CASCADE TOWNSHIP (AP) — Testing of private drinking wells near a western Michigan airport has found chemical contaminants after a report identified the airport’s extensive use of toxic firefighting foam.

Gordon Water Systems tested 20 wells at homes near the Gerald R. Ford International Airport southeast of Grand Rapids, WOOD-TV reported . Many residents requested testing after the news station revealed the airport used the toxic firefighting foam for more than two decades, mainly for training.

The company found perfluorinated chemicals in four wells. The chemicals are often found in the firefighting foam.

The tests didn’t find any perfluorinated chemicals above the state’s limit for drinking water. But many residents said the results show the necessity for widespread testing.

“I would hope that that expedites any kind of investigation, that there’s a sense of urgency in any of those parties to get going on what’s actually happening, whether there’s contamination going on in our water,” said Raul Alvarez, who lives near the airport.

Airport officials said they are investigating the contaminants but have no immediate plans to test neighboring wells.

The highest chemical levels were found at wells closest to the airport. But the tests don’t show if the chemicals came from the airport or how far they have spread, said Tom Duisterhof, Gordon Water System’s vice president.

“It tells me that Mother Nature can carry contaminants in water supplies underground in ways we don’t fully understand,” Duisterhof said.

One resident reported the findings to the state, according to the Michigan Department of Environmental Quality.

The department is working with airport officials to sample and test airport property, according to department spokesman Scott Dean.

“The MDEQ encourages residents with any test results to contact their offices,” said airport spokeswoman Tara Hernandez. “We continue to work with environmental specialists to conduct an investigation of the potential of PFAS exposure at the airport.”