Hundreds of thousands of people who lived or worked at Camp Lejeune in North Carolina more than 25 years ago are being asked to complete a detailed health survey to determine what diseases may be linked to contaminated water they drank and bathed in at the largest Marine base on the East Coast.

As many as 1 million people over three decades may have been exposed to well water that was contaminated by toxins, officials have said. Some of the toxins may have been present at levels as much as 40 times higher than current safety standards.

The federal Agency for Toxic Substances & Disease Registry, a sister agency of the U.S. Centers for Disease Control and Prevention, is sending the survey to about 300,000 people who lived or worked at the Marine base and about 53,000 to those who lived and worked at Camp Pendleton, Calif., before 1986. The responses from Camp Pendleton are being used for comparison purposes, officials said.

The survey is the largest ever conducted by the agency, which has been conducting research about potential health hazards at the base. Officials say they hope it will answer long-standing questions about the health effects of exposure to contaminants at Camp Lejeune. The information is likely to have broader relevance outside the Marine base population because the chemicals in question are widely used in industry and “quite common groundwater pollutants worldwide,” said ATSDR Director Christopher Portier.

“If we get a good response, we have the potential to see what is happening in populations in ways that we have been unable to do so before,” he said. Previous studies about chemical exposure have generally involved much smaller populations.

“This study is so big and large that it stands the chance of clearing up a lot of those questions,” he said.

Those included in the survey are former active-duty Marines and sailors who were stationed at Camp Lejeune between June 1975 and December 1985, and civilian employees who worked at the base between December 1972 and December 1985. The survey is not being sent to everyone who ever lived at Camp Lejeune because the agency can’t identify them all from available records, officials said.

The 26-page survey asks about eight types of cancer — including brain, breast and lung — and 18 other diseases and conditions, including multiple sclerosis, Parkinson’s disease and miscarriages, that are thought to be related to exposure to contaminated well water. The water contained benzene, a known carcinogen, and tricholorethylene and tetracholorethylene, possible carcinogens.

Individuals will also be able to report other diseases not listed in the survey.

Benzene was in the base fuel tanks. The other pollutants were in solvents used to clean equipment on the base and in chemicals used by a dry cleaning plant outside the base, Portier said. The chemicals were dumped into storm drains and leaked from fuel tanks and seeped through the groundwater into the wells.

Concerns over tainted water at Camp Lejeune have been the subject of congressional hearings. The survey is in response to a congressional mandate. Officials and community groups hope the results will provide the federal government with information that could prevent future exposures.

Cases of male breast cancer, which is rare, have been reported among patients with connections to Camp Lejeune, but there is limited scientific information about the health effects of drinking water contaminated with these compounds, officials said.

Jerry Ensminger, a retired Marine master sergeant who lived at the base and is co-founder of a Web site for the families, predicted that the results would hold no surprises.

“I truly believe the survey will show exactly what the Department of the Navy and the Marine Corps didn’t want it to show — the aftermath of their negligence,” said Ensminger, whose daughter Janey was conceived and born at the camp and died of childhood leukemia in 1985 when she was 9.

The specific toxins were first identified in 1982, Portier said. The base shut down the contaminated wells in 1984.

A spokeswoman for the Marine Corps said the issue “is a very important matter” for the entire corps, and that both the Marine Corps and Navy have been heavily involved with outreach, testing and research funding since the chemicals were discovered in the drinking water.

“We care about every person who has ever lived or worked at Camp Lejeune,” said Capt. Kendra Hardesty. “We understand that some of our Marines, family members and civilian workers have experienced tragic health issues they believe are associated with the water they drank or used at Camp Lejeune in the past. We are concerned about these individuals and are working hard with the scientific and medical communities to try to find them answers.”

The toxic substances agency is also studying birth defects and childhood cancers and mortality rates to determine whether there are links to the tainted water. The research is being funded by the Department of the Navy; the $25 million research cost includes the health survey and water-modeling to identify where and when certain areas of the base received contaminated drinking water.

The first wave of surveys were mailed Thursday to about 26,000 people. The survey asks people where they lived and worked and about their family history. The next mailing to nearly 80,000 people will take place in mid-July, and continue through November. Completed surveys are due Dec. 16. ATSDR expects to release its findings in early 2014.