A new study on managing wastewater produced by hydraulic fracturing finds the biggest risk of contamination to drinking water supplies occurs during the disposal process.

The report is by Stony Brook University and was published this month in the journal "Risk Analysis".

The researchers looked at several potential ways fracking wastewater could end up in the drinking supply, including transportation and leaks or spills.

"Based on the data we had available, it looked like the potential for contamination was much larger from wastewater disposal than from any of the other sources," said report co-author Dan Rozell in an interview with the Innovation Trail.

Fracturing a natural gas well requires millions of gallons of water mixed with sand and chemicals to release gas from the shale formation thousands of feet below the earth's surface. Not all of the water returns to the surface. Flowback amounts can range from 10 to 80 percent of what's sent down, but average around 30 percent according to Rozell.

What does return to the surface is highly contaminated. The fracking fluid mixes with salt and radioactive materials in the shale.

Municipal water treatment plants are incapable of dealing with the flowback, which is saltier than sea water, the report found. Industrial grade facilities aren't perfect either, according to Rozell.

"Still a substantial portion, sometimes anywhere from 30 percent or more of the original fluids are still making it through the process," he said.

Rozell said that the recycling of fracking fluid is helping to reduce the amount of water produced by each natural gas well, but the fluid can usually only be reused once.

Use of injection wells - sending the flowback water back thousands of feet underground away from aquifers - has been common in more developed shale formations in the South and West. But injection wells have been linked to causing minor earthquakes.

The report recommends "regulators should explore the option of mandating alternative fracturing methods to reduce the wastewater usage and contamination from shale gas extraction in the Marcellus Shale."

Development of the Marcellus Shale natural gas formation is underway in Pennsylvania, but has been on hold in New York while environmental regulators study the practice.