This document summarizes a student paper about challenges in treating wastewater from hydraulic fracturing. It discusses various contaminants found in fracking wastewater and detection methods used to analyze its composition. Current standard treatment methods include underground injection and transporting wastewater to centralized waste treatment facilities for advanced treatment and disposal or reuse. The paper also explores some innovative treatment methods under development, such as mixing fracking wastewater with acid mine drainage or using reverse and forward osmosis.

1. CEE 155
Hydraulic fracturing wastewater: Treatment challenges,
options and innovations
Group 1
Adam Richardson, Annie Yu, Reilly Clewes and Scott Braithwaite
December 4, 2015
Abstract: The United States has in recent years seen a boom in its oil and natural
gas industry, in part accelerated by the expansion of hydraulic fracturing, or
“fracking.” Although fracking offers many benefits for natural gas production, it
is highly controversial in terms of environmental effects. This is in no small part
due to the uncertain nature of the wastewater generated via fracking procedures,
which have been known to contain contaminants ranging from surfactants to
biocides to radioactive components. As of now the database of known information
is glaringly incomplete, highlighting the need for further collective research.
Relevant to this is the development of sophisticated detection methods, which will
facilitate study as well as assist in treatment technologies. Currently, fracking
wastewater management options include underground injection, wastewater
treatment, and wastewater recycling. Less conventional methods of treatment
include more recent innovations such as mixing fracturing fluid with acid mine
drainage, and reverse and forward osmosis.
Keywords: ​hydraulic fracturing, wastewater treatment, wastewater recycling,
underground injection, acid mine drainage
INTRODUCTION
Over the past decade the commercially unfeasible became feasible. Advances in
directional drilling and high­pressure hydraulic fracturing, known together as “fracking,” have
revolutionized natural gas production, positioning the United States to become the largest natural
gas producer worldwide (Lutz et al., 2013). On its current trajectory, fracking will produce more
than 75% of domestic natural gas by 2035 (Morrison, 2015). Yet as the vast production potential
becomes increasingly realized, so do the environmental management challenges.

2. Wastewater management and disposal have emerged as central concerns and drivers of
the controversy. Fracking, after all, involves injecting large volumes of fluid deep underground
to break up tight rock formations to extract natural gas and other hydrocarbons. For every well
drilled, 10 to 20 million liters (3 to 5 million gallons) of water are used, which includes sand and
surfactants as “proppants” to open fissures and optimize the amount of gas and oil extracted
(Arnaud, 2015) as well as assorted chemical additives that vary by the recovery method and
underlying geology (Morrison, 2015). The returning early­stage water is called “flowback” and
still contains the additives. Additional water continues to return throughout the life of the well
and is called “produced water,” which is a mix of underground water and the fracking fluid.
Together the flowback and produced water make up the wastewater from fracking, a complex
mixture of organics, metals and radioactive material. According to the U.S. Environmental
Protection Agency (USEPA, 2015), fracking wastewater management options include
underground injection control (UIC) well disposal, wastewater treatment and reuse, and
wastewater treatment and discharge at a centralized waste treatment (CWT) facility. See Figure 1
for an overview of water management for fracking.
As a major example, fracking of the Marcellus shale formation under Pennsylvania and
the surrounding region increased the wastewater generated by nearly 6­fold since 2004 (Lutz et
al., 2013), totaling over 6 million cubic meters by 2013 (Rahm et al., 2013). With only 9 UIC
wells available (USEPA, 2015), existing disposal capacity is being quickly saturated (see Figure
2). Future development becomes limited by novel logistical or technological solutions for
wastewater management. Treatment and reuse are becoming increasingly popular in this region,
especially given that less than 1% of the Marcellus shale has been explored to date (Lutz et al.,
2013). Fortunately, USEPA (2015) has not found evidence that fracking has led to widespread,
systemic impacts on drinking water resources in the United States thus far. ​
In an effort to clarify the unique challenges of hydraulic fracturing wastewater
management, this paper will first identify and analyze specific contaminants and water quality
problems that are prevalent throughout the fracking industry. The next area of focus will be on
methods of detection. Of particular interest are the advanced chemical techniques that prove
essential in detecting the extensive range of contaminants associated with hydraulic fracturing
fluid (HFF), as well as recently developed procedures and innovations. Lastly, various
wastewater management options will be discussed at length, with an emphasis on their respective
advantages and disadvantages with regard to efficacy and economy.
CONTAMINANT DESCRIPTION
Although a federal requirement to disclose the materials used in fracking fluids is
lacking, over 30 states have taken or are in the process of taking up the slack by requiring
disclosure (Morrison, 2015). To date, a number of analyses provide snapshots of parts of the
fracking water process, although a more comprehensive picture is still lacking. A voluntary
disclosure website (fracfocus.org) attempts to fill the gap.
Both the flowback and produced water can contain the original additives plus
contaminants acquired deep underground, including the following:
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3.
● Fine sand to prop open fractures so natural gas can escape
● Surfactants to reduce surface tension and friction, improve recovery of oil
and inhibit scale
● Antimicrobial compounds (e.g., glutaraldehyde) to kill microbes that
produce corrosive acid or form well­clogging biofilms
● Brine salts (e.g., iodide, bromide) because hydrocarbons formed in ancient
oceans
● High total dissolved solids (TDS) from underground minerals
● Radionuclides (e.g., radium­226) found naturally underground
● Natural gas and petroleum
Chemical reaction byproducts are also possible, with some reactions facilitated by the
fractured shale surfaces, and polymerization byproducts are possible due to the high temperature
and pressure used (Arnaud, 2015). The fate and degradation of the antimicrobial compounds,
known for their toxicity, have been reviewed by a group of Colorado researchers (Kahrilas et al.,
2015).
Several studies provide snapshots of the variety of compounds found in fracking
wastewater. From a Colorado well, Linden et al. (2015) identified 180 volatile organics,
including xylenes, acetone and 2­butanone. Looking for inorganic compounds, Harkness et al.
(2015) found elevated iodide, bromide and ammonium. The ammonium was at toxic levels (420
mg/L) and bromide and iodide are especially difficult to remove from drinking water, not to
mention they can lead to the formation of carcinogenic disinfection byproducts. Finally,
technologically enhanced naturally occurring radioactive material is brought to the surface in
particles from the fractured underground rock formations, which may be filtered out, end up in
landfills and subsequently leach out. Worker exposures can be worrisome because for
radium­226 the total radioactivity goes up by a factor of about 6 within 15 days in a closed
system due to the production of radon and other short­lived decay products (Arnaud, 2015).
3

4. DETECTION METHODS
While measurement of some of the characteristics of fracking wastewater is
straightforward (such as temperature, pH and TDS), the wide variety of organic compounds,
their degradation products, inorganics and radionuclides require modern analytical chemistry
techniques that are often quite expensive. Researchers at the University of Maryland have
identified over 2,500 organic chemicals in fracking wastewater using Fourier transform ion
cyclotron resonance mass spectrometry, and a group at Rice University used gas chromatography
with mass spectrometry to identify remnants of fuel in the wastewater (Arnaud, 2015).
Ethoxylated surfactants, including polyethylene glycols and linear alkyl ethoxylates, are major
components of flowback and have been detected by both ultrahigh pressure liquid
chromatography with Kendrick mass­defect quadrupole time­of­flight mass spectrometry
(Thurman et al., 2014) and more­standard high performance liquid chromatography with tandem
mass spectrometry (USEPA, 2014). The identification of bromide as an indicator of fracking
contamination has led to an innovative technique: a microfluidic paper­based analytical device
that uses quantitative colorimetric detection via a smartphone (Loh et al., 2015). Radionuclides,
particularly radium­226, have been detected using the more cost­effective technique of
inductively coupled plasma with mass spectrometry with results equivalent to the
more­expensive standard method of high­purity germanium gamma spectroscopy (Zhang et al.,
2015). Once the fracking wastewater has been well characterized, treatment options can be
tailored to the specific contaminants, as outlined by Lester et al. (2015).
STANDARD TREATMENT METHODS
Most fracking wastewater in the United States is disposed of through underground
injection. This is usually the least expensive management method, barring high transportation
costs (USEPA, 2015). According to the USEPA, more than 98% of produced water generated by
the oil and gas industry (including fracking operations) in the United States is injected
underground. While this is not a treatment method that actually removes contaminants,
underground injection protects the drinking water supply by placing the wastewater at depths
well below aquifers.
Specifically, Class II Underground Injection Control Wells, in accordance with EPA
regulations pursuant to the Safe Drinking Water Act, dispose of wastewater at depths of
approximately 2,000 to 8,000 feet (Marcellus Shale Coalition, 2015). These wells inject water
beneath confining geological layers such as shale. Around 40% of oil and gas industry
wastewater is injected into Class II wells. Although the proportion specifically for fracking is
hard to determine, the available data indicate that Class II wells are the main fracking wastewater
management method (USEPA, 2015).
The primary limitation to the use of injection into Class II wells is the geographic
distribution of the wells. Their location is limited by geology, and most are found in Texas,
4

5. Oklahoma and Kansas (USEPA, 2015). Moving forward, seismic concerns may also affect the
viability of underground injection (USEPA, 2015).
Another strategy is transporting the wastewater to a municipal treatment facility or a
central waste treatment (CWT) facility. A CWT facility accepts industrial waste from off­site,
treats it and discharges it to surface water or to a municipal facility for further treatment. Treated
wastewater can also be reused in fracking operations, which is a common strategy in areas where
access to Class II wells is limited, such as Pennsylvania (USEPA, 2015). According to the
USEPA, there are 73 CWT facilities currently treating or planning to treat fracking wastewater,
39 of which are in Pennsylvania.
The treatment processes at CWT facilities differ depending on the fate of the effluent. So
called “zero­discharge facilities” do not discharge either directly or indirectly to surface water,
and therefore do not require TDS removal (USEPA, 2015). Instead, their effluent is destined
primarily for reuse in fracking wells, as well as some disposal by evaporation or use for
irrigation. These facilities employ basic treatment processes effective for the removal of
suspended solids, oil and grease, scale­forming compounds, and metals (USEPA, 2015). The
treatment technologies are similar to those found at a municipal facilities: granular media
filtration, coagulation and sedimentation, chemical precipitation and dissolved air flotation
(USEPA, 2015).
During the early years of the fracking boom, a large proportion of the wastewater
transported for treatment was sent to municipal facilities. In Pennsylvania, the amount received
by municipal facilities increased from less than 30 million liters per year from 2001­2004, to 460
million liters in 2008 (Lutz et al., 2013). Most of these facilities, however, were not equipped to
treat TDS, resulting in a shift to treatment at CWTs (Ferrar et al., 2013; Lutz et al., 2013). Most
new CWT facilities have TDS removal capabilities (USEPA, 2015). These advanced treatment
technologies are more energy­ and labor­intensive because they include membrane filtration,
thermal distillation, ion exchange and adsorption (USEPA, 2015). A promising new technology
emerging is filtration with nano­structured membranes. The oily compounds in fracking
wastewater will degrade a traditional membrane, but nano­structured ones have the potential to
effectively repel oils as well as removing heavy metal ions (Stebe, 2015).
The recycling of fracking wastewater for use in new well development has increased in
recent years, rising from 13% before 2011 to 56% in that year (Lutz et al., 2013). Reuse has the
advantage of requiring much less treatment than for water destined for discharge to surface water
bodies; however, scaling from high ion concentrations and corrosion from anaerobic bacteria
byproducts must be addressed (Lutz et al., 2013). High transportation costs make on­site
treatment for reuse economically desirable and also avoid potential for spills or leaks during
transport (USEPA, 2014).
INNOVATIVE TREATMENT METHODS
One of the more creative treatment methods being developed is the mixing of HFF with
the runoff from mine tailings and works, called acid mine drainage (AMD). This is done to
remove the heavy metals and radioactive isotopes through binding, precipitation, and adsorption
5

6. with chemicals and particles that are found in the AMD (Kondash et al., 2014). This technique,
which is currently being studied by a team working from Duke University, has seen radioactive
isotope removal rates of 60­100% within 48 hours of mixing (Kondash et al., 2014). The
resulting mixed solution contains lower levels of TDS, heavy metals, and radioactive isotopes
than those of the original HFF and AMD. Needless to say, this method is attractive because it
takes two contaminated wastewaters and combines them into a far cleaner product, reducing the
need for further treatment as well as the amount of fresh water necessary to process either the
ADM or HFF alone (Kondash et al., 2014). Because this method requires the capture and
transport of AMD, it can be labor­intensive. It can also be moderately costly, because the
wastewater requires further processing after mixing. Laboratory tests are being scaled to
real­world situations to determine whether this method is cost­effective (Kondash et al., 2014).
Although reverse osmosis is a common treatment method, innovations are required to
apply it to HFF. Under reverse osmosis, a contaminated fluid is forced through a membrane that
has pores only large enough to allow water molecules through. Since the fluid is being driven
against its concentration gradient, high pressures must be applied to overcome osmotic pressure
(hence, “reverse” osmosis). Because larger pressures—and thus larger energy costs—are
necessary to treat water with high TDS levels (Younos and Tulou, 2005), reverse osmosis is
currently limited to treating TDS concentrations of under approximately 40,000 mg/L (USEPA,
2015), which poses a challenge to TDS­laden HFF. Fortunately, a team from the University of
Pennsylvania is developing a membrane that can process wastewater with high contamination
efficiently, and even remove a wider range of contaminants.
Forward osmosis, another innovative technology, uses a draw solution to draw water out
of the HFF across a membrane gradient. This technique is used when it is easier to remove the
draw solution from the water than it is to remove the original contaminants from the HFF (Coday
et al., 2014). After dewatering, the draw solution concentrate is recycled, and the HFF brine is
disposed of. The technologies used in these processes are well established and can be tailored to
the specific wastestream. The downside, however, is that this process is very energy­intensive,
requires costly machinery, and creates a large amount of byproducts; i.e., the HFF brine and
spent membranes (Gregory et al., 2011). Typically, the cost is not attractive to fracking
operators.
NATURAL TREATMENT METHODS
“Natural processes” is a broad, catch­all category that includes any treatment method
involving nature to purify the water with little or no pre­treatment. These methods require little
additional energy and are not labor­intensive, thus making them attractive if weather and
physical space permit.
Common methods in dry climates are evaporation and percolation. For example, HFF can
be spread across fields, placed in evaporation ponds, or sprayed on roads as an anti­dust agent
(USEPA, 2015). There is great concern with these treatment methods, however, because the
radioactive isotopes brought to the surface by the HFF are not adequately removed and end up
leaching into groundwater (Brown, 2014).
6

7. In colder climates, freeze­thaw is an option to improve the quality of the water with
minimal effort (Gregory et al., 2011). The process works exactly as the name suggest: HFF is
sprayed across “chilling sheets” during the cold months, where it freezes to form ice crystals.
Due to the lower freezing point of salt solutions, the now­concentrated HFF brine sloughs off
and can be disposed via other methods. When warm weather arrives, the ice thaws and is sent for
further treatment. Although freeze­thaw requires labor it is fairly low­energy, albeit with a rather
large time component.
As a final natural process, microbial organisms can be relied upon to remediate HFF.
This approach involves surface discharges or discharging to artificially created wetlands or reed
beds to bind/process the contaminants (USEPA, 2015). For surface discharges, a great deal of
treatment is required prior to discharge. For artificially created wetlands and reed beds, the level
of treatment before discharge is based on the tolerances and capture characteristics of the
organisms present (USEPA, 2015). It is difficult to estimate the efficiencies of these treatment
methods as a whole because pre­treatment is performed prior to discharge to the surface waters
or artificial environments.
CONCLUSIONS
Fracking wastewater presents the oil and gas industry with familiar wastewater treatment
challenges, although at larger quantities and with exotic additives. The most common form of
wastewater management is underground injection, which is low­cost but limited by geographic
distribution of injection wells. In the case where such wells are not available, wastewater can be
rerouted to central waste treatment facilities. These facilities may discharge treated effluent to
surface water or send it to a municipal facility for further treatment. Another option is to reuse
the water for fracking operations, which removes the need to process the water through advanced
treatment technologies that are energy­ and labor­intensive. On­site reuse also reduces associated
transportation costs. The disadvantage of reuse methods, however, is that they often face
problems with scaling and corrosion.
In addition to conventional methods, there are many innovative approaches to fracking
wastewater management. One such technique is to combine hydraulic fracturing fluid with acid
mine drainage, which effectively removes radioactive isotopes and heavy metals through
precipitation and requires very little fresh water to do so. As a new technology, however, the
costs are uncertain. Both reverse osmosis and forward osmosis use membrane technology to
filter out contaminants. Although membrane technologies have improved, they remain very
energy­intensive and result in a lot of byproduct. A less expensive treatment option is to exploit
natural processes to treat wastewater. Such natural processes include evaporation and percolation
(low energy and labor costs), freeze­thaw cycles (low energy but time­intensive), and biological
processes facilitated through natural organisms (generally requires pre­treatment).
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8. REFERENCES
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(2015). Characterization of hydraulic fracturing flowback water in Colorado:
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9. Morrison, J. (2015). Disclosure Debate. Chem. Eng. News, 93(7), 13­14.
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Thurman, E.M., Imma Ferrer, I., Blotevogel, J., Borch, T. (2014). Analysis of Hydraulic
Fracturing Flowback and Produced Waters Using Accurate Mass: Identification of
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Spectrometry. Environ. Sci. Technol., 49, 2969­2976.
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10.
TABLES
None.
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11.
FIGURES
Figure 1.​ Fracking operation water loop (Arnaud, 2015)
11

12.
Figure 2.​ Conventional and Marcellus shale wastewater volumes
by year for each management method
(Lutz et al., 2013)
12