Stormwater issues: The case for rain gardens | Mike Kaill
August 5, 2010 · Updated 10:27 AM
This document was written to speak to two concerns:
— Do rain gardens work? How do we know that an investment like this will pay off?
— What is the goal of a monitoring program? What are the reference points to show what the data means? Do we know that the data is appropriate? What do we do with the data?
I hope the following will answer both concerns. For the second concern, I will provide a case history to show the value of monitoring data, and how it can be applied to solve a real-world problem.
If not for monitoring, we would not know the reasons for the pollution of the aquarium and Friday Harbor. With additional monitoring, we will probably find problems at Eastsound and Fisherman’s Bay, and we can begin to deal with them. If we value the health of the near-shore marine communities, including rearing salmon, this is important.
Caveats— Rain gardens are a tool to control stormwater pollution such as that encountered at Spring Street Landing. They are effective for many surface water problems. However, each situation should be evaluated on its own merits.
— The program described here has goals related to health of the near-shore marine community. Other sampling programs may have a human health orientation, and thus measure other parameters, such as coliform bacteria, etc. So two “sampling programs” in the same area may be measuring different parameters, and show cause for concern on the basis of either or both of those orientations.
— How the project got started: In early spring of 2007, there was a major die-off of marine animals in the Spring Streert Aquarium. A water quality problem was suspected.
— How surfactants were identified as the problem: Sampling started with a field titration kit, then a photo spectrometer (both EPA-approved from LaMotte Chemical Co.). Of the parameters measured by the field kit, (including copper, phenolic, etc.) only surfactant (“detergent”) was significant. Of samples taken throughout Friday Harbor, only storm water from the Spring Street outfall had significant surfactants.
— Early progress working with Town of Friday Harbor and Department of Ecology: Major problems were discovered in the Spring Street drainage. Plumbing was misconnected; mop buckets were dumped into the street, washing with water containing strong detergents were poured into the gutters, and more. All discovered instances were corrected and water quality greatly improved.
— Current status: There is still surfactant coming into Friday Harbor from the storm drain. Many animals can now survive that could not in 2007. But currently, no animal can survive in contact with the silt and gravel on the aquarium floor.
After some citizen complaints regarding Spring Street, I checked the surfactant level of gutter water as well as a suspension of silt from the street surface. High surfactant levels were found, described below.
A proposal is on the table for a series of rain gardens on Spring Street that will, I contend, take out virtually all of the surfactant pollution. In addition, as other problems arise, as they have in other places, we will have suitable treatment capability already in place.
Characteristics of surfactants, and implications on managing surfactant-based pollution
— Effect of silt: Surfactant (surface-acting-agent) locks onto surfaces. After this exposure there is little or no “free” surfactant. Except where large plumes of suds are floating on the harbor, there is a direct positive relationship between silt and surfactant.
— Silt/surfactant settles: In the aquarium, the bottom is toxic (sampling suggests the same for Friday Harbor) a few days after cleaning. Bottom-living creatures do not survive.
— Removing silt will solve most of the surfactant pollution problem: Since rain gardens block particulate pollution, they will be effective for the Spring Street problems.
Monitoring and significance of the monitoring data
— Reference marker: A study of charity car washes and effects on local streams ran laboratory bio-toxicity tests on rainbow trout; 1.5 ppm surfactant was lethal (LC50 96 hours).
— Sampling: At the Spring Street outfall, as high as 3.0 ppm, commonly 1.0 ppm to 2.0 ppm during rain.
— Sampling: Aquarium silt, (diluted ~40X to allow the test to function), 1.0 to 4.0 ppm.
— Sampling: Silt scraped from the surface of Spring Street (also diluted), 4.0 ppm.
Relevance of this Friday Harbor program to other water applications.
— ”Stormwater pollution damages salmon habitat. It is the No. 1 water pollution problem in the urban areas of our state.”: The Department of Ecology produces an eight-page Environmental Education Guide that explains the problem, and describes Seattle’s Street Edge Alternatives Project. Rain gardens retro-fitted to a problem area removed pollutants and 98 percent of run-off.
— Surfactants at harmful levels have been found wherever sampled (with one exception) throughout San Juan County’s streams and lakes.
— EPA’s informational article Bioretention (Rain Gardens) states: “... rain gardens are commonly located in parking lot islands or within small pockets of residential land uses. Surface runoff is directed into shallow, landscaped depressions ... designed to incorporate many of the pollutant removal systems that operate in forested ecosystems. ... ideally suited to many ultra-urban areas ...” It cites pollutant removal of: copper, 43-97 percent; lead, 70-95 percent; zinc, 64-94 percent; phosphorus, 65-87 percent; ammonium, 92 percent.
Efficacy of rain gardens for treating surfactant and related (i.e. phenolics) pollution
How does a rain garden work?
— Rain gardens provide on-site treatment of polluted surface run-off (i.e., clean up the water at the source).
— Soil is placed in a pit with access to surface water (i.e. drainage from surrounding areas is directed to the pit).
— The soil is covered with compost to create a rich micro fauna.
— Special hardy and effective plants are installed.
— Connection with the stormwater drainage system is provided for overflow during surge, and for passage of treated water.
NB: In the case of Spring Street, the substrate is impermeable rock. The soil and compost will still do its job. Filtering of silt will still take place, but water soaking into permeable soil will not happen, since the substrate is rock. Processed storm water will return to the stormwater system, with storm surges dampened, and some water reduction from transpiration.
Examples of successful rain garden installations
— Seattle: A virtual tour is available to “see” the Seattle SEA (Street Edge Alternative) Project.
In this project, a corrected street with serious stormwater problems, 98 percent of stormwater is absorbed, and pollutants captured and metabolized.
— State Fairgrounds at Monroe: Throughout the fairgrounds, there are demonstration rain gardens, serving to process run-off from parking lots, roofs, streets. All are functioning well.
— Port Townsend: Many of the grassy strips next to sidewalks in Port Townsend are really rain gardens. A notch in the curbing allows water to flow off the street, where it sinks into the soil/compost/vegetation.
— Mike Kaill has a PhD in vertebrate zoology from Cornell University. He is a retired research supervisor for the Alaska Department of Fish and Game, and manages the Spring Street Aquarium at Spring Street Landing.