I
I
a
/A newsletter about soil, sediment, and groundwater characterization and remediation technologies
Issue 57
This issue of Technology News and Trends highlights strategies being used to remediate
contaminated soil, sediment, or groundwater while restoring a site's ecological system. The
strategies involve constructed wetlands, phytotechnologies, and soil amendments.
Multiple Technologies Used to Remediate Groundwater
Contaminated with Grain Fumigants
Removal actions at the Murdock
Groundwater Contamination Site in northeast
Nebraska involve an integrated-systems
approach to address groundwater and
surface water containing carbon
tetrachloride (CT). The contamination
resulted from past fumigation practices at a
U.S. Department of Agriculture (USDA)
grain storage facility in the Village of
Murdock. To contain the groundwater plume
and promote mechanisms such as
rhizodegradation or volatilization of
contaminants, the approach combines
phytotechnologies, constructed wetlands,
and a groundwater extraction and spray
treatment system. Investigative and remedial
work has been conducted collaboratively
by the USDA Chemical Commodities
Corporation (CCC), U.S. Environmental
Protection Agency (EPA) Region 7, Argonne
National Laboratory (ANL), and the
Nebraska Department of Environmental
Quality (NDEQ).
In 1985, routine testing of the Murdock
public water supply by the Nebraska
Department of Health (NDOH) identified
CT concentrations above the maximum
contaminant level (MCL) of 5 micrograms
per liter (ng/L). Further NDOH and EPA
testing confirmed these findings. In early
1986, EPA conducted an immediate
removal action and connected the village
to a nearby rural water district. Additional
investigations conducted by USDA/CCC
and ANL during 1991-1993 indicated a
contaminant plume affecting the 20- to 30-
foot-thick aquifer underlying the village. The
plume migrated from the former grain
storage facility in the direction of groundwater
flow. Groundwater sampling indicated CT
concentrations reaching 6,500 |0,g/L along
the plume's center line. Slightly farther
upgradient, a natural spring was found to
introduce CT into the headwaters of
Pawnee Creek, a tributary of the South Platte
River. Follow-up soil sampling revealed CT
concentrations as high as 361 micrograms
per kilogram (|0,g/kg), which confirmed
that the 5-acre area where the former storage
facility stood was the source of
contamination. Surrounding agricultural
fields showed no evidence of contamination.
The phytoremediation system focuses on
treating shallow groundwater and surface
water in the creek's headwaters. In 2005,
some 2,000 trees representing six species
(green ash, northern catalpa, Niobe willow,
black willow, eastern cottonwood, and hybrid
poplar) were planted on 4.5 acres to extract
contaminated groundwater, effectively
intercepting the plume at approximately 5-8
feet below ground surface (bgs) before it
reaches the creek. These six species were
selected based on their rapid growth, deep
rooting, disease tolerance, and non-
opportunistic character. Removal of the CT
occurs as a result of uptake, transpiration,
and volatilization of the contaminated
groundwater by the trees, degradation of the
CT within the plant tissue, and enhanced
microbial activity in the root zone.
[continued on page 2]
February 2012
Contents
Multiple Technologies
Used to Remediate
Groundwater
Contaminated with
Grain Fumigants page 1
Long-Term
Monitoring of
Phytoremediation
Underway at
Aberderdeen
Proving Ground page 3
Long-Term
Remediation
Combined with
Revitalization at
Former Chemical
Manufacturing Site page 4
Online Resources
The Phytotechnologies
area of EPA's CLU-IN Web
site explains the primary
mechanisms through which
plant-based methods
(extraction, degradation,
volatilization, sequestration,
and hydraulics) can ad-
dress environmental
contaminants. This resource
also offers a searchable
database currently contain-
ing 165 profiles of
phytotechnology projects.
Learn more at: www.clu-in.org/
techfocus/default.focus/sec/
Phvtotechnologies/cat/
Overview/.
Recycled/Recycl abl e
Printed with Soy/Carrola Ink on paper that
contains at least 50% recycled fiber
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[continued from page 1]
Groundwater modeling estimated that
trees planted along the creek bank would
each take up approximately 60 gallons of
contaminated groundwater daily during
the growing season.
"Tree wells" were installed beyond the
immediate creek banks to maximize
chances of tree rooting at target depths
within the aquifer (Figure 1). To aerate
the tree roots and promote growth of
naturally occurring contaminant-degrading
bacteria, a perforated tube was emplaced
as an open loop inside each well.
The phytoremediation system also
includes a mixture of native prairie grasses
(e.g., big bluestem, Indian grass, switch
grass, and western wheat grass) and wild
flowers (e.g., baby's breath, black-eyed
Susan, coreopsis, and purple coneflower)
along with other species planted between
the trees and adjacent areas. This cover
crop: (1) enhances erosion control; (2)
intercepts local precipitation and runoff
and, hence, promotes the uptake of deeper
contaminated groundwater by the trees;
(3) helps protect the trees from physical
damage; (4) provides a transitional buffer
zone between the tree planting areas and
the surrounding croplands; and (5) creates
a barrier to herbicide drift.
The shallow wetland constructed
immediately downgradient of the main
planting area provides an additional
remediation polishing step through further
degradation by microbial communities and
plants. The wetland contains bulrush,
arrowhead, sedge, zebra rush, and
spikerush covering approximately 800
cubic yards (yd3) over an undulating
bottom surface, which adds biodiversity
and increases residence time. As designed,
the water flows approximately 390 feet
through the wetland, which has an average
width of 60 feet. This results in a high
ratio of length to width (6.5:1). The
residence time of water entering from
the plantation discharge point ranges
from 4.2 to 11.8 days.
The groundwater extraction system is
designed to remove contaminated
groundwater from the upgradient, more
concentrated portion of the plume and
provide hydraulic control in hot spots. A
single well extending 77 feet bgs is used to
extract groundwater at a rate of
approximately 29 gallons per minute. The
extracted groundwater is piped to a spray-
irrigation treatment unit installed at nearby
school athletic fields. This custom unit
disperses a light spray of the extracted
groundwater at a radius of more than 500
feet, a process that simultaneously
volatilizes the CT and irrigates the fields.
School staff operate the extraction/
treatment system seasonally, depending
on local irrigation needs and weather.
Since 2005 start-up, hundreds of
thousands of gallons of contaminated
groundwater have passed through the
extraction/treatment system.
The spray irrigation treatment unit and the
extraction well are operated in accordance
with a National Pollutant Discharge
Elimination System (NPDES) permit issued
by NDEQ. Outfall from the spray irrigation
unit is classified by the NDEQ as a land
application; as a result, no specific targets
for CT removal have been established.
NDEQ specifies, however, that the
discharge not be toxic to aquatic life in
surface waters of the state outside the
Figure 1. Wells at the Murdoch site were
drilled to the level of groundwater and lined
withplastic to direct root growth downward
toward the aquifer while providing root
access to near-surface moisture.
mixing zones allowed under the Nebraska
Surface Water Quality Standards. The
standards define a maximum acceptable
level of 44.2 |0,g/L for CT in surface water
bodies, which applies to CT levels in
surface water discharge from the wetlands
to Pawnee Creek.
July-September 2011 groundwater
samples indicated an average CT
concentration ranging from less than 1.0
|0,g/L at the point of compliance to 5.1 |j,g/L
immediately upstream of the wetland, a
99% reduction from highest measured
concentrations in surface water (7,800
|J.g/L) prior to remediation. Concentrations
of chloroform, a CT breakdown product,
have remained at trace levels (below 1
|J.g/L or not detectable) at the same
locations established in the approved
monitoring plan.
CT uptake by the planted tree stand has
been confirmed by the seasonal presence
of CT and chloroform in branch tissue at
increasing concentrations and over an
expanding areal extent. Significant
concentrations of CT in samples from
native, deep-rooted grasses where elevated
concentrations were found in shallow
groundwater and branch tissues indicates
that the cover crop may aid the remediation
process, as intended.
Trees, native grasses, and wild flowers
needed to remediate the site were
purchased from local businesses. The
USDA engineering evaluation and cost
analysis for this project estimates a
$538,255 capital cost and $2,985,360
operation and maintenance cost, for a
total cost of $3,523,615.
Contributed by Jeff Field, EPA Region 7
(field.ieff(a),epa.sov or 913-551-7548)
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Long-Term Monitoring of Phytoremediation Underway at Aberderdeen Proving Ground
A phytoremediation field study began
at J-Field of the Aberdeen Proving
Ground (APG) in Edgewood, MD.
in the spring of 1996. The purpose
was to evaluate the feasibility of
phytoremedation as an alternative to
pump-and-treat (P&T) technology.
which was expected to have limited
success due to the site's hydrogeologic
conditions. Successful results led to
expansion of the study in 2001 by
installing approximately 600 additional
trees to provide more complete hydraulic
containment of the contaminant plume.
Monitoring since 2004 indicates that
the trees continue to influence onsite
groundwater flow and effectively
intercept a plume of volatile organic
compounds (VOCs). Evaluations also
indicate that phytotechnology helps
remediate groundwater by biotransforming
VOCs within the transpiration stream
and by enhancing in situ biodegradation
of contaminants in the rhizosphere.
APG is a military installation on the
western shore of the Chesapeake Bay.
From 1940 through the 1970s, J-Field
was used as a test area for chemical
warfare agents, munitions, and
industrial chemicals. Onsite disposal of
test waste, including use of several
trenches as burning pits, released
chemicals to groundwater and soil.
Remedial activities for contaminated
soil have involved excavation of
hotspots and offsite disposal of soil
and sediment with high concentrations
of polychlorinated biphenyls (PCBs)
and metals, placement of a 2-foot layer
of clean soil and geotextile fabric as a
protective cover over excavated areas.
erosion controls to reduce surface water
runoff into the bay, and institutional
controls for white phosphorous-
contaminated soil. Monitoring has confirmed
the presence of dense nonaqueous phase
liquid (DNAPL); however, DNAPL
recovery efforts are unlikely to be
successful due to the tight soil.
The majority of groundwater contamination
caused by the burning pits is confined to
a low-permeability, 30-foot-thick surficial
aquifer at 6 to 7 feet bgs. Groundwater
sampling in the surficial aquifer prior to
2001 expansion of the field study indicated
high concentrations of tetrachloroethene
(PCE) (11 mg/L), trichloroethene (TCE)
(93 mg/L), and 1,1,2,2-tetrachloroethane
(TeCA) (390 mg/L), as well as 1,2-
dichloroethene (DCE) (110 mg/L), 1,1,2-
trichloroethane (TCA) (7.1 mg/L), and
vinyl chloride (4.2 mg/L). The aquifer
discharges to nearby fresh water marshes.
Due to the tight soil structure of the silty
sand, the rate of groundwater flow is low.
at an estimated 10 to 15 feet year. The
cleanup objective for J-Field, as part of the
APG "Edgewood Area" National Priorities
List site, is to use the trees to maintain capture
of the plume until MCLs are reached.
The field study involved planting 183 two-
year-old hybrid poplar (Populus deltoids x
trichocarpa) saplings on approximately one
acre along the contaminant plume periphery.
The saplings were planted on 10-foot
spacings in a single stand. Two years later.
approximately 20 tulip trees and silver
maples were added to evaluate their
performance as native species. A passive
drainage system consisting of a series of
ditches was constructed to remove surface
and near-surface precipitation quickly.
thereby encouraging tree roots to access
groundwater. Standing water along the
drainage system in some areas, however.
prompted planting of tree species preferring
wetter conditions, such as bald cypress.
sycamore, and swamp white oak.
The trees' ability to intercept the plume was
evaluated over five years through
groundwater modeling and periodic
measurement of the water table elevation.
tree transpiration rates (based on sap flow
and tree growth rates), transpiration vapor
data, seasonal hydraulic gradients, natural
attenuation parameters in groundwater, and
contaminant levels in the plant tissue. A
tailored cylindrical dialysis sampler
(4 feet in length and 0.16 feet in diameter)
was used to measure VOC concentrations
in the root zone. Two dialysis samplers
also were installed, one directly in the
poplar grove (approximately 1 foot from
the trunk of a mature hybrid poplar) and
the other outside of the grove but in the
plume. Upgradient and downgradient
groundwater sampling results also were
used to evaluate the trees' ability to
intercept the contaminant plume.
Peak summer groundwater transpiration
rates for the poplar grove were estimated
at 2 to 12 gallons per day per tree, based
on sap flow measurements. By inducing
upward groundwater gradients towards
the tree roots during transpiration, the
poplars were estimated to shift gradients
at depths reaching 25 feet bgs in the
summer, effectively limiting discharge of
contaminated groundwater from J-Field
to the adjacent freshwater marsh. A
2001 groundwater treatability study
examined the process by which
contaminants are transferred from the
tree roots to the leaves and quantified
the transpiration rates achieved in the
field. Using the transpiration gas and
condensate sampling method, for
example, TeCA was detected in air
ranging from 2.0 to 170 parts per
billion by volume. As expected, the
highest rate of transpiration occurred
during summer growing seasons.
Results of the second five-year review
for J-Field in 2008 indicated significant
decreases in concentrations of PCE.
DCE, and TeCA in groundwater, with
increased concentrations of TCE, TCA.
and vinyl chloride likely due to
breakdown of TeCA. For example, total
VOC concentrations in one well had
decreased from 15,000 |j,g/L to 400 |j,g/L
by 2007. Cones of depression and water
flow reversals observed during
monitoring suggested that the grove
[continued on page 4]
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[continued from page 3]
provided hydraulic containment of the
VOC plume during the growing season
except during periods of significant
precipitation. During those periods,
nearby mature forests (with mixed ages
of trees) appeared to have a greater effect
on the water table than the seven-year-
old phytoremediation grove. This trend
suggested that the uptake capacity of
individual trees is limited but that the
collective capacity of the entire grove
would increase with maturity.
Full-scale phytoremediation at J-Field
now involves approximately 800 trees
(including the original 183 hybrid
poplars) covering approximately four
acres. In 2010, 32 canker-diseased
hybrid poplars were removed and
replaced by 130 hybrid poplars of anew
canker-free cultivar (Clone OP 367), and
15 additional sycamores, swamp white
oak, or bald cypress were installed in
drainage areas. Water uptake by the entire
grove is estimated at 1,600 to 9,600 gallons
per day, depending on the season.
Maintenance activities are conducted
monthly to promote health of the grove.
The trees are pruned as needed to
strengthen plant structure and encourage
development of a denser canopy. The grass
between the trees is typically mowed four
times during each growing season. Habitat
of ground-nesting birds is protected during
each mowing by 8-foot-wide "birthing
strips" between the tree stands and
adjacent open fields. Maintenance also
includes replacing individual trees affected
by weather extremes; for example,
approximately 15 poplars were replaced last
year following Hurricane Irene.
As part of ongoing land stewardship actions
at J-Field, APG is currently developing a
forest management plan for the
phytoremediation grove that will continue
to optimize remedial effectiveness of the
trees while restoring onsite ecosystems
(Figure 2). The plan includes periodic
thinning of the grove to avoid stress on
individual trees, which increases the
grove's susceptibility to disease and
decreases water uptake rates. Intermittent
replacement of mature trees also will
provide the desired mixture of tree ages
to maintain a uniform draw on the aquifer.
Since annual water uptakes are highest
during each tree's growing years, fully
mature poplars (12-15 years of age) will
be gradually replaced by canker-resistant
hybrid poplar saplings. Based on past
lessons learned, future plantings will
involve bigger spacing among individual
plants to avoid overcrowding and
nutrient deficiencies and shallower
installations to promote more pervasive
root systems. During drought conditions,
soil amendments or periodic watering
will be used to reduce tree stress and
assure continued growth. Additional plant
species also will be introduced over time
to increase plant diversity in the area.
Annual costs for maintaining the
phytoremediation grove total $20,000-
25,000. In contrast, APG estimates that
operation and maintenance O&M of a
comparable P&T system would cost
more than $200,000 each year.
Contributed by Rurik Loder
(rurik. a. loder. civ(a),mail.mil or
410-436-7313) and Scott English
(scott.d.english.civ(a)mail.mil or
410-436-9804), U.S. Army
Long-Term Remediation Combined with Reuitalization at Former Chemical Manufacturing Site
Remediation at the former Occidental
Chemical Corporation ("Oxy") site in
Montague, MI, is closely integrated with
revitalization and wildlife habitat creation
on this former industrial property. The
site restoration plan included amending
the sandy soils, expanding wetlands,
restoring shorelines, and planting native
vegetation that will co-exist with ongoing
groundwater remediation work. To date,
approximately 65 of 100 acres affected
by remedial efforts have been converted to
open prairie areas or wetlands. Expansion
of the prairie onto the remainder of the site
is underway to provide additional habitat
and complement long-term forest
management activities.
This 880-acre site is located within a region
of residential and commercial developments,
hardwood forests, dunes, and grasslands
in the Lake Michigan basin. A chemical
manufacturing facility covering 200 acres
operated on the site from 1954 until
closing in 1983. Investigations indicated
that the facility disposed of
approximately 506,000 cubic yards of
organic wastes containing hazardous
substances in unlined settling ponds
on approximately 50 acres. In
addition, PCB- andhexachlorobenzene-
contaminated sediment was found in
[continued on page 5]
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[continued from page 4]
adjacent surface water (White Lake) as
a result of point-source discharge.
Results of groundwater sampling
revealed dissolved VOC concentrations
exceeding 1 mg/L, which indicated the
presence of dense non-aqueous phase
liquid. Other contaminants of
concern included CT, chloroform,
PCE, TCE, andhexachlorobutadiene. The
groundwater is at 40 feet bgs within a
layer of sand extending 100 feet bgs.
Remedial efforts began in 1981, when
approximately 970,000 tons of
contaminated soil considered to be one of
several source areas was excavated and
placed in an onsite, conventional RCRA
landfill that included a bottom liner and
10-foot cover of impermeable clay. In
2003, additional soil from hot spots was
excavated and disposed of at an offsite
facility for hazardous waste, along with
approximately 10,500 yd3 of dredged and
de-watered sediment containing an
estimated 1,100 pounds of persistent,
bioaccumulative, and toxic compounds.
In addition, a 2-acre former equalization
pond was drained, decontaminated
through pressure washing and
vacuuming, re-lined with a synthetic
plastic liner covered by 24 inches of clay,
and allowed to refill with rainwater.
To intercept and treat a contaminant
plume affecting private wells and the White
Lake basin, eight purge wells extending
to depths of 100 feet bgs were installed in
1982 along 2,200 feet of shoreline. The
extracted groundwater is routed to an
onsite treatment plant relying on carbon
treatment. Under an NPDES permit,
approximately one million gallons of
groundwater is discharged each day to
White Lake at a point approximately one-
half mile downgradient of the plant.
Soil amendments were needed in
backfilled areas to physically stabilize the
loose soil and address the low organic
content left by construction and operation
of the former manufacturing facility.
Based on results from onsite soil test plots
for various plant species, the chosen
amendment consisted of a mixture of leaf
compost, wood shavings, and manure
obtained from a nearby dairy farm. The
amendment was mixed onsite and applied
on ground surfaces of half-acre parcels
through use of a mechanical manure
spreader to achieve a 6- to 8-inch layer. A
disc cultivator was then used to mix the
amendment into the upper soil and destroy
remaining weeds.
To stabilize soil and prevent weed
establishment during the first year of
revegetation, a nursery crop of Canada wild
rye (Elymus canadensis) was planted prior
to seeding. The areas were then seeded via
a standard drill (and broadcast techniques
where needed) with several hundred
pounds of native prairie grasses and
wildflowers. Annual maintenance includes
routine harvesting of seeds from the
revegetated areas and offsite grassland and,
if needed, seed dispersion in areas suffering
from drought or unexpected damage.
The vegetation is monitored annually for
survival, species composition, and invasive
plant species. Shipments of manure provide
soil amendment for the site on a periodic
(commonly weekly) basis. In April 2010,
prescribed burning was conducted in the
prairie areas to gain the benefits of
otherwise naturally occurring fire, which
includes control of invasive plant species
>f"f ***&%
such as spotted knapweed and provides
carbon-rich matter to the soil (Figure 3).
Common cattails (Typha latifolid) native
to the area were planted along shores of
the remediated pond to establish the new
wetland. To expand the prairie areas, native
short grasses, tall grasses, wildflowers, and
clover (as a winter cover crop) were
seeded in adjacent acreage upland of the
treatment plant and excavation areas. The
combined prairie-wetland now provides
a drinking water source for wildlife,
haven for migratory waterfowl and
wading birds, habitat for aquatic
insects, and year-around home to small
mammals such as muskrats and mink.
The shoreline enhancement is conducted
through the federal Great Lakes
Restoration Initiative in partnership with
the Muskegon Conservation District.
Most of the remaining 800+ acres of this
site are covered by forest managed by
Occidental Chemical Corporation under
the Michigan Department of Natural
Resources Forest Stewardship Program.
Other partners include the Wildlife Habitat
Council, Pheasants Forever, Ruffed
Grouse Society, and USDA Natural
Resources Conservation Service.
To date, costs to operate the groundwater
treatment plant total $1.2 million.
Cumulative costs for site remediation
over the project life, including long-term
[continued on page 6]
FigureS. Within six
months after prescribed
burning, prairie areas at
the Oxy site contained a
predominance of
desirable native plants
such as black-eyed
Susans (Rudbeckia
hirtaj.
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Solid Waste and
Emergency Response
(5203P)
EPA 542-N-12-001
February 2012
Issue No. 57
United States
Environmental Protection Agency
National Service Center for Environmental Publications
P.O. Box 42419
Cincinnati, OH 45242
Presorted Standard
Postage and Fees Paid
EPA
Permit No. G-35
Official Business
Penalty for Private Use $300
TEC
NEWS
TRENDS
[continued from page 5]
monitoring, are estimated at $10.8
million. Project partners are investigating
other opportunities for reuse of the site
as cleanup continues, such as
developing a hydroelectric system to
capture energy from outfall of the water
treatment plant and developing an
extension of the community's "rail to
trail" recreational network.
Contributed by Kenneth Bardo and
Carolyn Bury, EPA Region 5
(bardo. kenneth(a),epa. gov or 312-886-
7566 and bury. carolvn(a),epa. gov or
312-886-3020)
Ecological System Services
Ecosystems provide various services to human populations, such as flood
protection, water purification, and climate control. EPA's consensus-based
Valuing the Protection of Ecological Systems and Services: A Report of the
EPA Science Advisory Board (EPA-SAB-09-012) examines the value placed on
these services, including both the economic and non-economic methods of
valuation. Access the report at: www.epa.gov/ecologY/publications.htm.
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