Developing An Alternative To A Point Source Based Approach To Regulating Nutrients In Puget Sound

The Puget Sound (Sound) region has faced increasing pressures from growth and development. Increases in nitrogen in the Sound can result in increased phytoplankton and algae growth. This growth is also influenced by other variables like temperature and light and can result in drops in dissolved oxygen (DO) in spring to fall when surface waters heat up and thermal stratification of water isolates bottom water from atmospheric replenishment of oxygen. The Salish Sea Model (SSM) was developed by Pacific Northwest National Labs to simulate these complex interactions. The State of Washington Department of Ecology (Ecology) has a marine oxygen standard limiting human caused depletion to more than 0.2 mg/L. The threshold of hypoxia is generally set at 2.0 mg/L DO. Target DO standards are much higher with 4.0 mg/L fair, 5.0 mg/L good, 6.0 mg/L excellent, and 7.0 mg/L extraordinary. The SSM indicates that low DO is most concerning in shallow bays with poor circulation, which is consistent with monitoring data. This effect is most pronounced in the late summer and early fall because of thermal and salinity stratification. While the depressed DO levels are largely due to natural factors, it is important to consider that anthropogenic influences. Like other estuarine 'dead zones' the Puget Sound exemplifies a fjord issue that is increasingly common. Sills prevent circulation of deep water with oxygen-rich tidal exchanges. Distal zones of the fjord do not mix with pelagic waters. Water age below the thermo/halocline, or in stagnant shallow areas, allows for depletion of DO without because there is no replenishment from mixing with oxygen-rich waters. Hence the formation of anoxia, hypoxia, or depletion of DO below key habitat suitability thresholds.
A fundamental problem within these systems is that DO deficits tend to persist despite nutrient reductions because of positive feedbacks . This is well documented in other areas such as the Chesapeake Bay and the Baltic Sea. There is no evidence that the Puget Sound has a different DO dynamic. Thus, the findings of the SSM model need to be placed within this larger context. Ecology issued a report that reviewed the results of the SSM in January 2019. Using the SSM, Ecology mapped the modeled duration and extent of the dissolved oxygen depletion and examined the impacts from the wastewater treatment plants. While Ecology was pursuing the modeling and technical work to characterize DO impairment, Northwest Environment Advocates (NWEA) filed a petition with Ecology in November of 2018 to accelerate regulation of point source discharges in Thurston County Superior Court. The petition was denied. In response to the petition and court case, Ecology moved forward with the nutrient program. From 2020 to 2021, Ecology conducted a nutrient working group to develop a general permit to regulate municipal wastewater discharges into the Sound. The working group could not reach consensus on the best pathway forward to address this issue. Nevertheless, Ecology developed a draft permit, issued in September 2021, that focuses on municipal plants and requires optimization studies in the near term and plans to reduce municipal effluent discharges to 8 mg/L or 3 mg/L total nitrogen in the long term. The program will cost more than $10 billion to implement in capital alone with a projected benefit of 50% improvement in modeled days of DO depletion.
The following will present the work to date in developing science to define the impairment of the Sound and the current draft of the Permit. More importantly, it will propose complimentary pathways that achieve water quality improvements in a shorter timeframe, include realistic timeframes and represents responsible stewardship of the investment from the Utilities' rate payers.
The Puget Sound dischargers have maintained the Utility Caucus group that was formed as part of Ecology's nutrient work group. This group is tasked with advocating for their mutual interests and interested in developing alternative approaches to improve water quality in the Sound. About 5 million people in Puget Sound are served by the municipalities that make up the Caucus. They expect responsible stewardship and protection based on well-developed science that produces measurable benefits. These utility stakeholders have considered development of alternative approaches to addressing water quality concerns in the Sound as alternatives to the current point source based approach.
Improved data collection/modeling of the bays. The SSM is a large-scale model that is not accurate enough to detect changes in DO at the 0.2 mg/L level. Smaller scale models and/or data gathering to review critical bays and localized impacts may improve model accuracy at the bay level and allow testing of alternative management approaches to address concerns related to nitrogen and DO. For example, non-point source controls, interventions like oxygenation, or MS4 management actions could be weighted against the proposed point source actions for each bay.
Integrated Planning: Ecology's General Permit approach focuses solely on point source municipal wastewater outfalls and as a result, misses many of the larger water quality issues and influences in Sound. In 2019, integrated planning was codified in the Clean Water Act as a regulatory approach supported by EPA. Integrated plans offer the opportunity to view a watershed from a wider view (outside of a single outfall) and develop an action plan that improves water quality overall. The plan can include wastewater, stormwater, green infrastructure, non-point source control, source water protection, asset management and reuse. The integrated approach is a voluntary approach that lends itself to adaptive approaches that include feedback water quality loops.
Adaptive Management: Adaptive management is an iterative process to work towards water quality improvements. It begins when initial changes are made in a receiving water (load reduction, habitat modification, other BMPs) and then the environmental response is evaluated to guide decision making about the next step. In essence, adaptive management is learning by doing and using improved data and information over time to improve decision making with the intent of achieving a goal within a specified timeframe. This approach makes sense in the Sound where there are many stakeholders that are interested in improving the Sound, have available resources and staff and are willing to engage in a collaborative process that can make positive change.
Oxygenation: Supplying pure oxygen to the water directly addresses the water quality impairment and the associated environmental degradation. Oxygen is distributed in the water column in strategic locations using fine-bubble diffusers designed to raise dissolved oxygen levels without disturbing thermal or salinity stratification. The oxygen rich water then circulates throughout the impaired water body via natural currents. The stakeholders will work toward development of a comprehensive menu of both natural and engineering options for managing nutrients. These results will assist with providing a roadmap for the future.