The federal government may soon put the kibosh on a long-delayed, controversial plan to build an underground hydroelectric power plant near the Stone Arch Bridge.

Crown Hydro LLC obtained a license 13 years ago for a 3.4-megawatt plant powered by the Mississippi River. But the project stalled because of continued opposition from local activists and the Minneapolis Park and Recreation Board, which owns a proposed site.

Last month, the Federal Energy Regulatory Commission sent notice that it may soon revoke the license because "[Crown Hydro] has failed to complete construction of the project as licensed, and [the commission's] findings fail to show it can do so in the near future."

That could spell the end of the project, unless someone makes the case why the license should be extended. Park Board Commissioner Liz Wielinski, who has opposed the project, is not ready to declare victory.

"For me, it's a welcome sign that they're finally taking this seriously," Wielinski said. "But until every single door is closed, I'm not assuming that it's completed yet. Because it's come back many, many, many, many times."

An attorney for Crown Hydro, Tim Keane, said the company plans to file a motion to intervene before the July 19 deadline. He noted that they are now pursuing using a plot of land owned by the Army Corps of Engineers.

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Under Crown Hydro's proposed hydroelectric plant, a new intake structure would be built near the end of 5th Avenue South. Water would drop four stories underground through an angled pipe to two turbines and flow into an existing tunnel that will be re-lined with concrete. Water would flow out through an existing canal in Mill Ruins Park that is already filled with water diverted for historic aesthetics. It is unclear whether the existing intake would be removed. Landscaping and fencing would surround the new intake structure, which would rise to ground level.

"The FERC is aware of that -- that we are no longer pursuing the location on Park Board property," Keane said. FERC's notice addressed the new site plan, observing that "there is still no expectation that [Crown Hydro] will complete construction of the project in the foreseeable future."

Even the new site could prove problematic. The Army Corps has raised concerns with the plans, and using the land would require extensive analysis and sign-off from the corps' chief engineer in Washington, D.C.

"We support hydropower in general," said Nan Bischoff, the FERC coordinator for U.S. Army Corps of Engineers, St. Paul District. "This particular proposal, I can't say that we're thrilled about. We've stated our concerns, and those concerns are published on the FERC website."

Staff writer Masako Hirsch contributed to this report. Eric Roper • 612-673-1732 Twitter: @stribroper