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Uncertainties Associated with the Reuse of Treated Hydraulic Fracturing Wastewater for Crop Irrigation Linsey Shariq* Civil and Environmental Engineering, University of California, Ghausi Hall, Davis, California 95616, United States Under the Clean Water Act’s Subpart E of 40 CFR Part 435, the NPDES permit system allows for the specialized reuse of wastewater from oil and gas facilities west of the 98th meridian. To qualify for this exception, the wastewater must contain less than 35 mg/L of oil and grease and be used either for agriculture or livestock watering.1 The combination of the NPDES permitting allowance, the substantial requirement of water needed to perform the hydraulic fracturing process, and the widespread spatial overlap between extraction sites and agricultural land, has led to the dilution and reuse of treated hydraulic fracturing wastewater (THFW) for irrigation in Southern California and Wyoming.1 Third party analyses of chemicals used in hydraulic fracturing operations have documented the presence of several hundred compounds. Among these constituents are many associated with health effects, such as cancer, endocrine disruption, and individual organ deterioration, when present above experimentally determined concentrations.2 In addition to hydraulic fracturing fluid chemicals, wastewater also contains methane, highly concentrated salts, and naturally occurring radioactive roduction of hydraulic fracturing wastewater has increased material released from rock formations.1 However, as explained proportionally with the escalation of natural gas and oil by the Argonne National Laboratory, the best wastewater extraction throughout the United States. One wastewater treatment technologies available are not able to strip all toxic management strategy currently implemented in California and chemicals from the water and are often selectively implemented Wyoming is the reuse of diluted treated hydraulic fracturing 1 because of cost.1 Therefore, comprehensive laboratory analyses wastewater (THFW) for crop irrigation. Uncertainties are critical in cataloging the existing effluent constituent regarding the quantity of THFW applied as irrigation, the concentrations in THFW and in establishing a baseline concentrations and toxicities of chemical constituents in understanding of current treatment efficiencies. THFW, and the bioaccumulation characteristics of exposed Preliminary comparisons of hydraulic fracturing wastewater crops require further analysis in order to assess the long-term chemicals and USGS groundwater samples taken near safety of this practice with respect to food supplies and public California’s water reuse site in Kern County reveal an overlap health. An analysis of these uncertainties can provide a scientific of several constituents.3 A compilation of reference information foundation for the sustainable reuse of THFW for irrigation about these overlapping constituents is presented in Table 1. and contribute to the broader understanding of the natural gas Included in the data are the confirmed and suspected health and oil production life cycle. impacts of the constituents as identified by The Endocrine The hydraulic fracturing method blends together chemicals Disruption Exchange, technologically feasible treatment levels such as solvents, scale inhibitors and proppants with a published by the Argonne Nation Laboratory and agricultural substantial quantity of water, and uses the mixture to prop water quality goals implemented by California’s Regional Water open small fractures in reservoir rock that are created through Quality Control Board. It should be noted that while several controlled explosions. After fracturing has occurred, natural gas polycyclic aromatic hydrocarbons (PAHs) were reported as and oil, when present, flow through the fractures into the detected in hydraulic fracturing wastewater by the Argonne wellbore where it is collected and separated from wastewater. National Laboratory, the USGS groundwater samples were not This process has been applied to produce methane from shale analyzed for any PAHs other than naphthalene, which was not and coal deposits, as well as to enhance existing oil recovery detected in the 2006 set of groundwater samples.1,3 Also of efforts. As a result, production of domestic hydraulic fracturing 1 significance is the absence of agricultural water quality levels for wastewater has grown to over a billion gallons a day. While several contaminants of concern.4 approximately 90% of wastewater produced is injected into the The unique mixture of chemicals in THFW has not yet been subsurface, a daily quantity of over 80 million gallons is studied with respect to its uptake into crops. However, arsenic, managed by the EPA under the Clean Water Act’s National Pollutant Discharge Elimination System (NPDES) for beneficial reuses such as agricultural irrigation.1 Published: February 25, 2013
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© 2013 American Chemical Society
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Environmental Science & Technology
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Table 1. Health Impacts, Treatment Levels, and Water Quality Goals for Constituents Present in Both Hydraulic Fracturing Wastewater and Kern County Groundwater Samples
Notes
one of the known toxic inorganic constituents in wastewater, has been shown in several studies to bioaccumulate throughout rice plants, and organic hydrocarbons have also been identified in wheat plants grown in contaminated soil.5 These findings, together with the detection of THFW chemicals in Kern County groundwater, point to uncertainties that necessitate further examination. Opportunities for research include the direct sampling and analysis of THFW reused for irrigation, and evaluations of THFW constituent uptake into edible plants. Such research inquiries can help determine the adequacy of current wastewater treatment standards, and inform policy makers in developing specific guidelines for risk management from inadvertent bioaccumulation and exposure to THFW constituents, if needed. Scientific investigation into the removal efficiencies required for safe wastewater reuse can assist in guiding future technological advancements in hydraulic fracturing wastewater treatment. As the development of natural gas and oil production in the United States continues to grow, now is an appropriate time to promote sustainable energy exploration by clarifying uncertainties associated with hydraulic fracturing wastewater management. Encouraging collaboration between environmental scientists, health professionals, engineers and agronomists around the shared purpose of THFW evaluation for crop irrigation can result in improved insight into its reuse while considering long-term implications for the environment and human health.
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The authors declare no competing financial interest.
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REFERENCES
(1) Veil, J. A.; Puder, M. G.; Elcock, D.; Redweik, R. J. A White Paper Describing Produced Water from Production of Crude Oil, Natural Gas, and Coal Bed Methane; Argonne National Laboratory: Chicago, IL, 2004; W-31-109-Eng-38. (2) Colborn, T.; Kwiatkowski, C.; Schultz, K.; Bachran, M. Natural gas operations from a public health perspective. Int. J. Hum. Ecol. Risk Assess. 2011, 17 (5), 1039−1056. (3) Shelton, J.; Pimentel, I.; Fram, M.; Belitz; K. Ground-water quality data in the Kern County subbasin study unit, 2006Results from the California GAMA Program. U. S. Geol. Surv. 2008, Data Series 337. (4) RWQCBC (Regional Water Quality Control Board of California) 2007 Compilation of Water Quality Goals: Agricultural Water Quality Levels Website. http://www.waterboards.ca.gov/water_issues/ programs/water_quality_goals/. (5) Tao, Y.; Zhang, S.; Zhu, Y.; Christie, P. Uptake and acropetal translocation of polycyclic aromatic hydrocarbons by wheat (Triticum aestivum L.) grown in field-contaminated soil. Environ. Sci. Technol. 2009, 43 (10), 3556−3560.
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dx.doi.org/10.1021/es4002983 | Environ. Sci. Technol. 2013, 47, 2435−2436
