The North Side Canal Co. will play host to an unprecedented aquifer recharge effort in the next two weeks, when more than 20,000 acre feet of water will rush through its system of canals before seeping deep underground.

At least that's the hope of groundwater pumpers, who are required to replenish the aquifer with thousands of acre feet surface-water users say they've pumped out.

The recharge water is part of a deal, called a mitigation plan, between groundwater pumpers and surface users. The surface users say flows near Thousand Springs have declined, and the groundwater users hope the recharge water will flow through the aquifer to the springs.

But a recharge effort this large hasn't been tried through the North Side canals, and the company is uncertain the project will work. And if it doesn't, groundwater pumpers could again face well closures by Idaho Department of Water Resources Director Dave Tuthill, as they did earlier this spring.

"It's part of our mitigation plan so Dave (Tuthill) doesn't shut us off," said Lynn Tominaga, executivedirector for the Idaho Ground Water Appropriators, a group representing the groundwater pumpers. "This is new. There hasn't been a recharge effort this big."

The pumpers bought the recharge water from canal companies, among other sources, for about $20.60 an acre foot. They'll also pay the canal company for transporting the water.

The project could begin next week, a few days after North Side stops delivering water to its surface irrigators, said Ted Diehl, North Side manager.

The water will be released from Milner Dam at 450 cubic feet per second, a relatively low flow. Diehl and Tominaga said the water will then seep through leaks in the canal system and into the aquifer.

About a third of the water that flows through the North Side system during regular irrigation season leaks into the ground, Diehl said.

Project organizers expect the recharge effort to take several days, though no one is certain.

"I don't know what the answers are going to be," Diehl said. "We're just going to run it through and see what we get."

IDWR, which oversees the mitigation plan, declined to comment on the effort.

Matt Christensen may be reached at 735-3243 or at matt.christensen@lee.net.