The information comes from New York's Department of Environmental Conservation, which analyzed 13 samples of wastewater brought thousands of feet to the surface from drilling and found that they contain levels of radium-226, a derivative of uranium, as high as 267 times the limit safe for discharge into the environment and thousands of times the limit safe for people to drink.

The findings, if backed up with more tests, have several implications: The energy industry would likely face stiffer regulations and greater expenses, and have more trouble finding treatment plants to accept its waste -- if any would at all. And the state would have to sort out how its laws for radioactive waste might apply to drilling and how the waste could affect water supplies and the environment.

What is less clear is how the wastewater may affect the health of New Yorkers, since the danger depends on how much radiation people are exposed to, and there is still disagreement over the effects of low-level doses on people.

The DEC has yet to address any of these questions. But New York's Health Department raised concerns about the water samples in a confidential letter to the DEC in July.

"Handling and disposal of this wastewater could be a public health concern," DOH officials said in the letter, which was obtained by ProPublica. "The issues raised are not trivial, but are also not insurmountable."

The letter warned that the state may have difficulty disposing of the drilling waste, that thorough testing will be needed at water treatment plants, and that workers may need to be monitored for radiation much as they might be at nuclear facilities.

Health Department officials declined to comment on the letter. The DEC sent an e-mail response to questions stating that "concentrations are generally not a problem for water discharges, or in solid waste streams" in New York state. But the agency did not directly address the radioactivity levels, which were disclosed in the appendices of the agency's environmental review of gas drilling in the Marcellus Shale, released Sept. 30.

The Marcellus Shale is an underground rock formation that extends into southern New York and contains vast amounts of natural gas.

What scientists call naturally occurring radioactive materials -- known by the acronym NORM -- are common in oil and gas drilling waste, and especially in brine, the dirty water that has been soaking in the shale for centuries. Radium, a potent carcinogen, is among the most dangerous of these metals because it gives off radon gas and takes 1,600 years to decay. The tests taken so far suggest the amount of radioactive material measured in New York is far higher than in many other places.

Recognizing this, the environmental review said radioactive waste licensing and special disposal processes may be required, but said more study is needed before the DEC can lay out precise plans to deal with the waste.

The review said the DEC could not calculate how much radioactivity people may be exposed to, even though such calculations are routinely completed by scientists studying radiation exposure and should be very easy to do, according to Charley Yu, who runs a national dose modeling program for the U.S. Department of Energy.

Yet the review concluded radiation levels were very low and the wastewater does not present a risk to workers. DEC officials declined to explain their reasoning for this conclusion.

The DEC did answer questions about whether the additional sampling has begun and whether the state would allow drilling before the radioactivity issues are resolved.

"I don't believe anyone has taken a look, seriously, at what the unintended consequences are to dealing with these kinds of materials," said Theodore Adams, a radiation remediation and water treatment consultant with 30 years of experience. "It's got to go somewhere. It's not going to just go away."

The problem is particularly acute in New York because most other states that produce radioactive waste from drilling inject that waste back underground. But injection disposal wells are uncommon here. The EPA says none are licensed to receive radioactive waste or Marcellus Shale wastewater. Instead, most drilling wastewater is treated by municipal or industrial water treatment plants and discharged back into public waterways.

But it is not clear which treatment plants, if any in New York, are capable of handling such material. Asked for names of plants capable of removing the radioactive materials, DEC spokesman Yancey Roy said "there are currently no facilities specifically designated for treating them." The state would review disposal plans submitted by drilling companies, but has not yet received any, he said. "We do not know what treatment options are being considered or how effective NORM removal will be."

DEC officials have emphasized that the environmental review proposes testing all wastewater for radioactivity before it is allowed to leave the well site and that the volumes of brine water, which contain most of the radioactivity detected, would be far less than the volumes of fluid from hydraulic fracturing that are removed from the well.

Several plant managers in Syracuse and Endicott said they could not take the waste or were not familiar with the state's regulations.

Some plants in Pennsylvania can accept very low concentrations of radioactive metals, according to Rick Kessy, operations manager at Fortuna Energy, which produced five of the radioactive water samples in New York. But if a solution isn't found to take the higher concentrations, it could be crippling, he said.

"If we did not have a viable option for it, our operations would just shut down," Kessy said. "There is no other option."

Filtering the water is just one of several problems. Plants that can filter out the radioactive materials are left with a concentrated sludge that has substantially higher radioactivity than the wastewater. Sludge can also collect inside the pipes at well sites, in waste pits and in holding tanks.

Federal laws don't directly address naturally occurring radioactivity, and the oil and gas industry is exempt from federal laws dictating handling of toxic waste, leaving the burden on New York state. New York has laws governing radioactive materials, but the state's drilling plans don't specify when they would apply.

Experts who reviewed the concentrations of radioactive metals found in New York's wastewater said leftover sludge is likely to exceed legal limits for hazardous waste and would need to be shipped to Idaho or Washington, to some of the only landfills in the country permitted to accept it.

The same may be required of some of the equipment used in drilling, which can eventually emit much higher levels of radiation than the water itself.

According to Fortuna's Kessy, that's an acceptable cost of doing business. "We'll be willing, of course, to fund the necessary disposal means," he said.

ProPublica's Sabrina Shankman contributed to this article.