WASHINGTON — After pressure from the Defense Department, the Environmental Protection Agency significantly weakened a proposed standard for cleaning up groundwater pollution caused by toxic chemicals that contaminate drinking water consumed by millions of Americans and that have been commonly used at military bases.

Standards released by the agency on Thursday eliminated entirely a section that would have addressed how it would respond to what it has described as “immediate threats posed by hazardous waste sites.” Those short-term responses, known as removal actions, can include excavating contaminated soil or building a security fence around a toxic area.

Exposure to the class of toxic chemicals, called per-and polyfluoroalkyl substances, has been linked in recent years to kidney cancer, testicular cancer, thyroid disease, high cholesterol and ulcerative colitis, among other diseases. Animal studies also show delays in development.

For decades, the substances, more commonly known as PFAS, have been placed in all kinds of everyday products — nonstick pans, clothing, furniture. They can also be found in firefighting foams used on military bases, on airfields and by municipal firefighters.