A new study by the U.S. Environmental Protection Agency says the controversial oil extraction method known as fracking poses no widespread danger to the country's drinking water supplies.
The congressionally-mandated study took five years and cited more than 900 separate reports along with the EPA's own research.
Fracking involves blasting large amounts of water, chemicals, and sand into underground rock to extract oil and gas.
The oil and gas industry defends the practice. It says it rigidly follows all federal and state safety regulations to protect the environment.
But environmentalists say fracking is dirty and dangerous no matter how many precautions are taken.
The EPA study said fracking could harm drinking water if proper safeguards were not followed.
Risks include isolated incidents of improperly cemented fracking wells that allow oil and gas to seep into the ground, untreated wastewater entering drinking water and spills.
But the EPA report said the risks are "small compared to the large number of hydraulically fractured [the scientific term for fracking] wells across the country."
Amy Mall of the National Resources Defense Council says the study still provides "solid scientific evidence" that fracking has contaminated drinking water around the country.
"The report, while limited, shows fracking can and has impacted drinking water sources in many different ways...much more science will be necessary to fully understand all of the risks."
The EPA says the study is not intended to conclude whether fracking is safe, but was made to show federal and state regulators how to handle the risks and the best ways to protect drinking water.