In a new study, researchers tallied spills at hydraulic fracturing sites between 2005 and 2014 in Colorado, New Mexico, North Dakota and Pennsylvania.

Researchers surveyed state records of incidents at 31,481 fracking wells. According to their work, the decade yielded 6,648 spills in just four states.

"State spill data holds great promise for risk identification and mitigation," Lauren Patterson, policy researcher at Duke University's Nicholas Institute for Environmental Policy Solutions, explained in a news release. "However, reporting requirements differ across states, requiring considerable effort to make the data usable for analysis."

In Colorado and New Mexico, spills of less than 210 gallons don't have to be reported to the state. In North Dakota, any spill of more than 42 gallons must be documented. The legal discrepancies may explain differences in total reported spills.

According to state records, North Dakota hosted the most spills, a total of 4,453 incidents. Pennsylvania was home to 1,293 fracking spills. Colorado had 476 and New Mexico had 426.

"As this form of energy production increases, state efforts to reduce spill risk could benefit from making data more uniform and accessible to better provide stakeholders with important information on where to target efforts for locating and preventing future spills," Patterson said.

Researchers found most spills were related to the storage and transport of oil, gas and other fracking fluids. They also found a large portion of wells hosted multiple spills -- 26 percent in Colorado to 53 percent in North Dakota -- and thus warrant closer regulatory attention.

"Analyses like this one are so important, to define and mitigate risk to water supplies and human health," said Kate Konschnik, director of the Harvard Law School's Environmental Policy Initiative. "Writing state reporting rules with these factors in mind is critical, to ensure that the right data are available -- and in an accessible format -- for industry, states and the research community."

Researchers published their findings in the journal Environmental Science & Technology.