The Environment Protection Agency on Friday released a new analysis that concludes almost 700 chemical additives are used in hydraulic fracturing for oil and natural gas.

Ninety-eight percent of the fluid injected into wells is water mixed with sand, which is used to keep fractures open so that oil and gas can be removed from shale.

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But the EPA’s analysis released Friday provides a more comprehensive look at the remainder of the fracking chemicals, which the industry says are used to protect equipment, reduce bacteria and keep fluid flowing, among other things.

The EPA’s analysis was based on more than two years of data from FracFocus, an industry-backed website that fracking companies in 20 states must use to publicly disclose the chemicals they inject into wells.

“Collectively, this report and the related products provide a detailed picture of the information available on chemicals and water use amounts, and we feel that this report will be a really important resource for states, industry and communities working to safeguard our drinking water resources,” Tom Burke, a research and development official at the EPA, told reporters Friday.

The EPA’s researchers analyzed more than 30,000 disclosures from fracking operations.

Hydrochloric acid, methanol, and hydrotreated light petroleum distillates were the most common additives the EPA found. They were reported in 65 percent of the disclosures.

The median number of chemical additives per fracking job was 14, EPA said.

The chemicals used in fracking are one of the top concerns for environmentalists, health advocates and others who are opposed to the practice or want it more strictly regulated.

The Friday report was one piece of a wide-ranging assessment the EPA is conducting into fracking. The practice is exempt from many environmental rules under a 2005 law, but the EPA can still conduct research into it.

The analysis does not make any judgments about the chemicals or their safety.

“This report really focuses on the first step, and that is collecting information about what is used and the volumes of what is used,” Burke said when asked about whether the chemicals are dangerous. “As part of our broader assessment, we will definitely be focusing on toxicity, though.”

Researchers also found that fracking can be a water-intensive operation.

The files the EPA analyzed found that each well required between 30,000 and 7.2 million gallons of water.

And, because of the limits of FracFocus, such as the states that do not use it and frackers’ ability to keep certain chemicals confidential, Burke warned that the EPA could be missing a lot.

“We think that the information on chemicals, proppants and cumulative water volumes from FracFocus 1.0 may actually be an underestimate of what’s actually used in the United States during this time period because not all states are actually required to report chemicals,” he said.