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Collection: Stormwater Solutions: Curbing Toxic Runoff

Checklist for a Healthy Rain Garden

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Maintenance guide
Maintenance guide
Cover of “Field Guild: Maintaining Rain Gardens, Swales and Stormwater Planters”

Rain garden maintenance has emerged as one of the big hurdles to expanding the use of green stormwater solutions. You build it. The rain comes. Then what?

In some ways, the water-absorbing gardens are not much different than other landscaping features. They need weeding, some summer irrigation, and basic pruning. But they also require more nuanced care.

The standard “mow, blow, and go” strategy that sends some commercial landscapers whacking plants and lawns with mowers or hedge trimmers, then revving up the leaf blower to blast the ground clean just won’t cut it. Rain gardens need lusher plantings to catch rain in their leaves and branches and healthy roots to help water soak into the ground. The green infrastructure often features a thicker cover of water-trapping mulch. Good rain garden maintenance means saying ‘no’ to Edward Scissorhands-inspired pruning and bare soil. It requires attention to how the water flows into—and sometimes out of—the garden, and how quickly the water seeps into the ground.

To help solve these maintenance challenges, some smart stormwater folks in Oregon have released “Field Guide: Maintaining Rain Gardens, Swales and Stormwater Planters (2013),” a handy how-to for keeping rain gardens functional as well as beautiful. The guide opens with specific recommendations on what tools you’ll need for rain garden maintenance, gives cautionary notes—and scary photos!—of some of the injury-inducing weeds lurking out there, and provides explicit instructions on how to maintain the gardens’ stormwater treating capacity.

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Rain Gardens, the Glamour Issue

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Flowers
Flowers
Plants suitable for rain gardens, “Rain Garden Handbook for Western Washington”

Foodies get to drool over countless images online and in print of perfectly posed burgers, mouth-watering slices of pies, and other culinary treats. Now rain garden junkies and the bioretention-curious can indulge in inspiring photos and illustrations of green stormwater solutions in the newly released “Rain Garden Handbook for Western Washington: A Guide for Design, Installation, and Maintenance.”

The handbook is a step-by-step guide on how to plan, build, plant, and maintain a smaller-scale rain garden. It explains how even a modest-sized rain garden will capture and treat significant amounts of polluted runoff that flow off rooftops and driveways.

Suitable to an experienced landscaper or even a novice, the guide provides straightforward instructions in layman’s terms and lots of images to illustrate what’s being discussed. The handbook also answers questions and fears about rain gardens, including the persistent worry about standing water and mosquitoes (well-designed rain gardens drain in one to three days, the guide explains, and mosquitoes go from egg to adult in four or more days).

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The Skinny on Washington’s New Stormwater Bible

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stormwater pollution

In addition to new municipal stormwater permits that will soon go into effect in Washington State (which we’ve written about here and here), the state has also issued a new version of Western Washington’s stormwater management bible. In this post, we’ll detail some of the most important changes.

The 2012 Stormwater Management Manual for Western Washington (“SWMMWW” or “manual”) is a bedrock document that guides how nearly everyone involved in regional stormwater management does his or her job. It outlines how to control the quantity and quality of stormwater pollution that typically increases as new development replaces natural landscapes with roads, driveways, roofs, and other impenetrable surfaces that no longer soak up rain. Once it hits the ground, that rain picks up pollutants—from oil and grease to toxic metals to nutrients in animal waste and fertilizers—and washes them into state waters.

The SWMMWW manual is an incredibly important resource for managing and minimizing that pollution, which is one of the largest threats to Puget Sound. Local cities and towns use it to set stormwater requirements for development projects. Land developers and engineers use it to build stormwater facilities and reduce pollution coming off construction sites. Businesses use it to help design their stormwater pollution prevention plans. The regional manual applies to all types of land development—including residential, commercial, industrial, and roads—although other manuals provide additional guidance for specific circumstances.

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It’s the Soil, Stupid

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Rain garden
rain garden
Seattle rain garden, Lisa Stiffler.

The recent dust up over troublesome amounts of pollutants leaching out of a Redmond rain garden got me thinking about soil. That’s because the soil in a rain garden has to meet a lot of needs, some of which are in conflict with each other. It needs to soak up potentially large volumes of stormwater quickly, filter and capture pollutants, keep plants alive through sodden winters as well as summer droughts, and avoid leaching nutrients. Plus, the ingredients for the soil need to be locally, readily, and affordably available.

We’re asking a lot of this dirt.

In Washington, the state’s official rain garden guide and its “2012 LID Technical Guidance Manual for Puget Sound” include specific recommendations for the “bioretention soil mix”—that’s the layer of soil that lines the rain garden. Washington calls for a mix that is 60 to 65 percent sand or soil excavated from the site, and 35 to 40 percent compost. The sand component helps with the drainage and filtering, while the compost provides nutrients needed by plants and trees and can help capture pollutants.

But the nutrients in the compost don’t always stay put, as Redmond and others have demonstrated. When these nutrients pollute rivers and lakes they stoke blooms of nasty algae that muck up the water, then die and suck oxygen out of the waterbodies as the tiny plants rot. If too much nitrate leaks from rain gardens into drinking water, the tainted water can cause “blue baby syndrome” in which infants are deprived of oxygen, turning their lips blue.

So I put the question: “Why so much compost in bioretention soil mixes?” to green stormwater engineers that included Curtis Hinman, the guy in charge of Washington State University’s Puyallup Green Stormwater Infrastructure Program.

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Redmond’s Rain Garden Challenge

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Rain garden
Rain garden
Rain garden, Lisa Stiffler.

In the stormwater world, if a rain garden is releasing more pollution into the environment than it’s capturing, word gets around.

So when the city of Redmond crunched its first flush of data from a new roadside rain garden and discovered the water coming out of it was tainted with alarming levels of phosphorus, nitrates, and copper, the stormwater community took notice. Washington State regulators went on the record to say that they would be studying the data and possibly revising their rain garden recommendations. Proponents of the technology fear that the results will be overblown and exploited by skeptics of so-called low-impact development solutions.

But even city officials in Redmond caution that they’re far from giving up on rain gardens.

“It definitely has not lost its merit in my mind,” said Andy Rheaume, Redmond’s senior watershed planner.

Indeed, there’s a decade worth of data showing that rain gardens and related “natural” technologies are effective at treating polluted stormwater runoff. They can do a terrific job soaking up the renegade rain water, diverting it from house basements and preventing it from scouring streams or causing overflows of sewage. And numerous studies demonstrate that rain gardens will filter out and capture a toxic mix of heavy metals, petroleum pollutants, particles and nutrients. In fact, the Redmond rain garden did treat some of the pollution gushing into it.

But rain gardens aren’t fool proof. Depending on the design of the system and the soil mix that’s used, a rain garden’s ability to remove pollutants can vary—and vary dramatically.

So what is a city or county stormwater engineer to do? Don’t panic.

“We’ve been promoting the message ‘Don’t throw away the baby with the bathwater,’ ” Rheaume said. “We’re pretty sure that (low-impact development) is here to stay.”

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The Skinny on WA’s New Stormwater Permits (#2)

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Tox-Ick poster

We recently updated you on the new stormwater permits that will soon dictate how Washington State’s most populated areas manage polluted runoff that damages water quality and can flood low-lying property. Here we’ll tackle the new Phase II Municipal Stormwater Permit, which covers the next most populated areas and affects nearly 100 cities around the state.

These cities are legally obligated to try to control water that runs off pavements, roofs and streets in built areas every time it rains. Along the way, that water picks up toxic metals, motor oil, lawn fertilizers, animal droppings, and a cocktail of other pollutants before it washes into local waterways and oceans. The rules governing how cities and other jurisdictions manage this dirty runoff are contained in municipal permits, which were recently updated in Washington State and are about to kick in throughout much of the state.

There are actually two Phase II Municipal Stormwater Permits: one for western Washington and one for eastern Washington. That’s because each side of the state has very different climate conditions, soils, and geology, which are important considerations when thinking about how water moves around.

The Western Washington Phase II Municipal Stormwater Permit, which goes into effect on August 1, 2013, covers 80 medium and small cities and the urban portion of four counties. The Eastern Washington Phase II Municipal Stormwater Permit, which takes effect one year later, covers 18 cities and urban areas in six counties. Both will remain in effect for five years.

As you may imagine, there are significant differences between two region’s Phase II permits. In particular, the new low-impact development (LID) regulations are very different. So let’s take a look at each permit in turn.

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The Skinny on WA’s New Stormwater Permits (#1)

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In a little less than three months, Washington State’s largest cities and counties must start following new rules on how to manage dirty runoff that washes toxic metals, oil and grease, fertilizers, and other pollution into our streams, lakes, and ocean. Polluted stormwater is one of the largest threats to Puget Sound, so it’s worth taking some time to demystify just what will be required.

The updated rules of the road are contained in the state’s new Municipal Stormwater Permits, which are administered by the Washington Department of Ecology. The permits cover everything from reducing construction pollution to educating citizens on good stormwater practices as they wash cars to adopting green low-impact development techniques like permeable pavement and green roofs.

In this blogpost, we’ll focus on updates to the Phase I permits, which go into effect on August 1, 2013 and will remain in force for five years. The permits cover discharges from large and medium municipal separate storm sewer systems, commonly known as “MS4s,” found in the most populated areas of the state. (We’ll get into the details of the Phase II permits for smaller municipalities in a subsequent post).

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Seattle’s Green Stormwater Goals

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Seattle roadside rain garden

Recently, the city of Seattle announced a goal to dramatically increase the amount of water treated by rain gardens, green roofs, green streets, permeable pavement and other alternatives that seek to treat stormwater more naturally instead of carry it away in pipes.

Right now, as the graphic below shows, the city estimates it’s managing somewhere north of 100 million gallons of polluted runoff with “green stormwater infrastructure,” which helps control flash flooding and helps filter out pollution that might otherwise wind up in Puget Sound. Mayor Mike McGinn and some city council members want to ramp that number up to 700 million gallons by 2025.

The city has a road map to get about half of the way there by incorporating green stormwater techniques into streets and other public spaces, providing utility rebates for homeowners who handle rain from their roofs and gutters with cisterns or gardens, updating codes and partnering with developers, or helping neighborhoods incorporate stormwater swales into traffic calming projects or other amenities. But the bulk of the gains will have to come from projects and approaches that city staff will spend a little more than a year identifying.

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Are Rain Gardens Mini Toxic Cleanup Sites?

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If you’re concerned about water pollution, you’ve likely heard this message: The water that gushes off our roofs, driveways, streets, and landscaped yards is to blame for the bulk of the pollution that dirties Puget Sound and other Northwest waterbodies. You probably also know about the most popular stormwater solutions, including rain gardens and other green infrastructure that soak up the filthy water, cleaning it before it reaches sensitive waterways that are home to salmon, frogs, orcas, and other wildlife.

But those two ideas taken together are making some people anxious. If stormwater is the source of such devastating amounts of petroleum and heavy metals, won’t the rain garden in my front yard become a mini toxic waste site that could harm children and pets?

It Takes a Cluster to Build a Rain Garden

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Rain garden in Ballard

As he stands admiring his front-yard rain garden on a recent fall morning, Steve Severin is darn near giddy.

“Isn’t it great?” he asks. “My yard before was all grass. I’m very, very happy.”

A copper “rain chain” that looks like a series of tulip blossoms strung together hangs down from a corner of his roof. At the bottom of the chain is a hammered copper bowl nestled among river rock ready to catch the rain that drips down. The rocks lead downhill to a rain garden planted with small grasses and shrubs. On the other side of the walkway to his front porch is a second, smaller rain garden.

In addition to the rain chain, PVC pipe wraps around Severin’s Ballard-neighorhood house and underground, draining all of the water that hits his 1,800-square-foot roof into the rain gardens.

In an average year in Seattle, Severin’s rain gardens will capture and treat about 41,500 gallons of water that would otherwise have become polluted runoff.

“It looks beautiful,” he said, “but it’s also functional.”

There’s an added bonus: the $5,500 rain garden was paid for by Seattle Public Utilities’ RainWise program, which reimburses residents in certain neighborhoods for installations of green stormwater solutions.

While stormwater experts agree that rain gardens and similar strategies are essential tools for cleaning up and shrinking the amount of filthy runoff that pours from our roadways and roofs, the technologies have been slow to take off in most places. Property owners often don’t  understand how big of a problem stormwater is, or they fear that rain gardens won’t work because of a couple of well-publicized problem gardens in the past.

But new public-private partnerships are cropping up in Seattle to help residents learn more about rain gardens and take advantage of programs like RainWise. Nonprofit groups including Stewardship Partners, Sustainable Seattle and Sustainable Ballard — all of whom promote environmentally friendly practices — are helping in the effort.

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