Characterization of liquid waste streams from shale gas development.
Vol. 30, no. 1 (2013), s. 297-309, 
Hydraulic fracturing has been practiced for over thirty years to improve effective porosity and stimulate oil and gas production. In the Appalachian Basin it has been used with horizontal drilling since 2008 to extract methane and natural gas liquids from source rock such as the Marcellus Formation. Hydraulic fracturing generates large volumes of waste water known as flowback: about 3,800 m3/well. Literature regarding the chemical composition of this waste stream is limited. This study examined injected hydraulic fracturing fluid from two wells and flow- back from four hydraulically fractured wells. Wells were sampled at various times during the flowback cycle and in sections of the basin known to produce either wet or dry gas, the former producing higher volumes of natural gas liquids. Concentrations were compared to available literature values and to drinking water standards as a basis for determining which parameters might compromise nearby, domestic wells in the event of an accidental release. Measured parameters included three classes: organic, inorganic ions and radioactive isotopes. Concentrations of all three classes of contaminants tended to increase during the flowback cycle. Organic contaminants including BTEX were substantially higher in the wet gas well. Radioactive isotopes, particularly alpha, beta, radium 226 and radium 228 increased during flowback. All contaminants were found in much higher concentrations in flowback water than in injected hydraulic fracturing fluids suggesting that the bulk of contaminants originate in the Marcellus formation rather than in the injected hydraulic fracturing fluids. Primary and secondary drinking water standards for all classes of contaminants were generally exceeded in flowback water. In addition to summarizing the chemical composition of flowback water, the presentation recommends practices for controlling the risk of environmental exposure.