More than 20 of the 90 hazardous-waste disposal facilities that handled or received waste from Superfund cleanups are being investigated for leaks, according to an internal Environmental Protection Agency document.

The document, prepared by EPA policy analyst William Sanjour, provides further evidence of the difficulty of disposing of toxic wastes. Sanjour, who has frequently tangled with his bosses on waste issues, also found that dozens of sites that received waste from Superfund sites are in violation of one or more provisions of the federal law governing hazardous-waste disposal, according to the document.

EPA officials said the landfills under investigation may not threaten public health.

Assistant EPA Administrator Lee M. Thomas also said the Superfund material may be going to different parts of the landfills, where contamination has not been found.

Nevertheless, Thomas said the Sanjour report "does raise questions."

In at least four cases, according to the document, Superfund waste went to municipal dumps that are not designed to handle toxic materials and are not subject to hazardous-waste disposal rules.

"In a nutshell, this shows that the EPA has a double standard when it comes to handling hazardous waste," said Sanjour. "When it comes to handling hazardous waste there is no technical difference between a Superfund site and one of these landfills. They're just high-technology dumps."

Under current EPA policy, no waste from Superfund sites is to be sent to landfills suspected to be leaking or found to be violating any other provision of the toxic-waste disposal law.

Thomas acknowledged that the agency has had difficulty getting its regional offices to abide by the two-year-old policy, despite repeated warnings from Washington.

"I've not only sent out written emphasis to the regions, I've met with them twice," Thomas said.

Asked if he was confident that the policy is being followed now, Thomas said: "I can't tell you that in fact that's happening."

Part of the problem, according to Thomas, is that "we're running into real capacity problems now. There is the geographical availability of facilities, and the shipment problem. This is a very real issue."

According to Sanjour's analysis, which was based on an EPA-generated list of sites receiving Superfund material, four of the five landfills in the Northeast that received Superfund waste are leaking.

Three of those are run by major commercial waste companies, including the Cecos International facility in Niagara Falls, N.Y., which has taken in thousands of tons of chemical waste from Superfund sites even though tests last year found high levels of dangerous chemicals in the ground water around the site.

The EPA document also lists Cecos International facilities in Illinois and Ohio as "in assessment" -- the agency's formal term for a leak investigation. The agency is also checking into leaks at facilities operated by SCA Services Inc. in New York, Browning-Ferris Industries in Louisiana, Rollins Environmental Services Inc. in New Jersey and Chemical Waste Management Inc. in Alabama and Kansas.

"Almost every one of the commercial landfills are leaking and only about four or five account for 50 percent of the waste," said Sanjour.

Among the biggest sites on the list is Chemical Waste Management's 2,400-acre landfill near Emelle, Ala., the nation's largest hazardous-waste facility and one that industry officials have often praised as "the Cadillac of landfills."

Chemical Waste Management agreed last year to install new monitoring wells after discovering that the ground water under the site flows in the opposite direction of what they had thought. According to EPA sources, the new downstream wells showed contamination that the old upstream wells hadn't detected.

Nevertheless, EPA memos show that regional officials in Atlanta decided to keep sending Superfund waste to Emelle and strongly resisted a plan to take enforcement officials to Alabama for a hands-on training session.

In a September memo to Superfund chief Thomas, regional administrator Charles R. Jeter said he understood that the trainees could take any enforcement action they deemed necessary.

"I don't feel that either the philosophy or the choice of facilities is appropriate," he said, noting that his staff had already evaluated the Emelle site and determined it was an acceptable site for Superfund waste.