As the Twin Cities suburbs rapidly grew, thousands of homeowners unable to access a water system drilled their own wells to tap the aquifers.
Now the state and counties are sealing the unused wells before they can be used to contaminate the groundwater -- a huge undertaking because there are so many.
Within the last year, Minnesota passed the 250,000 mark for the number of sealed wells in the state, according to Department of Health statistics. But at least that many unused wells are left, and perhaps as many as 500,000 more, officials say.
It's easy for people to forget that the innocuous-looking pipe in their yard or basement is actually a well, says Jill Trescott of Dakota County's Water Resources Office. Even if homeowners know, they may be tempted to use it to toss out things they don't know what to do with.
"Crankcase oil is one of our favorite" things tossed down a well, said Mike Convery, a hydrologist with the well management section of the Minnesota Department of Health.
In Hennepin County, commissioners recently accepted a $42,000 state grant to help homeowners seal 30 wells that extend into or below aquifers used for drinking water. More than 1,100 wells were sealed last year in Hennepin, more than any other metro county.
Anoka County's environmental services department held its 13th annual "Well Water Wise" promotion this week to analyze well water turned in by residents.
Minnesota bears primary responsibility for making sure that groundwater is safe. Eight counties and two cities -- including Dakota County, Bloomington and Minneapolis -- have authority delegated by the state to inspect and monitor wells in their jurisdictions.