According to Government Accountability Office and Obama administration EPA, there are no documented cases where properly conducted fracking has caused groundwater contamination. However, there have been isolated fracking accidents, like other energy sources, including biofuels. Opponents of fracking blame it for natural gas in groundwater, but in areas that are rich in natural gas, it commonly seeps into the water table through natural processes. And because natural gas is odorless, invisible, and generally nontoxic, people are often unaware of its presence until they test for it.