Joint Base Lewis-McChord has stopped drawing drinking water for base use from three wells that have been found to contain higher-than-acceptable levels of chemicals once used, among other things, to manufacture fire-retardant foam used on the facility.
JBLM officials announced the action Thursday.
"In accordance with Environmental Protection Agency Safe Drinking Water Act guidelines, JBLM is notifying on-base consumers of drinking water that three of the base's 28 drinking water wells have been shut down and removed from the base drinking water system because they exceed the new EPA lifetime health advisory level for PFOS and PFOA," according to a statement.
PFOS and PFOA are "fluorinated organic chemicals" that historically have been used to make carpets, clothing, fabrics for furniture, paper packaging for food and nonstick cookware, according the EPA.
No illnesses have been tied to drinking water from the contaminated wells.
The EPA requires water-system operators to issue notices to consumers and state health officials if the levels of PFOS and PFOA in a drinking-water supply exceed 70 parts per trillion.
Tests last year showed the three wells now closed at JBLM -- McChord Field south, McChord Field north and Lewis Main Well 17 -- had levels of 250, 216 and 71 ppt, respectively.
JBLM officials said the water from the wells still online has the chemicals below 70 ppt and is safe to drink.
"JBLM leadership is committed to providing safe drinking water for everyone served by JBLM Water systems," the base said. "They are working to identify, fix and prevent adverse impacts created in JBLM's water supply."
PFOS and PFOA are among a group of chemicals called perfluoroalkyls. They have been used to make firefighting foam often used at airfields.
Such foams were used for "firefighter training at several locations on the east side of McChord Field's runway and on Lewis Main's Gray Army Airfield through the early 1990s," JBLM said Thursday.
Use of foams containing the chemicals was discontinued at JBLM more than 20 years ago, according to the base.
Despite numerous studies, how exposure to the chemicals affects human health is not a settled question, according to the federal Agency for Toxic Substances & Disease Registry.
"It is difficult to interpret the results of these studies because they are not consistent," the agency said in a public health statement updated in January 2015.
Some research has shown increased cholesterol levels among people who inhaled or otherwise ingested the chemicals, and there is evidence that exposure might increase a person's chance of getting liver cancer, the agency said.
"There is limited information on whether perfluoroalkyls can cause cancer in humans," the public health statement said. "Some increases in prostate, kidney and testicular cancers have been found in workers or in community members living near a PFOA facility.
"These results should be interpreted cautiously because the effects were not consistently found, and most studies did not control for other potential factors such as smoking."
JBLM began testing its wells for the chemicals after the issue of potential contamination on military installations arose within the Department of Defense last spring.
Results from a battery of tests conducted in November came back in January, showing the three problem wells, JBLM reported.
They were immediately taken off line and will remain so indefinitely, JBLM said Thursday.
"Before any of the three isolated wells are returned to use, public notice will be provided, which will include additional test results for PFOS and PFOA and an explanation of treatment or other actions taken to return the wells to service," JBLM said.
All JBLM wells will be subject to recurring tests, the base said.
The base is among six of the 140 military installations tested to date where unacceptable levels of the chemicals were found.