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Water | Environment

How Does An Industrial Rain Garden Grow?

TACOMA, Wash. — Standing upper deck of a six-story massive cargo ship, Rand Lymangrover looked out over chronically polluted Commencement Bay and the surrounding acres of asphalt that make up the Port of Tacoma terminals.

His company, Totem Ocean Trailer Express, or TOTE, has something that none of his neighboring cargo shipping companies have —- rain gardens.

About this time two years ago, TOTE found itself in a tricky situation. They were no longer meeting their benchmark goals for stormwater pollution standards and if they didn’t do something, and quick, they would soon be out of compliance.

The Washington Department of Ecology had strengthened the stormwater regulations in an effort to curb the amount of polluted runoff emptying into urban bays like Tacoma’s Commencement Bay, where clean-up efforts have been ongoing for decades.

The runoff leaving TOTE, which operates a fleet of ships transporting cargo weekly from Commencement Bay to Anchorage, Alaska, didn’t look to be full of polluted grit.

“The water was crystal clear,” said Lymangrover, who is the terminal facility, environmental and security manager at TOTE.

But much of the pollution that degrades water quality can’t be seen. Tests of TOTE’s stormwater showed high levels of dissolved metals. Heavy metals, including lead, copper, zinc and cadmium, are commonly found in urban runoff and contaminate surface waters and present health problems for fish and aquatic animals. In fact, a National Oceanic and Atmospheric Administration Northwest Fisheries Science Center study published in December has found high instances of salmon mortality in urban streams polluted by stormwater runoff.

Where do the heavy metals come from?

“We have a lot of galvanized metals here,” Lymangrover said. “Lots of galvanized pipes and gutters and fencing.”

Much of the steel found at industrial sites is galvanized, or coated with a layer of zinc to prevent rust. When rain washes over galvanized metal it picks up trace amounts of dissolved zinc. Although zinc isn’t harmful to humans at concentrations normally found in stormwater, it can be deadly for aquatic life. And trace amounts can add up to make a big problems for the health of a waterway.

Company officials decided to address the problem by building what may seem completely out of place in an industrial park — rain gardens. These gardens were intended to collect and filter the runoff and the plants in the garden were supposed to absorb the dissolved metals.

With a price tag of $24,000 for site preparation and plants, the project cost a fraction of a more traditional, industrial filtering system that would treat the same amount of runoff, Lymangrover said.

Last April a team of 75 people including employees, volunteers and rain garden experts tore up three swaths of pavement. Once past the foot-deep asphalt, they found sandy, mulchy well-draining soil. It was ideal for rain gardens, said David Hymel of Rain Dog Designs, who helped design and build the rain gardens at TOTE.

They mixed the soil with compost and planted about 600 shrubs and other small plants that are native to the region and can withstand wet and dry conditions.

And then they waited to see what would happen.

“Even when we had really heavy rains in the spring, you could see standing water for about 30-45 minutes and then it was gone. It was absorbed into the soil,” Lymangrover said. “At their peak, the rain gardens are probably handling 100 to 120 gallons per minute.”

That’s about 250,000 gallons a year.

By building rain gardens, Lymangrover said, they were able to redirect so much runoff that in September they completely closed off a stormwater outfall.

Now instead of four outfalls emptying into Commencement Bay, TOTE only has three. And it’s reduced stormwater pollution levels so much that they’re now well within range, Lymangrover said.

“We’re really happy with what we’ve been able to do. All the drainage from this industrial area used to go straight into the waterway. Now none if it goes into the waterway,” Lymangrover said.

Hymel said he hopes to build more rain gardens in industrial and commercial sites in the coming years. This past year Hymel’s company built 58 rain gardens in the Puget Sound region, including clusters at residential sites in Puyallup, Eatonville and West Seattle.

“I’ve not received any negative feedback from the rain gardens we’ve built,” Hymel said. “All of our projects are infiltrating well.”

There are now more than 706 rain gardens in the Puget Sound region, according to a tally kept by Stewardship Partners, the nonprofit group that’s partnered with Washington State University Extension in a campaign to build 12,000 rain gardens in the Seattle/Puget Sound region by 2016.

View Rain Gardens in Puget Sound in a larger map

The Department of Ecology is in the process of strengthening stormwater regulations for new development and redevelopment in Washington’s cities and counties in the coming years. They’re putting a greater emphasis on requiring green stormwater infrastructure like rain gardens. The latest draft rules are open for public comment until Feb 3.

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