NARP: A Novel Watershed-Based Permitting Approach To Address Nutrient-Related Impairments

BACKGROUND
Efforts to reduce nutrient loading from point sources (such as wastewater treatment plants and municipal separate storm sewer systems or MS4s) and non-point sources (stormwater runoff, agriculture) are being used to address the Gulf of Mexico hypoxia, harmful algal blooms in Western Lake Erie, and numerous other nutrient-related impairments in local water bodies. These efforts are picking up pace across the U.S.. The US Environmental Protection Agency (EPA) has been working with states, U.S. territories, and tribes (hereinafter referred to as 'states') to adopt numeric nutrient criteria (NNC) for total phosphorus (TP) and total nitrogen (TN) since 2000. These NNC are then used to develop effluent limits for National Pollution Discharge Elimination System (NPDES) permits for point source discharges. EPA released new guidance to help states adopt NNC for lakes and reservoirs in 2021 (EPA, 2021). Few states, however, have been able to develop NNC for all lakes/reservoirs due to the complexity of the relationship between stressors (nutrients) and response (algae blooms, dissolved oxygen, pH, etc.). The development of NNC for streams has proved to be even more challenging. For example, Illinois's Nutrient Science Advisory Committee (NSAC) developed recommended NNC for streams and rivers (Illinois NSAC, 2021). However, these criteria have not been adopted by Illinois. Illinois EPA received numerous comments that the NSAC's recommendations were unsupportable, did not account for site-specific conditions, and were unnecessarily stringent. The complexity of nutrient impacts on receiving water requires adoption of innovative strategies for nutrient load reduction planning and implementation. The strategies involve watershed approaches which include load reductions from both point and non-point sources and other measures.
NUTRIENT ASSESSMENT REDUCTION PLAN
Illinois EPA had proposed a total phosphorus effluent standard of 1.0 milligrams per liter (mg/L) for major publicly owned treatment works (POTWs). Environmental non-governmental organizations (ENGOs) were concerned that an effluent limitation of 1 mg/L would not address phosphorus-related impairments or protect local waterways and instead proposed an effluent limitation of 0.1 mg/L. The Illinois Association of Wastewater Agencies (IAWA) was concerned that the ENGOs' proposed 0.1 mg/L would impose significant financial burdens on ratepayers and would not necessarily achieve measurable water quality benefits due to site-specific conditions. This disagreement created a substantial permitting backlog in Illinois. Illinois EPA, IAWA, and the ENGOs negotiated the Nutrient Assessment Reduction Plan (NARP) permit requirement in 2018 to overcome the permitting backlog, make progress towards reducing phosphorus loads at POTWs, and restoring local water bodies. The NARP requirements apply to POTWs discharging to downstream segments of water bodies which are impaired related to phosphorus loads or at risk of eutrophication. These major POTWs are required to develop a NARP to address phosphorus-related impairments in streams. The purpose of the NARP is to identify phosphorus input reductions and other measures needed to help ensure that numeric dissolved oxygen (DO) criteria and narrative criteria for offensive conditions (aquatic algae and plants) are met in the respective segments of the water body. The POTW can work with other stakeholders in the watershed to develop the NARP or develop a stand-alone NARP. This unique watershed-based approach has resulted in several POTWs forming watershed groups to develop the NARP. Currently, there are 90 major POTWs that are part of six major watershed groups. These watershed groups have embarked on multi-year monitoring and modeling efforts to identify phosphorus reductions and other measures needed to eliminate phosphorus-related impairments. In addition to the POTWs participating in the watershed groups, Illinois EPA has put the NARP requirements in 53 other major POTWs and the agency is currently in the process of determining the status of the NARP requirement for another 33 major POTWs. Figure 2 shows the status of NARP requirements for major POTWs in Illinois.
METHODOLOGY FOR DEVELOPING A NARP
Illinois EPA has provided flexibility to POTWs on developing a NARP since each watershed is different. Figure 2 shows a suggested NARP development process. A key requirement of the NARP is to establish site-specific water quality targets or adopt the NSAC's statewide recommendations. The NARP needs to identify point source reductions, non-point source reductions, and other measures to eliminate the impairments. Illinois EPA acknowledges that it is possible that the NARP may not recommend point source reductions. Finally, the NARP needs to include an implementation schedule.
CASE STUDIES ON NARP
This presentation will provide case study descriptions of different approaches to develop a NARP. The case studies will include examples of stand-alone NARPs including a large regional utility developing a PARP (Phosphorus Assessment Reduction Plan) for a network of receiving water bodies and a POTW located in headwaters of a watershed. The case studies will also include several different examples of watershed groups that are developing NARPs to address impairments throughout a watershed.
RELEVANCE
The complexity of nutrient impacts on receiving waters requires the use of watershed-based approaches to eliminate impairments. Illinois' novel strategy of allowing POTWs to develop watershed-based NARPs, including site-specific NNC, will be helpful to stakeholders in other states to address nutrient-related impairments in receiving waters.