Green Streets in Portland, Oregon: Bio-Swales or Biohazards? (by Patty Hines)

kermit-284x300Everyone knows that green is friendly; green is good. Green says we care about the environment. With the exception of Kermit the Frog,[1] most people align with the general idea of being “green.” Is green measureable or has it become a cultural norm? If something is labeled as green, is it? When a city says “Green Streets” are healthy, are they? Green has such a positive connotation that it’s easy to gloss over larger problems that might be lurking under the surface. A strong environmental ethic is an inherent community value, especially in Portland – everyone cares about the environment and wants to be good stewards. When the city touts a Green Street Program as a healthy, sustainable solution worthy of policy changes and capital investments, should its citizens go along with their assessment? The city may be staking its future on what could turn out to be a long-term problem of environmental contamination.

Green is so omnipresent that it has become a sales tactic for everything from food to cars, houses to streets. The City of Portland defines Green Streets as: “Green Street facilities manage stormwater runoff as a resource rather than a waste. Green Streets are landscaped streetside [sic] planters or swales that capture stormwater runoff and allow it to soak into the ground as soil and vegetation filter pollutants. This replenishes groundwater supplies that feed fresh, cool water to rivers and streams. ( other words, bioswales constitute the “green” in the Green Streets program.

To understand the city’s use of the term green, the sunken bioswales must be evaluated and measured to see if they are actually performing their assumed green function. “Bioswale is the term generally given to any vegetated swale, ditch, or depression that coveys stormwater. Bioswales … are being used more and more to address pollutants in stormwater runoff. Many installations … have failed or have not been as successful as was hoped when their use was first contemplated. Most of the limited success or failures can be attributed to insufficient information being available or to bad or no expert input into the design, construction, vegetating, or maintenance or the bioswale …” (Jurries, Dennis. State of Oregon Department of Environmental Quality (January 2003.): Page 14. Print.). All bioswales are green, but not all bioswales are equally effective.

Long-term studies that assess pollutant build up/intensification in bioswale soils have not been conducted. The Oregon Department of Environmental Quality (DEQ) is the leading expert on Portland’s bioswales. DEQ studies have shown that “pollutant removal from vegetative uptake drops after the vegetation matures unless the dead vegetation is constantly removed to break the cycle of re-entrainment through the re-release of the pollutants from the decaying vegetation … an important concern is whether the heavy metals will accumulate to toxic levels in the bioswale underlain soil and whether they will migrate into and contaminate the ground-water. In removing heavy metals either through vegetation uptake or through soil filtration, a bioswale concentrates them. (Jurries, Dennis. State of Oregon Department of Environmental Quality (January 2003.): 9,16. Print.). Continuous maintenance of bioswales is a critical factor in their long-term effectiveness.

The oldest bioswales in Portland were constructed in the Oregon Museum of Science and Industry (OMSI) parking lots. These swales are now 20 years old and have become a test case for what works and what doesn’t. On a recent site visit, I spoke with Jerry B., the Facilities Manager at OMSI who oversees maintenance of the bioswales. Last year, the bioswales were replaced. Workers removed 4 feet of soil from the bioswales, and replaced it with new soil and plants. Jerry regretted that soil samples were not taken and tested for pollutants. He now realizes it was a lost opportunity to learn about the long-term effects of pollutants. (B. Jerry. Personal interview. 23 July 2015.)

Pollutants in bioswales have only been measured during the rainy season or by simulating high water conditions. Studies during the dry summer months and the effects of pollutant build up in a bioswale’s filtering capacity using minimal irrigation have not been conducted. Portland is dry in the summer with “90% of the annual rainfall occurring from October through May.” ( Even if bioswales are irrigated through the summer months, is that enough water to flush through the system to provide the crucial filtering effects? “Bioswales can only filter pollutants in stormwater when there is rain. Water must be present to flow through the system to provide the filtering benefits bioswales perform … slower velocities within a bioswale allow higher retention times of pollutants and settling of the larger particle sized pollutants. (Jurries, Dennis. State of Oregon Department of Environmental Quality (January 2003.): 6. Print.). Without rain, bioswales may not be green.

The City, DEQ, and prominent environmental scientists tout the ability of bioswales to filter millions of gallons of stormwater and clean pollutants before water can reenter the stormwater system and our rivers. However, they all recognize that design, siting, and maintenance play a crucial role in how effectively these systems function. But testing bioswales for being green all year is incomplete. Bioswales save the city money. The cost of sewer pipe infrastructure, costs to clean polluted rivers and streams, and stormwater treatment are all reduced. Portland’s 1,350 bioswales effectively filter pollutants and stop 125 million gallons of dirty, oily, polluted water from entering the stormwater system. (Walker, Mason. January 15, 2014. Web.) Bioswales protect the environment by removing pollutants through a natural filtration process.

As Kermit said, being green is not easy and is not a one-way street. Green can be used by environmentalists, or by anyone who has an agenda. Questioning long-term, assumed outcomes of “being green” and “doing good” is critical to our environment. It keeps us from becoming complacent about our assumptions. When public safety, welfare, health and important environmental issues are at stake, when policy is being made, and tax payer money is being spent, rigorous standards must be used to evaluate ideas, and tested to avoid accumulated pollutants becoming a bio-hazard.

Works Cited

Walker, Mason. “World cities looking to Portland for ‘Green Street’ ideas.” January 15, 2014. Web.

Jurries, Dennis. “Biofilters (Bioswales, Vegetative Buffers, & Constructed Wetlands) For Storm Water Discharge Pollution Removal”. DEQ Northwest Region Document.

State of Oregon Department of Environmental Quality (January 2003.): Print. Web. MWCOG Green Streets Workshop. 8 April, 2013.


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