Oct. 23, 2007 -- When Ray Manygoats describes his childhood -- playing with marbles, messing around with his brother, visiting his father at work and grilling his family's livestock -- one might mistake his stories for fond memories of growing up in the Navajo Nation.

But today, these memories are nothing more than evidence of the damage done to him and his family by uranium mining on Navajo lands during the Cold War, all part of an effort to provide the federal government with the uranium yellowcake it needed for nuclear weapons.

"We cooked on grills my father brought back from the mill. These grills had been used to sift the yellowcake uranium," Manygoats told Congress at a House Oversight and Government Reform Committee hearing on Tuesday.

"My brother Tommy and I would often bring lunch to my father at the mill. Yellow stuff was always everywhere. We would play in the yellowcake sand at the mill, jumping and rolling around in it. We also found small metal balls at the mill. The balls were used to crush and process the uranium. We played marbles with them and had contests to see how far we could throw them."

Living on Poisoned Land

It wasn't until years later that the damage done became horrifyingly clear.

In his testimony to the committee, Manygoats blames the illnesses on uranium.

"Our land today is poisoned. Today I am a man who has lost his health, his family and his ancestral way of life because of uranium," he told the committee.

Manygoats described the devastating details of living on poisoned land.

"My father began to have trouble breathing," he recounted. "His breathing troubles never went away, even after the mill was closed. I have always had problems with my ears and eyes. I have had surgery three times to remove growths from my eyes and often have sores on my ears."

Although no comprehensive study has ever been done on the health problems resulting from uranium mining in the Navajo nation, researchers believe that exposure to mining almost certainly triggered a dramatic rise in cancer among the Navajo.

Manygoats blamed the widespread illnesses among his family and his community on the uranium.

"Our land today is poisoned," he told Congress. "Today I am a man who has lost his health, his family, and his ancestral way of life because of uranium."

Echoes of the Cold War

According to the U.S. Environmental Protection Agency, between 1944 and 1986 nearly 4 million tons of uranium ore were mined from the Navajo Nation, an area larger than the state of West Virginia, which occupies parts of Arizona, New Mexico and Utah.

These mines have since been shut down.

At present, the EPA says there are 520 abandoned uranium mines in the Navajo Nation, while the Southwest Research and Information Center estimates there may actually be as many as 1,200 abandoned mines and related sites on Navajo land.

Although the mines are no longer operational, Manygoats and other Navajos are upset that the surface and groundwater contamination from the mines continues to plague the Navajo population.

"My family's land is poisoned," says Manygoats. "But no one helps us to remove the poison. I am here on behalf of my community to ask for your help."

George Arthur represented the Navajo Nation government at the hearing.

"Uranium mining and milling on and near the reservation has been a disaster for the Navajo people," Arthur said.

"We are still undergoing what appears to be a never-ending federal experiment to see how much devastation can be endured by a people and a society from exposure to radiation in the air, in the water, in the mines, and on the surface of the land. We are unwilling to be the subjects of that ongoing experiment any longer."

Lawmakers on both sides of the aisle were outraged. Committee chairman Henry Waxman, D-Calif., called the government's behavior "absolutely unacceptable" and a "modern American tragedy".

Federal Government Defends Cleanup Efforts

Officials from various federal agencies also testified, highlighting their respective efforts to solve the problem.

Wayne Nastri of the Environmental Protection Agency cited an investigation of uranium mining areas on Navajo lands from 1994 to 2007 that built an inventory of the 520 abandoned sites, an inventory now being used by the Navajo Nation government to prioritize the mine sites.

Nastri said the EPA is taking action at sites that "present an imminent and substantial endangerment to human health or the environment" and providing a total of $3.9 million annually through 11 grant programs.

Nastri also added that over the last 16 years the EPA has provided $7.8 million for the Navajo Nation Superfund program, legislation that makes polluters pay for the remediation of toxic sites.

David Geiser of the Department of Energy noted that DOE has remediated four inactive uranium milling sites on Navajo land, including the Tuba City, Arizona mill at which Ray Manygoats' father worked.

But many lawmakers were far from satisfied with the responses from the various officials.

Accusing the agency officials of having "a conspiracy of silence and do-nothingness", Rep. Elijah Cummings, D-Mary., demanded that they do better in the future.

"These are human beings they share this land with us," Cummings said, "And it's just not right. And if there's not more empathy for our fellow human beings, then maybe somebody's got to replace you guys."

The outrage of the lawmakers was matched by the sadness of the Navajo representatives.

Nuclear Waste's Effects Linger

Edith Hood still sees the remains of the uranium mining every morning.

"As I pray in the early morning dawn, there is a man-made mesa of radioactive and hazardous waste about a quarter of a mile northeast of my residence. In the other direction, to the south about 1,000 feet away, is another mound of uranium mining waste," Hood said.

Hood and her family have also experienced serious health problems.

"I was diagnosed with lymphoma in the summer of 2006. My father has a pulmonary fibrosis. My mother was diagnosed with stomach cancer. My grandmother and grandfather died of lung cancer. Many of my family members and neighbors are sick," she says.

Hood describes a community ravaged by uranium.

"Mining has already contaminated the water, the plants and the air. People are sick and dying all around us," she says.

Hood, Manygoats and other Navajo such as Phil Harrison, whose father died of lung cancer and whose brothers and sisters all have thyroid problems and disorders, want the government to take action.

"Assist my people and my land in recovering from the devastation caused by short-sighted and in some cases mean-spirited people who put their own private interests first and ignored the fact that their choices and decisions would result in an inhumane experiment being conducted on an indigenous people," Harrison will tell the committee.

Harrison suffered kidney failure in 1999, only to receive a kidney transplant from his sister.

"You have the power to change things," Harrison told Congress. "You have the power to end this tragic experiment."

"It's been about 25 years since the last mines closed," Harrison concluded. "My people shouldn't have to wait another 25 years for the federal government to accept a responsibility it should have accepted many years ago."

ABC News' Tom Shine contributed to this report.