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A Clean Water Act Approved Strategy for Temperature Compliance: City of Boise Clean Water Act 316(a) Thermal Variance Demonstration Project, V2.
Kate Harris1, Thomas Dupuis2
1City of Boise; 2HDR; ,
Temperature effluent limits are challenging to meet and several alternative compliance strategies have been litigated. Section 316(a) of the Clean Water Act provides that the EPA (and delegated state agencies) may authorize alternate thermal conditions in NPDES permits where the effluent limitation is more stringent than necessary to assure the protection and propagation of a balanced, indigenous community (BIC) of shellfish, fish, and wildlife in and on the receiving waterbody. The City of Boise applied for a 316(a) thermal variance and completed a demonstration project. The initial demonstration strategy and results were presented at a previous PNCWA meeting. The strategy for the demonstration project was modified in coordination with Idaho DEQ as administration of the NPDES permitting program was transferred to the state. The results of the modified demonstration project will be presented.
The city conducted aType II Demonstration: a predictive demonstration based on literature, laboratory, and field studies conducted to evaluate that proposed alternate thermal effluent limitations (ATELs) will provide adequate protection and propagation of the BIC, as characterized by Representative Important Species (RIS). Near field (mixing zone) and far field analyses were performed separately but considered collectively. The potential for adverse effects was evaluated in terms of temperatures in the context of RIS specific biothermal attributes from the scientific literature, local expertise, and Idaho field data. Results demonstrated that the city’s ATEL’s would assure the protection and propagation of the RIS and maintenance of the BIC in the Lower Boise River. The city’s thermal load does not, and will not, cause lethal or sublethal effects that would affect the protection and propagation of the RIS populations; i.e., not interfering with the RIS’s completion of life history functions of reproduction, spawning, growth, and migration. The city’s IPDES permit is anticipated in fall 2021, therefore the presentation will also include a description of the permitting process and outline implementation planning.
11:15am - 12:00pm
Taking a Watershed-Based Approach to Developing and Optimizing a Thermal Compliance Strategy
Scott Mansell, John Dummer, Bob Baumgartner, Rajeev Kapur, Ken Williamson
Clean Water Services, United States of America;
The Tualatin River is a small river that receives wastewater discharges from over 600,000 residents and many large industries.The river and its tributaries contain salmonids which are impacted by water temperature increases caused by anthropogenic activities. Due to the relatively large discharges of wastewater to the relatively small river, the discharges can have a large effect on the temperature of the river that must be mitigated to protect aquatic life. Even more significant population and economic growth is projected in the watershed over the next 50 years. While Clean Water Services currently mitigates the thermal loads from its discharges through a Themal Management Plan that includes reuse, cogeneration, flow augmentation, and riparian shade projects, the projected growth of the population in the watershed and the expected effects of climate change require that an updated Temperature Compliance Strategy (TCS) be developed that will meet the temperature challenges into the future. However, there are a large number of potential actions that could be taken at the treatment plants and in the watershed to help decrease the temperature of the river and mitigate the effects of the thermal loads from the treatment plant discharges. Each of these actions has different strengths and weakness as well as variable temporal and spatial effectiveness which can often be affected by the other actions being taken. Optimizing which actions to take and when to take them is a difficult process. CWS has developed an updated Thermal Compliance Strategy that includes a suite of actions to be taken over time between 2025 and 2075. A tool was developed that can analyze a large array of potential actions in numerous combinations and predict their effectiveness, costs, benefits, and impacts. The tool relies on complex hydrodynamic and water quality models, data collection, economic analyses, and engineering analyses to compare and contrast the different actions over time, alone and in combination. Using the tool, CWS optimized the suite of actions and the timing of their implementation to maximize benefits to the river while minimizing cost and other impacts. This holistic method provides a much more effective TCS than effluent cooling alone.