United States
Environmental Protection
Agency
Solid Waste and
Emergency Response
(5102G)
EPA 542-N-01-007
October 2001
Issue No. 41
Ground Water Currants
CONTENTS
GCWs Used with Air
Stripping and UV
Technologies to Remove
TCEandRDX Pg. 1
Bioaugmentation Field
Testing for MTBE
Treatment Pg. 2
SurfactantFlooding
Used to Remove
PCEDNAPL Pg. 3
About this Issue
This issue highlights innovative
technologies for remediating
ground water at military sites
contaminated with ordnance,
MTBE, and chlorinated solvents.
Currently, monethan21,000
potentially contaminated sites
exist on defense-related facilities
across the country. These
facilities offer unique
opportunities for collaborative
efforts on technology innovation
involving the U. S. EPA, other
Federal departments and
agencies, and the private sector.
It is estimated that cleanup of
these sites will cost about $3 0
billion.
GCWs Used with Air Stripping
and UV Technologies to
Remove TCE and RDX
by Tom Graff, U.S. Army Corps of
Engineers, and Curt Elmore,
Ph.D., University of Missouri-
Rolla
In March 2001, the U.S. Army Corps of
Engineers completed pilot studies on a
dual system for using ground-water
circulation wells (GCWs) equipped with
an in-well air stripper system to treat
trichloroethylene (TCE) and an ultra-
violet (UV) light treatment unit to destroy
cyclotrimethylenetrinitramine (RDX).
After nine months of operation at the
former Nebraska Ordnance Plant (NOP)
site near Mead, NE, the systems have
demonstrated mass removal rates greater
than 96 percent. This project marks the
first known applications of GCWs
involving shallow-tray air stripping
technology to remove TCE and UV
technology to destroy explosives.
Currently used by the University of
Nebraska's Agricultural Research and
Development Center and the National
Guard, the pilot study sites contain
ground water contaminated from past
U.S. Department of Defense activities.
The underlying Todd Valley and Platte
River aquifers are relatively prolific, with
the capability of sustaining large-
capacity irrigation wells producing 700 or
more gallons per minute (gpm). The
highest concentrations of TCE and RDX
occur in sand and gravel portions of the
aquifers, while the bedrock portions have
very limited areas of contamination. The
depth to ground water at the site is
typically 30-40 feet below ground surface
(bgs), and the depth to bedrock is
typically 100 feet bgs.
The dual treatment system used at the
NOP site comprises two GCWs equipped
with treatment units in partially buried
vaults. One of the GCW treatment
systems contains a shallow-tray air
stripping unit for TCE removal, while the
second contains a UV photolysis unit for
RDX destruction. Contaminated ground
water is pumped into a GCW, treated in
the vault, and returned to the aquifer
through a separate portion of the same
well (Figure 1). A packer is installed
midway between the zone of aquifer
extraction and zone of recharge to
separate the extraction and recharge well
screens.
After treatment and recharge to the
aquifer, some of the treated ground water
travels downstream and away from the
GCW influence, while some mixes with
untreated ground water and re-enters the
GCW for another treatment. Sixteen
monitoring wells are used to obtain
analytical data at the TCE study area,
while ten are used at the RDX area. Field
analytical techniques are used for
process monitoring, with some samples
sent to fixed off-site laboratories for
confirmation.
[continued on page 2]
Figure 1. General Ground-Water
Circulation Well Process
Recycled/Recyclable
Printed with Soy/Canola Ink on paper that
contains at least 50% recycled fiber
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[continued from page 1]
The air stripping system uses a 12-inch
well to extract ground water from the
aquifer at 60-70 feet bgs, at a rate of 50
gpm. TCE concentrations at the point of
extraction average 7,000 ug/L, but after a
single pass through the shallow-tray air
stripper the concentration drops to an
average of 110 ug/L at the point of system
exit (89-108 feet bgs).
Designed slightly differently, the UV
system uses a 6-inch well to extract
ground water at 50-60 feet bgs and at a
rate of 21 gpm. After passing through the
treatment vault holding a U V contactor,
RDX concentrations averaging 70 ug/L in
the extraction zone are reduced to non-
detect levels in the recharge zone at 14-40
feet bgs. The widespread impacts of
these treatment systems on ground water
were estimated using ground-water
models and subsequently verified using
data from downgradient monitoring wells,
which showed significant TCE and RDX
concentration reductions. It was esti-
mated that the treatment zone width in the
aquifer was approximately 180 feet.
This GCW system provides several
benefits over the alternative pump and
treat system for ground-water remediation
at the NOP site. (1) Treated ground water
is conserved through recharge to the
aquifer, thereby gaining public accep-
tance. (2) Fewer pipelines are required, so
the real estate acquisition costs are
reduced. (3) Large masses of contami-
nants can be removed quickly, with
downstream hydraulic containment wells
providing safeguards against contamina-
tion of clean areas. Full-scale
construction costs for the systems are
similar (approximately $1.9 million each),
but it is estimated that the GCW system
costs over 50 percent less for operation
and maintenance (approximately $44,000
annually) and will require 50 percent less
restoration time than would pump and
treat methods.
Full-scale application of the dual system
using 12 additional circulation wells will
begin in early 2002. For more information,
contact Tom Graff (U.S. Army Corps of
Engineers/Kansas City District) at 816-
983 -3 3 51 or e-mail Thomas. Graff@
nwk02.usace.army.mil.
Bioaugmentation Field
Testing for MTBE Treatment
by GerardSpinnler, Ph.D., Equilon
Enterprises LLC, Paul C. Johnson,
Ph.D., Arizona State University,
and Karen Miller, Naval Facilities
Engineering Service Center
In situ biostimulation and bioaugmenta-
tion field tests were conducted at the U.S.
Navy's Hydrocarbon National Environ-
mental Test Site at Port Hueneme, CA,
where a dissolved MTBE (methyl tert-
butyl ether) ground-water plume extends
for more than 1,500 meters. Comparative
tests were designed to assess the
efficacy of creating an MTBE biobarrier
by inoculating the aquifer with a bacterial
consortium and maintaining well-
oxygenated conditions. The results
indicated that MTBE cleanup levels were
achieved significantly faster through a
process combining both oxygen and
microbial injection than through either
oxygenation alone or naturally-occurring
biodegradation.
Tests were conducted in three experimental
plots to compare MTBE concentrations in
treatment areas receiving: (1) intermittent
oxygen (O2) injection (biostimulation) only,
(2) biostimulation and inoculation with
specialized MTBE-degrading microbes
(MC-100™) (bioaugmentation), and (3) no
treatment (control). Each test plot con-
tained a 6- by 15-meter cell aligned parallel
to the estimated ground-water flow. A total
of 188 monitoring wells were installed
upgradient and downgradient of the cells at
depths ranging from 3 to 6 meters. In the
two treatment areas, 96 O2 delivery wells
also were installed.
Oxygenation was achieved by periodic O2
injection directly into the aquifer (Figure 2).
Periodic pulsing provides more than
adequate dissolved oxygen to the local
subsurface environment and minimizes
hydraulic conductivity reduction possible
with continuous sparging. About 1,700
liters of O2 were delivered to each test cell
4-8 times each day. Within 44 days of
beginning the series of gas injections, well-
oxygenated zones extending 3 meters
upgradient and downgradient of the test
cells were established.
Figure 2. Bio stimulation/Bio augmentation Overview
During 1984-1985,
approximately 10,000
gallons of gasoline
containing MTBE
and 1,2-dichloro-
ethane were released
from fuel delivery
lines of a leaking
underground storage
tank (LUST) at Port
Hueneme. The area's
uppermost aquifer,
which was the focus
of this study,
consisted of an
upper clayey-silt (fill)
unit from 0 to 3
meters below ground
surface (bgs), and a
fine- to medium-
grained sand unit
from 3 to 6 meters
bgs underlain by a
competent clay layer
at 6 meters bgs. Low concentrations of
dissolved oxygen (less than 2 mg/L)
within and outside the plume inhibit the
potential for natural biodegradation of
MTBE.
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The ether-metabolizing bacterial culture
used in the field test was grown from an
MTBE-enriched activated sludge culture for
three to four months at ambient outdoor
temperatures. An open-ended, direct-push
[continued on page 3]
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[continued from page 2]
rod and grout pump assembly were used
to inject the culture into the aquifer under
pressure at several points along a 6.1-
meter transect perpendicular to the
ground-water flow and vertically at 2.7-6.1
meters bgs. Microbial solutions were
delivered at pressures of 10-100 pounds
per square inch across the cell transect in
20-liter injections spaced 0.3 meters apart.
A one-time injection of approximately 6,000
liters of solution was conducted.
Data indicated that MTBE removal by
volatilization was negligible due to the
short duration of oxygen pulses. Initial
MTBE concentrations of 2-9 mg/L de-
creased in the O2-only plot to 0.01 -0.1 mg/L
after a lag period of 186-261 days. In
contrast, MTBE concentrations decreased
significantly within 30 days of seeding
with the microbial injection and through-
out the three-year test period, eventually
reaching less than 0.001-0.01 mg/L.
In the seeded plot, less spatial variability
in concentrations was found than in the
O2-only area, and no decrease in MTBE-
degrading activity has been identified
throughout three years of operation. Data
indicated that the combined biostimu-
lation/bioaugmentation technology
degraded MTBE at least five times faster
than did the naturally occurring bacteria in
the ground water.
Because of the success of these initial
bioaugmentation test plots in reducing
MTBE concentrations, a 150-meter pilot
biobarrier system was installed across the
entire width of the Port Hueneme plume in
an area of mixed MTBE and BTEX (ben-
zene, toluene, ethylbenzene, and xylenes)
in the summer of 2000. Results after seven
months of operation have demonstrated
dramatic reductions of MTBE from
approximately lOmg/Lupgradientofthe
biobarrierto less that 0.005 mg/L immedi-
ately downgradient of the biobarrier.
Similar results were observed in BTEX
concentrations.
For more information, contact Karen Miller
(Naval Facilities Engineering Service
Center) at 805-982-1010 ore-mail
millerkd@nfesc.navy.mil, or Gerard
Spinnler (Equilon Enterprises LLC) at 281 -
544-7319 or e-mail gespinnler@
equilontech.com.
Surfactant Flooding Used to
Remove PCE DNAPL
by Laura Yeh, Naval Facilities
Engineering Service Center, Leland
Vane, U.S. EPA National Risk
Management Research Laboratory,
and Frederick Holzmer, Duke
Engineering & Services
A demonstration of surfactant-enhanced
aquifer remediation (SEAR) was con-
ducted at Camp Lejeune, NC, to validate
SEAR field results for the remediation of
sites contaminated with dense non-
aqueous phase liquids (DNAPL). The
project also was designed to evaluate the
feasibility and cost benefit of surfactant
regeneration and reuse during SEAR,
based on three scales of operation.
Demonstration results indicated that 72
percent of the DNAPL was removed from
the treatment zone. Associated costs for
the use of SEAR were found to be
dependent upon permeability conditions
and scales of application.
The demonstration site contained approxi-
mately 100 cubic yards of soil
contaminated with perchloroethylene
(PCE) DNAPL that was released over the
years from a central dry-cleaning facility
on the base. The DNAPL zone is located
below the facility in a low permeability,
heterogeneous shallow aquifer at a depth
of about 16-20 feet below ground surface.
Permeability decreases downward through
the sequential layers from fine sand to silt
and clayey silt. The permeability in the
fine sand and silty layers, which contain
the free-phase and residual DNAPL
targeted in the demonstration, was
estimated to be in the range of 5 x 10~4 cm/
sec to 5 x 10'5 cm/sec. The initial partition-
ing interwell tracer test (PITT) estimated
that the average DNAPL saturation was
approximately 4 percent near the facility,
decreasing to about 0.4 percent 15-20 feet
away from the building. The initial PITT
estimated a DNAPL volume of 81 ± 7
gallons, which was confirmed later to be
an underestimate by approximately 30
percent as a result of the strong perme-
ability contrast.
The demonstration comprised an 8-day
pre-SEAR water flood and a 58-day
surfactant flood, followed by a 74-day
water flood in a 20- by 30-foot well field.
The custom surfactant that was used,
Alfoterra 145 4-PO sulfate™, was devel-
oped to meet the dual objectives of high
PCE solubilization (Figure 3) and favorable
properties for recovery and reuse of the
surfactant. Low flow rates of injection
and extraction (0.4 gallons per minute and
1 gallon per minute, respectively) were
used to accommodate the site's low
permeability.
[continued on page 4]
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Figure 3. SEAR Results: Upper-Level Monitoring Point
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[continued from page 3]
Extraction well effluent was treated using two
membrane-based processes to remove the
contaminant and reconcentrate the surfactant
forreinjection. The pervaporationprocess
removed 99.94 percent of the PCE from the
effluent prior to surfactant breakthrough, and
95.8 percent during periods of peak surfactant
concentrations. The micellar enhanced
ultrafiltration process concentrated surfactant
in the extraction well effluent from 1.1 to 5
percent by weight, slightly above the reinjec-
tion concentration of 4 percent. Recovered
surfactant was reinjected into the contami-
nated aquifer for the final 20 days of the
surfactant flood. [Additional information on
the pervaporation process, which is a surface
treatment process for removing volatile organic
compounds from suspended micelles without
creating foam, is available from Leland Vane
(U. S. EPANational Risk Management
Research Laboratory) at 513-569-7799.]
A total of 76 gallons of PCE was recovered
from the upper, more permeable fine-grained
sand layer of the aquifer, but the low-
permeability basal silt layer was found to be
relatively unaffected by the surfactant flood.
Approximately 29 gallons of DNAPL remain
within the basal silt layer. Over a 70-day
operation period, approximately 3,500 pounds
of surfactant were recovered, of which about
one-half was reinjected into the aquifer.
Cost estimates were prepared for implement-
ing SEAR in a heterogeneous shallow aquifer
with an order of magnitude permeability
contrast (based on the Camp Lejeune site, but
assuming conventional wastewater treatment
costs) for full-scale scenarios involving three
sizes of DNAPL source zones: approximately
3,000 square feet (0.07 acre), 0.5 acres, and 1.0
acre. Full-scale SEAR costs for the three site
sizes ranged from approximately $1.4 million
to $12.2 million.
Recognizing that SEAR costs are a function of
permeability, researchers estimated additional
parallel full-scale costs under high permeabil-
ity conditions (0.01 to 0.001 cm/sec) with all
other parameters similar to Camp Lejeune.
This cost analysis showed that implementing
SEAR under high permeability conditions
costs only one- to two-thirds that of SEAR
under low permeability conditions. In
addition, a cost benefit analysis of surfactant
recovery at Camp Lejeune suggested marginal
benefits (no more than 3 percent of the total
project costs) for the given site conditions.
As the first field application of surfactant
recycling in the U. S., this demonstration
indicates that additional technical improve-
ments are required for surfactant regeneration
to be economically viable. Results also
indicate that technical improvements are
required for SEAR to be economically viable at
shallow, low permeability sites such as this.
Comprehensive details of the SEAR cost
analysis are included in the Final Cost and
Performance Report for Surfactant-Enhanced
DNAPL Removal (Battelle/Duke, 2001) that
will be available in early 2002 on the ESTCP
Web site, www.estcp.org.
Conducted under the U. S. Department of
Defense's Environmental Security Technology
Certification Program, this demonstration
serves as one of seven models sponsored by
the U.S. as part of the North Atlantic Treaty
Organization's Committee on the Challenges
of Modern Society [described in the Septem-
ber 2001 issue of Tech Trends,
www.clu-in.org]. For more information,
contact Laura Yeh (Naval Facilities Engineering
Service Center) at 1-888-484-3372 or e-mail
help@nfesc.navy.mil.
Mention of trade or commercial products does not constitute endorsement by the U. S. Environmental Protection Agency.
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October 2001
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