PROVIDENCE, R.I. (AP) — The military is checking whether chemicals from firefighting foam might have contaminated groundwater at hundreds of sites nationwide and potentially tainted drinking water, the Defense Department said.

The checks will be carried out at 664 sites where the military has conducted fire or crash training, the department told The Associated Press this week.

So far, 28 naval sites have been tested, with one site in Virginia and one in New Jersey showing chemicals in water at levels above the EPA's guidance, the Navy said. Tests at 26 other naval sites in mostly coastal areas have either come up under federally acceptable levels or are pending.

The Navy is giving bottled water to its personnel at a naval landing field in Virginia and is testing wells in a nearby rural area after the discovery of perfluorinated chemicals in drinking water, which the federal Agency for Toxic Substances and Disease Registry says may be associated with prostate, kidney and testicular cancer, along with other health issues.

The Navy found perfluorinated chemicals in the groundwater monitoring wells at Naval Weapons Station Earle in Colts Neck, New Jersey, but not in the drinking water supply. Test results from off-base drinking water wells are expected this month.

And several congressmen are raising concerns about the safety of drinking water near two former Navy bases in suburban Philadelphia. The lawmakers say firefighting foams might be the source of chemicals found in nearly 100 public and private wells near the Naval Air Station Joint Reserve Base Willow Grove and the Naval Air Warfare Center in Warminster.

The Navy began sampling water at bases in December.

The foam is used at locations where potentially catastrophic fuel fires can occur, such as in a plane crash, because it can rapidly extinguish them. It contains perfluorooctane sulfonate and perfluorooctanoic acid, or PFOS and PFOA, both considered emerging contaminants by the U.S. Environmental Protection Agency.

The Defense Department said that until foam without perfluorinated chemicals can be certified for military use, it is removing stocks of it in some places and also trying to prevent any uncontrolled releases during training exercises.

The military is beginning to assess the risk to groundwater at the training sites not only to determine the extent of contamination, but also to identify any action the Defense Department needs to take, said Lt. Col. Eric D. Badger, a department spokesman.

California has the most, with 85, followed by Texas, with 57, Florida, with 38, and Alaska and South Carolina, each with 26, according to a list provided to the AP. Each state has at least one site.

The EPA in 2009 advised on the threshold of contamination by the chemicals at which action should be taken to reduce exposure. The advisory is considered a guideline, and not anything that can be legally enforced.

The EPA said then that it was assessing the potential risk from short-term exposure through drinking water. It later began studying the health effects from a lifetime of exposure. Those studies remain in progress.

The Navy started handing out bottled water in January to about 50 people who work at the Naval Auxiliary Landing Field Fentress in Chesapeake, Virginia, and it worked with the city to set up a water station for concerned property owners after it found perfluorinated chemicals in on-base drinking water wells above the concentrations in the EPA advisory.

The Navy is testing private wells of nearby property owners; those results are due next week.

Chris Evans, of the Virginia Department of Environmental Quality, credited the Navy with being proactive but said he's concerned anytime there's a potential threat to human health and the environment.

Some states have established their own drinking water and groundwater guidelines for the maximum allowable concentrations of the chemicals; Virginia uses the EPA's.

"We'll follow EPA's lead as this develops," said Evans, the director of the office of remediation programs.

There's a lot of evolving science around perfluorinated chemicals, said Lawrence Hajna, a spokesman for the New Jersey Department of Environmental Protection.

"The more that we hear, the more that we realize that this is a very important health concern," he said.