Hood Canal report finds septic systems a problem

An investigation into the causes of low-oxygen conditions in Hood Canal is coming to a close with this week’s release of a final report by the Hood Canal Dissolved Oxygen Program.

The pattern of fall oxygen levels show severely depleted waters from Twanoh State Park to Hoodsport with much better conditions to the north. (Click to enlarge.)
Map courtesy of Hood Canal Dissolved Oxygen Program

I described the report in general terms in a story published in yesterday’s Kitsap Sun. You may read the report for yourself at the HCDOP website.

What the five-year study learned about Hood Canal seems quite impressive. The full report contains extensive discussions about what causes oxygen to decline, the triggering mechanism for fish kills, the inputs of nitrogen that drive the system and much more.

One of the conclusions, which I focused on in my latest story, is that nitrogen from septic systems in Southern Hood Canal appears to be a pivotal factor in fish kills. When the natural decline in oxygen approaches a dangerous range, the added nitrogen from septic systems can tip the balance, causing excessive stress and sometimes death for marine creatures.

According to the report, one cannot easily separate the natural factors from the human factors that create problems in Hood Canal. The long, narrow fjord is flushed slowly compared to most marine systems. Organic carbon and nitrogen, which are the major players in oxygen decline, naturally come in from streams, groundwater and the Pacific Ocean. Numerous human sources, such as septic systems and fertilizers, must be taken into account.


Early on, researchers understood that nitrogen was the driving factor in Hood Canal. Whenever nitrogen was introduced with sunlight, it triggered the growth of algae. As in lakes where low oxygen is a problem, algae sink to the bottom, where they are consumed by bacteria, using up available oxygen in the process.

To get a handle on the nitrogen and other factors, researchers and volunteers involved in the study monitored 43 streams and tributaries, studied groundwater flows and analyzed the workings of septic systems. Specialized equipment was used to measure current flows. A series of buoys monitored conditions in Hood Canal 24 hours a day, backed up by data collected by volunteers working from boats.

To describe the system and calculate plankton production, researchers had to understand the exchange of seawater with the ocean and account for seawater density, oxygen and nutrient content of the water, freshwater inputs from streams and groundwater, sunlight, winds, tides, and the shape and size of Hood Canal.

Quoting from the report’s summary:

“Dissolved oxygen in the mainstem of Hood Canal varies significantly from year to year,. In 2009, average DO concentration … exhibited some of the highest levels on record, with the January 2009 data point being the highest January concentration on record. However, the subsequent January (2010) showed the lowest average concentration on record, more than 2 milligrams per liter less than the previous year.”

Low-oxygen levels persisted through the spring and summer of last year, leading up to fish kills in September. Check out Kitsap Sun, Sept. 20, 2010, and Sept. 28, 2010. This spring, things are back to a more normal condition.

The five-year study revealed that oxygen in Hood Canal is not evenly distributed but exists in “patches” that can expand and contract and move about with the tides and currents.

A powerful but subtle influence on the system is the dense seawater that pushes in from the Pacific Ocean in the late summer and fall. It comes in at the bottom of Hood Canal and is generally higher in oxygen content than the depleted waters it displaces. The effect is to push low-oxygen waters toward the surface and help establish conditions for a fish kill.

Fish kills typically occur near Potlatch and Hoodsport when winds out of the south push the surface waters away, bringing low-oxygen waters to the surface and leaving fish no place to escape.

Researchers also have discovered a “jet” of low-oxygen water that shoots north around the Great Bent in the fall. Aimed at Hoodsport and areas north, this low-oxygen water can contribute to already stressful conditions for fish and other sealife.

Meanwhile, concerns are growing about “chronic” low-oxygen conditions that affect bottom-dwelling organisms unable to escape the deadly waters. Some of the worst conditions have been seen between Twanoh State Park and Belfair, where oxygen levels have approached zero at times, leaving little more than a mat of fluffy white bacteria.

Since nitrogen is the driving factor in reducing the oxygen levels, the researchers identified the sources of nitrogen and calculated their influence. They concentrated their efforts on the summer months, because nitrogen inputs in the fall and winter had less effect when sunlight is more limited. It turns out that septic systems produce more nitrogen at that time than all other human sources, according to the study.

Using seven methods of calculation, the researchers concluded that contribution from septic systems may be as low as 12 percent of all the nitrogen in Lower Hood Canal or as high as 30 percent, with an average of about 20 percent.

The scientists used two methods to estimate the decline of oxygen caused by septic systems. One method estimated that septic systems cause oxygen to decline by 0.24 to 0.6 mg/L. The other method estimated a range between 0.6 and 1.2 mg/L. That compares to a typical annual drawdown of about 2 mg/L total.

From the report:

“The confidence in any conclusions drawn from the results presented above rests in the use of multiple methods that all give a fairly similar answer. The range of septic to total nitrogen loading is 13 to 30 percent, and this would have a directly proportional percentage impact on reducing ambient oxygen in Lower Hood Canal during summer.

“We note that all estimates and values presented here represent current-day values based on the study period (2005-2009). The level of future development to Mason, Kitsap and Jefferson counties will affect the loads and conclusions.”

My stories about oxygen levels and the relative contribution to the problem by septic systems always seem to generate confusion and skepticism among some people.

Reading the comments at the bottom of the story, it appears that many people have their own simplistic solutions about saving Hood Canal, based on personal experience. If such folks have read the reports or attended public meetings about the problem, it appears they did not learn much.

It is a complex subject, and I’m not sure my stories are answering the questions that people have. If you would like me to track down specific answers, please leave your questions in the comments section at the bottom of this page. I will find the right scientists to provide the answers.

One thing I should point out is that there remains a great deal of uncertainty about how much nitrogen an individual septic system can release to Hood Canal. While some people focus on “failing” septic systems, I’m told that the issue is bigger than that. While the design of a septic system could make a big difference, traditional systems are not designed to remove nitrogen.

What can remove nitrogen, however, is vegetation. Unfortunately, studies so far have not determined how much nitrogen flowing out of a drainfield gets captured by soils and plants before reaching Hood Canal.

Certainly, undersized drainfields at the edge of the canal remain the greatest concern among those who have studied the problem. But it would be helpful for all of us living in the Hood Canal watershed to understand how much we may be personally contributing to the problem.

Hood Canal Coordinating Council is taking the issue to the next level with an action plan. I expect that more public discussions are around the corner.

One thought on “Hood Canal report finds septic systems a problem

  1. Now that the data clearly point to septic systems as the culprit of low DO, it will be important to educate residents about small, manageable steps they can take to help reduce the amount of nitrogen finding its way into Hood Canal. In a recent focus group we learned that automotive businesses do not believe that small amounts of runoff contribute to pollution. That attitude is an obstacle in getting some businesses to make small changes. To address the Hood Canal water quality issue successfully, there should be less focus on the costly replacement of septic systems and more attention to manageable solutions, such as proper maintenance.

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