More than 100 systems statewide are digging new wells, adding treatment systems or arranging to buy water from neighbors.
Fifty aren't expected to make a December Eighth deadline, but may negotiate for extra time. Without it they could be fined.
Radium isn't an issue for Chicago and other cities that get their water from Lake Michigan. It also isn't an issue for most homes using shallow wells, but water systems that drill deep into aquifers have heightened levels.
Groundwater in northeastern Illinois is especially susceptible.
Federal regulators say the state accounted for nearly half of the 333 federal radium violations between 1992 and 1999.
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