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Flowback water generated during shale gas extraction in Pennsylvania is mostly reused for hydraulic fracturing operation. Abandoned mine drainage (AMD), one of the most widespread threats to water quality in Pennsylvania, can potentially serve as a make-up water source to enable flowback water reuse. This study demonstrated co-treatment of flowback water and AMD produced in northeastern Pennsylvania in a pilot-scale system consisting of rapid mix reactor, flocculation tank and sedimentation tank. Sulfate concentration in the finished water can be controlled at a desired level (i.e., below 100 mg/L) by adjusting the ratio of flowback water and AMD in the influent. Fe contained in the AMD can serve as a coagulant to enhance the removal of suspended solids, during which Fe is co-precipitated and the total iron is reduced to a desirable level. Solid waste generated in this process (i.e., barite) will incorporate over 99% of radium present in the flowback water, which offers the possibility to control the fate of naturally occurring radioactive materials (NORM) brought to the surface by unconventional gas extraction. Sludge recirculation in the treatment process can be used to increase the size of barite particles formed by mixing flowback water and AMD to meet specifications for use as a weighting agent in drilling fluid. This alternative management approach for NORM can be used to offset the treatment cost and promote flowback water reuse, reduce environmental impacts of AMD and reduce pressure on fresh water sources.

The reuse of produced water generated by natural gas extraction from Marcellus Shale for hydraulic fracturing is the dominant management option in Pennsylvania (PA), USA. The advantages and disadvantages of this management approach are reviewed and discussed together with long‐term concerns and technology development needs. Abandoned mine drainage is a promising alternative make‐up water, but high sulfate concentrations will lead to barite precipitation once it is mixed with the produced water. Bench‐scale studies were conducted to optimize barite separation from this mixture that meets the finished water quality criteria for sulfate. Conventional separation processes are very effective in removing these solids but radium (Ra) co‐precipitation may be a concern for their disposal in municipal landfills. If the produced water volume exceeds the reuse capacity for hydraulic fracturing, lime–soda ash softening can be used to remove divalent cations, including radium, to enable the production of pure salts using subsequent thermal processes.

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