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/A newsletter about soil, sediment, and ground-water characterization and remediation technologies
Issue 38
mt/e o/ Technology News and Trends highlights innovative approaches for addressing
contaminated sediment sites. Elements of these approaches include sediment dewatering through
use ofgeotextile containers, designed armor stone layers in caps to withstand harsh surface and
subsurface conditions, new models to predict navigational vessel impacts on cap performance,
and placement of caps in very thin lifts over soft sediments.
October 2008
Innovative Dredging Technology Accelerates Removal of Residual
Contamination in Ashtabula River
L
The U. S. EPA's Great Lakes National Program
Office (GLNPO) and their non-federal sponsor,
the Ashtabula City Port Authority, along with
the State of Ohio, the U.S. Army Corps of
Engineers (USAGE), and a consortium of
private companies collaborated to design and
implement an innovative approach for
addressing extensive sediment contamination
in a portion of the Ashtabula River near Lake
Erie. The approach employed a linked system
for hydraulic dredging, an aboveground,
double-walled pipeline for sediment slurry
transfer, and containment of the transported
contaminated sediment in "dewatering tubes"
at a newly constructed landfill. Over 13 months,
the system remediated approximately 500,000
yd3 of sediment containing 25,000 pounds of
poly chlorinated biphenyls (PCBs), along with
heavy metals, chlorinated organics, uranium,
radium, and thorium.
In 1985, the Ashtabula River was designated a
Great Lakes area of concern (AOC). Extensive
mapping of AOC sediment characteristics
began in 1990. Site investigations indicated that
an industrial area along the Fields Brook
tributary served as the primary source of river
contamination. Past industrial activities
included foundries and chemical plants,
tanneries, and World War II weapons
production. In 2003, under direction of U.S.
EPA Region 5's Superfund Program remedial
work on Fields Brook was completed from the
headwaters of the brook to its confluence with
the Ashtabula River. Additional source control
work is underway.
Since 1962, the USAGE had been unable to
complete routine navigation dredging of a 1.4-
mile stretch of the federally authorized
navigation channel due to the presence of
highly contaminated sediments. Although
dredging in the navigation channel was
authorized to a depth of 16 feet or more, much
of this river stretch experienced restricted
navigation depth as shallow as 0-2 feet.
Additionally, fish consumption advisories have
been posted in the lower two miles of the river
since 1983. Average PCB concentrations
measured in the sediment were 7.5 mg/kg, with
a maximum concentration of 660 mg/kg. Targeted
sediment contained approximately 150,000 yd3
of T SC A-regulated material.
To address the sediment contamination and
stakeholder goals, federal and state agencies,
local organizations, and private stakeholders
formed the Ashtabula River Partnership in 1994
to comprehensively address the river's
environmental and navigational problems.
Between 1994 and 2004, the USAGE led the site
investigation, alternatives analysis, and
preliminary design work (including two value
engineering studies) to derive a proposed
dredging and disposal remedy for the river. A
primary recommendation from the value
engineering studies was to use a single, project-
specific landfill to confine both T SC A-regulated
and non-TSCA regulated materials.
In April 2004, the Ashtabula City Port Authority,
with the support of the Ashtabula River
[continued on page 2]
Contents
Innovative Dredging
Technology
Accelerates Removal
of Residual
Contamination in
Ashtabula River page 1
39-Mile Dredging/
CappingApproach
Used to Treat Fox
River PCBs page 3
Pilot Study Shows
Effective Cap
Design for Containing
PCB-Contaminated
Sediment page 4
CLU-IN Resources
CLU-IN's web page on
sediment remediation
provides key technical
resources on related cap-
ping, dredging, and moni-
tored natural attenuation
issues. The web page also
provides important guidance
documents and summaries
of large-scale projects
developed by organizations
such as EPA's Great Lakes
National Program Office,
the U.S. Army Corps of
Engineers, and the U.S.
Department of Defense.
Visit the sediments page at
http:/www.cluin.org by clicking
on the "Remediation" tab and
the "Issue Areas" subtab.
J
Recycled/Recy cl abl e
Printed with Soy/Canola Ink on paper that
contains at least 50% recycled fiber
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[continued from page 1]
Partnership, submitted a request to the
GLNPO requesting funds under the newly
authorized Great Lakes Legacy Act
(GLLA). After extended technical, legal,
and financial discussions, active
remediation on the $58 million river project
began in 2006, with the GLLA providing
$29 million in funding. The final design
called for hydraulic excavation of
sediments; hydraulic transport of the
dredged slurry to the landfill through a 2.5-
mile long, double-walled pipeline;
dewatering of the sediment slurry using
geotubes; and treatment of the water
through a 5,000-gpm water treatment plant.
Dewatering was designed to occur at the
l,000,000-yd3TSCA-permitted landfill, with
geo-textile tubes (geotubes) left in place
for final disposal (Figure 1).
Construction of the landfill, pipeline, and
water treatment plant commenced in May
2006 and concluded in September 2006, at
which time full-scale dredging operations
began. Initial dredging operations were
conducted using a 12-inch, 750-hp,
hydraulic cutterhead dredge to remove
sediment at a depth of 0-20 feet below water
surface. The dredge operated at a rate of
approximately 3,800-4,200 gpm and
produced a slurry with 6-15% total solids
by weight. Dredged material consisted of
mostly fine-grained sediment, which was
pumped through a 12-inch, double-walled,
HOPE piping system installed along the
Fields Brook corridor. Three 500-hp
booster pumps were used to maintain a
consistent flow along the entire length of
the pipeline, which involved a 60-foot
vertical rise between the river and landfill.
At the landfill, the sediment slurry was
pumped into geotubes that were
approximately 300 feet long and 75 feet in
diameter. As slurry moved into each tube, a
polymer was added to increase coagulation
of sediment particles. Coagulated particles
remained inside the geotubes while slurry
water exited by gravity through pores of
the geotube's woven material. Filled tubes
were allowed to air dry for approximately 15
days in order to achieve a solids content of
approximately 40% before additional tubes
were placed on them. The 13.5 -acre T SC A-
permitted landfill was constructed with two
60-mil synthetic liners, a geosynthetic clay
liner, and several drainage layers along with
a leachate collection system.
Water exiting each geotube entered the
leachate collection systems and was pumped
to a nearby water treatment system consisting
of Lamella® gravity settlers, sand filters, and
activated carbon filters. The water treatment
process was designed to meet discharge limits
ofO.OOl |Jg/LPCBs,0.16ng/Lmercury,andlO
mg/L total suspended solids in the water prior
to discharge to the river.
In June 2007, operations integrated a second
but smaller (8-inch) hydraulic dredge
equipped with an innovative Vic-Vac™
suction dredge-head (Figure 2). The 8-inch
dredge operated in parallel with the 12-inch
dredge, with both simultaneously
discharging to the double-walled pipeline.
By operating in parallel, the 12-inch dredge
could focus on high production dredging
that generated thicker cuts, while the 8-
inch dredge focused on cleanup dredging
that generated thin residual sediment
layers. Typically, cleanup dredging results
in hydraulic slurries with just 1 -2% percent
solids, which can present problems with
dewatering and water treatment. By
operating parallel dredges and combining
the slurry streams, however, operations
were able to maintain a consistent and
reasonably high solids content (8-15%) in
the combined slurry while performing
cleanup operations specifically targeted at
reducing residual contamination. The 8-
inch dredge operated at an average
production rate of approximately 1,000 gpm,
and the 12-inch dredge operated at an
average rate of 3,500 gpm. Cleanup
dredging was performed on approximately
10 of the site's total 30 acres where
underlying bedrock prevented
overdredging of contaminated sediments.
Previous experience at this and other sites
suggested that significant amounts of
residual contamination would remain in
these dredged areas. Confirmation
sampling after dredging indicated,
however, that in areas where the Vic-Vac
was used, the surface-weighted average
concentration was 0.1 mg/kg total PCBs,
well below the long-term cleanup goal.
[continued on page 3]
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[continued from page 2]
Several areas required 2-3 dredging passes
with the Vic-Vac in order to achieve the long-
term cleanup goal of 0.25 ppm PCBs.
Construction and operational costs for
hydraulic dredging, dewatering, transfer,
and disposal of the sediment totaled
approximately $58 million. In accordance
with GLLA provisions, GLLA funds
covered 50% of the cost and the State
provided an additional $7 million; the
remaining $22 million was paid by the
consortium of private companies.
A total of 25,000 pounds of PCBs have
been removed from the river, and
commercial and recreational vessels no
longer are restricted from any portions of
the river. The GLNPO continues to work
with the Port Authority, State, and the private
companies to implement a post-dredging
monitoring plan, including evaluation of fish-
tissue PCB concentrations. Project
partners also are developing and
initiating implementation of a habitat
mitigation plan to restore 3-5 acres of
shallow water habitat.
Contributed by Scott Cieniawski, EPA
Region 5 (cieniawski.scott(q),epa.gov or
312-353-9184) and Natalie Farber, OH
EPA (natalie.farber(a),epa. state, oh. us or
614-644-2143)
39-Mile Dredging/Capping Approach Used to Treat Fox River PCBs
The Lower Fox River in Wisconsin contains
approximately 8 million yd3 of PCB-
contaminated sediment targeted for active
remediation. The site's records of decision
(RODs) were amended in 2007 and 2008 to
specify dredging of nearly 4 million yd3 of
sediment with high concentrations of PCBs,
followed by in situ capping of approximately
560 acres of sediment comprising operable
units (OUs) 1 through 4. The cap design
included development of an innovative
method for determining an armor stone
dimension sufficient to withstand propeller
wash from frequent recreational vessel traffic.
The site extends 39 miles from the outlet of
Lake Winnebago into Green Bay.
Contamination is found primarily in the first
six miles (OU1) and the last 20 miles (OU3
and OU4) of the river, reaching PCB sediment
concentrations as high as 3,000 ppm.
Contaminated sediment extends to depths
of up to 13 feet. Commercial shipping is
confined to the last 3.5 miles of OU4, which
ends at the mouth of Green Bay. Sediment
distribution in the middle 13 miles (OU2) is
patchy with intervening bedrock exposures.
OU2 contains the site's greatest elevation
drop and consequently the majority of the
river's locks and dams. OUS comprises the
entire bay, but dredging and capping are
anticipated only near the river mouth;
monitored natural recovery was selected as
the remedy for mo st of OU2 and OUS.
Based on experience in OU1, dredging did
not always remove all sediment above the
site-specific cleanup goal of 1 ppm. This goal
and the surface weighted-average
concentration goal of 0.25 ppm can only be
met with a combined approach of dredging,
capping, and sand covers. Dredging could not
be used in areas with in-water infrastructure
such as bulkhead walls or docks, near utility
crossings associated with commercial
facilities, or near shorelines with steep banks.
As a result, a capping approach using four
designs (differing in stone and/or sand
components) was used to contain residual
contamination and non-dredged areas.
Design criteria for dredging included maximum
horizontal/vertical slopes of 3:1 for submerged
areas and 5:1 for shorelines with nearby
infrastructure. A typical dredge management
unit covers approximately 6 acres, which
involves approximately 1 week of dredging per
unit. Prior to full-scale dredging operations,
models were used to develop final plans.
Dredging was initiated in OU1 in 2004 followed
by the placement of sand covers in areas where
residual PCB concentrations remained above
5 ppm; cover thickness ranged from 3 to 6
inches, depending on PCB concentrations.
Sand covers also were placed on undredged
areas with lower PCB concentrations; caps
composed of sand and armor stone were
placed over higher PCB concentrations. To
date, more than 370,000 yd3 of PCB-
contaminated sediment have been removed
fromOUl, of which approximately 8,000yd3
contained PCB concentrations above 50 ppm
and were classified as T SCA in situ sediment.
The sediments were disposed at local state-
regulated landfills. Water generated by
dredging, sand recovery, and dewatering is
treated through bag filters, sand filtration,
and granulated activated carbon prior to
river discharge. Air monitoring to date has
shown no exceedance of thresholds for
particulates or PCBs.
Similar operations will continue downstream
(mainly in OUs 3 through 4) from2009to 2017.
Hydraulic dredges and in-water pipelines are
used to remove and transport contaminated
sediment to a staging area where sand
fractions will be washed or otherwise treated
for possible beneficial onsite or offsite use.
Engineered caps will be placed at locations
where the final cap height allows for at least
3 feet of water and at least 2 feet below the
authorized navigational water depth. In order
to ensure caps will have long-term stability
and effectively contain PCBs, the following
conditions were evaluated during cap design:
> Frazil ice, particularly in areas of turbulent
waters downstream of dams or possible
high water velocities due to ice dams;
> High flows from tributary flooding; and
> Combinations of river flow, due to
seiche effects or lake level changes.
To further ensure effective caps, different
cap designs will be employed for different
river conditions. Innavigable areas, nearshore
areas, or where sediment contains PCB
concentrations exceeding 50 ppm, the armor
[continued on page 4]
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[continued from page 3]
consists of a 3 3-inch layer of sand, gravel.
and quarry spall. For design and construction
purposes, this cap type was designated as a
"Cap C." (Figure 3). In other areas, the cap
consists of 13 inches of sand and gravel (Cap
A) covering approximately 200 acres, or 16
inches of sand and gravel (Cap B) covering
approximately 70 acres. An estimated 25
additional acres of shoreline caps will be
constructed using larger armor stone to be
determined case by case. The areal extent of
each cap and total acreage of cap types is
subject to ongoing refinement. Other areas
having sediment profiles with PCB
concentrations below 2 ppm or in thin
deposits (6 inches or less) are covered with 6
inches of clean sand imported from local sand
and gravel pits. Shortly after placement, the
thickness of each cap layer is verified to
specified engineering standards.
Design of the cap for the navigation
channel of OU4 involved site-specific
models considering erosive forces such
as wave-induced currents, river flows, ice
scour, seiche, and vessel propeller wash.
This "JETWASH" model is similar to that
recommended by the U.S. EPA and
USAGE but includes additive velocities
accounting for the propeller shaft pitch and
reflection relative to the river bottom, which
are critical factors for recreational boats.
The model includes a momentum-based
approach to analyze stability of a bed
armoring particle that is subjected to time-
dependent propeller wash velocity
fluctuations typical of recreational
vessels. Due to the wide variety of
recreational vessels and modes of
operation used in the Fox River, the
propwash model relied on Monte Carlo
simulations using 2,500 parameter
combinations for water depths of 3, 5, 7,
and 10 feet each. In addition, two-
dimensional hydrodynamic models were
evaluated for OUs 1,3,4, and 5 to predict
bottom shear stresses during maximum
flow anticipated in a 100-year flood event.
USAGE empirical models were used to
predict characteristic vessel waves. To
consider potential impacts from propwash,
a Monte Carlo statistical model was
applied, incorporating:
> Capping costs and stone size;
> Magnitude of likely damage if movement
occurs; and
> Degree to which a cap can "self-heal" to
re-cover areas where cap materials may
have moved due to propwash or other in-
fluences such as vessel anchors.
Finally, if regularly scheduled or event-
triggered monitoring indicates that caps have
been eroded or otherwise adversely impacted,
the caps will be repaired as necessary to
provide continued containment.
Contributed by Jim
Hahnenberg, EPA Region 5
(hahnenberg.james(a)eDa.so\
or 312-353-4213)
Institutional controls currently include
fish consumption advisories throughout
the site, establishment of no-wake areas
in OUs 3 and 4, and limited public access
to waters undergoing active dredging or
cap construction. Monitoring during
active dredging and cap construction
includes routine geophysical surveys
and core sampling 2 and 4 years after the
initial post-construction survey and
every 5 years thereafter. Details of this
monitoring plan are being developed
during the design phase for OUs 2-5.
Long-term monitoring also will include
testing of cap integrity and performance
with respect to contaminant containment,
and analytical sampling of water and fish
tissue at least every 5 years to evaluate
environmental results.
Approximately 30 acres of caps have been
installed to date. Following dredging and
cap construction, additional time will be
needed for natural recovery, which
will result in additional
contaminant reductions meeting
other cleanup goals. In OU 3, for
example, an estimated nine years
of natural recovery are needed
to reduce PCB fish tissue
concentrations to 0.049 ppm, the
threshold for unlimited walleye
consumption. Construction
completion is scheduled for 2018.
Pilot Study Shows Effective Cap Design for PCB-Contaminated Sediment
A 1 -acre pilot study was used to evaluate
multiple cap designs at Silver Lake in
Pittsfield, MA, prior to construction of a
full-scale cap over the entire 26-acre lake
bottom. Sediment in Silver Lake is
contaminated with PCBs and other chemicals
from past discharges of process water and
wastewater from the nearby General Electric
(GE) facility. Monitoring indicated that the
pilot caps provided an effective barrier to
upward transport of PCBs from the
underlying sediment. Use of geosynthetic
materials, however, did not appear to
improve cap performance significantly.
[continued on page 5]
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[continued from page 4]
Between early October and late November
2006, the pilot study was conducted at three
contiguous 45-ft by 300-ft sub-areas. An
isolation layer was placed directly on the
soft sediment in one sub-area (Figure 4). This
layer contained 2.5 parts pond sand (by
volume) mixed with 1 part topsoil using
conventional earth-moving equipment to
achieve approximately 1% total organic
carbon (TOC) in the dry mix. Acustom-made,
barge-mounted, spreader box broadcasted
slurried material in thin 1- to 2-inch lifts to
minimize the potential forresuspension and
mixing of the underlying sediments. The thin
lifts also help avoid settlement or slope
failure resulting from the relatively low-
strength, highly-compressibile sediments
and steep slope of the lake floor near the
shore. The lifts were broadcasted until a
depth of 12-14 inches was achieved.
The second sub-area was covered with a
non-woven geotextile before subsequent
placement of the same isolation materal.
Three 15-ft wide by 300-foot long rolls of
Mirafi 1 SON non-woven geotextile fabric were
unrolled from a barge. The adjacent edges were
sewn together to form one contiguous piece
(with about 2-foot overlap at each seam) and
anchored temporarily to the banks with
sandbags attached in an approximate 20-ft
grid. Due to puckering of the emplaced
geotextile-likely resulting from its buoyancy-
more sandbags were added to ensure that the
fabric would lay flat over the sediment. A
fourth roll was later placed using rebar to add
structural support to the geotextile and
maintain the width of the fabric during
placement to fully cover the sub-area.
The third sub-area was covered with a
composite geotextile mat before placement
of the isolation layer. The composite geotextile
was constructed of two layers of a non-woven
geotextile sewn together and filled with a thin
layer (less than 1 inch) of a sand/organo-clay
mix. The mix had a TOC similar to the isolation
layer. This composite configuration was
prepared in nine rolls (about 15-feet wide by
100-feet long) that were sewn together and
unrolled from the barge similar to the non-
Figure 4. Three
cap designs were
used in the pilot
study at Silver
Lake in Pittsfield,
MA.
Geotextile and Isolation Layer
Non-woven Geotextile
Polyester Geocore
Non-woven Geotextile
• Water
Isolation Layer
Sediment
Water
Isolation Layer
Non-woven Geotextile
Sediment
Water
Isolation Layer
Composite Geotextile
Sediment
Geocomposite and Sand Cap
woven geotextile cap. Puckering during
installation led to the addition of rebar, for
structural support to maintain the full width
of the fabric.
Armor stone was installed along the
shoreline to protect all three caps from
erosion due to wind-induced waves. The
armor consisted of riprap placed over a
woven geotextile above and below the mean
water surface elevation. A gravel layer was
placed over the armor stone below the water
line to improve habitat for aquatic species.
The thickness of the three pilot caps was
measured using a combination of acoustic
profiling, probing, and coring. The thickness
of all three caps was found to be fairly
uniform, averaging 12 to 14 inches.
Physical survey plates and vibrating wire
settlement cells were used to measure
sediment settlement during, immediately
after, and six months after construction of
the caps. The results generally indicate a
relatively uniform, slow rate of settlement
and compaction of the underlying native
sediment, averaging 11-12 inches over the
first nine months. The majority of settlement
occurred during placement of the isolation
layer and appeared to be complete within
two to six months of cap placement. Use of
geosynthetic layers did not appear to create
any variations in the extent of settlement.
Although settlement rates greater than the
target of 1 inch/day were occasionally
measured, there was no indication of
sediment instability or other deleterious
effects on cap performance. Coring and
sediment profile imaging showed some
mixing of the sediment and isolation layer
material in the isolation layer-only cap, but
mixing appeared to be limited to the lower 2
inches of material.
PCB concentrations in sample cores were
low (non-detect to 14 mg/kg) relative to
underlying sediments (25.2 to 178 mg/kg),
with about 70% of the detections less than 1
mg/kg. Collectively, the PCB distribution in
the post-construction cores suggests that
isolation layer materials, when placed in
[continued on page 6]
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Solid Waste and
Emergency Response
(5203P)
EPA 542-N-08-005
October 2008
Issue No. 38
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
[continued from page 5]
thin lifts, caused only limited disturbance
to or mixing with the underlying sediments.
No indication of upward transport of
PCBs through the cap material was noted.
A reduction in overall TOC in the isolation
layer before and after placement was
observed; however, the average TOC was
at or approaching the post-construction
target level (approximately 0.5%).
PCB concentrations detected in the Silver
Lake water column were lower during
implementation of the pilot study than
those prior to the study, indicating that
little or no re-suspension of existing
sediments occurred as a result of cap
placement. Turbidity increased while the
isolation material was broadcasted, but it
returned to pre-construction levels within
a month. A portion of the decrease in PCBs
in the surface water may be attributable to
sorption of PCBs to suspended particles
when turbidity was increased.
The study results show that the sand cap
amended with organic carbon installed in
thin lifts produced minimal disturbance to
the underlying sediments of Silver Lake
and provides an effective barrier to PCB-
contaminated sediment. Addition of
geosynthetic materials did not appear to
benefit construction significantly.
General Electric is now designing a full-
scale cap for Silver Lake based on the
conceptual cap design of the pilot study.
Contributed by Susan Svirsky, U.S. EPA
Region 1 (svirsky.susan(a),epa.gov or
617-918-1434)
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Office of Superfund Remediation
and Technology Innovation
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Fax:703-603-9135
EPA is publishing this newsletter as a means of disseminating useful information regarding innovative and alternative treatment techniques and
technologies. The Agency does not endorse specific technology vendors.
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