In an effort to stem the flow of excess nitrogen into Puget Sound, Washington Department of Ecology has proposed a new type of permit for some 60 sewage-treatment plants operating throughout the region.

The flexible permit, called the Puget Sound Nutrient General Permit, aims to hold nitrogen releases close to or below their current levels at most of the treatment plants while offering plant operators options for how to meet those goals. It’s a temporary solution, because the long-term goal is to make significant cuts in the total amount of nitrogen going into Puget Sound.

Nitrogen, as we’ve discussed many times, is a major problem for Puget Sound. This so-called nutrient feeds the growth of plankton, which die and decay, consuming oxygen during the process. Low oxygen levels are a serious problem for fish and many other marine creatures, particularly in southern Hood Canal as well as several bays in South Puget Sound.

Sewage treatment plants have been found to be a significant source of nitrogen, thanks to findings from an elaborate computer simulation called the Salish Sea Model. The model, now housed at the Puget Sound Institute, describes the effects of nitrogen throughout Puget Sound based on the amount and location of nitrogen inputs, the size and shape of the waterway and currents created by tides and rivers. For a description of the problem, check out the overview in the Encyclopedia of Puget Sound, which also features a variety of focused articles addressing the issue.

The Salish Sea Model has revealed that nitrogen from sewage-treatment plants can create much more than localized water-quality problems. For example, large amounts of nitrogen from treatment plants in Seattle and Tacoma can be pushed by currents into South Puget Sound. There, the resulting low-oxygen levels create adverse effects in the inlets and shallow bays, which look like crooked fingers on a map.

One goal of the modeling effort is to calculate how much nitrogen can go into different parts of Puget Sound without triggering water-quality violations. Once these amounts of nitrogen are determined, actual limits can be calculated and theoretically imposed on the effluent coming out of each treatment plant. But those findings are not expected before 2023. See Puget Sound Nutrient Reduction Project.

The nutrient general permit for sewage-treatment plants would be separate from existing wastewater permits for each plant. While perhaps not as enforceable as strict numerical limits, the proposed “action levels” for each treatment plant in the general permit could be a first step in turning things around, according to members of an advisory committee helping to draft the new permit.

“We needed to get some kind of backstop,” said Mindy Roberts of Washington Environmental Council and a member of the advisory committee. “This permit has a kind of reasonable bound to it. Having said that, we are 20 years into this kind of assessment.”

It is obvious that something must be done, she said, because the Puget Sound ecosystem is already suffering from excess nitrogen. See the advisory committee’s 12-page summary of discussions (PDF 372 kb).

What to do about nitrogen pollution seems to have a lot of people tied in knots. Operators of many sewage-treatment plants are saying they need to see more scientific data before they commit to making upgrades to their plants. Total costs could amount to billions of dollars for the region.

In December, the city of Tacoma and four other sewer utilities filed a lawsuit in Thurston County Superior Court. They allege that the Department of Ecology effectively changed the state’s water-quality standards for dissolved oxygen through the use of computer modeling but without going through required rule-making procedures. The case is a first volley in what could be ongoing legal challenges to proposed controls on nitrogen. Other parties to the case are Birch Bay Water and Sewer District, Kitsap County, Southwest Suburban Sewer District, and Alderwood Water and Wastewater District.

Meanwhile, the environmental group Northwest Environmental Advocates is continuing to pursue its lawsuit, now on appeal. The lawsuit is designed to force the Department of Ecology to require upgrades to sewage-treatment plants that don’t already reduce nitrogen through tertiary treatment. Under a 1945 state law, state regulators must demand “the use of all known, available and reasonable (technology) … to prevent and control the pollution of the waters of the state of Washington.” This is the so-called AKART law.

Thurston County Superior Court rejected the arguments of NWEA. The ruling supported Ecology’s argument that a broad requirement for expensive treatment technology would not be “reasonable” under the law. Check out the appeal briefs by NWEA (PDF 1.1 mb) and by Ecology (PDF 2.3 mb). See also the first Water Ways post I wrote on this issue, Jan. 31, 2019.

As proposed in a “conceptual” draft (PDF 708 kb), the nutrient general permit would apply to the majority of sewage-treatment plants in the Puget Sound region and would go into effect for all at the same time. Ecology proposes to exclude 26 treatment plants that discharge into rivers, nine privately owned plants, all facilities on federal and tribal lands, and industrial operations. These various exclusions could be covered with nitrogen controls through other types of permitting.

The general permit establishes two action levels. The baseline level is roughly equivalent to the treatment plant’s current annual release of nitrogen. A second level, 5 percent higher than the baseline, allows for additional growth for plants where Ecology has already approved higher design capacities.

The draft permit calls for an “optimization framework,” in which treatment plant operators must implement low-cost measures to reduce nitrogen and then measure the outcomes. Operators would be allowed to customize their actions to suit their own plants, but they would need to share their successes and failures with Ecology and other operators. These low-cost actions, called Tier 1, could include adjustments to flow rates, aeration patterns and treatment cycles.

Tier-2 actions would be triggered when the baseline level of nitrogen is exceeded at the end of an operational year. Actions could include the purchase of new equipment, changes in piping configurations and the addition of one or more chemicals to reduce nitrogen.

Tier-3 actions would be triggered when a facility exceeds the higher (+5%) action level. These actions, which would be approved by Ecology in advance, could include more extensive operational changes, treatment process upgrades, and planning for advanced treatment such that design and construction would start as soon as formal effluent limits are established.

“We’re not proposing to require major infrastructure investments in the first five-year permit,” said Ecology spokeswoman Colleen Keltz in a blog post. “Depending on the current capabilities of each (treatment plant) and their community’s plans for growth and development, they will have a reasonable amount of time to plan appropriate upgrades or other improvements while remaining in compliance with their permits.”

Some 14 plants already remove nitrogen to some degree, with their nitrogen concentrations averaging below 10 milligrams per liter. Under the proposed permit, those 14 would not be subject to Tier 1 or Tier 2 actions but would still be expected to undergo low-cost optimization.

The general permit also calls for expanded monitoring of nitrogen and other constituents of sewage, as well as extensive planning and scientific studies at both facility and regional levels. The ultimate goal, according to Ecology, is to figure out the most effective ways to reduce nitrogen to improve water quality in Puget Sound and meet state standards for dissolved oxygen.

The comment period for the informal draft permit runs until March 15. (See comment form.) After that, the draft will be revised and resubmitted as a formal document with public hearings, written comments and official responses.

Meanwhile, the advisory committee continues to discuss the permit and related issues. For documents and meeting schedules, go to the committee’s EZ View page.

As discussions continue, Gov. Jay Inslee has submitted a $9-million funding request to implement the general permit as part of his overall budget to the Legislature. The money would be used to help the affected treatment plants develop plans and finance small nitrogen-reduction projects.

Related efforts:

• Puget Sound Nutrient Reduction Project, addressing all sources of excess nitrogen.
• Marine Water Quality Implementation Strategy, influencing the Puget Sound Action Agenda under the Puget Sound Partnership
• Salish Sea Modeling Center, the Puget Sound Institute, and Salish Sea Model Updates and Bounding Scenarios, January 2019 (PDF 12.4 mb)