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Since late 2013, crews have been digging and moving more than 160,000 cubic yards of soil, transforming a 66-acre lot behind Steak and Shake into a stormwater processing facility.

For most visitors, the area between Shiloh Road and South 44th Street West will look like a city park — the area will be complete with pedestrian trails, two fishing ponds and a series of wetlands — but its primary function will be to remove sediment and pollutants from West End waterways and slow water runoff during heavy storms.

Twice the size of Pioneer Park, the $6.1 million Shiloh Conservation Area is expected to be completed in September.

In the state of Montana, the project is one of a kind.

“I’m hard-pressed to find anything like it in the West,” said City of Billings Engineer Tyler Westrope.

The SCA is a culmination of many years of discussions on what to do about West End drainage. The park is the first step in containing floodwaters if and when severe weather rumbles through Billings, dropping inches of rain in hours.

During the flood of 1937, fast-rising waters turned dry creek beds northwest of town into raging rivers, swelling the Billings Bench Water Association ditch until it burst. Billings was inundated with water from creeks on the West End and that water rushed through downtown.

Rebuilding Billings cost more than $2 million.

“If you put a dollar amount on that today, it would be absolutely catastrophic,” Westrope said.

As homes and businesses flow westward, the City of Billings has tried to address potential drainage issues on what used to be more absorbent and sparsely populated agricultural land.

“We’re trying to get ahead,” Westrope said. “Based on the current development, our site meets the community’s needs.”

Unlike water run through the pipes of homes and businesses that is processed by the sewage treatment plant, stormwater flows back into the Yellowstone River with minimal modification. The water picks up contaminants as it flows over urban and agricultural areas and can pollute waterways, disrupt normal stream flows, destroy aquatic habitats and kill fish.

Controlling runoff

The SCA sits at the bottom of a 35-square-mile basin extending south along Cove Creek from Molt Road to near the Yellowstone Country Club in two main bodies of water — Hogan’s Slough and Shiloh Drain.

Both are fed by waters year-round from areas of higher elevation and are filled with sediment, nitrogen, phosphorus, greases and oils from runoff both agricultural and urban. They meet at the SCA.

Shiloh contributes more stormwater and irrigation runoff and Hogan’s contributes more agricultural runoff.

They both flow at different levels during different times of the year, said Greg Gabel, the project engineer at Dowl HKM, which helped design the project.

“The challenge was controlling different volumes of water,” Gabel said.

The sophisticated series of ditches, ponds and depressions have to flow through the whole complex of channels and spillways during dry times, but during flood events the area naturally reverses direction and bypasses the wetlands, sending water downstream.

The wetlands, which have the capacity to retain about 17.5 million gallons of water on the site, are expected to purify between 3.2 million and 12.9 million gallons of water each day depending on flow level, he said.

The area will go a long way to increasing the stormwater containment capacity on the West End, but if development continues eventually an expansion will be required. On the site, an additional pond can be dug to accommodate more water, and smaller wetland facilities can be built elsewhere in Billings.

By expanding early, the city hopes it won’t have to play catch-up like engineers have done in the North Park neighborhood.

East End project

On the east end of town, stormwater removal has been outpaced by the volume of water running into the area and homeowners have been getting water on their property as a result, said Travis Harris, city engineer.

“When we get these 100-year events, we’re going to exhibit some flooding,” Harris said. “This project should help that flooding.”

The East End project, which begins in the spring of 2015, will add additional capacity along Fourth Avenue and will include a widening and clearing of debris out of the Yegen Ditch, but does not provide a stormwater treatment component, a benefit of the Shiloh Conservation Area.

“Pipes are very expensive and don’t offer treatment,” Westrope said.

Wetlands are inexpensive in comparison. They give sediments a chance to sink out of the water and specialized water plants, known as hydrophytes, retain nutrients and oils found in runoff.

They also help Billings uphold an agreement with the Montana Department of Water Quality and the Environmental Protection Agency to keep stormwater from polluting state waterways.

To keep as many pollutants out of their Municipally Separate Storm Sewer System, Billings enforces regulations on construction sites, industrial plants, farmers and homeowners to limit sediment and pollution. They also run information campaigns to inform the public about where their stormwater goes.

By adding wetlands to the mix, the city is adding an additional layer of filtration to their stormwater and a community education tool. The recreation paths will be dotted with signs written for a fourth to sixth-grade level describing the wetlands’ function and how they naturally purify water on a fourth-grade to sixth-grade level.

“Wetlands are very efficient at nutrient cycling,” said Tom Parker of the Hamilton consulting firm Geum Environmental, which is in charge of the wetland plants. “They can take them out of the water and turn them into plant tissue.”

Not only will the plants absorb excess nutrients considered pollutants, they rid some nitrogen from the site by turning nitrogen in the soil into atmospheric nitrogen — a process called nitrification.

About 60,000 bulrushes, rushes and sedges — plants specifically chosen for their ability to grow well in Eastern Montana — will be planted along the shore, blending in with the existing wetlands along the banks of Hogans Slough.

“We actually looked around the Billings area to identify some natural wetland plants,” Parker said. “These wetlands will look like natural wetlands you will see around the Billings area.”

It will take a few years for the wetlands and landscaping around the ponds to get fully established. But once the project is completed, maintenance costs will be minimal, and creating a park that teaches its attendees about stormwater quality and retention is priceless, said Westrope.

“It’s a perfect project from a city project management standpoint,” he said. “This is the future of where stormwater needs to go.”

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Chris Cioffi covers city news for The Billings Gazette in Montana.