WASHINGTON — After an impasse with a South Carolina senator was broken, the Senate passed a historic bill Wednesday by unanimous consent that would help thousands of ill Marine veterans and their families exposed to contaminated water at Marine Corps Base Camp Lejeune, N.C.

Sens. Patty Murray, D-Wash., head of the Senate Veterans' Affairs Committee, and Jim DeMint, R-S.C., brokered the deal on the Senate floor moments before she was expected to force his hand.

Instead, she said they'd reached a "gentlemen's agreement" on modifications DeMint had been seeking in the bill.

"These families have waited for decades to get the assistance that they need and should not be forced to wait any longer," Murray said.

DeMint said he was always supportive of the "underlying bill," but that he'd put a procedural hold on it and charged there weren't enough safeguards to prevent fraud by those whose illnesses weren't due to contaminated water.

"The modification would make sure the veterans who deserve these benefits get them and they're not taken advantage of by fraud from others who don't deserve it," he said.

Last month, the House and Senate veterans committees agreed on a bill that would provide health care to ill military personnel and their relatives provided they had lived or worked at least 30 days on the base from 1957 to 1987. They also must have a condition listed within the bill that's associated with exposure to these chemicals.

The agreed-on changes add language from existing laws that provides exceptions if a doctor can prove the person didn't contract the illness from the base's contaminated water. For example, if the person had the illness before being at Camp Lejeune.

The changes ended a standoff between DeMint and Sen. Richard Burr, R-N.C., the bill's lead sponsor.

The legislation also includes other provisions, including measures that will expand veterans health-care programs, improve Department of Veterans Affairs efforts to help homeless veterans and make more veterans with disabilities eligible for housing-assistance grants.

"This comprehensive legislation makes improvements to almost every aspect of care and services for veterans," Murray said after Senate passage of the bill.

Congressional aides said the House might take up and pass the bill in the next couple of weeks. It could be on President Obama's desk by the end of the summer.

The measure is expected to help as many as 750,000 veterans and their families who were exposed to drinking water that was poisoned with trichloroethylene, tetrachloroethylene, benzene and vinyl chloride.

Times reporter Hal Bernton contributed to this report.