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The Madison Water Utility’s latest tests for toxic chemicals in drinking water found further indications the source of the hazardous material is the nearby Wisconsin Air National Guard base.

The tests looked for, and found, additional types of PFAS — synthetic chemicals linked to cancers and other serious health problems — that have been used in the military’s firefighting foam, the water utility said in a statement Tuesday. PFAS stands for “per- and poly-fluoroalkyl substances.”

“Because firefighting foams contain a mixture of PFAS compounds, we did expect to find some additional PFAS chemicals at low levels when testing was expanded,” said Joe Grande, the utility’s water quality manager.

Four additional types of PFAS were revealed to be in drinking water from Well 15 on East Washington Avenue. Each of the four was measured at just above the detection limit of 2 parts per trillion.

Meanwhile, two of the most common forms of the toxic chemical were found at levels roughly the same as in previous tests.

Tests analyzed at two labs averaged 11.4 parts per trillion, which is below a controversial 2016 U.S. Environmental Protection Agency health advisory of 70 parts per trillion for the two compounds, the water utility said.