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The city of St. Paul has laid out ambitious plans for the redevelopment of the West Side Flats, the 40-acre brownfield site just across the Mississippi River from downtown. At the heart of the work is something that is usually considered too prosaic to care much about — stormwater management.

It is a topic that’s traditionally been relegated to afterthought status because dealing with stormwater hasn’t changed much for decades. It gets directed to holding ponds or underground tanks, then released untreated into the watershed.

But stormwater is being reassessed as a valuable resource to be captured, naturally cleaned and filtered, and reused for aboveground amenities such as green space and water features. In urban redevelopment areas, the newest concept is “shared, stacked-use green infrastructure,” in which a stormwater “district” is established to serve several properties, funneling their runoff into a common system.

Under the St. Paul concept, a 1,450-foot-long, six-acre greenway of plants and trees irrigated by “daylighted” stormwater would snake through the Flats past new apartment buildings, before emptying, cleaned and “bio-filtered,” into the Mississippi.

It is being done in the Prospect Park neighborhood of Minneapolis, where ground was broken this summer for the Towerside District Stormwater System, designed to treat 4.5 million gallons of runoff for reuse each year.

That project resulted from a voluntary funding agreement between four private apartment developers who own adjacent parcels along 4th Street SE., and was helped along by a $1.3 million grant from the Mississippi Watershed Management Organization. The result will be a block-long green oasis filled with iris, bluestem, honeysuckle and many other kinds of vegetation acting as bio-filters to remove pollutants before the runoff is eventually released into the watershed.

That same stacked-use concept is a key part of the master plan for the West Side Flats accepted last year by the St. Paul City Council. The West Side Flats Greenway would be much larger than the Prospect Park effort and would be pioneer of its type — if, that is, a sustainable financing model can be forged for it.

Its promise has already enticed the U.S. Environmental Protection Agency to award it a planning grant under which several different design scenarios have been laid out and are now being presented at community meetings for initial public feedback.

But just as important, in an era of strained city budgets, St. Paul planning officials say they are in the early stages of an “innovative” effort to work across departmental lines to figure out how to pay for its construction and maintenance.

“We’ve been looking around the country for other examples of shared stormwater districts of this size to reference, but so far we haven’t found any,” said Kristin Guild, deputy director of the city’s department of planning and economic development. “So what we’re doing is essentially trying to establish a national model on how to build and operate something like this.”

Two apartment developers are planning projects adjacent to the proposed greenway. Sherman Associates hopes to build a third phase of its West Side Flats complex on a city-owned lot, and Weidner Apartment Homes last year purchased a 13-acre parcel that fronts the lion’s share of the proposed greenway route.

Jonathan Sage-Martinson, planning and economic development director for St. Paul, said planners have been “working closely” with both firms on the “public realm” portions of their plans. That includes funding construction of the shared stormwater system as an alternative to the tradition of building and relying on individual underground holding tanks.

Don Jacobson is a freelance writer based in St. Paul. He is the former editor of the Minneapolis-St. Paul Real Estate Journal.