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Portable Bio Retention Planters at Port of Seattle

Case Study by David Hymel, Splash Boxx and Amy Waterman, Gealogica, LLC
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Portable Bio Retention Planters at Port of Seattle
Site and Stormwater
Bioretention Soils
Portable Biorentention Planters
King County/Port of Seattle
Paul Meyer, Port of Seattle
Doug Howie, Department of Ecology
Port of Seattle
Splash Boxx


The "Moving Green Infrastructure Forward" Project is a two-year stormwater monitoring project at Terminal 91, Port of Seattle.  Using the Splash Boxx, a bioretention planter box used for stormwater management, the project compares the pollutant removal efficiency two bioretention soil mix designs: one with conventional sand/compost and another with volcanic sand/compost. Splash Boxx is recognized by the Washington Department of Ecology as equivalent to a bioretention facility, so the project was easily approved by the Port of Seattle. It was also designed consistent with City of Seattle guidelines for bioretention planter boxes.

Permitting Process

Splash Boxx has been approved by the Department of Ecology as equivalent to bioretention systems as detailed in BMP T7.30, Bioretention Systems, 2012 Western Washington Stormwater Manual.  This project was a retrofit installation, so a permit was not specifically required for this project; In a new construction installation, the Splash Boxx would be part of the stormwater treatment system subject to stormwater permit requirements from City of Seattle DPD (or other jurisdiction having authority).

Code RequirementCompliance Path
BMP T7.30, Bioretention Systems, 2012 Western Washington Stormwater Manual (see Vol. V, Ch. 7, pg 3 - pg 873 of the document). Portable bioretention planters are approved by the Department of Ecology as equivalent to a bioretention system.  Their Decision Letter.
Seattle would have approved based upon WA Department of Ecology Ruling, but a permit was not required in this case.  Seattle provides a Permitting Tip Sheet on permitting of bioretention planters to guide such permitting.

Project Description

The Port of Seattle is hosting this two-year stormwater monitoring project at one of the older buildings at Terminal 91 in Seattle.  To start the Moving Green Infrastructure Forward (MGIF) project, Sustainable Seattle applied for and received a grant through the King Conservation District to test for and compare the removal efficiency of pollutant loads using two innovative soil mix designs, one with conventional sand/compost and another with volcanic sand/compost.  The project is being led by Gealogica, LLC through a contract with Sustainable Seattle.  Gealogica hypothesizes that the volcanic sand/compost mix reduces pollutants in water more effectively than do riverine sands mixed with organic matter.  There is also experimental evidence that volcanic sands facilitate better moisture retention in the soil.

"Splash Boxx" is a vertical-walled, 12' x 8' bioretention planter box, constructed of steel and painted with non-toxic paint, which accommodates a profile of aggregate (with underdrain), bioretention soil, vegetation, and live storage (ponding) to promote the detention and filtration of stormwater runoff.  As portable system, it has been determined by the WA Department of Ecology to be functionally equivalent to a bioretention facility, based on a submittal from the designer, which was created using information contained in a report "Splash Box Design Guidance:  Demonstrating Compliance with Ecology's Minimum Requirements" prepared by Herrera Lava Rock, photo by Allessandra ZuinEnvironmental Consultants.  The report contains methods for sizing Splash Boxx best management practices (BMPs) to fully comply with Ecology minimum requirements for water quality treatment (Minimum Requirement #6) and for evaluating the performance (i.e., partial or full compliance) of Splash Boxx BMPs relative to Ecology flow control (Minimum Requirement #7) and On-site Stormwater requirements (Minimum Requirement #5).

Riverine Sand, photo by Allessandra Zuin

Ongoing Research

Splash Boxx provides an opportunity for Gealogica to build upon laboratory tests in a soil column that showed volcanic sands reduce some pollutants in water more effectively than riverine sands mixed with organic matter.  The Port Project offers a larger, controlled field test of soil performance. The water going into each box from the roof runoff and the water that has moved through the box will be tested once a month during the rainy season for: phosphorus, nitrogen,bacteria, zinc, and copper. Soil moisture will also be measured with monitors in the soil, to show how the water moves through the two different soils and how much water is available to plants. Preliminary research by Gealogica has shown the volcanic sands to significantly surpass riverine sands in keeping water available to plants. This is important information for plant survival in metal boxes during the two month-long drought that is a Seattle summer.  The lava sands come from a local source. “Lava rocks are present all along the West Coast. Their pores can hold air and water and create favorable conditions for rich microbial life and strong root systems.,” says Alessandra Zuin of Gealogica LLC.  Zuin is also interested in testing the water quality performance of the bioretention planters, although they meet DOE water quality requirements through their volume detention.   Monitoring of pollutant levels and soil moisture will continue through the winter of 2015 and results will be available next spring. The public will get an opportunity to see the installation during the course of the research.

Cost / Benefit

Two basic Boxxes were installed for about $18,000 and would have to be compared to several factors in a new construction project in order to arrive at a realistic cost-benefit analysis: design and engineering, permitting, construction, GSI credits, long term maintenance, and life cycle costs. Some of the benefits of the Boxx technology: they are pre engineered with modeling done to predict the amount of impervious surfaces that can be treated; above ground installation so that no excavation is required or the permits associated with near shore and similar; small footprint and easily relocated or replaced; connectable in series for large area treatment; provides water quality and flow control through outflow orifice reductions; established as an Ecology approved BMP, but can also be a delivery system for TAPE-approved special media for water quality treatment.

Resources & Supporting Documentation:

"Splash Boxx Essentials" technical specifications and design diagrams.  December 2013, Eatonville, WA
Hymel, David.  Splash Boxx, LLC
Splash Box Design Guidance:  Demonstrating Compliance with Ecology's Minimum Requirements Lancaster, Alice, Herrera Environmental Consultants
Treating Stormwater Pollution Port of Seattle Video on MGIF
Port of Seattle video on YouTube
"How MGIF Came to Be," May 7, 2014 Zuin, Allessandra.  Blog post at
"Seattle Permits TIP #536: Green Stormwater Infrastructure (GSI) on Private Property:  Bioretention Planters." Seattle Department of Planning and Development:


Updates from ongoing research are expected in Spring 2015,

Project Contacts
Designer: David Hymel and Marilyn Jacobs, Owners Splash Boxx, LLC/RainDog Designs 235 389 2060 Owner: Amy Waterman and Alessandra Zuin , Project Creators Gealogica, LLC 206-719-0534 Owner: Hannah Kett, Neighborhood Programs Manager Sustainable Seattle 206-622-3522
Owner: Paul Meyer Port of Seattle 206-787-3127 Approving Offcial: Douglas Howie, Stormwater Engineer Washington Department of Ecology 360-407-6444 Other: Alice Lancaster, Senior Civil Engineer Herrera Environmental Consultants 206-787-8250
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