Minneapolis pool to offer swimming without chlorine

Mother Nature is giving life to a long-awaited pond-like swimming pool in north Minneapolis. She's also taking it away, at least for now.

Natural filtration will make it possible to operate the 500,000-gallon pool at Webber Park without a dosing of chlorine, but nature also disappointed those who hoped that the pool would open in August as scheduled. Park planners once hoped to open it in 2013.

Instead of swimmers, the future pool is full of construction workers and heavy equipment. A snowy winter, abnormally deep frost and the June deluge mean that the first swimmer probably won't dip a toe into the pool until at least next June.

The delay has frustrated residents, but park officials say the pool will be well worth the wait, an important amenity in a part of the city without lakes and where the nearest Minneapolis pool is more than 2 miles away.

"This is really a signature piece for north Minneapolis and the whole Minneapolis park system," said park Commissioner Jon Olson, the chief advocate for restoring swimming to the neighborhood after the Webber Park pool closed in 2010.

Park Board officials have described the pool as the nation's first naturally cleansed public swimming pool in the nation.

"It's not sterile. It's pristine lake condition," said engineer Robert Schunicht of Minneapolis-based Landform, project manager for the Park Board. The new pool will use a combination of filtration, microorganisms and bacteria that feed on harmful bacteria and aquatic plants that extract nutrients that can degrade water quality.

St. Paul considered natural techniques when it rebuilt pools several years ago, but decided it couldn't delay to wait for the Legislature to change the law that requires public pools to be chlorinated, a change Minneapolis won. Instead, three St. Paul pools use sphagnum moss as their main water-conditioning medium but still use chlorine, albeit at a reduced rate.

The pool complex got a financial boost in 2013 when the Legislature expanded the boundaries of North Mississippi Regional Park to include part of Webber Park, making the project eligible for a special pool of Metropolitan Council interest earnings on park bonds. That brought in $2.2 million, the second-largest source after property tax-supported city bonds. The total cost is projected to be $6.76 million.

The pool will recirculate its water twice each day. Water drained through from the pool by overflow gutters will flow by gravity to a storage tank before passing through a fabric filter — to be cleaned daily — in a filtration tank.

From there, the flow enters the bottom of a "regeneration tank," where it will rise through pH-balancing layers of granitic and limestone gravel of varying sizes harboring bacteria and microorganisms that begin cleansing. Dozens of varieties of plants growing in the gravel will consume nutrients.

The flow will also move laterally through another filter as it moves across the pond. Then it will be pumped back to the main pool and re-enter the pool's bottom. That will involve more than 2 miles of buried pipes.

The pool also will be used for ice skating, and a new changing building will double as a warming house with a fireplace.

The closest outdoor pool in Minneapolis is at North Commons Park, which is 2 ½ miles away.

But start-up depends on the plants that will filter the water being planted by Labor Day so they can grow sufficiently to test the filtration regimen before pipes are drained for the fall freeze. If not, the opening may lag into the 2015 swim season. The delays have attracted community attention, said Linda Koelman, chairwoman of the Webber-Camden Neighborhood Organization.

"A lot of them are very unhappy, but once you explain why, they're OK with it," she said. "When it's done, it will be absolutely wonderful. It's great to see how they listened to people."

Olson played a key role. He said the idea was planted by a talk at the State Capitol years ago with then-state Sen. Michael Jungbauer, R-East Bethel, who had a background in designing sewage treatment systems, where biofiltration is sometimes used. The park system sent four people, representing maintenance, aquatics and construction, to inspect European systems before construction.

Concern over increasing pollution in the creek led to Webber-funded renovations feeding the pool with city water. Construction of a new pool was complete in 1979, but its innards wore out after 30 years, prompting the current project.

Steve Brandt • 612-673-4438

Twitter: @brandtstrib