mainstem Des Plaines River, LDWG worked with Tetra Tech Consultants to develop a NARP strategy to develop the tools needed to identify an appropriate target or threshold for nutrients in large rivers and then determine appropriate wastewater treatment plant effluent limits to meet the threshold. Tetra Tech provided memos summarizing the outcomes of five tasks – 1. Review Existing Data, 2. Identify Goals to Meet for Large River NARP, 3. Evaluation of Need for Water Quality Modeling, 4. Evaluation of Data in Support of NARP Development Strategy, 5. Final Strategy with recommendations. This project provided the basis for recommendations set forth in the NARP document that were submitted to Illinois EPA on December 22, 2023.
For the tributary subwatersheds of the Lower Des Plaines, the LDWG worked closely with the Lower DuPage River Watershed Coalition (LDRWC) and the DuPage River Salt Creek Workgroup (DRSCW) to utilize the Identification Prioritization System (IPS) Tool that they developed using fish, macroinvertebrate, water chemistry and habitat data from over 600 wadeable stream sites across northeastern Illinois. The IPS tool has identified instream thresholds for many pollutants and stressors to aquatic life, including for total phosphorus which is the focus for the NARP. The LDWG used this threshold as the basis for the NARP for the wastewater treatment plants that discharge to a Lower Des Plaines tributary. The NARP for the Lower Des Plaines River Watershed Tributaries was submitted to Illinois EPA on December 31, 2024.