A newsletter about soil, sediment, and groundwater characterization and remediation technologies
Technology
News & Trends
SEPA
EPA 542-N-12-003 | Issue No. 59, June 2012
This issue of Technology News & Trends highlights technologies for characterizing and
remediating sites with persistent organic pollutants (POPs) such as polychlorinated biphenyls
(PCBs), dioxin/furans, and certain pesticides. A total of 22 POPs are now recognized by the
Stockholm Convention as having the properties of:
• Remaining intact for exceptionally long periods of time
• Becoming widely distributed throughout the environment
• Accumulating in the fatty tissue of living organisms, and
• Posing toxicity threats to humans and wildlife.
Historically, cleanup of soil, sediment, and groundwater contaminated with POPs commonly
involved excavation, dredging, or ex situ thermal processes followed by offsite disposal. Use of
these technologies can result in significant project costs, landfill burdens, potential dispersion
of contaminants, and/or combustion-related creation of carcinogens. New alternatives
undergoing tests in laboratory or field settings often involve bioremediation, plant-based, or
oxygenation technologies.
FEATURED ARTICLES
Emerging Technologies: 1,4-Dioxane Occurrences and
Treatment Options in Private Wells
Contributed by Thomas K. G. Mohr*
1,4-Dioxane is a persistent organic pollutant that is highly mobile and tends to form long
plumes significantly advanced from the leading edge of a chlorinated solvent plume, and its
detection is often missed during site investigation and plume delineation. Consequently, many
monitoring well networks, capture zones, and treatment trains are designed to characterize,
recover, and remove chlorinated solvents but not associated 1,4-dioxane contamination.
Certain volatile organic compounds (VOCs) such as trichloroethane (TCA) are often
co-contaminants of 1,4-dioxane and may be used to trigger consideration of 1,4-dioxane's
extreme mobility and whether testing of private wells far beyond the extent of the VOC plume
is warranted. Results of a 2006 U.S. Geological Survey study of 1,208 domestic wells, as
summarized in Volatile Organic Compounds in the Nation's Ground Water and Drinkina-Water
Suoolv Wells, detected the presence of 1,1,1-TCA, 1,1-dichloroethane, and 1,1-dichloroethene
(as potential 1,4-dioxane co-contaminants) in as many as 102, 26, and 19 wells, respectively.
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1,4-Dioxane in groundwater is resistant to natural biodegradation or treatment technologies
such as air stripping, carbon adsorption, reverse osmosis, and ion exchange. Advanced
oxidation technologies employed ex situ (such as ozone peroxidation, ultraviolet-oxidation,
and catalyzed photo-oxidation) often are used for this purpose but carry a high capital and
operating cost. For owners of private wells affected by contaminated sites, these costs are
prohibitive. Alternatives such as connecting to a municipal supply or exclusively using bottled
water also may be costly or infeasible.
Granular activated carbon (GAC) filters typically have been used to treat chlorinated solvents
in domestic supply wells and are now being used in an attempt to treat 1,4-dioxane
simultaneously. Although GAC is not expected to perform well for 1,4-dioxane removal due to
its low organic carbon partitioning coefficient (l^c)/ in some cases the retention rates in GAC
have exceeded the calculated sorption rates, suggesting that matrix diffusion by 1,4-dioxane
into the carbon structure is a potential removal mechanism. Due to its anomalously high
dipole moment in aqueous solutions, 1,4-dioxane is an efficient water-structure breaker
capable of penetrating the tightly held monolayer of water on clay surfaces, and may similarly
penetrate activated carbon's porosity in a way that more hydrophobic non-polar contaminants
cannot.
Adaptations for deploying GAC in 1,4-dioxane removal have proven more effective than
expected at several sites where small privately-owned wells are used for residential or
industrial purposes. Successful methods for employing GAC technology have included
installing conventional well carbon cartridges in series with frequent midpoint sampling and
frequent lead vessel change-out; operating at flow rates substantially lower than the carbon
vessel flow capacity; and using substantially over-sized carbon vessels operating in series.
For example, in the Tylerville section of Haddam, Connecticut, two 3-cubic-foot carbon
vessels were installed in series on a well with 10-20 micrograms per liter (ug/L) 1,4-dioxane
as part of remedial investigations under the Connecticut Department of Energy and
Environmental Protection (CTDEEP) Superfund Program. Breakthrough of 1,4-dioxane was
experienced after four and nine months, prompting frequent replacement of the carbon
vessels despite their continued removal of targeted TCE and other chlorinated solvents.
Purchase and installation costs for a typical GAC filter system in this type of setting average
approximately $2,500, with single filter replacements costing about $700.
CTDEEP field experience at Tylerville and other sites found that 1,4-dioxane concentrations in
mid-point and end-point samples of water lines are occasionally higher than in influent
samples, suggesting buildup and subsequent release of 1,4-dioxane (sloughing). This finding
is consistent with previous research by others, which suggests that the observed
breakthroughs at the Tylerville well were due to the carbon absorption and adsorption
reaching their capacity for retaining 1,4-dioxane, or to a "chromatographic effect." i.e., initial
adsorption followed by displacement by compounds with stronger affinity to adsorb to carbon.
Absorption of 1,4-dioxane into GAC pores, as opposed to adsorption onto GAC surfaces, is
among the possible mechanisms for complete removal of 1,4-dioxane in groundwater at the
U.S. Department of Energy's Stanford Linear Accelerator Complex (SLAC) in California. The
treatment process's very slow flow rate (0.2 gallons per minute (gpm)) coupled with a
106-cubic-foot capacity in each GAC vessel (634 gallons in both vessels, accounting for a
40% void volume) leads to a slow bed-volume exchange (0.45 bed volumes per day) and a
long contact duration (53 hours of transit time through the two GAC vessels). The grade of
carbon selected for VOC removal is a coconut shell-based GAC (AquaCarb® 1230C) designed
to remove poorly adsorbable organics from water such as MTBE and other trace-level
organics. This product is an acid-washed pH-neutral GAC with a low ash content designed for
use in potable water systems and in high-purity water systems for the microelectronics and
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other industries. It also passes the ANSI/NSF Standard 61 for use in potable water applications.
Figure 1. Single in-line water treatment
system involving both ozone/perozone
injection and air stripping technologies.
To remove 1,4-dioxane in smaller private wells, one option is an advanced oxidation system
known as ClearDioxane™. The system uses a micro-bubbler and ozone generator to inject
ozone and perozone (peroxide-coated micro- to nano-bubble ozone) into a pressurized
hydrodynamic tank to achieve mixing and optimal residence time (Figure 1). The tank
discharges to a modified shallow-tray air stripper (the Clearadon™ stripper) for ozone and
VOC removal, and the treated water is then repressurized for delivery within the water line.
Preliminary results from bench-top testing of the oxidation system show a significant
reduction in 1,4-dioxane concentration, from 100 ug/L 1,4-dioxane to less than 3 ug/L.
Follow-up field trials are underway in New Jersey and Florida. The cost to equip a 10-gpm well
with this system is estimated at $18,000-$20,000. Its operating cost is strongly driven by
electricity consumption. Application for a 6- to 10-gpm well, for example, may involve an
energy demand of 20 kilowatts/hour (kWh). If deployed at a site where electricity costs
$0.12/kWh, the cost to operate a system of this size is estimated at $2.40 for each 1,000
gallons of water treated. While prohibitive in many cases, these costs may be necessary in
rural areas where hookup to a municipal water supply is infeasible.
Using GAC or the advanced oxidation system as a point-of-entry treatment (POET) system for
private wells is preferred over a point-of-use treatment (POUT) system installed on individual
faucets, since a POET system is installed on the primary water intake valve that routes treated
water to all connected faucets. Most POET systems, however, are designed to treat only
specific contaminants rather than all contaminants or potentially harmful bacteria and
consequently cannot be used for all-purpose filtration.
Most state health agencies do not issue operating permits for small private well systems, and
securing an independent certification of a well-water treatment system can involve a lengthy
process. Additional case studies and information exchange are needed to help cleanup
decision-makers better understand the fate and transport of 1,4-dioxane and implement
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reliable treatment technology for affected private wells. More information on 1,4-dioxane can
be obtained from the U.S. Environmental Agency's Treatment Technologies for 1.4-Dioxane:
Fundamentals And Field Applications report and the 1.4-Dioxane and Other Solvent Stabilizers
White Paper available from the Santa Clara Valley Water District.
* Thomas K.G. Mohr is a past President of the Groundwater Resources Association of
California and author of "Environmental Remediation and Investigation: 1,4-Dioxane and
Other Solvent Stabilizers" (CRC Press, 2010). Mr. Mohr is currently employed by the Santa
Clara Valley Water District and independently pursues the 1,4-dioxane challenge.
Treatability Studies: Using Ferns for Arsenic Bioaccumulation
at Georgia Superfund Site
Contributed bv Charles King and Linda Georae, U.S. EPA Region 4; and Joe Owusu-Yaw,
Ph.D., ILS
The U.S. EPA Region 4 office recently completed a treatability study on the use of ferns to
remediate arsenic contamination at the 31-acre Woolfolk Chemical Works, Inc. Superfund site
in Fort Valley, Georgia. At various times from the 1910s to the early 1980s, approximately 18
acres of this site were used to manufacture arsenic trichloride as well as pesticides,
insecticides, and herbicides such as DDT, lindane, and toxaphene. Removal and remediation
actions initiated in 1984 have involved soil excavation and offsite disposal, groundwater
extraction and treatment, and/or installation of lined containment cells across four operable
units.
The recent treatability study supports remedy selection for a fifth operable unit (OU5)
associated with offsite drainage potentially affecting adjacent commercial or residential
neighborhoods and approximately three miles of watershed downstream. The study involved
bench-scale tests using native ferns and non-native ferns that are known to hyperaccumulate
arsenic in downstream wetlands and riparian buffers. Selected fern species also were tested
under greenhouse conditions.
Initial activities involved collecting surface soil or sediment samples from five stations at OU5
in 2009. To confirm that the collected samples provided a range of arsenic concentrations
suitable for treatability testing, x-ray fluorescence was used to screen dried samples prior to
analysis at EPA Region 4's Science and Ecosystem Support Division (SESD) laboratory.
Analytical results showed arsenic concentrations in soil ranging from 22 mg/kg to 180
milligrams per kilogram (mg/kg) dry weight (dw) with a pH of 3.52 to 5.07, below the
optimum pH 6-7 needed for arsenic extraction.
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Figure 1. Diverse fern community at a
reference station near the Wool folk
Chemical Works, Inc. site.
Several species of native ferns existing along a downgradient creek and in adjoining
floodplains also were collected for analysis. Observed species included ebony spleenwort
(Asplenium platyneuron), wood ferns (Dryopteris sp.), netted chain fern (Woodwardia
areo/ata), bracken fern (Pteridium aquilinum'), cinnamon fern (Osmunda cinnamomea'), royal
fern (Osmunda regalis), and sensitive fern (Onoclea sensibilis) (Figure 1). The fern samples
were analyzed at an offsite Contract Laboratory Program (CLP) facility using inductively
coupled plasma (ICP) atomic emission spectroscopy. Results indicated arsenic concentrations
were highest in ebony spleenwort (30 mg/kg dw with a co-located soil concentration of 180
mg/kg dw).
Two bench-scale studies were conducted at the SESD laboratory. The studies focused on three
fern species expected to have the greatest accumulation potential for this site: Cretan brake
(Pteris cretica 'Mayi') and ladder brake (Pteris w'itata) available from a bioremediation
specialty firm, and native ebony spleenwort obtained from a local supplier. Using soil/sediment
collected from the five sampling stations, the ferns were grown under ambient laboratory
illumination of 1,000-1,500 lux at a temperature of 2lT
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125PCA 1Z7PCA 1MWPCA 1S5PCA 1550PCA 15«PCA
Sanpt* ID. Woolfolk Chtmcaf Works Site. Fort Valley, GA
Figure 2. Arsenic accumulation in the fern Pteris cretica 'May;'
during bench-scale studies.
Similar conditions were used in the second bench-scale study, which was performed on ladder
brake fern and ebony spleenwort. In addition, lime or fertilizer was added to some samples to
determine if such amendments would enhance arsenic uptake. The ladder brake ferns did not
grow as expected, possibly due to transplanting shock, and achieved little to no arsenic
uptake; the maximum concentration uptake for arsenic was 26 mg/kg dw. Growth of the
three-year-old ebony spleenwort was more robust, resulting in a maximum arsenic uptake of
39 mg/kg dw (Figure 3), which was slightly higher than the 30 mg/kg dw concentration earlier
found in ebony spleenwort growing naturally at the same field station. Adjusting the soil pH to
neutral or fertilizing the plants had little or no effect on arsenic uptake in this study.
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Samplc ID, Waolfolk Chcrrtcal Works Site. F«t Valley, GA
Figure 3. Arsenic accumulation in the ferns Pteris vittata and
ebony spleenwort during bench-scale studies.
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Researchers at the nearby Fort Valley State University (FVSU) conducted the companion
greenhouse tests in 2011, using Woolfolk soil (or sediment) associated with differing onsite
drainage conditions and arsenic concentrations ranging up to 150 mg/kg. Testing focused on
the ladder brake fern as well as silver ribbon fern (Pteris cretica 'Albo-lineata'), which are both
hardy perennials that can be harvested up to three times in a six-month period. Based on the
results of routine soil analysis performed by the University of Georgia's Agricultural and
Environmental Services Laboratories, lime was added to the experimental pots to raise soil pH
to levels needed for optimal fern growth. Soil treatments involved individual six-inch pots
containing either ladder brake fern, silver ribbon fern, ladder brake fern with triple
superphosphate, silver ribbon fern with triple superphosphate, or soil with triple
superphosphate but no fern.
Both species of fern were observed to flourish in the Woolfolk soil under greenhouse
conditions, regardless of the soil moisture or arsenic content. Four of the eight treatment pots
and two of the four control pots were sacrificed after six weeks of plant growth, and the
remaining were sacrificed after 13 weeks. Samples of the fern fronds, roots, and soil were
separately composited and submitted to the EPA Region 4 SESD laboratory for analysis.
Analytical results indicated arsenic reductions in soil reached 26.8%, although higher removal
rates are expected in more mature plants during a normal growing season. The ladder brake
fern and silver ribbon fern accumulated arsenic at similar rates with no apparent influence
from phosphorus amendment. In addition to supporting remedy selection for OU5, results of
the greenhouse tests are being integrated into broader phytoremediation studies led by
Cornell University and the University of Maryland.
Based on final results of the SESD treatabilitv study and FVSU greenhouse tests, EPA Region
4 will conduct an onsite pilot-scale field project if funding is available. The project would rely
on ladder brake, Cretan brake, or silver ribbon ferns as the arsenic hyperaccumulators and
may involve plant fertilization, irrigation, soil enhancements such as aeration and pH
adjustment, and/or soil amendments.
CLU-IN Website
• POPs: treatment technology reports
• PCBs: an overview of aspects such as toxicology, detection and site characterization, and treatment
technologies
• 1.4-Dioxane: an overview
State Initiatives: California Biomonitoring Program
Under this new program, the State of California will measure the toxic chemicals accumulating
in the bodies of Californians. The measurements will provide a snapshot of which chemicals in
Californians are rising, which are falling, and which are emerging chemicals of concern
(including POPs). The California Department of Toxic Substances Control will use information
on the levels of chemicals in humans and wildlife to identify problem chemicals, understand
where to focus pollution prevention efforts, prioritize chemical cradle-to-cradle efforts, and
use these chemicals as indicators to measure success of state interventions.
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New Tools: User Guide: Uniform Federal Policy Quality
Assurance Project Plan Template for Soils Assessment of
Dioxin Sites
EPA developed this user guide to provide a consistent approach for using incremental and
compositing techniques in assessment of dioxin in shallow soil. A companion template is
available to use as a platform for compiling site-specific and technical background information.
EPA is publishing this newsletter as a means of disseminating useful information regarding innovative and alternative
treatment technologies and techniques. The Agency does not endorse specific technology vendors,
Contact Us:
Suggestions for articles in upcoming issues of Technology News and Trends may be submitted to
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