A gas well pad in Dimock, Pa.

(Amanda Hrycyna for APM Reports)

According to an investigation by APM Reports & Marketplace, the Environmental Protection Agency last year made "critical" changes at the eleventh hour to a highly anticipated, five-year scientific study of hydraulic fracturing's effect on the nation's drinking water.

"Earlier draft versions emphasized more directly that fracking has contaminated drinking water in some places," according to the story.

The EPA's deputy administrator, Tom Burke, and his boss, EPA Administrator Gina McCarthy, declined requests for interviews, according to the report. Asked about the late changes, Tom Reynolds, who ran the agency's communications office when the study was released, declined to comment.

Read The Investigation: EPA's Late Changes To Fracking Study Downplayed Risk Of Polluted Drinking Water

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