Members of Arizona's congressional delegation are calling on the U.S. Department of Defense to prioritize cleanup of underground contamination linked to two military installations in Tucson.

A letter sent by Sens. Krysten Sinema and Mark Kelly and Reps. Raul Grijalva, Tom O'Halleran and Ann Kirkpatrick to Defense Secretary Lloyd Austin cites chemical plumes emanating from Davis-Monthan Air Force Base and the Air National Guard installation at Tucson International Airport.

Tucson on Tuesday announced plans to shut down a water treatment plant that draws from wells in the airport area.

The delegation members' letter noted that the shutdown means that Tucson will have to rely more heavily on Colorado River water transported by the Central Arizona Project aqueduct system and on groundwater pumped from wells located away from the contamination plumes.

The letter called for Austin to take steps to complete investigations into the contamination and to give high priority for remediation efforts.

Grijalva said he'll work to secure remediation funding quickly.

News of the shutdown came right before Kelly, who calls the city his hometown, took part in a hearing on the same kinds of chemicals.

A group of man-made chemicals called PFAS were the focus of a Senate Environment and Public Works Committee hearing.

Kelly told lawmakers that PFAS are causing the treatment plant closure in Tucson. The facility produces roughly 8 percent of the city’s drinking water. It’s also part of a federal superfund site.

“And has been cleaning contaminated drinking water since the early 1990s, yet the PFAS contamination proved too significant,” he said.

The pending closure is at least the second time this year PFAS made water undrinkable in an increasingly water-deficient state. The other incident forced the military to take drastic action in February.

“Telling more than 1,600 homeowners near Luke Air Force Base to avoid drinking tap water and they began distributing bottled water,” Kelly said.

Arizona’s largest PFAS contaminations are near its two biggest cities, Kelly told lawmakers. He also noted the amount of known pollution has grown as testing has improved.