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The hydroelectric project that Minneapolitans have wrestled with for two decades is back for a third try at St. Anthony Falls.

Crown Hydro is seeking to amend the federal hydro power license it was granted in 1999 but has never put to use. This time it wants to install its powerhouse at the upper end of the lock complex owned by U.S. Army Corps of Engineers, then tunnel underground past the Stone Arch Bridge to release water downstream. Two previous proposals fizzled.

The 3.4-megawatt hydro project would provide power for 2,300 homes. But nearly 70 Minneapolis residents told the Federal Energy Regulatory Commission (FERC), which will rule on the license amendment, that they think the firm should be required to obtain an entirely new license. Park and city officials agree. A FERC official also advised Crown Hydro in 2013 to seek a new license, calling the latest proposal “essentially a different project” that needs new engineering and environmental analysis.

It has been 21 years since Crown Hydro began pursuing a license to turn falling water into energy at the falls. It obtained that license in 1999, but couldn’t reach agreement with the owner of Crown Roller Mill to install generating equipment at that site. It then sought to switch to land owned by the Minneapolis Park and Recreation Board, but the board said no.

By shifting to land owned by the corps, Crown is trying to work with a federal agency that’s been friendly to hydro development.

But the proposed tunnel that would send up to 1,000 cubic feet of water per second to the Mississippi River poses new complications. Residents have expressed concern over impacts on the Stone Arch Bridge, between whose piers the tunnel would pass. Another issue is the area’s geology, described as fragile by the Department of the Interior in its license comments. The proposed tunnel would be bored through sandstone for its upper end, about 40 feet below a corps parking lot, but be dug from the surface by the time it reaches the bridge, where the sandstone is thinner.

The Interior Department suggested that geologic conditions and previous tunnels in the area create the potential for “a disaster similar to the Eastman Tunnel collapse,” an 1869 incident in which efforts to tunnel from Nicollet Island for water power development threatened to take out the falls.

Joel Toso, the project’s engineer at Wenck Associates, said Crown is well aware of an abandoned tunnel that runs near its proposed tunnel. He said that barriers will be installed to prevent eroding of sandstone in the tunnel area.

Toso said that the bottom of the tunnel will remain at least 12 feet away and 3 ½ feet above the bridge footing.

“We did not identify anything that appeared to be a showstopper,” said David Seykora, a lawyer for the Minnesota Department of Transportation, which owns the bridge.

Toso added, “Constructing a lock was far more detrimental to the Stone Arch Bridge than what we would be doing.”

But the lock opened 52 years ago, after construction removed several arches, in a different era for both historic preservation and the riverfront. Area residents and park officials emphasize the several hundred million dollars in public investments in the central riverfront since then, with such developments as the Guthrie Theatre, nearby condos, and the rising popularity of the bridge and falls since the Crown license was granted.

The Park Board has authorized a $26 million Water Works Park next to corps property.

The hydro project would install its powerhouse in part of the channel that fed intake water to the locks, introducing a new building to what’s designated a heritage zone.

Toso said a large window will allow the public to view the workings of the powerhouse.

The project has an estimated construction cost of $10 million — not including about $1.5 million already spent on engineering and also on turbine generators ordered years ago that sit at the Canadian manufacturer that made them. That money comes from a $5 million grant awarded in 2002 and funded by Xcel Energy customers under a legislative renewable energy mandate.

Besides the fight to amend its license, Crown Hydro still needs to negotiate a power purchase agreement with Xcel, the largest hydro generator at the falls. Another small hydro project was recently granted a license to make power in the basement of the Pillsbury A Mill, generating less than 20 percent of what Crown proposes.

Both entities still need to negotiate with Xcel an arrangement on how to share water when low river flow triggers a clause that requires Xcel to make sure at least 100 feet per second of water flows over the dam. That’s a key issue for the Park Board, which is pushing FERC to raise that minimum 20-fold.

Toso said he hopes to start construction in about 14 months. But it took more than five years after licensing for a hydro project at the lower lock and dam to begin generating power.

Steve Brandt • 612-673-4438

Twitter: @brandtstrib