Town of Manson tries to save soft water

The northwest Iowa town of Manson, sitting atop what likely is the continent's largest meteorite impact crater, could lose its distinction as the state's only city with naturally occurring soft water.

Since 1905, the Calhoun County town of 1,637 has drawn naturally soft water from wells tapping that crater, but those wells are slowly going dry, according to State Geologist Robert Libra.

'The quality of our water is second to none, and we don't want to give it up,” Mayor Dave George said.

Though three deep and expensive test wells have come up dry, George said he is confident that the city will hit the right spot soon enough to preserve its soft water legacy - created, scientists believe, when the impact vaporized limestone layers that give the rest of Iowa hard water.

The city's 1905 well and a nearby 1928 well, both more than 1,200 feet deep, intersect a series of chaotic rock formations that until the past decade produced ample quantities of soft water.

'The thought is, they have used it up. They are trying to hit another pocket like it without much luck,” Libra said.

While water levels in the two active wells have dropped, the town's population has grown, increasing demand for water.

Since 2006, city officials have struggled unsuccessfully to meet the state requirement that it have at least two reliable sources of water.

The city has also at times failed to meet peak daily demand, resulting in occasional use restrictions, said Julie Sievers, a Department of Natural Resources environmental specialist in Spencer.

'Geologists believe there is adequate water in the crater deep beneath the town, but there is no good way to predict where they will find it,” Sievers said.

George said each test well, ranging between 1,300 and 1,750 feet deep, costs about $250,000. That cost is borne by water system users, spread over 40 years by a U.S. Department of Agriculture loan, he said.

The city's original well is expected to dry up within 10 years.

The first test will, drilled to 1,300 feet in 2011, yielded less than 100 gallons per minute, not nearly enough to meet the city's needs. Test wells drilled to 1,550 and 1,750 feet in 2013, yielded even less water.

Residents and city officials hope the fourth test well, begun earlier this month, will tap a plentiful source of the naturally occurring soft water.

Scientists believe a mile-wide meteorite, weighing about 10 billion tons and traveling about 45,000 mph, crashed a mile into the earth near the present site of Manson about 74 million years ago.

It had been suspected of causing the extinction of the dinosaurs until isotopic age tests proved that it happened well before the extinction.

No sign of the strike can be seen at the surface, which has been covered by glacial till. Beneath the surface, however, at a depth of 66 to 295 feet, is a 24-mile-wide crater.

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