A PROTOCOL TO CHARACTERIZE FLOWBACK WATER CONTAMINATION TO SHALLOW WATERS FROM SHALE GAS DEVELOPMENT

Hydrofracking of methane-producing shales commonly results in flowback waters with high concentrations of dissolved solids and trace metals including: chloride, iron, manganese, barium and strontium. These solutes also occur naturally in ground waters and in other common contamination. Therefore, the regulatory environment needs to unequivocally address the problem of "false positives,” where flowback water contamination might be suspected, but does not actually occur.

We present the preliminary design of a protocol to address false positives, using as an example, a heuristic site-specific geochemical mixing model between representative flowback waters from the Marcellus Shale and dilute potable ground water from the Mississippian-age Catskill Formation in Clinton County, Pennsylvania. Potentially harmful dissolved trace metals and dissolved organic compounds associated with flowback water are associated with high salinity, so we focused on the relatively non-reactive solutes: major cations, lithium, chloride, and bromide that, as an assemblage, can be used as forensic geochemical tools.

Our preliminary results show that, in the absence of natural attenuation, as little as a 0.1% addition of flowback water would potentially exceed drinking water standards for some trace metals. Furthermore, the ratios of halogens and major solutes can be used characterize alternative sources of salinity, thereby clarifying probable sources of associated elevated trace elements. We are now incorporating the stable isotopes of water, isotopes of natural gas, and the chemical processes related to solute natural attenuation and to further refine our forensic approach to identify flowback water and produced brine mixing with other waters.