Uncertainties Associated with the Reuse of Treated HydraulicFracturing Wastewater for Crop IrrigationLinsey Shariq*

Civil and Environmental Engineering, University of California, Ghausi Hall, Davis, California 95616, United States

Production of hydraulic fracturing wastewater has increasedproportionally with the escalation of natural gas and oil

extraction throughout the United States. One wastewatermanagement strategy currently implemented in California andWyoming is the reuse of diluted treated hydraulic fracturingwastewater (THFW) for crop irrigation.1 Uncertaintiesregarding the quantity of THFW applied as irrigation, theconcentrations and toxicities of chemical constituents inTHFW, and the bioaccumulation characteristics of exposedcrops require further analysis in order to assess the long-termsafety of this practice with respect to food supplies and publichealth. An analysis of these uncertainties can provide a scientificfoundation for the sustainable reuse of THFW for irrigationand contribute to the broader understanding of the natural gasand oil production life cycle.The hydraulic fracturing method blends together chemicals

such as solvents, scale inhibitors and proppants with asubstantial quantity of water, and uses the mixture to propopen small fractures in reservoir rock that are created throughcontrolled explosions. After fracturing has occurred, natural gasand oil, when present, flow through the fractures into thewellbore where it is collected and separated from wastewater.This process has been applied to produce methane from shaleand coal deposits, as well as to enhance existing oil recoveryefforts. As a result, production of domestic hydraulic fracturingwastewater has grown to over a billion gallons a day.1 Whileapproximately 90% of wastewater produced is injected into thesubsurface, a daily quantity of over 80 million gallons ismanaged by the EPA under the Clean Water Act’s NationalPollutant Discharge Elimination System (NPDES) forbeneficial reuses such as agricultural irrigation.1

Under the Clean Water Act’s Subpart E of 40 CFR Part 435,the NPDES permit system allows for the specialized reuse ofwastewater from oil and gas facilities west of the 98th meridian.To qualify for this exception, the wastewater must contain lessthan 35 mg/L of oil and grease and be used either foragriculture or livestock watering.1 The combination of theNPDES permitting allowance, the substantial requirement ofwater needed to perform the hydraulic fracturing process, andthe widespread spatial overlap between extraction sites andagricultural land, has led to the dilution and reuse of treatedhydraulic fracturing wastewater (THFW) for irrigation inSouthern California and Wyoming.1

Third party analyses of chemicals used in hydraulic fracturingoperations have documented the presence of several hundredcompounds. Among these constituents are many associatedwith health effects, such as cancer, endocrine disruption, andindividual organ deterioration, when present above exper-imentally determined concentrations.2 In addition to hydraulicfracturing fluid chemicals, wastewater also contains methane,highly concentrated salts, and naturally occurring radioactivematerial released from rock formations.1 However, as explainedby the Argonne National Laboratory, the best wastewatertreatment technologies available are not able to strip all toxicchemicals from the water and are often selectively implementedbecause of cost.1 Therefore, comprehensive laboratory analysesare critical in cataloging the existing effluent constituentconcentrations in THFW and in establishing a baselineunderstanding of current treatment efficiencies.Preliminary comparisons of hydraulic fracturing wastewater

chemicals and USGS groundwater samples taken nearCalifornia’s water reuse site in Kern County reveal an overlapof several constituents.3 A compilation of reference informationabout these overlapping constituents is presented in Table 1.Included in the data are the confirmed and suspected healthimpacts of the constituents as identified by The EndocrineDisruption Exchange, technologically feasible treatment levelspublished by the Argonne Nation Laboratory and agriculturalwater quality goals implemented by California’s Regional WaterQuality Control Board. It should be noted that while severalpolycyclic aromatic hydrocarbons (PAHs) were reported asdetected in hydraulic fracturing wastewater by the ArgonneNational Laboratory, the USGS groundwater samples were notanalyzed for any PAHs other than naphthalene, which was notdetected in the 2006 set of groundwater samples.1,3 Also ofsignificance is the absence of agricultural water quality levels forseveral contaminants of concern.4

The unique mixture of chemicals in THFW has not yet beenstudied with respect to its uptake into crops. However, arsenic,

Published: February 25, 2013

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one of the known toxic inorganic constituents in wastewater,has been shown in several studies to bioaccumulate throughoutrice plants, and organic hydrocarbons have also been identifiedin wheat plants grown in contaminated soil.5 These findings,together with the detection of THFW chemicals in KernCounty groundwater, point to uncertainties that necessitatefurther examination.Opportunities for research include the direct sampling and

analysis of THFW reused for irrigation, and evaluations ofTHFW constituent uptake into edible plants. Such researchinquiries can help determine the adequacy of currentwastewater treatment standards, and inform policy makers indeveloping specific guidelines for risk management frominadvertent bioaccumulation and exposure to THFW con-stituents, if needed. Scientific investigation into the removalefficiencies required for safe wastewater reuse can assist inguiding future technological advancements in hydraulicfracturing wastewater treatment.As the development of natural gas and oil production in the

United States continues to grow, now is an appropriate time topromote sustainable energy exploration by clarifying uncertain-ties associated with hydraulic fracturing wastewater manage-ment. Encouraging collaboration between environmentalscientists, health professionals, engineers and agronomistsaround the shared purpose of THFW evaluation for cropirrigation can result in improved insight into its reuse whileconsidering long-term implications for the environment andhuman health.

■ AUTHOR INFORMATION

Corresponding Author*E-mail: lshariq@ucdavis.edu.

NotesThe authors declare no competing financial interest.

■ REFERENCES(1) Veil, J. A.; Puder, M. G.; Elcock, D.; Redweik, R. J. A White PaperDescribing 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. Naturalgas operations from a public health perspective. Int. J. Hum. Ecol. RiskAssess. 2011, 17 (5), 1039−1056.(3) Shelton, J.; Pimentel, I.; Fram, M.; Belitz; K. Ground-waterquality data in the Kern County subbasin study unit, 2006Resultsfrom the California GAMA Program. U. S. Geol. Surv. 2008, DataSeries 337.(4) RWQCBC (Regional Water Quality Control Board of California)2007 Compilation of Water Quality Goals: Agricultural Water QualityLevels Website. http://www.waterboards.ca.gov/water_issues/programs/water_quality_goals/.(5) Tao, Y.; Zhang, S.; Zhu, Y.; Christie, P. Uptake and acropetaltranslocation of polycyclic aromatic hydrocarbons by wheat (Triticumaestivum L.) grown in field-contaminated soil. Environ. Sci. Technol.2009, 43 (10), 3556−3560.

Table 1. Health Impacts, Treatment Levels, and Water Quality Goals for Constituents Present in Both Hydraulic FracturingWastewater and Kern County Groundwater Samples

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