The Environmental Protection Agency’s final version of a comprehensive study of hydraulic fracturing, or fracking, concludes the controversial shale-oil extraction method can contaminate drinking water. The new finding completely reverses course from the agency’s first report, issued in 2015, which said there was “no evidence that fracking systemically contaminates water.” That initial conclusion has been entirely deleted from the final study. “EPA scientists chose not to include that sentence. The scientists concluded it could not be quantitatively supported,” said Thomas A. Burke, the agency’s science adviser. Burke said the new report reflects evidence that fracking has contributed to water contamination in at least five stages of the process. The report is the most comprehensive of its kind but remains “full of gaps and holes” and requires more research, Burke said.