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OCR for page 162
Sealable Joint Steel Sheet Piling for Ground-Water Pollution
Control
David I.A. S myth and John A. Cherry, WaterIoo Centre for Groundwater Research
(WC GR), University of Waterloo, Waterloo, Ontario, Canada; arid Robin I. Hewett,
Waterloo Barrier, Inc., Rockwood, Ontario' Carlada
ABSTRACT
The Waterloo Barrier_ (patents pending) system employs modified steel sheet piling for
use in the control and containment of subsurface contamination. The interlocking joints of
adjacent sheet piles have been modified to incorporate a cavity that can be flushed and filled
with a sealant subsequent to installation of the sheet piles in the ground. Field hydraulic tests
indicate that bulk hydraulic conductivity values of the barrier wall system of less than 10-8 cm/s
can be achieved using a variety of sealant materials. The installation and sealing process affords
opportunities to ensure that the integrity of the barrier wall is good. The technology was
developed recently; it has been used to construct test cells for field research pertaining to the
behavior and rememation of contamination in ground water and also has been applied
commercially for ground-water pollution control at industrial, military and waste management
sites.
INTRODUCTION
Ground-water contamination arising from inappropriate handling and disposal practices
for industrial chemicals, products, and wastes has been identified as a problem at tens of
thousands of commercial, industrial, military and government agency sites across North America
and Europe. More than a decade of experience and expenditures of billions of dollars have
demonstrated that ground-water rememation is a difficult task and that ground-water
remediation programs, particularly In cases where full restoration of the ground-water system to
a condition suitable for unrestricted water supply use is required, have generally fallen short of
expectations. The apparent failures in subsurface restoration have resulted from a lack of clear
~ , .
... ~ ,~ ~ ~ 1 ~ ¢ ~ ~:~:~ ~1~ LEA ~
recognition about the nature ana cnaracrensr~;~ o~ cut; ~'lll~acl~l1 ~lVIJl~lll Ct11~1 11
limitations or inappropriate applications of technologies used in the remediation process.
Subsurface contamination problems generally have two components: a zone or plume of
dissolved contaminants emanating with ground-water flow from a source zone, where the
contaminants were introduced and continue to exist in the subsurface. The characteristics of the
source zone are dependent on the contaminant type. For marry inorganic contaminants, the
source zone may contain solid, soluble materials. Industrial organic contaminants may be present
as immiscible-phase liquid pools and residual within the geologic media, or as organic vapors in
the zone above the water table. For ENAPEs (light, non-aqueous phase liquids) such as
petroleum hydrocarbons, contamination In the source area is generally confined to the vadose
and shallow ground-water zones. DNAPEs (dense, non-aqueous phase liquids), such as
chlorinated solvents, may penetrate to significant depths below the water table, so contaminant
D-144
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APPENDIX~PAPERS PRESENTED
D-145
distribution in the source zone may extend from the vadose zone to significant depth within the
ground-water zone.
The solubility of some of the industrial organic compounds, including most of the
volatile organic compounds associated with typical LNAPLs and DNAPLs, and inorganic
contaminants in water may exceed the levels corresponding to regulatory human health and
environmental criteria. In their dissolved form, these contaminants may also be quite mobile in
ground water. In general, the mass of contaminants present in the source zone far exceeds that
present in the dissolved phase in the associated plume, although the plume may be spatially more
extensive. Potential risks and impacts to human health and the environment, however, are often
more immediate for the dissolved-phase contaminants in the plume than for the source zone.
The most common approach to ground-water remediation has been based on gro~,nd-
water extraction by wells or drains, with subsequent treatment of the contaminated water prior to
its ultimate discharge back to the environment. This pump-and-treat approach can be effective in
the control or containment of plumes, but as indicated by Mackay and Cherry (1989), it generally
requires long-term operation. Heterogeneities of geological materials within the Round-water
~ ~ _
system may prolong the time frame required for removal of dissolved-phase contaminants.
Further, if subsurface sources of contaminants are present, it can be anticipated that pump-and-
treat control will be required for decades and longer, and dissolved-phase plumes will be re-
established if pump-and-treat operations are terminated.
The growing recognition of the limitations and inefficiencies of pump-and-treat has
provided strong impetus to develop alternate approaches and new technologies for ground-water
remediation. Cherry, Feenstra, and Mackay (1992) and Mackay, Feenstra, and Cherry (1993)
outline an approach to gro~nd-water remediation that recognizes the distinct implications of
contamination within the source zone and the plume. They suggest three levels of remediation,
including:
plume containment, which leaves the subsurface source in place, but leads to no
further expansion of the plume;
· partial aquifer restoration, which involves long-term isolation of the source zone in
combination with remediation of the plume;
aquifer restoration, which involves full remediation of both the plume and source
zone. In cases involving DNAPL contamination, full aquifer restoration may be an impractical
goal using current technologies.
Cherry et al. (1992) and Mackay et al. (1993) further suggest four approaches to source
zone isolation. As shown in Figure 1 for the DNAPL case, source zone isolation may be
provided by containment within a low-permeability cutoff wall or barrier, long-term hydraulic
control using an active pump-and-treat system, or ~n-situ treatment of contaminants emanahng
from the source zone using permeable reaction curtains and funnel-and-gate systems. Each of the
approaches will have their merits and limitations for different contaminant problems in different
hydrogeological settings; however, in many circumstances, there may be good opportunities for
using vertical barriers for contaminant source zone isolation.
OCR for page 164
D-146
BARRIER TECHNOLOGIES FOR E~IRONMENTALMANAGEMENT
(a) - ~_ ~
. .
;_
. .
. __
_ ZONE -
· _ -
_ ~ .
CUTOFF WALL
~ (God
(C) i___ (d ) ~
-Gil ~ ~
PERMEABLE
REACTION CURTAIN
__
FUNNEL & GATES'
FIGURE ~ Contaminant source zone isolation using (a) Tow-permeability barrier enclosure,
(b) hydraulic containment by pump-and-treat, and contaminant containment by (c) permeable
reaction curtain and (~) funnel-and-gate system.
Starr and Cherry (1992) and Mutch, Ash, and Cavalli (1994) provide discussions
pertaining to the use of low-permeability barriers for control of ground-water contamination.
Hydraulic performance and the degree of containment provided by an enclosure can be
optimized in situations where the barrier can be keyed into an underlying aquitard of low-
permeability geological materials beneath a source zone. in circumstances where this is not
possible due to the absence of such conditions, significant containment can be achieved by an
enclosure that extends to depths beneath the source zone but that is not keyed into an underlying
aquitard if a pump-and-treat system is operated within the enclosure. The presence of the
enclosure will reduce significantly the volumes of water that must be pumped to maintain
hydraulic control In comparison to systems where an enclosure is not used, and hence will also
reduce operational and treatment costs for the contaminated water. It is also conceivable that
restoration of a source zone using chemical flushing technologies for enhanced removal or in-
situ destruction of contaminants will be more efficient in cases where an enclosure is present.
As Mutch et al. (1994) indicate, there has been a resurgence in research, development
and application of various battier wall construction technologies within recent years. This
resurgence has resulted in the development of capabilities to improve the hydraulic performance
and extend the depths to which barrier walls can be constructed. Given the variety of
construction techniques available, it is reasonable to assume that there will be technical and cost
advantages of using particular battier walls In different situations. Conventional construction
techniques include compacted clay barriers and slurry trenches, which typically incorporate soil
bentonite, soil attapulgite, and cement-bentonite mixtures in the battier. New and developing
technologies for barrier construction include vibrated beam cutoff walls, deep soil mixing or
auger cast walls, jet grouted walls, geomembrane barriers, and sealable joint steel sheet piling.
OCR for page 165
APPENDIX PAPERS PRESENTED
D-147
The remainder of this paper provides an overview of the development and application of sealable
joint steel sheet piling (Waterloo Barrier_ _patents pending) for barrier wall construction.
Waterloo Barriers
The initial concept and field applications of the Waterloo Barrier_ arose from a
requirement for secure test cells for contaminant-related gro~'nd-water research at the University
of Waterloo (UW) in the late 1980's and early 1990's. Field research involving the controlled
introduction of DNAPL chemicals to a shallow sand aquifer was being conducted at Canadian
Forces Base Borden approximately 100 km northwest of Toronto, Ontario, Canada. The sand
aquifer is underlain by a cIay-rich aquitard at depths ranging from several meters to in excess of
10 m below ground surface. A trial application of jet-grouting technology for construction of a
test cell proved to be unsatisfactory. Slurry wall barriers were also considered. The required test
cells were quite small, involving total wall lengths of up to 40 m, and projected costs were high,
primarily as a consequence of the costs associated with the mobilization of the construction
equipment. Thus, other construction options were sought.
Some preliminary experimentation was undertaken using conventional steed sheet piling.
It was soon recognized that the leakage of water through the joints of conventional sheet piling
may not always be suitable for contaminant-controT applications. The search for methods to
improve the seal between adjacent sheet piles ultimately led to the development of a sealable
cavity at the joints. Although the initial version involved the modification of conventional sheet
piling with an angle-welded sealable cavity at each joint, the capability to produce a special cold-
rolled sheet pile with the sealable cavity joint incorporated directly in the production process was
developed In cooperation with Canadian Metal Rolling Mills of Cambndge, Ontario, by 1991.
The essential components of the Waterloo Ba~TierTM are shown In Figure 2. Barner
construction employs conventional sheet piling Installation equipment. As described above, the
unique feature of the battier system is the sealable cavity at each joint. The configuration of the
bottom of the cavity largely prevents pebbles and debris from entering the cavity as the piles are
driven. Subsequent to Installation of the balker, soil that does enter the cavities is removed by
jetting with water. Following this process, the Integrity of the joints throughout their entire
length can be assessed and any imperfections or blockages noted. This inspection process has
been enhanced recently through the use of downhole camera techniques. Once the cleaning and
inspection of the cavities has been completed, the sealant can be emplaced from bottom to top In
each cavity.
~N ~
WATERLOO BAR
STANDARD SHEET PILE
SECTION \
\ `7
PLAN VIEW
WATE=OO B~R
SHEET PILE DETAIL
FIGURE 2 The Waterloo Barrier_ system, showing Interlocking steel sheet piling and
modified joint with the sealable cavity.
OCR for page 166
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BARRIER TECHNOLOGIES FOR ENVIRONMENTAL MANAGEMENT
A variety of joint sealant materials can be used. Selection of sealant will be based on
project requirements. The types of issues that may be considered in the sealant selection process
may include sealant/contaminant compatibility, the presence of unusual ground-water chemistry
conditions such as high salt content, the ability of the sealant to withstand the anticipated
differences In hydraulic head across the baITier, the amenity of the sealant to removal of the
balTier system following a specified period, permeability characteristics, pumpability
characteristics, thermal expansion characteristics of the sealant, design life of the system' and
cost. The types of sealants available include cIay-based grouts such as bentonite and attapulgite,
cement-based grouts (modified with expanding agents), epoxy polymers, urethane polymers, and
miscellaneous sealants such as vinyl esters, polysufides, swelling gaskets and bituminous grouts.
Hydraulic Testing
In excess of twenty test cells have been constructed for field research purposes, and
several of these cells have been designed in a manner that facilitates rigorous hydraulic testing.
Some of these cells have been constructed using concentric double walls, such that the hydraulic
head In the moat bounded by the two walls can be maintained at a constant level. Further, these
cells all penetrate to an underlying aquitard.
Figure 3, from Starr et al. (1992), shows a schematic diagram of such a cell. In this case,
the cell extends through a surficial aquifer of approximately 12 m In thickness and terminates in
a clay aquitard at a depth of approximately 14.7 m. The cavities were seated with a bentonite
slurry. Hydraulic testing was conducted by elevating the hydraulic head within the Internal cell,
maintaining a constant hydraulic head within the moat, and monitoring the decline in relative
difference between the hydraulic head measurements with time. The plot of this decline,
accounting for losses by evaporation, is shown in Figure 4, also from Starr et al. (1992~. In
applying the analytical solution, all water flux from the cell was attributed to leakage through the
internal cell wall, and the clay aquitard was assumed to be impermeable. In reality, some leakage
would have occurred through the aquitard at the base of the cell. This assumption aside, the bulk
hydraulic conductivity of the cell wall was calculated to be 6 x 10-9 cm/s. Similar tests in other
cells, one of which was sealed with an organic polymer sealant, have indicated that bulk
hydraulic conductivities of less than 10-9 cm/s can be achieved.
A
-
l
~V - B
FIGURE 3 Plan and section view of test cell used to conduct hydraulic testing (after Starr et
al., 19921.Figure 3. Plan and section view of test cell used to conduct hydraulic testing (after
Starr et al., 19921.
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APPENDIX~PAPERS PRESENTED
0.8
0.6
0.4.
0~a
O.0
D-149
\ (1~-7~81
; ~ -]
JOE~cngs ~
~- ~
_
lOE~ants |~
~,
1 1 5 10 15 20 25
Elapsed Time (days)
30 35 40
FIGURE 4 Observed response of representative hydraulic test of test cell showing bulk
hydraulic conductivity of barrier wall (after Starr et al., 19921.
Applications and Commercialization
Commercialization rights for Waterloo Barrier_ are held under license from UW by
Waterloo Barrier, Tnc. of Rockwood, Ontario. A sub-license agreement for the production of the
modified sheet piling has been made with Canadian Metal Rolling Mills (CMRM). CMRM
currently produces a cold-rolled 7.5-mm (0.295-inch) section incorporating the modified cavity;
a 9.5-mm (0.375-~nch) section will be available by the last quarter of 1995. To date, three
companies have been issued sub-licences covering supervision of installation, joint sealing, and
quality assurance/quality control measures. The companies include: C3 Environmental of
Breslau, Ontario; Slurry Systems, Inc., of Gary, Indiana; and RCI Environmental, Inc. of Kent,
Washington.
Waterloo Barrier has been applied for contaminant control purposes in more than
twenty experimental cells as large as 10 x 10 m at several Canadian sites in association with the
gro~'nd-water research program at UW. The maximum depth of these applications is
approximately 15 m, and the sealants used have included bentonite grout and an organic
polymer.
Waterloo garner_ systems have also been installed at seven sites on a commercial
basis. These installations have included test cells for trial applications of various remediation
technologies at Hill Air Force Base (Utah) and Dover Air Force Base (Delaware); enclosures
around contaminant source zones at industrial facilities In Toronto, Ontario, and in the Seattle
area; a battier system used in conjunction with a methane gas collection system at a municipal
landfall in Kitchener, Ontario; and barrier walls used in conjunction with pump-and-treat systems
nt an industrial facility in Vermont and a military facility in Colorado. The size of the barrier
systems have ranged from approximately 5,500 m2
(60,000 ft2) to 275 m2 (3,000 ft21. The design
OCR for page 168
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BARRIER TECHNOLOGIES FOR ENVIRONMENTAL MANAGEMENT
depths of the installations have ranged from approximately 5 to 15 m. Various sealants have
been used, including bentonite grout, cementitious bentonite and attapulgite grouts, and epoxy
polymers. Rigorous joint-inspection procedures have been followed in all the projects, and
sealant operations generally have proceeded without serious impediments. Only one of the
commercial applications has been amenable to hydraulic testing, and In this instance, a bulk
hydraulic conductivity for a battier wall cell was estimated to be less than 10-8 calls. Overall
costs for these projects have ranged from $160.00 to $430.00 per square meter ($15.00 to $40.00
per square foot) of barrier.
DISCUSSION
The field applications have confirmed several advantages of the Waterloo Barrier_
system, including:
Clean and flexible installation. There are modest wastes generated during
installation of the barrier system, thus problematic and potentially expensive issues
associated with the handling or treatment of wastes are generally avoided.
Site-specific custom design. The design and installation of the barrier system can,
within reason, accommodate some unusual requirements arising as a consequence of
buildings or facilities on site. In one application, a barrier was installed through the
floor of an existing building and involved the sequential driving and welding of up to
three vertical sections of pile.
Detailed quality assessment/quality control (QA/QC). During pile driving and the
joint flushing process, it has been possible to provide very detailed monitoring and
inspection services. This has facilitated the preparation of excellent documentation
records, which may be quite advantageous in assurance of compliance with
regulatory requirements.
The systems following installation look to be fundamentally sound. Based on the
joint inspection and sealing activities, and hydraulic testing on enclosures where
such testing has been feasible, statements regarding the expected hydraulic
performance and integrity of the barrier system can be made with some confidence.
Like all engineered controls, installation of an effective barrier system using the
Waterloo BarTierTM may not be the most appropriate selection of barrier system for all
applications. It can be anticipated that Waterloo Banier_ may have limitations in some
circumstances including:
The general depth and installation limitations associated with conventional
sheet piling. I:n bouldery and rocky terrain, and in areas of dense unconsolidated
sediments, the use of sheet piling will not be possible. Even in apparently
appropriate media there will be limitations to the depth to which sheet piling can be
installed. This depth will vary, but it is not unreasonable to assume that applications
may be restricted to depths of less than 30-45 m or so. Although installation
capabilities for sheet piling might be enhanced by using features such as water jets at
the leading edge of the pile as driving occurs, or by resorting to measures such as
pre-drilling along the footprint pattern of the baITier, these will add to project costs.
OCR for page 169
APPENDIX~PAPERS PRESENTED
.
.
D-151
Keying systems to bedrock underlying unconsolidated deposits. Although
techniques have been developed for sealing the base of Waterloo garner_ system to
underlying rock formations, special precautions will be necessary, and effectiveness
of the sealing techniques may be difficult to confirm.
Vibration and noise associated with piling installation. Although all construction
may disrupt normal activities in the vicinity, the installation of sheet piling generates
loud noises, and the level of vibration induced by pile driving may not be acceptable
in some urban environments. The installation of sheet piling may result in some
compaction and subsidence of adjacent soils, which also can be a concern. It is also
worth noting, however, that all battier construction techniques will have similar
drawbacks associated with their implementation.
Based on development, testing, and application to date, the potential utility of Waterloo
garner_ systems in the control and containment of subsurface contamination has been
demonstrated. The technology has been commercially available for only less than two years, so it
is anticipated that further development will occur. It is also anticipated that the full capabilities,
including the advantages and limitations of the technology, will become more clear. Additional
experience is also necessary to better define the range of costs for projects involving application
of Waterloo Barrier systems.
ACKNOWLEDGMENTS
The authors acknowledge the contributions of Sam Vales (UW), Robert Starr (UW), Jack
Hammill (CMEtM), and Cam Wood and Murray Gamble (C3 Environmental) to the development
of Waterloo Barrier_ technology. Research funds were provided by the University Consortium
Solvents-in-Groundwater Research Program, which has been sponsored by The Boeing Co,
Ciba-Geigy, Dow, Eastman Kodak, General Electric, Laidiaw, Mitre Corporation, Motorola,
PPG Industries, United Technologies Corporation, and the Canadian (NSERC) and Ontario
(URIF) governments and the Ontario Environmental Technologies Program.
REFERENCES
Cherry, I. A., S. Feenstra, and D. M. Mackay. 1992. Developing rational goals for in situ
remedial technologies. Pp. 14-17 in Proceedings of the Subsurface Restoration
Conference, Dallas, Texas.
Mackay, D. M., and I. A. Cherry. 1989. Groundwater contamination: Limitations of pump-and-
treat remediation. Environmental Science & Technology 23~61:630-636.
Mackay, D. M., S. Feenstra, and I. A. Cherry. 1993. Alternative goals and approaches for
groundwater remediation. Pp. 35-47 in Proceedings of the Workshop on Contaminated
Soils: Risks and Remedies, Stockholm, Sweden.
Mutch, R. D., R. E. Ash, and N. I. Cavalli. 1994. Advancements in subsurface barrier wall
technology. Pp. 784-789 in Superfimd XV Conference Proceedings, Washington, D.C.
Starr, R. C. and I. A. Cherry. 1992. Applications of low permeability cutoff walls for
groundwater pollution control. Proceedings of the 45th Canadian Geotechnical
Conference, Toronto, Ontario.
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BARRIER TECHNOLOGIES FOR ENVIRONMENTAL MANAGEMENT
Starr, R. C., J. A. Cherry, and E. S. Vales. 1992. A new type of steel sheet piling with sealed
joints for gro~ndwater pollution control. Proceedings of the 45th Canadian Geotechnical
Conference, Toronto, Ontario.
Representative terms from entire chapter:
source zone
