penetrate shallow freshwater zones and contaminate them with fracturing fluid, but there is no evidence that this is occurring". This study blames known instances of methane contamination on a small number of sub-standard operations, and encourages the use of industry best practices to prevent such events from recurring. In a report dated 25 July 2012, the U.S. Environmental Protection Agency announced that it had completed its testing of private drinking water wells in Dimock, Pennsylvania. Data previously supplied to the agency by residents, the Pennsylvania Department of Environmental Protection, and Cabot Oil and Gas Exploration had indicated levels of arsenic, barium or manganese in well water at five homes at levels that could present a health concern. In response, water treatment systems that can reduce concentrations of those hazardous substances to acceptable levels at the tap were installed at affected homes. Based on the outcome of sampling after the treatment systems were installed, the EPA concluded that additional action by the Agency was not required. A Duke University study of Blacklick Creek (Pennsylvania), carried out over two years, took samples from the creek upstream and down stream of the discharge point of Josephine Brine Treatment Facility. Radium levels in the sediment at the discharge point are around 200 times the amount upstream of the facility. The radium levels are "above regulated levels" and present the "danger of slow bio-accumulation" eventually in fish. The Duke study "is the first to use isotope hydrology to connect the dots between shale gas waste, treatment sites and discharge into drinking water supplies." The study recommended "independent monitoring and regulation" in the United States due to perceived deficiencies in self-regulation. According to the US Environmental Protection Agency, the Clean Water Act applies to surface stream discharges from shale gas wells: "6) Does the Clean Water Act apply to discharges from Marcellus Shale Drilling operations? Yes. Natural gas drilling can result in discharges to surface waters. The discharge of this water is subject to requirements under the Clean Water Act (CWA)." Earthquakes Hydraulic fracturing routinely produces microseismic events much too small to be detected except by sensitive instruments. These microseismic events are often used to map the horizontal and vertical extent of the fracturing. However, as of late 2012, there have been three known instances worldwide of hydraulic fracturing, through induced seismicity, triggering quakes large enough to be felt by people. On 26 April 2012, the