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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.
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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.
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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.
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D-148 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
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D-150 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.
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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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D-152 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.
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