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A new investigation by the Associated Press reveals that at least three states — Pennsylvania, Ohio and West Virginia — have confirmed water pollution in response to complaints related to fracking operations.

The Associated Press requested information on drilling-related complaints filed by citizens and organizations and found that while authorities had confirmed water contamination on several occasions, the way in which they reported such issues varied dramatically. Texas was the state that provided the most detailed information, although there were no confirmed cases of fracking-related contamination there, while the other three states listed general data.

The cases in which drilling-related issues were confirmed as the source of contamination were a very small proportion of the total number of complaints, the investigation found. In Pennsylvania, there were close to 400 complaints filed last year while the number of confirmed cases of water contamination exceeds 100 for the past five years. The problems allegedly stemming from oil and gas drilling operations ranged from reduced water flow to substance pollution.

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In Ohio there were 40 complaints submitted between January and November 2013, with two confirmed cases of pollution but they were not related to fracking. There were 14 complaints under investigation, according to Mark Bruce, spokesman for the state's Department of Natural Resources.

In West Virginia, over 120 complaints were filed in the last four years and there was evidence of pollution in four cases. In all of these, the drilling company offered to take corrective action voluntarily. Meanwhile, in Texas, there were more than 2,000 complaints in a decade, with 62 alleging contamination linked to oil and natural gas drilling activities.