One Well Tested High for Manganese. The City Shut It Down and Got the All-Clear.

Marengo's drinking water is safe. That is the short version. But the path to that confirmation took five months, a shuttered well, a state-mandated public notice, and a round of follow-up testing that concluded in early March.

In the fourth quarter of 2025, one of four routine samples from Well 6 exceeded the Illinois EPA's maximum contaminant level for manganese: 0.15 milligrams per liter. The other three samples were within limits. ¹ City Administrator Derik Morefield said the city was notified on October 29 and voluntarily took Well 6 offline the same day.

The decision did not affect water service. Marengo's other wells continued supplying the system, and no other samples showed elevated levels of manganese or any other regulated contaminant. ¹

The Illinois EPA required the city to mail a public notice to all water system users, which went out in January 2026. ¹ That notice alarmed some residents. But city officials emphasized that the water being delivered to homes was not coming from Well 6 and met all state standards.

Follow-up testing in early 2026 confirmed that the system is in full compliance. The IEPA issued its all-clear on March 3. ² The city had said it would not put Well 6 back into service until levels were confirmed safe. That condition is now satisfied.

The timing is relevant because Marengo is in the middle of a major water infrastructure upgrade. A new water treatment plant addition is under construction, with pressure filter equipment expected to ship by the end of March 2026. ⁴ Once operational, the plant will add filtration capacity that can remove manganese and other naturally occurring minerals before water reaches customers.

Well 9 is also planned as a supplemental supply source, which would reduce the system's dependence on Well 6. ¹ These projects are part of a broader infrastructure program. The city has identified more than $14 million in water and sewer needs, with an average annual operating deficit of $56,000 in the water fund. ⁵

Illinois is one of the few states that sets an enforceable limit for manganese in drinking water. The federal EPA has no binding maximum contaminant level for the mineral. Illinois EPA's MCL of 0.15 mg/L is stricter than the federal secondary standard of 0.05 mg/L (which addresses taste and appearance, not health) and lower than the federal health advisory of 0.3 mg/L. ³ That stricter standard is what triggered the notice and the testing sequence that followed.

Residents with questions can contact Marengo Public Works at 815-568-7112 or marengopublicworks@cityofmarengo.com.