Larry Thompson sits high in his tractor cab and drives to a chain-link fence along his family property on the Mohawk Indians' Akwesasne Reservation, where they fished, grew vegetables and played as children. He points to a toxic landfill about 30 feet away, stretching toward the St. Lawrence River.

"The whole hill," he says evenly. "Our gardens were right here, where that sign is."

Thompson's family put up the sign 20 years ago, warning: "PCBs, danger area."

The rural landscape, with houses scattered among fields and trees and along the river, is part of ancestral tribal homelands that once extended 125 miles south to the Mohawk River. The reservation, about 21 square miles on the U.S. and Canadian sides of the St. Lawrence, is home to about 16,000 people.

Immediately upstream is a shuttered General Motors factory, now a federal Superfund site where tons of toxic waste have been removed. Tons more remain, including the 12-acre landfill that has been capped with a layer of clay and grass and declared safe, no longer a threat.

PCBs, or polychlorinated biphenyls _ considered probable carcinogens _ are the main contaminant, dumped as sludge after use as electrical equipment coolants. Studies 20 years ago documented higher than normal PCB levels in the breast milk of Akwesasne nursing mothers and more recently in adolescents; the toxins persist in human tissue for years. High levels have been found in St. Lawrence River turtles and fish, which the state cautions against eating.

"There's no question there's a legacy of PCB contamination in this area," said Judith Enck, regional administrator of the Environmental Protection Agency and a former top environmental official for New York. "And the Mohawks have raised legitimate concerns for decades."

Despite government assurances that immediate health and environmental hazards are gone, anger and fear persist over what some people here see as a long-running attack on their land, their lives and even their sovereignty. Thompson's wife, Dana Leigh, calls it environmental genocide and a continuation of George Washington's 1779 order to colonial troops to lay waste to their settlements.

Among 89 polluted ex-GM industrial locations around the country, the 270-acre site at Massena is getting the largest single share, about $121 million, of the $773 million cleanup budget established in bankruptcy court last year. The new, post-bankruptcy General Motors is no longer legally liable, but Thompson says the company, which posted 2011 net income of $7.6 billion, should pay for a full cleanup and remove the landfill.

"The fact that it's still there, people are frustrated about it," said Ken Jock, director of the St. Regis Mohawk Tribe's environmental division. "It seemed like it's a commonsense thing. When you dump your waste in the back, you clean up your mess."

The tribal council maintains it never consented to a permanent landfill, even in its agreement 20 years ago to a cleanup plan with EPA, the car manufacturer, and the state of New York.

Thompson, 57, drove his backhoe last summer through the fence and began digging up the landfill himself. The former steelworker, who was arrested and spent four days in jail, claims the Superfund site is actually on Mohawk land that was never legally ceded. His initial court appearances drew crowds of supporters.

"I hold the federal government responsible, New York state responsible, Chevrolet responsible," Thompson said. "As it is, they made a deal. They think that's over with? I don't think so."

He and his wife, who have three children and 13 grandchildren, said they have a responsibility to look ahead for the welfare of future generations.

Thompson is free on bond and faces trial, probably this fall, on a felony count of criminal mischief and misdemeanor charges of reckless endangerment and resisting arrest. RACER Trust, which owns the site, wants $70,000 for minor landfill repairs.

Prosecutors declined to comment.

"The real crime that's been committed here is by General Motors," said James Ransom, former St. Regis Mohawk chief. He said the issue is money _ and everyone at Akwesasne agrees with Thompson. "The United States basically let them shed their toxic assets. Communities like ours pay the price for that."

The tribal council said it doesn't condone what Thompson did but understands his aggravation. For his part, Thompson, who goes by the Indian name Kanietakeron, has renounced his affiliation with the tribe in court papers, saying he is "a true sovereign" who can claim the land under its original title, a claim that includes the GM site.

Altogether 82, or almost 5 percent, of federal Superfund sites designated for priority treatment nationally are classified as "Native American Interest," including Massena and four others in New York.

GM made aluminum cylinder heads here starting in 1958, polluting the land and water with PCBs, heavy metals and other toxics. It closed in 2009. The site was designated a federal Superfund priority in 1984, with contamination in two disposal areas, the industrial landfill and four lagoons.

The federal government says it has eliminated the "immediate exposure pathways" of contaminants leaking into the river and groundwater. After river dredging, groundwater containment and waste removal, the cleanup agreement calls for leaving the landfill as it is. Monitoring and other cleanup work continue.

"We believe that the 12-acre landfill has been contained and that it does not pose a threat to public health and the environment," said EPA's Enck.

But Dr. David Carpenter, director of the Institute for Health and Environment at the State University at Albany, said the landfill poses a health threat because of PCB air contamination.

"In fact landfills are not secure," Carpenter said. "PCBs volatilize and escape into the air. I'd be very much in favor of digging it up. It should be moved totally away from the reservation."

Enck said plans do call for the landfill to be moved 150 feet from the tribal border in 2014. Carpenter said the EPA has made real cleanup progress, but that would do more harm than good.

On Thompson's side of the fence, several houses on the reservation are a stone's throw from the landfill and along the river where people still live. The house where Thompson grew up is here at Raquette Point; Thompson and his wife moved out 24 years ago when they learned of the pollution.

Akwesasne also lies downstream and downwind from Reynolds and ALCOA aluminum factories that were also polluters. Ransom, the former chief, said fluoride from those factories made cattle sick.

Thompson believes cancer, diabetes, thyroid disease and other ailments have afflicted generations of people who lived on the reservation. While there are no definitive cancer studies proving the PCBs have caused illness at Akwesasne, Carpenter said recent research has shown a strong relationship between PCBs and low thyroid hormones, adult diabetes and heart disease.

Thompson says he was pushed to act partly because of his sister's kidney cancer and the liver cancer of a childhood friend, though neither illness is officially attributed to the pollution.

Neither the state health department nor St. Regis tribal officials have recent data on cancer cases in the region, spokesmen said.

Air and groundwater monitoring in the area continues, Jock said, and the tribe's environmental division plans to sample fish in the St. Lawrence and its tributaries this summer for PCBs and other contaminants, duplicating a major study in 1988 that found high levels of PCBs in fish.

"We expect that levels will be lower," Jock said. "But we aren't sure about how much or whether we're going to get to safe levels for Mohawks to consume."