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PVC Sheet Piling for Cut-off and Containment Barriers

Brendan Sheppard, P.E.1, Steve Hargrave2

1Director of Engineering, CMI Limited Co., Marietta, GA; e-mail: bsheppard@cmilc.com 2Director of Innovations, CMI Limited Co., Marietta, GA; e-mail: shargrave@cmilc.com ABSTRACT Engineers worldwide are choosing polyvinyl chloride (PVC) sheet piling as bulkhead replacement material for steel, concrete, and timber, due to its proven history over 25 years and its high corrosion resistance in marine environments. More recently, barrier walls have been constructed for cut-off and containment applications using PVC sheet piles. The goal of this paper is to look at real world levels for commonly contained chemicals and the resulting predicted permeation of the PVC sheet pilings used for their containment and to review cut-off and contamination case studies using PVC sheet piling. This paper will explore the use of (PVC) sheet piling and its compatibility with hydrocarbons, solvents, and common fuel additives like benzene, toluene, ethylbenzene, xylene, and naphthalene BTEX(N) along with creosotes and other similar chemicals that are of particular interest to engineers. For these pollutants, PVC sheet piling can offer increased chemical cut-off and containment performance and design life, as well as reduced costs over conventional solutions. This paper will also present several cases studies where PVC sheet piling is used to cut-off various types ground water contaminants, provide groundwater cut-off to construction areas and serve as secondary and primary containment in dams. INTRODUCTION Polyvinyl chloride (PVC) sheet piling has been used for over 25 years in bulkheads throughout the United States and beyond as a replacement for steel, concrete, and timber materials due to the high corrosion resistance offered in a marine environment. More recently, barrier walls have been constructed for cut-off and containment applications using PVC sheet piles.

Box Profile Z-profile Flat Panel

Figure 1. PVC sheet pile shapes.

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Figure 2. 30-ft long PVC sheet pile installed in with a fixed mast pile driver in August 2015. Polyvinyl chloride (PVC) sheet piling compatibility with hydrocarbons, solvents and common fuel additives like benzene, toluene, ethylbenzene, xylene, and naphthalene [BTEX(N)] along with creosotes and other similar chemicals are of particular interest to engineers and their clients (OH DOH, 2014). For these pollutants, PVC sheet piling can offer increased chemical cut-off and containment performance and design life, as well as reduced costs over conventional solutions. Because standard chemical resistance tables typically show these chemicals as “incompatible” or “not recommended” with PVC, there has been some hesitancy in the adoption of PVC sheet piling for chemical cut-off and containment applications. A goal of this paper is to review real world levels for commonly contained chemicals and the resulting predicted permeation of the PVC sheet pilings used for their containment. This paper will also present cases studies where PVC sheet piling has been used to cut-off various types ground water contaminants, provide groundwater cut-off to construction areas, and serve as secondary and primary containment in dams. The paper presents 4 case studies: a salt water contamination cut-off wall in Bolsa Chica, California; increasing storage for a fly ash Pond near Brilliant, Ohio; remediation for Superfund site in Michigan; and containment of groundwater and soil contamination in Corpus Christie, Texas. Key factors that engineers used in the decision making process of specifying vinyl sheet piles for these projects will also be highlighted.

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CHEMISTRY AND PERMEATION Chemical compatibility tables are usually built from exposing the PVC to the “neat” or a highly concentrated form of the chemical approaching 100% purity. Indeed, at extremely high concentrations of toluene for example, there can be deleterious effects ranging from degradation to swelling or softening. At lower concentrations, the degradation does not occur (Berens, 1985). Significant research has been dedicated to this subject. In Berens’ investigation of the “Prediction of Organic Chemical Permeation Through PVC Pipe”, he concluded that “Softening and significant permeation of PVC pipe seems possible only in the presence of nearly undiluted solvents or swelling agents for PVC. At lower activities [concentrations], which still correspond to unusually high levels of environmental pollution, solvent transport follows ideal Fickian diffusion kinetics…The calculated permeation rates are virtually zero for many centuries, indicating that rigid PVC pipe is an effective barrier against permeation of environmental pollutants.” (Berens, 1985) Mao, et al. (2011) validated and built on Berens’ research and developed a predictive model based on the behavior of toluene (the more aggressive PVC solvent component of BTEX) in National Institute of Standards and Technology (NIST) fuel. The following equation from “Microscopic Visualization Technique to Predict the Permeation of Organic Solvents through PVC Pipes in Water Distribution Systems” relates the swollen layer to the chemical’s concentration and time.

𝑳𝑳𝒔𝒔,𝒕𝒕 = �𝟐𝟐𝟐𝟐.𝟖𝟖𝟖𝟖−�𝟑𝟑.𝟐𝟐𝟐𝟐

𝒗𝒗𝒇𝒇�� 𝒕𝒕

𝟐𝟐𝟐𝟐

where: Ls = swollen layer thickness (mm) vf = volume fraction concentration t = time (days)

Applying this equation to three common PVC sheet pile products results in the predictions for permeation shown in Figure 1. At lower concentrations the time to permeate a given thickness is on the order of centuries.

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Figure 3. Permeation time as function of sheet piling thickness and chemical concentration.

612441,38412,850250,824

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SG-825 (t=0.485)

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Additionally, from the Practical Handbook of Environmental Site Characterization and Ground-Water Monitoring by Nielsen (2005), Ranney and Parker (1995, 1997) concluded from their research with known PVC solvents (see Table 1) many of which are on the Environmental Protection Agency’s (EPA) VOC and semi-volatile organic compound (SVOC) target list — that at concentrations of 10% or less, there was no measureable degradation of PVC sample well casings.

Table 1. List of known PVC solvents (Nielsen, 2005). Hydrocarbons (aliphatic and aromatic)

Benzene Gasoline (93 octane, unleaded) Hexane (85% N-hexane) Kerosene (K-1) Toluene o-Xylene

Chlorinated solvents (aliphatic and aromatic)

Bromochloromethane Carbon tetrachloride Chlorobenzene Chloroform 1,2-Dichlorobenzene 1,2-Dichloroethane trans-1,2-Dichloroethylene Methylene chloride Tetrachloroethylene Trichloroethylene

Oxygen-containing compounds (either a ketone, alcohol, aldehyde or ether)

Acetone Benzaldehyde Benzyl alcohol Cyclohexanone Methyl alcohol Methyl ethyl ketone Tetrahydrofuran

Nitrogen-containing compounds N-Butylamine Diethylamine Dimethylformamide Nitrobenzene

Acids and bases Acetic acid (glacial) Hydrochloric acid (25% w/v) Sodium hydroxide (25% w/v)

REAL WORLD CONTAMINATION LEVELS Many PVC sheet pile products have been installed in numerous cut-off and containment barriers. These products have been exposed to chemicals ranging from acid mine run-off consisting of very acidic sulfur and iron compounds to polychlorinated biphenyls (PCB) to salt water. However, the most commonly remediated contaminates are in the hydrocarbon family. These pollutants may consist of volatile organic compounds (VOC), solvents, and fuels including gasoline, which can contain up to 28% BTEX (Mao et al, 2011). Coal tar creosote also contains similar amounts of these compounds.5 The vast majority of remediation projects experience contamination levels in the parts per million (ppm) or parts per billion (ppb), which are magnitudes lower than the ≤10% level cited by the Practical Handbook of Environmental Site Characterization and Ground-Water Monitoring. A survey of remediation projects of contaminated sites in the United States containing BTEX, or the individual components that make up BTEX, showed pre-treatment contamination levels averaging 0.49% with a maximum level of about 9% (see Figure 2), (EPA Members 1995-2006).

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Figure 4. Contaminated sites with relative contamination levels. Data compiled from levels reported in Abstracts of Remediation Case Studies, Volumes 1-10 (Member Agencies of the

Federal Remediation Technologies Roundtable, 1995-2006). LIFE EXPECTENCY OF PVC WITH ORGANIC CHEMICAL CONTAINMENTS At contamination levels less than about 40%, PVC sheet piling will perform well in chemical cut-off and containment applications with hydrocarbons, solvents and common fuel additives (see Table 2). Real world contamination levels are most frequently in the ppm or ppb levels.

Table 2. Contamination level and PVC performance. Contamination

Level (%) PVC Performance < 10% Experts conclude there is no degradation

10-25% Nearly infinite design life may be expected 25-40% Evaluate the site specifics, but PVC will likely perform well

> 40% Evaluate the site specifics, but PVC may be a valid, finite life design

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PVC SHEET PILE EFFECTIVENESS IN CUTOFF APPLICATIONS The United States Army Corps of Engineers (USACE) recently published guidance on the use of vinyl sheet piling. The Interim Poly Vinyl Chloride (PVC) Sheet Pile Guidance document provides guidance on the applications of vinyl sheet piling as well as the important specification requirements. This document lists Hydraulic Cutoff Barriers as an application for PVC sheet pile. In addition, the USACE recommends that all virgin PVC used shall have a minimum cell classification of 1-42443-33 in accordance with ASTM D4216 and that the manufacturer provide a certificate of analysis attesting to this along with the product warranty (USACE, 2017). The effectiveness of PVC Sheet piling as a barrier can best be demonstrated by reviewing the real world results from case studies. The following case studies were chosen primarily because of their age, post construction monitoring of the effectiveness and proven continued performance. Many other case studies are available. However, in many cases post-construction monitoring data is not always readily available. Anecdotal evidence would suggest that the effectiveness of vinyl sheet piles for cut-off applications is more becoming more widely accepted by the engineering community as usage continues to increase. Bolsa Chica. The Bolsa Chica Lowlands Restoration Project is the largest wetland restoration in southern California history. The project created or restored over 600 acres of marine and wetland habitat and was built as required mitigation for the expansion of the Ports of Long Beach and Los Angeles. Restoring the wetlands involved reconnecting the lowland to the influence of ocean tides, and creating a full tidal basin and managed tidal areas. However, bringing the ocean tides back into the basin meant the possibility of saltwater contamination of neighboring groundwater of the local communities. To prevent this, engineers specified that a 4,500 linear foot impermeable barrier wall be constructed to prevent saltwater migration. In September of 2005, SG-325 vinyl sheet piling was installed to a depth of 30 feet to anchor the wall into a layer of impermeable clay layer. The wall installation was completed in just over 1 month using a steel mandrel and a fixed mast pile driving rig and with a vibratory hammer. The full tidal basin was opened to the ocean on August 24, 2006. Since the restoration of the wetlands, the seepage barrier has performed as intended. Figure 5 shows the aerial and ground level wall alignment.

Figure 5. Bolsa Chica vinyl sheet pile cut off wall alignment.

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AEP Cardinal Plant Fly Ash Pond. Cardinal Fly Ash Reservoir No. 2 (FAR2) dam is located near Brilliant, Ohio was originally constructed as a zoned earth dam in 1985. In 1997, the dam was raised to a height of 237 feet using roller compacted concrete (RCC) in conjunction with a downstream earth fill. In 2011, the dam was raised again. The engineer specified a unique approach to raising the dam. An MSE wall system using geosynthetic reinforcement and reinforced full-height concrete panels formed the upstream and downstream faces to raise the dam up to 13 feet. For seepage containment, a cement bentonite slurry wall was constructed which penetrated into the existing clay core. A vinyl sheet pile wall was then inserted 30 feet through the slurry wall and extended up 8 to 13 feet to the top of the raised dam in between the MSE reinforced zones. The use of vinyl sheet pile allowed the cut-off wall to be a continuous element eliminating a horizontal joint and was flexible enough to tolerate anticipated differential settlement. The benefits of the method chosen also included a reduced construction schedule to a single season, “Avoidance of weather sensitive materials, such as clay soils which could slow the construction schedule” (Rowland and Evans, 2014), redundancy for seepage protection and reduced overall project cost. Figure 6 shows the vinyl sheet pile wall installed and the MSE wall under construction.

Figure 6. Concrete Panel MSE wall and vinyl sheet pile cut off wall under construction at

the Cardinal Fly Ash Pond Dam.

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CASE STUDIES INVOLVING ORGANIC CHEMICALS Florida Gas Plant Site. The Florida Gas Plant site located in Houghton County, Michigan is a former Manufactured Gas Plant (MGP) which historically released coal tar waste into a drainage ditch that received seasonal flows of water into a nearby creek. Residential areas, a wetland, and commercial businesses are adjacent to the site. Offsite migration of coal tar and dense and light non-aqueous phase liquids (D/LNAPL) and organic chemicals posed a threat to groundwater, wetlands and nearby residents. Based on the results of a site investigation, engineers recommended installation of a cutoff wall. While traditional methods such as a slurry wall were initially considered for construction, engineers ultimately chose to install over 600 linear feet of SG-525 vinyl sheet pile for containment. The PVC sheet piles were installed starting in August 2007 without any sealant in the locks to a depth of 17 feet (Fig. 7). The sheets were installed into soils with blow counts in excess of 50 using a steel mandrel system. Engineers monitored the groundwater post installation of the sheet pile system through the use of monitoring wells on a quarterly basis. The sheet pile wall was effective in containing the flow of contaminants from the site. (EPA, 2008).

Figure 7. Vinyl sheet pile cut off wall installed and under construction at the Florida Gas

Plant Site. El Paso Elementis, TX. The groundwater and soils at this Corpus Christi, TX location became contaminated with high concentrations of benzene at a manufacturing plant due to operations at the petroleum facility. Engineers were tasked with developing a cut-off wall solution that had a high resistance to degradation and minimized excavation and ground disturbance. The engineers working on the project specified SG-625 vinyl sheet piling manufactured using co-extrusion technology and hydrophilic sealant to be used in the interlocks to create an all but impermeable barrier. The SG-625 profile is 30-inch wide. This width minimizes the number of interlocks in the barrier wall as well as reducing the number of driving episodes for the contractor, thereby expediting the installation speed. The 32-ft long sheets piles were installed into difficult soil conditions by a geotechnical contractor using a steel mandrel. The 1000 linear foot wall was installed in November of 2009 (Figure 8). Numerous monitoring wells were established around the site and the groundwater is sampled on an ongoing basis to confirm the effectiveness of the barrier wall.

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Figure 8. Aerial view of the vinyl sheet pile cut off wall alignment at El Paso Elementis.

SUMMARY AND CONCLUSIONS (PVC) sheet piling and its compatibility with hydrocarbons, solvents and common fuel additives is often misunderstood in the context of real world contamination levels. It has been demonstrated that concerns over compatibility using commonly available compatibility charts is not the right approach. Vinyl sheet piling has been used successfully for cut-off and containment applications on sites where organic containments are present. Even if difficult soil conditions, vinyl sheet piling can be installed effectively and efficiently using the right equipment and the right contractor. In many cases the use of a mandrel allowed contractors to install vinyl sheet piles to depths of 30 feet or more and many contractors chose to use a fixed mast pile driving rig to speed up the installation process. The 30” and 24” width of the vinyl sheet piles used in these case studies was also a factor in the selection of the sheet pile products selected due to the speed of the installation and reduced number of interlocks. Engineers preferred the use of vinyl sheet piling in applications involving contaminants due to the superior corrosion resistance and reduced ground disturbance. Engineers should be comfortable specifying vinyl sheet piling in cut-off and containment applications because VSP has demonstrated real world long term effectiveness.

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REFERENCES Ohio Department of Health, Bureau of Environmental Health. (2014). Health Assessment

Section, BTEX: Benzene, Toluene, Ethylbenzene, and Xylenes, Columbus, OH. Berens, Alan R. (1985). Prediction of Organic Chemical Permeation Through PVC Pipe,

American Water Works Association Journal: 57-65. Mao, Feng, Gaunt, James A., Cheng, James A. and Ong, James A. (2011). Microscopic

Visualization Technique to Predict the Permeation of Organic Solvents through PVC Pipes in Water Distribution Systems, Journal of Environmental Engineering:137-145.

Nielsen, D. M. Ed. (2005). Practical Handbook of Environmental Site Characterization and Ground Water Monitoring, Second Edition, CRC Press, Taylor & Francis Group, Boca Raton, FL, USA.

World Health Organization. (2004). Identity, Physical/Chemical Properties, and Analytical Methods, Concise International Chemical Assessment Document 62, Coal Tar Creosote, Geneva, Switzerland, Section 2.

Member Agencies of the Federal Remediation Technologies Roundtable. (1995-2006). Abstracts of Remediation Case Studies, Volumes 1-10, (Abstracts: EPA-542-R-95-001, EPA-542-R-97-010, EPA-542-R-98-010, EPA-542-R-00-006, EPA-542-R-01-008, EPA-542-R-02-006, EPA 542-R-03-011, EPA 542-R-04-012, EPA-542-R-05-021, EPA-542-R-06-002), Cincinnati, OH, USA, National Service Center for Environmental Publications.

United States Environmental Protection Agency. (2008). Florida Gas Plant, EPA, response.epa.gov/site/site_profile.aspx?site_id=2752.

Rowland, M. G. and Evans, W. D. (2014). Raising Cardinal Dam Using a Unique Double-Sided MSE Wall System, Annual Conference, Association of State Dam Safety Officials, Sand Diego, CA, USA, 2: 773-784.

CMI Limited Co., Cutoff and Containment Case Studies, CMI, cmisheetpiling.com/applications/cut-off-containment/casestudies/.

US Army Corps of Engineers. (2017). Interim Poly Vinyl Chloride (PVC) Sheet Pile Guidance, Engineering and Construction Bulletin 2017-04.