1,4-Dioxane Treatment Technologies

Abstract

The chlorinated solvent stabilizer 1,4-dioxane (DX) has become an unexpected and recalcitrant groundwater contaminant at many sites across the United States. Chemical characteristics of DX, such as miscibility and low sorption potential, enable it to migrate at least as far as the chlorinated solvent from which it often originates. This mobility and recalcitrance has challenged remediation professionals to redesign existing treatment systems and monitoring networks to accommodate widespread contamination. Furthermore, remediation technologies commonly applied to chlorinated solvent co-contaminants, such as extraction and air stripping or in situ enhanced reductive dechlorination, are relatively ineffective on DX removal. These difficulties in treatment have required the industry to identify, develop, and demonstrate new and innovative technologies and approaches for both ex situ and in situ treatment of this emerging contaminant. Great strides have been made over the past decade in the development and testing of remediation technologies for removal or destruction of DX in groundwater. This article briefly summarizes the fate and transport characteristics of DX that make it difficult to treat, and presents technologies that have been demonstrated to be applicable to groundwater treatment at the field scale.

Full text

REMEDIATION Winter 2016
1,4-Dioxane Treatment Technologies
William DiGuiseppi
Claudia Walecka-Hutchison
Jim Hatton The chlorinated solvent stabilizer 1,4-dioxane (DX) has become an unexpected and recalcitrant
groundwater contaminant at many sites across the United States. Chemical characteristics of DX,
such as miscibility and low sorption potential, enable it to migrate at least as far as the chlorinated
solvent from which it often originates. This mobility and recalcitrance has challenged remediation
professionals to redesign existing treatment systems and monitoring networks to accommodate
widespread contamination. Furthermore, remediation technologies commonly applied to chlori-
nated solvent co-contaminants, such as extraction and air stripping or in situ enhanced reductive
dechlorination, are relatively ineffective on DX removal. These difculties in treatment have re-
quired the industry to identify, develop, and demonstrate new and innovative technologies and
approaches for both ex situ and in situ treatment of this emerging contaminant. Great strides
have been made over the past decade in the development and testing of remediation technolo-
gies for removal or destruction of DX in groundwater. This article briey summarizes the fate and
transport characteristics of DX that make it difcult to treat, and presents technologies that have
been demonstrated to be applicable to groundwater treatment at the eld scale. c⃝2016 Wiley
Periodicals, Inc.
INTRODUCTION
1,4-Dioxane (DX) has historically been used as a stabilizer in chlorinated solvents, with
more than 95 percent of its production in the 1970s being used as an additive to
1,1,1-trichloroethane (1,1,1-TCA; Mohr et al., 2010). This usage, coupled with the
widespread use of chlorinated solvents from the 1950s to the 1980s, suggests that DX may
be present at thousands of solvent sites in the United States alone. Because it is not a
standard analyte in typical analytical suites run on hazardous waste sites (e.g., U.S.
Environmental Protection Agency [EPA] testing methods SW846 Methods 8260 and
8270), it is often overlooked as a contaminant of potential concern. However,
observations at dozens of impacted sites suggest DX is likely to be present in groundwater
at concentrations and locations comparable to those for chlorinated volatile organic
compounds (CVOCs; Adamson et al., 2014). Additionally, DX has been identied above a
0.35 𝜇g/L reference concentration in approximately 7 percent of drinking water supplies
across the United States as a result of sampling for the Unregulated Contaminant
Monitoring Rule third list, which occurred under the Safe Drinking Water Act from 2013
through 2015 (EPA, 2016). These widespread occurrences, coupled with a recently
heightened awareness of drinking water issues among the news media and the public,
suggest that DX will be identied as a contaminant of concern (COC) at an increasing rate
in the near future. DX’s unique physical and chemical properties create challenges for its
c⃝2016 Wiley Periodicals, Inc.
Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/rem.21498 71

1,4-Dioxane Treatment Technologies
DX’s unique physical
and chemical properties
create challenges for its
remediation. The com-
pound is not treated well
by traditional groundwa-
ter treatment commonly
(and cost effectively) ap-
plied at CVOC sites, such
as carbon adsorption, air
stripping, zero-valent iron
chemical reduction, and
anaerobic biostimulation.
remediation. The compound is not treated well by traditional groundwater treatment
commonly (and cost eectively) applied at CVOC sites, such as carbon adsorption, air
stripping, zero-valent iron chemical reduction, and anaerobic biostimulation. DX’s unique
physical and chemical properties create challenges for its remediation. The compound is
not treated well by traditional groundwater treatment commonly (and cost eectively)
applied at CVOC sites, such as carbon adsorption, air stripping, zero-valent iron chemical
reduction, and anaerobic biostimulation. Therefore, at contaminated sites where DX is
newly discovered, existing remedies will need to be supplemented or replaced and, at
newly discovered sites, the selection of treatment technologies will be driven by the
presence of DX.
Because DX has a low soil adsorption coecient and a high solubility (e.g.,
miscibility), it is not typically identied as a COC in vadose zone soils. While present
brute force methods such as excavation and o-site disposal are certainly viable, costs are
highly dependent on the location of the site relative to permitted disposal facilities.
Chemical oxidation through injection ooding with activated sodium persulfate or
catalyzed hydrogen peroxide (CHP) could be viable technologies to consider for in situ
treatment, depending on contaminant mass present, natural oxidant demand,
hydrogeologic conditions, and other factors. Recent research into extreme soil vapor
extraction (XSVE) under an Environmental Security Technology Certication Program
(ESTCP) project has eld tested injection of heated (e.g., 90 ◦C) air into the vadose zone
coupled with soil vapor extraction for removal of volatilized DX. Early ndings are
promising, with removals in the test wells of as much as 90 percent (Hinchee, 2016). It
should be noted that the bulk of that removal has occurred as soil moisture approaches
zero, further demonstrating DX’s propensity to remain in water if any is present. Thermal
treatment (which is further discussed later) could also be used to address vadose zone
contamination. It can be eective in the presence of water, but its eectiveness is based on
the behavior of DX at high temperatures,which allows more eective stripping and
treatment than at ambient conditions.
The remainder of this article is focused on groundwater remediation technologies,
both ex situ and in situ, including:
•Ex Situ Treatment
-Sorption
-Advanced oxidation
-Biological
•In Situ Treatment
-Phytoremediation
-Chemical oxidation
-Biostimulation
-Natural attenuation
-Thermal
This comprehensive technology overview does not capture every study of DX
treatment, but instead focuses on the most viable technologies for eld application, in the
opinions of the authors. The reader is directed to the book, Environmental Investigation and
Remediation: 1,4-DX and Other Solvent Stabilizers (Mohr et al., 2010) for discussion of less
72 Remediation DOI: 10.1002/rem c⃝2016 Wiley Periodicals, Inc.

REMEDIATION Winter 2016
commonly applied technologies, for example, pervaporation, palladium sorption, and
sonochemical oxidation.
CHEMICAL CHARACTERISTICS AND MOBILITY
DX is a cyclic organic molecule with two opposed ether linkages. Its two oxygen atoms
make it hydrophilic and innitely soluble (miscible) in water. Because of its high solubility,
DX is highly mobile and only weakly retarded by sorption during transport. DX is a cyclic
organic molecule with two opposed ether linkages. Its two oxygen atoms make it
hydrophilic and innitely soluble (miscible) in water. Because of its high solubility, DX is
highly mobile and only weakly retarded by sorption during transport. DX’s solubility in
water and moderate vapor pressure may result in potential volatilization, but transfer from
water to air is generally negligible. Contrary to EPA guidance on vapor intrusion (VI;
EPA, 2014), which uses vapor pressure to identify volatile compounds capable of being
released from groundwater and migrating into buildings, DX is only a VI concern in the
unlikely situation where soil moisture is essentially absent. Barring that, DX will reside in
soil moisture with little chemical or physical impetus to migrate into buildings. This
assessment of VI likelihood for DX is conrmed in another EPA document (Pivetz et al.,
2013) that states, “Volatilization from shallow ground water can occur with the
chlorinated solvents; however, volatilization is unimportant for dioxane due to its very low
Henry’s Law constant.” P. 5.
Because of its miscibility, low Henry’s Law constant, and low sorption to soil organic
matter, DX is extremely mobile in groundwater. Although DX’s chemical characteristics
suggest plumes should be larger than the associated CVOC plumes, an assessment of more
than 100 documented plumes indicates that greater than 60 percent of DX plumes are the
same size or smaller than the associated CVOC plumes (Adamson et al., 2014). Possible
explanations for this divergence between theoretical and actual plume migration involve
the release timing and volume, as well as physical constraints on groundwater migration.
Most impacted sites in the United States initiated usage and likely release of CVOCs in the
1950s during the expansion of manufacturing following World War II. DX, although
identied in 1863 (Mohr et al., 2010), did not come into widespread use as a solvent
stabilizer until the late 1960s and early 1970s as manufacture of 1,1,1-TCA increased in
response to eorts to reduce usage of trichloroethene (TCE), which was identied as
being toxic. Therefore, overall CVOC plume migration likely began a full two decades
prior to DX plume migration. Additionally, DX was present in the 1,1,1-TCA solvent
blends purchased at approximately 3 to 8 percent (Mohr et al., 2010) and while
1,1,1-TCA losses during usage would have resulted in a higher concentration of DX in the
residual waste product, the solvent characteristics of the blend would have been lost well
before a point where DX concentrations equaled 1,1,1-TCA concentrations in the solvent
solution. It is estimated that the maximum likely DX concentration in waste 1,1,1-TCA
would be on the order of 15 to 20 percent. Based on this estimate, CVOCs would have
been released at approximately ve times the volume as DX, resulting in substantially
greater mass ux over time as plumes formed and migrated. Finally, highly mobile plumes,
such as DX and CVOCs do not have innite space for migration. Groundwater migration
is typically limited by ow into surface water bodies and man-made barriers like
production wells and sewers. For a plume migrating into a nearby surface water body, the
DX is a cyclic organic
molecule with two op-
posed ether linkages. Its
two oxygen atoms make it
hydrophilic and innitely
soluble (miscible) in water.
Because of its high solu-
bility, DX is highly mobile
and only weakly re-
tarded by sorption during
transport.
c⃝2016 Wiley Periodicals, Inc. Remediation DOI: 10.1002/rem 73

1,4-Dioxane Treatment Technologies
For a plume migrating into
a nearby surface water
body, the migration dis-
tance will be the same
for all compounds given
enough time.
migration distance will be the same for all compounds given enough time. For a plume
migrating into a nearby surface water body, the migration distance will be the same for all
compounds given enough time. These factors likely contributed to the observation of DX
plumes generally being no larger than the associated CVOC plumes.
EX SITU TREATMENT TECHNOLOGIES
Because DX is highly mobile in groundwater, extraction and ex situ treatment (also known
as pump-and-treat) can be a viable contaminant-removal approach. However, it should be
noted that even though DX is highly mobile in groundwater systems, back diusion from
low permeability subsurface materials makes pump-and-treat a long-term proposition and
it should not be implemented without rst considering the life cycle costs of prolonged
pumping. On the other hand, if contaminant plume containment to limit mass ux or
o-site plume migration is the remedial objective, DX is particularly well suited to
application of this technology due to its miscibility and low sorption to aquifer solids. The
following sections summarize ex situ treatment technologies that have been demonstrated
and applied at a number of impacted facilities.
Sorption
Pump-and-treat with granular activated carbon (GAC) sorption is one of the most
commonly applied treatment technologies for organic contaminants (e.g., CVOCs) in
groundwater, especially to achieve containment rather than cleanup. Pump-and-treat with
granular activated carbon (GAC) sorption is one of the most commonly applied treatment
technologies for organic contaminants (e.g., CVOCs) in groundwater, especially to
achieve containment rather than cleanup. However, the low partitioning coecient
between soil organic matter and dissolved DX in water (log Koc) of 0.54 suggests that DX
would not preferentially sorb to organic soil particles or other sorption media. DX has
been shown to be partially sorbed to GAC (Johns et al., 1998); however, removal rates at
reasonable bed contact times are in the 50 to 60 percent range,which are not sucient for
most environmental remediation applications.
Recent research into adsorption/desorption media has identied a viable treatment
alternative—AMBERSORBTM 563 Polymeric Adsorbent. AMBERSORBTM is a
carbonaceous synthetic resin that is hydrophobic and has a unique pore size distribution.
These characteristics create a high anity for organic compounds through a simple
adsorption mechanism. Regeneration is through steam heating and condensation of the
extracted DX, which then requires disposal. AMBERSORBTM1 was developed by The
Dow Chemical Company (Midland, MI; Mohr & Niles, 2014). Multiple full-scale eld
projects have been implemented successfully with DX concentrations as high as
40,000 𝜇g/L, volatile organic compounds (VOCs) and other organics up to 33,000 𝜇g/L,
and ow rates in the 100 gallons per minute (gpm) range. Treatment to below 0.04 𝜇g/L
has been consistently attained (Woodard et al., 2014).
Advanced Oxidation
Chemical oxidation is a demonstrated remediation technology for destruction of organic
contaminants, such as petroleum hydrocarbons and CVOCs. Chemical oxidation involves
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REMEDIATION Winter 2016
a reduction–oxidation (redox) reaction in which organic contaminants are oxidized to
nonhazardous or less toxic compounds. Oxidizing agents driving the reaction in water
include ozone, hydrogen peroxide, persulfate, hypochlorite, chlorine, potassium
permanganate, and iron CHP (also known as Fenton’s Reagent; Mohr et al., 2010).Due to
its stable ring structure, DX is resistant to chemical breakdown and requires an oxidation
potential (eV) of greater than 2 V for its eective oxidation (Mohr et al., 2010). CHP,
ultraviolet (UV) +peroxide, ozone +peroxide, and sodium persulfate exhibit a
suciently high eV to destroy DX. These higher level oxidation methods are collectively
referred to as advanced oxidation processes (AOPs), which are the remedial technology
most commonly employed in the removal of DX from groundwater ex situ (Mohr et al.,
2010). AOPs use the hydroxyl radical (OH.) as an oxidant and can achieve substantial
reduction in DX groundwater concentrations (EPA, 2006; Zenker, 2003). The two most
commonly used AOPs at eld-scale application include hydrogen peroxide with UV light
and hydrogen peroxide with ozone (EPA, 2006). Other AOPs include hydrogen peroxide
with ferrous iron (Fenton’s Reagent), TiO2catalyst, and electrolysis. However, full-scale
applications of these processes for DX remediation were not identied during this review.
Advanced oxidation reactions rely on contact between the oxidant and the contaminant
and may require multiple units in series for successful treatment of contaminant
concentrations above 1 mg/L (EPA, 2006). Exhibit 1 lists the oxidation potential for some
common oxidizing agents.
Hydrogen Peroxide and UV
DX is weak absorber of UV light and is poorly degraded by direct photolysis. However,
UV light in combination with hydrogen peroxide (H2O2) can be used to release hydroxyl
radicals, which can react with DX, oxidizing it to harmless reaction products (water,
carbon dioxide, and chloride; Mohr et al., 2001). Numerous full-scale eld applications of
the UV/H2O2system have been documented as successfully reducing DX concentrations
from up to 103,000 𝜇g/L to the regulatory limits (EPA, 2006). The electrical energy
required by the UV/H2O2technology to reduce the DX concentrations in 1,000 gallons
of water by one order of magnitude (90 percent) typically ranges from 2 kilowatt-hr to 6
kilowatt-hr. Capital costs range from $80,000 to $500,000 with operations and
maintenance costs ranging from $0.20 to $1.50 per 1,000 gallons of water treated (Nyer,
2009). For example, the electrical demand of the UV/H2O2system at the Pall-Gelman
Sciences site in Michigan where inuent DX concentrations ranged from 3,000 𝜇g/L to
4,000 𝜇g/L averaged $850 a day with overall treatment costs of approximately $3.50 per
1,000 gallons of water treated. The high costs led to conversion of the system to an ozone
and H2O2-based technology that was estimated to reduce treatment costs to
approximately $1.50 per 1,000 gallons groundwater treated (EPA, 2006).
Hydrogen Peroxide and Ozone
The hydroxyl radical can also be generated by combining H2O2and ozone. The use of the
H2O2and ozone process in treating DX-contaminated groundwater ex situ is well
established and fully commercialized at full eld-scale application. The use of the H2O2
and ozone process in treating DX-contaminated groundwater ex situ is well established and
The use of the H2O2
and ozone process in
treating DX-contaminated
groundwater ex situ is well
established and fully com-
mercialized at full eld-
scale application.
c⃝2016 Wiley Periodicals, Inc. Remediation DOI: 10.1002/rem 75

1,4-Dioxane Treatment Technologies
Exhibit 1. Oxidation potentials for common oxidants
Oxidant Oxidation Potential (eV) Relative Strength (Chlorine =1)
Hydroxyl radical (OH.)2.7 2
Sulfate radical (SO4.)2.6 1.8
Ozone (O3)2.21.5
Persulfate anion (S2O82−)2.1 1.5
Hydrogen peroxide (H2O2)1.8 1.3
Permanganate ion (MNO4−)1.7 1.2
Chlorine (Cl−)1.4 1
Oxygen (O2)1.2 0.9
From Mohr et al. (2010).
fully commercialized at full eld-scale application. Various sites in the United States with
inuent DX concentrations ranging from 4.6 𝜇g/L to 320 𝜇g/L are successfully
remediating the compound to their respective target levels using the APTWater
(Sacramento, CA) HiPOx system (EPA, 2006). Ozonation of bromide-containing water
can result in the formation of bromate, a Group B2 (probable human) carcinogen with a
maximum contaminant level (MCL) of 10 𝜇g/L (EPA, 2009). However, the HiPOx
system is capable of controlling bromate. The technology involves injecting H2O2into the
water stream followed by the injection of high pressure ozone at specic locations along
the in-line reactor ow path, which can be engineered to avoid excess ozone and the
resulting undesirable creation of bromate (DiGuiseppi & Whitesides, 2007). A
commercial HiPOx unit installed at Air Force Plant 44 in Tucson, Arizona, operates at a
ow rate of 2,000 gpm and is successfully reducing groundwater DX concentrations from
10 𝜇g/L to below the detection limit of 0.5 𝜇g/L. Annual operating costs of the system
include approximately $60,000 in H2O2costs and $5,000 in oxygen generation costs for
ozone production (Mohr et al., 2010). The capital costs for that large-scale HiPOx
system, including engineering design, installation and integration, and construction
oversight, was approximately $2.5 million.
Biological
Ex situ biological treatment of DX has been implemented as part of industrial wastewater
treatment systems at a number of locations, principally for treatment of polyester industry
wastes. CH2M (T. Sandy, personal communication, 2012) incorporated an aerobic
bioreactor into existing treatment systems for treating process wastewater at a polyester
manufacturing facility in the southwest United States. Aerobic stimulation of bacteria
extracted from the wastewater plant sludge resulted in reductions to meet euent
discharge limits of 40 𝜇g/L. The bacteria cultured at this facility were transferred to other
facilities within the company’s portfolio to successfully seed additional bioreactors
(T. Sandy, personal communication, 2012).
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REMEDIATION Winter 2016
The cometabolic relationship between DX and tetrahydrofuran (THF) has been
observed by a number of authors (Masuda et al., 2012; Sales et al., 2013). An aerobic
bioreactor was eld piloted, then implemented full scale at the Lowry Landll Superfund
site in Denver, Colorado, for treatment of DX levels of 8,000 𝜇g/L to 12,000 𝜇g/L in
groundwater (Stanll et al., 2004). The site groundwater, from a former municipal
landll, was contaminated with high concentrations (20,000 𝜇g/L to 30,000 𝜇g/L) of
THF. The site originally had a conventional wastewater treatment system with
UV/oxidation and GAC treatment for DX and other organic wastewater. However, the
treatment eciency was not satisfactory due to low UV transmittance and hydroxyl
scavenging with wastewaters. Ex situ biological treatment was pilot tested using parallel
300-gallon xed-lm and moving bed bioreactors. The eld pilot system was operated at
less than 1 gpm at an inuent temperature of 15 ◦Cto25◦C to allow direct biological
destruction of the DX, which was reduced by 95 percent (Stanll et al., 2004). During the
pilot study, THF in the waste stream was observed to be required for DX degradation.
Both THF and DX were biodegraded in the presence of indigenous microbial populations.
Based on the success of the pilot study, a full-scale treatment system was designed,
constructed, and operated to replace the UV/oxidation processes. During the pilot study,
THF in the waste stream was observed to be required for DX degradation. Both THF and
DX were biodegraded in the presence of indigenous microbial populations. Based on the
success of the pilot study, a full-scale treatment system was designed, constructed, and
operated to replace the UV/oxidation processes. This system has been operating for more
than a decade, and the operational data are described in an article elsewhere in this DX
special issue of Remediation.
IN SITU TREATMENT TECHNOLOGIES
Phytoremediation
The use of vegetation to remove environmental pollutants (phytoremediation) is an
economically favorable remediation alternative with costs only 10 to 50 percent as high as
other conventional treatment options, including excavation (Aitchison, 2000). The
technology typically relies on one or more processes, including the following: (1) direct
plant uptake followed by metabolism or volatilization from the plant leaves and (2)
microbial stimulation and biotransformation in the rhizosphere through the release of root
exudates and plant enzymes (EPA, 2006; Kelley et al., 2001; Nyer,2009).
Microorganisms capable of synthesizing DX-degrading enzymes are rare in nature;
therefore, the latter process is believed to be relatively ineective in DX removal (Kelley
et al., 2001) and the dominant process is thought to phytovolatilization for transfer into
the atmosphere where the half-life is estimated to be on the order of 8.8 hr to 22.4 hr
(Mohr et al., 2010). Due to their tolerance to high concentrations of organics, deep root
systems, high water uptake rates, and ease of propagation, hybrid poplars are
predominately used in phytoremediation (Aitchison, 2000).
Several studies have demonstrated that phytoremediation may be a viable alternative
to removing DX from contaminated sites. Sorensen (2013) reviewed site characteristics at
12 sites in North Carolina impacted by DX in groundwater to assess whether these sites
would be candidates for phytoremediation. Six of the 12 were found to have the optimal
site conditions, including room for phytoremediation tree stands, shallow depth to
During the pilot study,
THF in the waste stream
was observed to be
required for DX degrada-
tion. Both THF and DX
were biodegraded in the
presence of indigenous
microbial populations.
Based on the success of
the pilot study, a full-scale
treatment system was de-
signed, constructed, and
operated to replace the
UV/oxidation processes.
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1,4-Dioxane Treatment Technologies
groundwater, relatively thin aquifer, and suitable groundwater geochemistry for plant
growth (Sorensen, 2013).
Gatli et al. (2013) described installations of engineered phytoremediation systems
(Applied Natural Sciences’ patented TreeWell) at several sites impacted with DX. For a
DX manufacturing site in the Netherlands, DX concentrations were as high as
822,000 𝜇g/L in the source area, declining to 20 𝜇g/L at the facility boundary. More
than 200 hybrid poplar (Populus deltoides xnigra) trees were planted/installed across this
greater than four-acre site, approximately 50 using a “straw” method where a water
extraction tube was placed adjacent to the root structure to allow extraction of deeper
(e.g., 7 m to 8 m below ground surface) water (Exhibit 2). The results after 14 months
indicate a shift in groundwater gradient with the plume being drawn toward the planting
area, restricting o-site migration (Gestler, 2016). At this site, assessment of deeper
aquifer gradients is convoluted by tidal inuence. Lack of tree mortality suggests high
tolerance of up to 300 mg/L of DX in groundwater, and evidence of rhizodegradation was
noted. At a second site, in Sarasota, Florida, groundwater impacted with up to 200 𝜇g/L
DX was migrating in a fractured bedrock, inaccessible to existing vegetation along the
downgradient edge of the approximately three-acre property where DX was migrating
into a residential area. More than 150 TreeWell units were planted on 20-foot centers,
including slash pine (Pinus elliottii), pond cypress (Taxodium ascendens), and laurel oak
(Quercus laurifolia) species. After approximately 18 months of operation, the
phytoremediation system had successfully reversed the groundwater gradient at the site,
providing mitigation to o-site migration, and reduced concentrations in a well 30 feet
downgradient of the planting area two orders of magnitude to nondetect levels (Gestler,
2016).
Silva (2010) performed eld testing to compare two tree species native to Ontario as
alternatives to the commonly utilized hybrid poplar. Studies were performed at an
industrial site using black willow (Salix nigra) and Ontario balsam poplar (Populus
balsamifera) with water impacted by up to 5,000 𝜇g/L DX and 100 million 𝜇g/L ethylene
glycol (Silva, 2010). The poplar trees had a higher survival rate (71 percent vs. 19
percent), greater growth, and higher evapotranspiration rate, although variations during
dry versus wet seasons impacted those rates substantially. The author concluded that,
overall, the poplar trees were more eective at phytocontainment and phytovolatilization
than the willow (Silva, 2010).
These studies demonstrate the eectiveness of phytoremediation for DX containment
and/or treatment under a variety of site conditions and climate characteristics. In addition
to the primary benets provided in plume containment and reduction in both
concentrations and mass ux at a low operating cost, secondary benets of
phytoremediation projects include aesthetic enhancement and are consistent with green
and sustainable remediation (GSR) practices.
Chemical Oxidation
In situ chemical oxidation (ISCO) involves introduction of chemical oxidants into the
subsurface to transform contaminants into less harmful chemical species. ISCO is the most
rapidly growing remedial technology applied at EPA hazardous waste sites (EPA, 2012).
The technology has the potential for relatively fast subsurface treatment and reduction in
remediation costs. However, due to reactive transport and aquifer heterogeneities, oxidant
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REMEDIATION Winter 2016
Exhibit 2. TreeWell system with “straw” for extracting deeper groundwater (Gestler, 2016)
delivery with ISCO may be problematic (Huling & Pivetz, 2006). Furthermore,
depending on site geochemistry, the technology has the potential to mobilize other
contaminants, including bromate and hexavalent chromium (Huling & Pivetz, 2006; Mohr
et al., 2010). Oxidants used for groundwater DX remediation via ISCO include H2O2and
ozone, H2O2and ferrous iron, and persulfate. Each of these is discussed next.
Hydrogen Peroxide and Ozone
An oxidant’s retention time in the subsurface aects its contact time for advective and
diusive transport and ultimately its subsurface delivery to the target contaminated zone.
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1,4-Dioxane Treatment Technologies
An oxidant’s retention
time in the subsurface
affects its contact time for
advective and diffusive
transport and ultimately
its subsurface delivery to
the target contaminated
zone.
An oxidant’s retention time in the subsurface aects its contact time for advective and
diusive transport and ultimately its subsurface delivery to the target contaminated zone.
For example, the reactivity of H2O2with nontarget chemical species, including soil
organic matter and heavy and transition metals, results in its rapid decomposition, short
subsurface persistence (on the order of minutes to hours), and limited advective and
diusive transport (Huling & Pivetz, 2006). Ozone also rapidly reacts with a wide range of
naturally occurring nontarget chemical species, including soil organic matter, reduced
minerals, and the hydroxide ion (OH−; Huling & Pivetz, 2006). Based on thermal
decomposition only, the typical half-life of gaseous and aqueous ozone at pH 7 is reported
at three days and 20 min, respectively (Huling & Pivetz, 2006). Furthermore, in situ ozone
oxidation results in the formation of ozone/air channels that generally contact only a small
cross section of the aquifer. Therefore, transport and distribution of ozone gas in the
saturated zone is limited to very short distances from the gas channels formed during
injection. Finally, the fast reaction rates and scavenging of the hydroxyl radical (generated
during the mixing of H2O2and O3) by various nontarget species (i.e., H2O2,NO
3-,
SO42−,Cl-,HPO
42−, HCO3−,CO32−) result in its limited subsurface transport distance
of only a few nanometers (Huling & Pivetz, 2006).
In spite of these potential handicaps associated with H2O2and ozone oxidation, eld
pilot testing has demonstrated eective destruction of DX from levels as high as 690 𝜇g/L
down to a detection limit of 3 𝜇g/L, a 99.6 percent removal (Haley & Aldrich, 2005;
Schreier et al., 2006). We should note that, while this technology was demonstrated at the
eld scale more than a decade ago, the paucity of published full-scale eld applications
speaks to the limitations described earlier.
Hydrogen Peroxide and Ferrous Iron
Fenton-driven ISCO involves CHP with ferrous iron to produce hydroxyl radicals. Due to
its abundance in the soil environment, naturally occurring iron may serve as an important
source of catalyst for the Fenton mechanism. The reaction between Fe2+and H2O2is
rapid (Huling & Pivetz, 2006). Consequently, the reaction between the ferrous iron and
peroxide needs to be controlled, either by controlling how and where the substances mix,
or by stabilizing the reaction. Ferrous iron is also vulnerable to various reactions
(oxidation, complexation, precipitation), which result in its immobilization and
minimized transport within the aquifer. However, iron can act as an electron shuttle in the
activation process and cycle between ferrous and ferric states. A poorly managed injection
of Fe2+and H2O2may result in the Fenton reaction occurring in or very near the injection
site and Fe precipitation and immobilization in or near the well screen (Huling & Pivetz,
2006). The injection of high concentration H2O2required in the Fenton process results in
the generation of O2gas and may cause temporary reductions in hydraulic conductivity
and groundwater transport (Huling & Pivetz, 2006). Because of H2O2instability,
contaminant oxidation eciency, and iron solubility and availability are greater under
acidic conditions (pH 3 to 4), the solution must be acidied to keep the catalyst in
solution, or the catalyst must be kept in solution using a chelation agent. Acidication of
the injected H2O2may enhance transport of pH-sensitive metals under acidic conditions
(Huling & Pivetz, 2006). In situ Fenton oxidation is a relatively inexpensive technology
with average cost of H2O2of $0.26 per pound (Huling & Pivetz, 2006).
80 Remediation DOI: 10.1002/rem c⃝2016 Wiley Periodicals, Inc.

REMEDIATION Winter 2016
Borchert et al. (2014) demonstrated eective reductions of DX in bench-testing to
support full-scale design for ISCO in low permeability source area soils at a site impacted
with mixed CVOCs, petroleum contaminants,and DX. TCE was as high as 596,000 𝜇g/L,
1,1-DCA at 99,800 𝜇g/L, and DX at 45,200 𝜇g/L (estimated value). Laboratory studies
were performed with activated sodium persulfate and CHP, including an assessment of
various stabilizers (citrate, sodium phytate, and diethylenetriaminepenta acetic acid) to
enhance longevity of CHP in the subsurface. Phytate resulted in extending the peroxide
eectiveness to four days, which was one day longer than the activated persulfate
eectiveness. The CHP achieved DX reductions in the laboratory of 87 percent versus
29 percent reduction for activated persulfate, which led to the conclusion that a full-scale
implementation of CHP was optimal. However, petroleum light nonaqueous-phase liquid
(LNAPL) was identied at the site during predesign drilling late in the planning and design
process, and activated persulfate was instead selected to avoid the exothermic reactions of
CHP in combination with LNAPL. Although activated persulfate was less eective for DX
at this site in bench testing, the trade-o was deemed necessary to address the multiple
high concentration contaminants present at the site. Groundwater monitoring following
the two persulfate applications has indicated reductions of DX between 78 percent and
91 percent; the higher removals in the eld versus bench tests attributed to higher oxidant
dosage (S. Borchert, personal communication, 2016).
Persulfate
The use of persulfate (S2O82−) in ISCO is an emerging technology (Huling & Pivetz,
2006), although a strong oxidant (oxidation potential of 2.1 eV) persulfate can be
catalyzed to form the more powerful sulfate radical (SO4−) with an oxidation potential of
2.6 V. The formation of the sulfate radical may also initiate the formation of the hydroxyl
radical (Huling & Pivetz, 2006; Cronk, 2008). Persulfate catalysis can be achieved at
elevated temperatures (35 ◦Cto40◦C), with Fe2+, UV activation, alkali, and H2O2
(Cronk, 2008; Huling & Pivetz, 2006; Mohr et al., 2010). Potential sinks of the sulfate
radical include Fe2+, carbonate, and bicarbonate (Huling & Pivetz, 2006). However,
sulfate radical scavenging is currently not well understood. Persulfate is more stable in the
subsurface than H2O2and O3and the sulfate radical is more stable than the hydroxyl
radical (Huling & Pivetz, 2006; Mohr et al., 2010). The persulfate anion is not
signicantly involved in sorption and does not react readily with soil organic matter.
Therefore, persulfate can persist in the subsurface for weeks making it an attractive
oxidant with fewer mass transfer and mass transport limitations. The persulfate anion is
not signicantly involved in sorption and does not react readily with soil organic matter.
Therefore, persulfate can persist in the subsurface for weeks making it an attractive
oxidant with fewer mass transfer and mass transport limitations. Sodium persulfate is the
most common persulfate salt used in ISCO with approximate costs of $1.20 per pound
(Huling & Pivetz, 2006). The relatively higher costs of persulfate with respect to other
oxidants may be oset by the lack of its demand by nontarget aquifer materials.
Removal of DX using persulfate ISCO has been successfully demonstrated at
numerous eld applications with a variety of activation methods. Borchert et al. (2014)
discussed the full-scale implementation of alkaline activated sodium persulfate after the
discovery of petroleum LNAPL at a site made the implementation of CHP dangerous due
to the potential for violent release of gases from the exothermic reactions involved.
The persulfate anion is
not signicantly involved
in sorption and does not
react readily with soil
organic matter. Therefore,
persulfate can persist
in the subsurface for
weeks making it an attrac-
tive oxidant with fewer
mass transfer and mass
transport limitations.
c⃝2016 Wiley Periodicals, Inc. Remediation DOI: 10.1002/rem 81

1,4-Dioxane Treatment Technologies
While all the mechanisms
of activation are not un-
derstood, it is thought that
the soils of a candidate
site should contain iron
and manganese concen-
trated on the soil surfaces.
Reductions were noted after one injection in all ve monitoring wells in the plume, with
reductions ranging from 78 to 91 percent, from concentrations as high as 3,940 𝜇g/L. At
least two additional injections were implemented; however, that additional information is
not available, nor are monitoring data assessing the potential for rebound in areas with
high concentrations (S. Borchert, personal communication, 2016). Natural mineral
activation (NMA) of sodium persulfate was evaluated through performance of bench
testing at six sites, eld pilot testing at four sites, and full-scale eld implementation at
two sites (Berggren & Hatton, 2016; Conkle et al., 2016). NMA provides a simpler
activation that avoids problematic or expensive activators, and can lead to a longer lasting
treatment relative to more aggressive, quick-acting activators. While all the mechanisms
of activation are not understood, it is thought that the soils of a candidate site should
contain iron and manganese concentrated on the soil surfaces. While all the mechanisms
of activation are not understood, it is thought that the soils of a candidate site should
contain iron and manganese concentrated on the soil surfaces. Other contributing modes
of activation may include dissolved iron and manganese, reactive organic compounds
generated by anaerobic processes, and the presence of other mineral surfaces (Berggren &
Hatton, 2016). Bench-test results demonstrated complete activation of sodium persulfate
in controlled microcosms, accompanied by 100 percent DX removal from levels as high as
250 𝜇g/L, within 21 days (Conkle et al., 2016). Field pilot testing at a site in Texas
yielded DX reductions six months after injection at a location 60 feet downgradient of the
injection location. Concentrations of DX were reduced from 205 𝜇g/L to less than 0.465
𝜇g/L (99.8 percent reduction in concentration). Additionally, there was evidence of
unactivated persulfate 60 feet from the injection wells as long as one year after injection,
indicating the longevity of the persulfate was extended by relying on naturally occurring
minerals for activation (Conkle et al., 2016). The author describes a second eld case
study treating DX concentrations as high as 2,750 𝜇g/L in a 150-foot-thick aquifer with
65,000 pounds of unactivated persulfate. In the treatment zone, 90 percent reductions
were observed after two months, which rebounded, then equilibrated at 65 percent
reductions. A well 50 feet downgradient exhibited 50 percent reductions at two months,
with less than 20 percent sustained reductions, and most geochemical parameters
indicating minimal impact from the injection. The author’s conclusion of the principal
dierence between the two case study results was that the rst case study aquifer was
aerobic with initial oxidation-reduction potential (ORP) readings of 0 mV to 200 mV and
dissolved oxygen (DO) readings of 1 mg/L to 4 mg/L, whereas the second case study
aquifer was mildly anaerobic, with initial ORP readings of –50 to –150 mV and DO
readings of 0 mg/L (Conkle et al., 2016). These anaerobic conditions suggested naturally
occurring minerals in the aquifer represented an increased oxidant demand that the
persulfate injection struggled to overcome.
Biostimulation
Due to the high dissociation energy of the ether linkage (360 kJ per mole), ether
functional groups are particularly resistant to biodegradation (White et al., 1996).
However, microcosm studies have reported metabolic and cometabolic biodegradation of
DX under aerobic conditions (Gedalanga et al., 2013; Mahendra et al., 2013). A
nocardioform actinomycete (CB1190) isolated from DX-contaminated industrial sludge
(Parales et al., 1994), was the rst reported pure culture that demonstrated sustained
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REMEDIATION Winter 2016
Exhibit 3. Isolated bacteria reported to grow on 1,4-dioxane
Strain Genus Source
Cell Yield
(mg-protein/
mg-DX)
Degradation Rate
(mg-dioxane/
mg-protein-hr)
Half saturation
concentrations
(mg/L) Reference
CB1190 Pseudonocardia
dioxanivorans
0.002–0.09 0.0198 160 ±44 Li et al. 2010
Adamus
et al.
1995
Mahendra
and
Alvarez-
Cohen
2006
D1 Gram-negative
Apia sp.
Soil in the
drainage area
of a chemical
factory
0.185 0.263 25.8 Sei et al. 2013
D6 Gram-positive
Actinomycetes
Soil in the
drainage area
of a chemical
factory
0.185 0.139 20.6 Sei et al. 2013
D11 Gram-positive
Actinomycetes
Soil in the
drainage area
of a chemical
factory
0.179 0.052 69.8 Sei et al. 2013
D17 Gram-positive
Actinomycetes
Soil in the
drainage area
of a chemical
factory
0.223 0.096 59.7 Sei et al. 2013
PH-06 Top of Fo rm
Mycobacterium
Bottom of Form
Top of form
river sediment
bottom of
form
0.47a0.006a- Kim et al. 2009
mg-protein-hr =milligram(s) of protein per hour. NA =not available.
aEstimated from presented results.
growth on DX as a sole carbon and energy source. Growth of CB1190 on DX is relatively
slow (maximum growth rate of 90 𝜇g/L/hr) and results in low cell yields (0.09 g
protein/g DX) (Mahendra & Alvarez-Cohen, 2005). The culture can also grow on THF,
gasoline aromatics, and several other environmental contaminants (Mahendra &
Alvarez-Cohen, 2005; Parales et al., 1994). Other isolated bacteria reported to
metabolize DX are summarized in Exhibit 3.
Cometabolic transformation of DX is a fortuitous biological process in which the
contaminant does not serve as an energy source for the microorganism and is only
c⃝2016 Wiley Periodicals, Inc. Remediation DOI: 10.1002/rem 83

1,4-Dioxane Treatment Technologies
degraded due to a broad enzyme specicity. Another substrate must be present to sustain
microbial growth. Kinetics of DX degradation and identication of the intermediates for
cometabolic degradation of DX by monooxygenase-containing bacteria were evaluated
and indicated that intermediates would not cause an accumulation of toxic compounds in
the environment (Mahendra & Alvarez-Cohen, 2006; Mahendra et al., 2007). In addition,
Peudonocardia sp Strain ENV478 was isolated by enrichment culturing on THF and was
found to degrade DX after growth on sucrose, lactate, yeast extract, 2-propanol, and
propane (Vainberg et al., 2006). These microcosm studies verify the potential of aerobic
DX biodegradation and the potential of in situ bioaugmentation for DX remediation.
Mahendra et al. (2007) identied the aerobic DX degradation pathways for metabolic and
cometabolic monooxygenase-expressing bacteria. In all cases, DX was mineralized
without the accumulation of toxic by-products. Major intermediates included
2-hydroxyethocyacteic acid (HEAA), ethylene glycol, glycolate, and oxalate while CO2
was the expected major end product. The study demonstrated that bioremediation of DX
via this pathway is not expected to cause an accumulation of toxic compounds in the
environment. Major intermediates included 2-hydroxyethocyacteic acid (HEAA),
ethylene glycol, glycolate, and oxalate while CO2was the expected major end product.
The study demonstrated that bioremediation of DX via this pathway is not expected to
cause an accumulation of toxic compounds in the environment.
In situ bioremediation (ISB) of toxic pollutants has become an increasingly important
remediation strategy for contaminated water resources. It is an eective, economical, and
sustainable technology that can be used in conjunction with or as an alternative to
physical–chemical treatment technologies. ISB can be implemented by (1) allowing
intrinsic microorganisms in the subsurface to biodegrade the COC without human
intervention other than monitoring, referred to as natural attenuation; (2) supplying
necessary amendments or nutrients to enhance biodegradation of the contaminant by the
microorganisms, referred to as biostimulation; or (3) introducing microorganisms to the
subsurface that have been shown to be capable of degrading the COC, referred to as
bioaugmentation. In recent years, microcosm studies have been conducted to understand
DX biodegradation rates under cold regimes (4 ◦C and 14 ◦C; Li et al., 2010), in the
presence of co-occurring metals and chlorinated solvents (Mahendra et al., 2013;
Pornwongthong et al., 2014; Zhang et al., 2016), or under bioaugmentation conditions
for direct metabolic biodegradation by CB1190 (Gedalanga et al., 2014; Kelley et al.,
2001). All these microcosm studies built a better understanding of the feasibility of DX
biodegradation for in situ or ex situ applications and optimum conditions needed for
successful applications.
Researchers at Rice University (Li et al., 2015) performed bench-scale microcosm
studies to assess the eects of cometabolic biostimulation of indigenous bacteria with
methane and propane. In addition to monitoring for reductions in concentration, copy
numbers of THF/dioxane monooxygenase and 16S ribosomal ribonucleic acid genes were
quantied by real-time qualitative polymerase chain reaction using TaqMan assays to assess
the changes in genetic markers tied to DX biodegradation. Methane biostimulation was
unsuccessful in this test and the project team noted that the form of methane
monooxygenase (MMO) enzymes present (particulate vs. soluble) may have been
incapable of degrading DX. Propane stimulation was eective at reducing DX
concentrations by approximately 80 percent, but only after the propane was exhausted
(Li et al., 2015). Biostimulation was found to be inadequate to stimulate propanotrophic
84 Remediation DOI: 10.1002/rem c⃝2016 Wiley Periodicals, Inc.

REMEDIATION Winter 2016
bacteria during a eld pilot study at Vandenberg Air Force Base necessitating
bioaugmentation using Rhodococcus ruber ENV425 (Lippincott et al., 2015). In a single
well injection study, biodegradation of DX began rapidly after bacteria were added and
progressed with an apparent rst-order decay rate of 0.021 day−1to 0.036 day−1.DX
concentrations declined from 1,090 𝜇g/L to nondetect at 2 𝜇g/L. Eects were also
observed in a distal downgradient monitoring well where reductions of 95 percent were
observed. In a control well where only propane and oxygen were added, no DX
degradation was observed (Lippincott et al., 2015).
Valuable recent research has been performed to develop microbiological tools capable
of identifying the biological mechanism or developing biodegradation rates for DX in
aquifer solids or groundwater. Specically, the development of compound-specic isotope
analysis (CSIA) for DX and identication of DX monooxygenase and aldehyde
hydrogenase enzymatic markers has allowed more thorough evaluation of DX
biodegradation, both for biostimulation and natural attenuation approaches (Chiang et al.,
2012; Gedalanga et al., 2013).
Additional biostimulation studies are detailed elsewhere in this special issue of
Remediation.
Natural Attenuation
Monitored natural attenuation (MNA) is a well-established and accepted remedial
approach for numerous VOCs, including CVOCs and petroleum constituents, such as
benzene, toluene, ethylbenzene, and xylenes (BTEX). Demonstrating MNA requires
evidence to support three lines of evidence, as outlined in EPA guidance (EPA, 1999): (1)
direct evidence of stable or shrinking plume and decreasing concentration trends, (2)
indirect hydrogeologic or geochemical data identifying the mechanism of attenuation, and
(3) direct evidence demonstrating the attenuation mechanism. Attenuation mechanisms
demonstrated to reduce contaminant concentrations include biodegradation,
volatilization, sorption, diusion, dilution, and dispersion, as well as abiotic chemical
reactions between contaminants and aquifer or groundwater minerals and naturally
occurring compounds. Dispersion, dilution, and diusion into low permeability materials
are important attenuation mechanisms for DX because of its miscibility. Volatilization is
“unimportant for DX due to its very low Henry’s Law constant,” according to Pivetz et al.
(2013), which, as discussed previously, speaks to the low likelihood of VI issues with DX
even though it is a volatile compound. Sorption is not expected to play a major role in
attenuation due to low Koc. Abiotic chemical reactions may play a role in DX attenuation;
however, this mechanism is only recently becoming understood for CVOCs and BTEX
after decades of data gathering, whereas DX abiotic attenuation mechanisms have not been
evaluated in the literature to the authors’ knowledge. Sorption is not expected to play a
major role in attenuation due to low Koc. Abiotic chemical reactions may play a role in
DX attenuation.
Because of its recent discovery, it is dicult to meet the rst line of evidence because
few sites have a long enough history of detections to track long-term declining trends
or shrinking plumes. The second line of evidence has also been dicult to prove until
recently, where there are now studies linking biodegradation of DX to several cometabolic
and direct oxidizing (catabolic) organisms and specic enzymes (Gedalanga et al., 2013;
Mahendra & Alvarez-Cohen, 2006). The third line of evidence,demonstration of a specic
Sorption is not expected
to play a major role in at-
tenuation due to low Koc.
Abiotic chemical reactions
mayplayaroleinDXat-
tenuation.
c⃝2016 Wiley Periodicals, Inc. Remediation DOI: 10.1002/rem 85

1,4-Dioxane Treatment Technologies
degradation process, is futile in the absence of decreasing concentration trends and lack of
a mechanism. However, a metadata study of plume lengths suggested that despite its known
mobility, DX did not often out-distance chlorinated solvent co-contaminants, suggesting it
was not as mobile or recalcitrant as initially thought (Adamson et al., 2014). A second data
mining eort that estimated decline in concentrations in wells over time suggested DX was
degrading at rates similar to groundwater contaminants that are known to degrade, such
as commingled chlorinated VOCs (Adamson et al., 2015). A study of DX groundwater
sites in California indicated evidence of DX degraders present at all three sites
(Li et al., 2014). In microcosm studies performed at Rice University, DX concentrations
declined over time relative to killed control microcosms, suggesting biodegradation
was active at these sites. All these studies indicate DX degraders are present in
DX plumes and that degradation of this compound can occur in the natural environment.
A thorough assessment of natural attenuation of DX is presented elsewhere in this
issue of Remediation.
Thermal
The boiling point of DX at 101.320 ◦C (Smith & Wojciechowski, 1937) is close to but
slightly higher than the boiling point of water, which taken at face value suggests all the
water would need to be boiled away before the DX would be removed. However, a DX
solution in water has an azeotropic decrease in boiling point to a minimum of 87.7 ◦C.
There is also a 50-fold increase in Henry’s Law Constant between the standard testing
temperature of 25 ◦C and the boiling point of water (Oberle et al., 2015), which results
in substantially higher concentrations in the steam o-gas than the solution. These
characteristics allows for removal of DX from water at elevated temperatures,but less
than the boiling point of water. Following observations of greater than 98 percent
reductions in DX concentrations in groundwater at a site being thermally treated for other
COCs (TCE, DCE, trichlorobenzene, xylenes, and Freon-113), Oberle et al. (2015)
conducted DX thermal treatment testing of both water and soil. The initial site
observations that supported this research direction were reductions in DX concentration
from 140 𝜇g/L to 1.4 𝜇g/L in the highest concentration well and from 44 𝜇g/L to
nondetect at 0.5 𝜇g/L in a deeper well at the same location.
Subsequent treatability testing by Oberle et al. (2015) used a high concentration
(1,000 mg/L) DX spiked sample of distilled water that was heated slowly and both the
water and the released condensate were sampled at regular intervals as the water was
brought to a boil. Spiked soil samples were heated until 20 percent, 45 percent, and
80 percent of available moisture was boiled o, and then the treated soil was analyzed
using the EPA Method 8260B SIM. Testing determined 69.2 percent of the DX was
removed from solution when only 13.2 percent of the water had been removed. This
jumps to 98.9 percent DX removal when 39.5 percent of water had been removed,
demonstrating that not all of the water in a system needs to be driven o to attain
substantial reductions in DX mass in the residual water. Soil test results yielded
comparable conclusions, with 87.6 percent of DX removed from the soil after only
20 percent of the soil moisture was boiled o. Building o the previous eld observations
and treatability testing, Oberle et al. (2015) conducted a eld pilot test of electrical
resistive heating (ERH) at a site impacted by TCE and TCA, applying 175 kilowatt-hr of
energy per cubic yard of impacted saturated soil. After 186 days of treatment,
86 Remediation DOI: 10.1002/rem c⃝2016 Wiley Periodicals, Inc.

REMEDIATION Winter 2016
groundwater DX concentrations had been reduced from as high as 90,000 𝜇g/L to less
than 50 𝜇g/L, representing a 99.8 percent removal rate. Steam and vapor were extracted
and the steam condensed and vapors treated before being released to the atmosphere.
These results demonstrate that DX can be eectively removed from impacted soil and
groundwater, at levels greater than 99 percent. And, although the project demonstration
did not achieve groundwater levels as low as the EPA RSL of 0.46 𝜇g/L, the test was
terminated at 186 days without an objective of achieving those low numbers. Thermal
treatment is a source zone treatment technology, and it is likely that project objectives can
be met without meeting the low risk–based standards being applied to drinking water
aquifers. Based on these testing results, Oberle et al. (2015) estimate that the cost of
thermal treatment of DX will range from $150 to $300 per cubic yard.
SUMMARY/CONCLUSIONS
The changing regulatory landscape and increasing attention from regulatory and
community stakeholders has made DX an emerging contaminant. Several ex situ remedial
technologies are fully developed for this recalcitrant compound, having been implemented
successfully at numerous sites.Additional technologies have recently emerged that have
the promise of reducing capital or operational costs for cleanup. In situ technologies are
not as well developed and proven; however, ample evidence exists from bench-scale and
eld pilot studies to suggest that these technologies have been demonstrated suciently to
be worthy of consideration, depending on site conditions. Of these in situ technologies,
ISCO has the greatest proof of eectiveness with a variety of oxidants in a variety of
hydrogeologic conditions. Of course as with all applications of ISCO, hydrogeologic
characteristics and factors such as back diusion have a large impact on ISCO success.
Thermal treatment is well demonstrated and overcomes some of these hydrogeological
uncertainties, but is not well suited to plume capture or plume treatment, as opposed to
source area cleanup. In situ biological technologies have developed rapidly over the past
several years and a growing body of evidence indicates that DX-degrading bacteria are
indigenous to most locales, those bacteria are often active, especially in aerobic
conditions, and growth of those bacteria can be stimulated through injection of propane,
or in select conditions, methane. Biodegradation rates and details on the mechanism of
degradation are yet to be well dened, and the recent development of microbiological
tools will help answer those important questions. Natural attenuation has recently been
demonstrated at a few sites and is expected to play an important role in long-term
management of large diuse plumes, which are common for DX impacts. Natural
attenuation has recently been demonstrated at a few sites and is expected to play an
important role in long-term management of large diuse plumes, which are common for
DX impacts. The research, both by academics and industry practitioners, has allowed for
rapid progress in DX treatment technology assessment and demonstration and it is certain
that the next several years’ of work will add condence to the decision-making process.
NOTE
1. TMTrademark of The Dow Chemical Company ("Dow") or an aliated company
of Dow
Natural attenuation has
recently been demon-
strated at a few sites and
is expected to play an im-
portant role in long-term
management of large
diffuse plumes, which are
common for DX impacts.
c⃝2016 Wiley Periodicals, Inc. Remediation DOI: 10.1002/rem 87

1,4-Dioxane Treatment Technologies
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William DiGuiseppi, is a principal hydrogeologist and program technology manager with nearly 30 years
of applied experience on hundreds of soil and groundwater investigation and remediation sites. He is a licensed
Professional Geologist and is the leader of CH2M’s Chemicals and Issues of Emerging Concern Community of
Practice. In that role, Bill directs a team of professionals in the identication, prioritization, and management of
chemicals such as 1,4-dioxane, peruorinated compounds, 1,2,3-trichloropropane, hexavalent chromium, and
other critical emerging pollutants. Bill has led large and complex environmental investigation and remediation
projects, published technical articles, chaired sessions at international conferences and co-authored a denitive
book on 1,4-dioxane with Tom Mohr. Bill earned a B.S. in geology from George Mason University and an M.S. in
geology from the University of Utah.
Claudia Walecka-Hutchison, PhD, is an EH&S Remediation Manager at The Dow Chemical Company.
In this role she is involved in developing site-specic solutions for Dow’s global remediation projects including
maintaining active research studies. Claudia has over 10 years of experience in site investigation and remediation
with extensive expertise working with chlorinated solvents and petroleum hydrocarbons. Claudia specializes in
bioremediation and holds a PhD in Soil, Water, and Environmental Science and an MS in Hydrology from the
University of Arizona.
c⃝2016 Wiley Periodicals, Inc. Remediation DOI: 10.1002/rem 91

1,4-Dioxane Treatment Technologies
Jim Hatton is a Principal Technologist and Senior Engineer in CH2M’s Site Remediation and Restoration
group, in Englewood, Colorado. Mr. Hatton supports the remediation of contaminated sites with innovative
technologies and supports CH2M’s emerging contaminants program. Mr. Hatton received his B. S. in Petroleum
Engineering from West Virginia University in Morgantown, West Virginia.
92 Remediation DOI: 10.1002/rem c⃝2016 Wiley Periodicals, Inc.