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Life Cycle Impact and Benefit Tradeoffs of a Produced Water and Abandoned Mine Drainage Co-Treatment Process Yan Wang, Sakineh Tavakkoli, Vikas Khanna, Radisav D. Vidic, and Leanne M. Gilbertson Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b03773 • Publication Date (Web): 07 Nov 2018 Downloaded from http://pubs.acs.org on November 8, 2018
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Environmental Science & Technology
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Life Cycle Impact and Benefit Tradeoffs of a Produced Water and Abandoned Mine Drainage Co-Treatment Process Yan Wang1, Sakineh Tavakkoli1, Vikas Khanna1, Radisav D. Vidic1,2, Leanne M. Gilbertson1* 1Department
of Civil and Environmental Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, United States
2Department
of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, United States
In Preparation for Resubmission to: Environmental Science & Technology
September 30, 2018
*Corresponding Author: Phone: (412) 624-1683, e-mail:
[email protected] ACS Paragon Plus Environment
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Environmental Science & Technology
ABSTRACT
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A co-treatment process for produced water and abandoned mine drainage (AMD) has been
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established and demonstrated at the pilot-scale. The present study evaluates the potential of the
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proposed process to aid in management of two high volume wastewater resources in Pennsylvania.
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A systems-level approach is established to evaluate the primary tradeoffs, including co-treatment
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process environmental impacts, transportation impacts, and environmental benefits realized from
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precluding direct AMD release to the environment. Life cycle impact assessment was used to
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quantify the environmental and human health impacts as well as to identify ‘hot spots’ of the co-
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treatment process. Electricity use was found to be the dominant contributor to all impact
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categories. Extending the system boundary to include transportation of the two wastewaters to a
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to-be-determined co-treatment site revealed the important impact of transportation. An
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optimization approach was employed (using the region of Southwest Pennsylvania) to evaluate
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minimization of transportation distance considering the location and number of treatment sites.
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Finally, a quantitative analysis of environmental benefits realized by precluding direct AMD
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release to the environment was performed. The results suggest that the magnitude of benefit
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realized in treating a highly polluted AMD is greater than the magnitude of impacts from the co-
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treatment process.
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1. INTRODUCTION
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Pennsylvania’s unique geology and geography enabled the state to become the second-largest
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natural gas producer (primarily produced from the Marcellus Shale) and the third-largest coal
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producer in the nation in 2016.1 The extraction of these two primary energy resources introduces
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environmental and economic burdens, including significant volumes of wastewater. Natural gas
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extraction using hydraulic fracturing generates large quantities of produced water (around 1
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million gallons per gas well on average in Marcellus Shale region)2, 3, which is most notably
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characterized by extremely high salinity and the presence of naturally occurring radioactive
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materials. (Note: Produced water is defined herein to include both the flowback, first 2-3 weeks,
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and in-production periods.) Another prominent polluted aqueous waste stream in Pennsylvania is
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abandoned mine drainage (AMD), which is produced when water fills abandoned coal mines and
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is released direct to the environment. The estimated rate of AMD production is 700-2,000 gallons
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per minute throughout Pennsylvania’s western and central regions.4 More than 3,000 miles of
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contaminated surface and ground waters are said to be caused by AMD leading to the destruction
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of local ecosystems.5, 6
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Potential solutions to technical, economic, and regulatory issues related to the use of AMD for
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hydraulic fracturing operations were proposed in a roundtable conference hosted by the RAND
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Corporation in December 20114 and disseminated in the White Paper released by the Pennsylvania
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Department of Environmental Protection (PADEP) in January 2013.7 The feasibility of using
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AMD for hydraulic fracturing was agreed to be technically viable, but the suitability of direct use
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was questioned due to large variation in the chemical composition (e.g., sulfate, pH, iron). Despite
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these proposed action plans,4, 7 there remains an opportunity to implement an effective and lasting
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solution. One potential solution has been demonstrated at the lab- and pilot-scale by Vidic, et al.6,
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8, 9
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remediate both waste streams through a straightforward mixing process. The treated water is
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proposed for use in hydraulic fracturing operations, offering the benefit of offsetting freshwater
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demand. In the Marcellus Shale, only 10-30% of the injected fracturing fluid returns to the surface
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as produced water during the flowback period.10-12 Thus, freshwater - termed ‘make-up’ water –
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must be added to the produced water for use in subsequent injections. The estimated volume of
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make-up water ranges from 3-8 million gallons per well.2,
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Pennsylvania is abundant for the implementation of the proposed co-treatment approach.
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Approximately 600 billion gallons of AMD is discharged annually, which is more than ten-fold
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the estimated water demand annually for hydraulic fracturing even for exceedingly optimistic
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assumption of 5,000 active wells per year.4, 14 The proximity of AMD discharge sites to shale gas
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wells further supports the opportunity to utilize this co-treatment process.
and involves leveraging the complementary chemistries of produced water and AMD to
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The volume of AMD in
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Sulfate concentration is the most important water quality requirement for use in Marcellus Shale
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region and is restricted to
