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Decorah Edge protection gains unanimous approval

By Jeffrey Pieters

jpieters@postbulletin.com

That water you took from the tap this morning tasted clean -- and it should stay that way, if a new Rochester ordinance has its desired effect.

The Rochester City Council voted unanimously on Monday to approve new laws meant to protect from development parts of the land where cleansed surface water filters underground.

The areas, known as Decorah Edge recharge zones, are hillside wetlands that rainwater and runoff pass through, and where the contaminants in the water somehow are removed.

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Even after years of study, the exact science of how it works isn't completely known. It might have something to do with wetland plants feeding on the contaminants, called nitrates.

What is known is that disturbing those areas, whether removing trees and plants or deeply carving the land, upsets the process. The wetlands lie atop a thick layer of shale, called Decorah shale, that water can't easily pass through. The shale delays the water's descent and directs it to the wetlands. Puncturing the shale gives it a chance to escape prematurely.

Passage of the ordinance is the culmination of many years of work, study and negotiation with home-builders.

By the time of Monday's vote, almost everyone -- from environmental groups to the Rochester Area Builders organization -- was in support of the new law.

The law includes modifications to two existing ordinances, the city zoning ordinance and the wetland ordinance. It prohibits building in zones found to play a role in recharging groundwater, but it compensates developers for that loss by permitting higher-density development on the remaining parts of their properties.

Decorah-edge zones are found at a certain elevation, and, given the bowl-shaped contour in which Rochester lies, they form basically a ring around the city, in the areas the sprawling urban area is now starting to touch.

An estimated 50 percent of the water in Rochester's deep aquifers is believed to have passed through a Decorah Edge wetland on its way underground.

A similar ordinance has been prepared that would govern the unincorporated areas of Olmsted County. The county board is expected to vote on that ordinance before summer's end.

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