United States
Environmental Protection
Agency
Solid Waste and
Emergency Response
(5102G)
EPA 542-N-98-004
March 1998
Issue No. 27
vvEPA Ground Water Currants
^tefier Treatment
CONTENTS
Air Sparging/High
Vacuum Extraction
to Remove Chlorinated
Solvents in Ground
Water and Soil Pg. 1
1,200-Foot Permeable
Reactive Barrier in
Use at the Denver
Federal Center Pg. 2
GWRTAC Updates Pg. 3
EPA Releases
Monitored Natural
Attenuation Directive Pg. 4
New Phytoremediation
Report Issued Pg. 4
Technology Vendor
Opportunities Pg. 4
About this Issue
This issue highlights
methods for remediating
ground water contaminated
with chlorinated solvents
through the use of air
sparging, vacuum
extraction, and in situ
treatment walls.
Air Sparging/High
Vacuum Extraction to
Remove Chlorinated
Solvents in Ground Water
and Soil
by Jim Phelan, U.S. Department
of Energy, Sandia National
Laboratories
Two technologies—air spaiging coupled
with high vacuum extraction—are
expediting the cleanup of both ground
water and soil at the U.S. Department of
Energy's (DOE's) Mound facility in
Miamisburg, Ohio. In 1995, DOE and
EPA had selected pump and treat as the
baseline remedy for contaminated ground
water. Although hydraulic containment
was achieved with the pump and treat
system, the system proved limited in its
ability to clean up the aquifer expedi-
tiously. For this reason, an air sparging
(AS) system was installed to remove
dissolved phase contaminants in the
ground water and a high vacuum soil
vapor extraction (SVE) system was
installed to remove source contaminants
in the vadose zone.
The southwestern portion of the Mound
Facility, which is a former nuclear
weapons component research and
manufacturing facility, is located directly
above the eastern flank of a sole source
aquifer that provides drinking water to a
large population. In this locale, the
aquifer is shallow (20 feet below ground
surface) and characterized as highly
permeable sand, silt, and gravel. As a
result of past activities at the facility, a
small portion of the aquifer has been
contaminated with various chlorinated
solvents. Remediation of this two-acre
area (known as Operable Unit 1) is
complicated further by a landfill located
over a portion of the site.
The major ground water contaminants
include trichloroethene (TCE),
tetrachloroethene (PCE), and 1,2-cis-
dichloroethene (DCE), with average
concentrations in the tens of parts per
billion (ppb) for each contaminant, and
highest concentrations of 200, 300, and
600 ppb, respectively. Vinyl chloride
also is present in average concentrations
of a few ppb, and up to 50 ppb in certain
locations. In addition, unanticipated
concentrations (up to 220 parts per
million) of toluene were identified during
early operation of the system.
Soils overlying the aquifer include
complex lenses of glacial till, silts and
sands, and fill material, and contain the
same contaminants as detected in the
ground water (typically in the 100 ppb
range but up to 300 ppm in isolated
areas). Past activities have disturbed the
entire area, resulting in a heterogeneous
distribution of both soil type and con-
taminant concentration.
During pilot tests completed in 1996,
approximately 13 pounds of total volatile
organic compounds were removed from
an extraction well (not screened within
the till unit), operating over a four-day
period at a steady air flow rate of 80
standard cubic feet per minute (scfm)
with 13 inches of mercury vacuum at the
well bore. A screened extraction well
within the low permeability till unit
resulted in very low mass removal, with
steady flow at around 4 scfm and with 24
inches of mercury vacuum at the well
bore. Air sparging in the permeable sand
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and gravel produced an approximate
radius of influence of 20 feet at a flow rate
of20scfm.
Pilot test data were used to select an
appropriate spacing for the AS/SVE wells.
The heterogeneous nature of both the
contaminant distribution and permeability
within the overlying soils provided a
challenge in selecting an optimal screen
location for the SVE wells. Where
contaminated glacial till existed, it was
important to ensure the SVE well was
screened only within the low permeability
till and did not extend into a horizon of
higher permeability. Conversely, it was
appropriate to utilize a relatively long-
length screen where till was absent.
Field samples were taken during installa-
tion of the AS/SVE system to determine
the presence of the till unit, location of the
till outwash contact, and the three-
dimensional distribution of contaminants.
Based on field analysis of these samples,
SVE screen intervals providing for
optimal mass removal at each wall were
identified. [A three-dimensional illustra-
tion of the AS/SVE system may be viewed
in the electronic version of this newsletter
on the Internet site: www.clu-in.com.]
Preliminary results from the system have
shown that approximately 450 pounds of
contaminants have been removed from the
soils in the first six weeks of operation.
Figure 1 shows concentrations of several
of the principal contaminants overtime.
During the next several months, investiga-
tors will monitor the system to determine
its effectiveness in mass removal and its
effect on the ground water containment
system (pump and treat).
This demonstration is sponsored by the
Innovative Treatment Remediation
Demonstration (ITRD) Program coordi-
nated by the U.S. Department of Energy's
(DOE's) Sandia National Laboratories.
The ITRD is a public-private partnership
among DOE, Clean Sites, Inc, and EPA
with the goal of reducing barriers to the
use of new technologies. Through the
ITRD Program, advisory groups com-
posed of DOE, EPA, private industry, and
regulatory agency representatives were
established to work on this project in
conjunction with the DOE Mound Facility
Environmental Restoration Program.
For more information, contact Jim Phelan
(DOE/Sandia National Laboratories) at
505-845-9892, Mike Hightower (DOE/
Sandia National Laboratories) at 505-844-
5499, or Mark Gilliat (Babcock and
Wilcox of Ohio) at 937-865-4407.
1,200-Foot Permeable
Reactive Barrier in Use at
the Denver Federal Center
by Alex Caruana, State of
Colorado, Department of Health
and Environment
An in situ ground water treatment system
was installed in the Fall of 1996 at the
Denver Federal Center (DFC) to minimize
the off-site migration of ground water
contaminated with halogenated volatile
organic compounds.
The 1,200-foot barrier consists of iron
sheet-pilings driven across the aquifer
perpendicular to the direction of ground
water flow, acting as an underground dam.
Contaminated ground water is funneled
through four 40-foot-wide aperatures, or
"gates" in the barrier, containing iron
filings. The iron filings are capable of
chemically degrading dissolved chlori-
nated hydrocarbons in the ground water.
The DFC "funnel and gate" system is
illustrated conceptually in Figure 2.
The dimensions of each gate were varied
based on modeled ground water flow
velocities. In the direction parallel to
ground water flow, the basic design for
each gate consists of a gravel-iron-gravel
sandwich capped by a bentonite plug to
below the water table, such that ground
water flows into each gate through two
feet of gravel before entering the iron
treatment zone. After passing through the
iron, ground water exits through another
two feet of gravel. Iron thicknesses
parallel to ground water flow direction
were six feet, four feet, two feet, and two
feet. Iron thicknesses were varied to
account for varying contaminant concen-
trations and ground water flow velocities
along the length of the barrier. Total
volume of iron used on the project was
approximately 6,800 feet3 (2,880 feet3 in
gate 1; 2,400 feet3 in gate 2; 880 feet3 in
gate 3; and 640 feet3 in gate 4.
In addition to the chemistry of the zero
valent iron reduction process, the geology
of the aquifer plays a critical role in the
application of this technology. At the
DFC, the aquifer consists of three litho-
logic units of decreasing permeability with
depth: alluvium, weathered claystone, and
hard claystone. In order to achieve
maximum containment, the base of the
system should be keyed into the unit with
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the lowest permeability; at the DFC, this
unit is the hard claystone. At the north end
of the DFC system, however, the driving
of sheet-piling to this horizon (a depth
greater than 45 feet) was not feasible.
This situation is mitigated by a decrease in
transmissivity (aquifer thickness x
hydraulic conductivity) in the alluvium to
the north, as it transitions from sand and
silt in the south to increasing clay north-
wards. Also, ground water contamination
had not been observed at significant levels
at the northern end of the barrier.
Trichloroethene (TCE), 1,1-
dichloroethene (DCE), and 1,1,1-
trichloroethane (TCA) at concentrations
on the order of hundreds of parts per
billion are present in the aquifer
upgradient, (west) of the barrier. In
passing through the iron filings, all
contaminants (with the exception of 1,1-
dichloroethane, which persists at concen-
trations of a few parts per billion) are
reduced to non-detect levels in the
treatment cells or "gates."
Twin monitoring wells, screened to
monitor vertical gradients between the
alluvium and the underlying confining
layers, were located at points midway
between the treatment cells ("3 & 4" in
Figure 2) [corresponding to well pairs
GSA-23,22D; GSA-28,27D; GSA-33,32D
on the site map provided in the Internet
version of this newsletter]. Additional
monitoring wells are located in the
treatment cells.
Wells 1 and 2 are located to monitor for
by-pass at either end of the permeable
barrier wall [corresponding to GSA-18a
and 19a on the site map]. As of the latest
monitoring event (November 1997)
elevated concentrations of TCE, DCE,
and TCA in well 18a (the well at the south
terminus of the barrier) indicate that some
by-pass has started to occur. At this time,
some downgradient wells have shown
significant decreases in concentrations for
specific contaminants. Other wells that
generally are further downgradient,
however, have yet to show significant
decreases in contaminant concentrations
after one year of operation. Some
underflow also is being observed at one of
the four gates [Gate 2 on the site map].
Remedies to these situations currently are
being evaluated and should be imple-
mented within six months.
The General Services Administration and
Federal Highway Administration jointly
undertook this project in response to an
April 1996 compliance order from the
State of Colorado's RCRA program.
Today, the DFC is in many respects a
research campus whose major tenants are
more than 23 different federal agencies.
The DFC was formerly a U.S. Department
of Defense munitions site called the
Denver Ordnance Plant.
Use of this zero-valent iron treatment
technology is planned or in place at other
facilities in Colorado, including the U.S.
Department of Energy's Rocky Flats
Environmental Technology Site near
Denver and Colorado Crystal in Loveland.
For more information, contact Alex
Caruana (State of Colorado) at 303-692-
3340, Kevin Phillips (General Services
Administration) at 303-236-7131 exten-
sion 232, Rick Gushing (Federal Highway
Administration) at 303-716-2138, or Peter
McMahon (U.S. Geological Survey) at
303-236-4882 extension 286.
GWRTAC Updates
Technology Evaluation Report:
Phytoremediation
The Ground-Water Remediation Tech-
nologies Analysis Center (GWRTAC)
recently issued this technology evaluation
report discussing the current status of
phytoremediation for treating soils and
ground water, as well as the economics,
regulatory requirements, and limitations of
the technology. Readers may download
the report at no cost from GWRTAC's
Internet site at http://www.gwrtac.org, or
contact GWRTAC at 800-373-1973 for
more information.
Advances in Innovative
Ground Water Remediation
Technologies Conference
GWRTAC and EPA's Technology
Innovation Office will co-sponsor a
one-day conference on May 6, 1998,
at the Cathedral Hill Hotel, San
Francisco, CA. Anticipated technical
sessions will address topics such as
natural attenuation, phytoremediation,
treatment walls, and remediation of
dense non-aqueous phase liquids. For
agenda information and a registration
form, contact GWRTAC at the
Internet site http://www.gwrtac.org or
by calling 800-373-1973. To register,
e-mail karen_devlin@philip-serv.com
or call 215-643-5466.
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Ground Water Currents
welcomes readers' comments and contributions.
Address correspondence to:
Ground Water Currents
8601 Georgia Avenue, Suite 500
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Technology Evaluation Report:
Remediation of Metals-Contaminated
Soils and Groundwater
GWRTAC issued this technology evalua-
tion report to address the persistent
problem of metals contamination at many
hazardous waste sites. The report presents
several field demonstration summaries
(including information such as compounds
treated, site characteristics, project results,
participants, and contacts) and describes
the current status of existing technologies
for treating metals-contaminated soils and
ground water. This evaluation report and
additional information on ground-water
remediation also may be downloaded from
GWRTAC's Internet site.
EPA Releases
Monitored Natural
Attenuation
Directive
In December 1997, EPA issued
the interim final directive, Use of
Monitored Natural Attenuation at
Superfund, RCRA Corrective
Action, and Underground Storage
Tank Sites. This directive
clarifies EPA's policy regarding
the use of monitored natural
attenuation for remediation of
contaminated soil and ground
water at sites regulated under all
programs that are administered by
EPA's Office of Solid Waste and Emer-
gency Response (OSWER). The docu-
ment (OSWER Directive #9200.4-17)
may be downloaded from the Internet at
http://www.epa.gov/swerustl/directiv/
d9200417.htm. Paper copies of the
document are available from EPA's
RCRA, Superfund, OUST, and EPCRA
Hotline at 800-424-9346 or 703-412-
9810.
New Phytoremediation
Report Issued
Phytoremediation ofTCE in Groundwater
Using Populus was prepared under grant
for EPA by Jonathan Chappell, a National
Network of Environmental Management
Studies fellow. The publication provides
a basic understanding and current status of
Phytoremediation for shallow groundwa-
ter. The report may be downloaded from
the Internet at http://clu-in.com/
techpubs.htm.
Technology Vendor
Opportunities
Site Characterization and Field Analysis
Technology Verification
Over the next few months, the Environ-
mental Technology Verification (ETV)
Program will offer several opportunities
for site characterization and field analysis
technology vendors to participate in the
ETV's Consortium for Site Characteriza-
tion Technology (CSCT) verification
program, including a call for vendor
interest.
For more information, check CSCT
information posted on the ETV's Internet
site, www.epa.gov/etv, or the Hazardous
Waste Cleanup Information System at
www.clu-in.com. Also, subscribe to
EPA's "TechDirect" technology informa-
tion service to receive a monthly e-mail
message on new developments and
publications related to remediation and
site characterization/field analysis
technology.
United States
Environmental Protection
Agency
Solid Waste and
Emergency Response
(5102G)
EPA 542-N-98-004
March 1998
Issue No. 27
vvEPA Ground Water Currants
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