By Brian Fraser, Steven Roades, Mike Neal and Alex Gersch
Chlorosulfonated polyethylene (CSPE) is a synthetic rubber-based material manufactured by a calendaring process into multiple layers and combines with a polyester reinforcement fabric for additional strength. Hypalon is a DuPont trademark for CSPE synthetic rubber (CSM) noted for its resistance to chemicals, temperature extremes and ultraviolet light (Wikipedia contributors 2018). Hypalon was originally developed by planned polymer chemistry efforts to manufacture a new-generation material to address some of the limitations at the time of materials produced from polyvinyl chloride, polyisoprene and butyl rubber. In the early 1950s, the resin producer commercialized the development of CSPE and began to market the material as Hypalon. This material referred to a group of sulphur-and-peroxide-cured elastomers created through a cross-linking process with chlorinated polyethylene (CPE) and CSPE. In the late 1960s, Burke Industries in San Jose, Calif., began working with the resin producer on the development of a flexible liner-grade material from this CSPE resin.
Beginning in the mid-1970s, Hypalon was introduced as a next-generation engineered liner primarily positioned for water and wastewater containment applications. The initial markets and applications included potable storage and wastewater treatment for government municipalities and tailings ponds for the mining sector. The first floating covers on record using CSPE were installed in the late 1970s in Southern California reservoirs for municipal potable water storage (Figures 1 and 2). The covers were designed and used for evaporation control and to prevent dirt and debris from contaminating the water storage supply.
In June 2009 the resin producer made the decision to exit the production of certain resin products, including CSPE. Fortunately, there was a qualified backup source of CSPE resin out of Japan. This company continues to be the primary source of resin used in CSPE products today. Since the resin’s inception as a liner-grade product, the manufacturer has confirmed more than 500 million square feet (46.5 million m2) of CSPE has been supplied into the market as a geomembrane, floating cover or single-ply roofing material. A good portion of this material, as reported by the main CSPE producer, is still in service.
Properties of CSPE
CSPE has many advantages over other commonly used polymers such as polyvinyl chloride (PVC), polyolefins and ketone ethylene ester (KEE) resin technology. One primary difference is that CSPE is manufactured as a thermoplastic material that will vulcanize over time, becoming a thermoset material capable of surviving thermally stressful and high-temperature environments and ultraviolet (UV) exposure. When formulated and calendared into a lining-grade material, it provides outstanding UV resistance and weathering properties allowing it to be used for long-term exposed containment applications. In standard exposed applications, it demonstrates slow reduction of its mechanical and endurance properties.
The material’s unique cross-linking properties provide very good overall resistances to several chemicals used as disinfectants in municipal water treatment. These include chlorine, sodium hypochlorite and chloramines. In water treatment these three main chemicals often act as accelerators, attacking and breaking down the antioxidant packages of a number of geomembrane types. This can result in environmental stress cracking and premature material failure (Mills 2011). Since plasticizers are not used in the formulation of CSPE geomembranes, there are no issues related to plasticizers, such as leaching out and causing embrittlement/cracking of plasticized liners. Its inherent low coefficient of thermal expansion and contraction provides excellent dimensional stability and lay-flat characteristics. CSPE also has a very low thermal expansion coefficient compared to that of rigid membranes such as high-density polyethylene (HDPE), and so expansion and contraction problems caused by temperature changes are virtually nonexistent. Elasticity is important in liners because of the settling that occurs after reservoirs or impoundments are filled (Scheirs 2009).
CSPE’s synthetic rubber properties also provide it with a unique combination of flexibility and durability. In geomembrane and floating cover applications, CSPE is typically factory fabricated. Fabricated geomembranes are lining materials that are flexible enough for panels to be joined in a factory environment, creating large prefabricated panels of material that can be folded, rolled and transported efficiently to a containment project site. From there these large prefabricated panels are unrolled into position and field welded on-site. Factory fabrication can significantly reduce the amount of field welding required, which reduces installation time and construction costs. It also provides consistent seam integrity and liner quality (Fabricated Geomembrane Institute 2018).
Standard reinforced CSPE geomembrane-grade products are available in 36-, 45- and 60-mil (0.91-, 1.14- and 1.52-mm) thicknesses and meet the Geosynthetic Institute standard GM28 (Geosynthetic Institute 2018). This specification provides the test methods, properties and testing frequency for reinforced CSPE material. CSPE also has good overall thermal properties, allowing it to be installed and handled in temperatures ranging from -22˚F (-30˚C) to 115˚F (46˚C).
Test results showed that the material’s tensile breaking strength, tensile elongation and hydrostatic resistance after 20 years exceeded the published specifications.
Project profiles
CSPE is one of a few industry materials with more than 40 years of confirmed history showing the performance as a liner and floating cover in potable water containment applications. There are several important factors that contribute to achieving long-term performance of floating covers in any containment project. These include the initial cover design; selection of the material; and quality of the workmanship, including factory fabrication and field installation. On the operations side, an important factor is the need for regular inspections and preventative maintenance of the cover systems, recommended on an annual basis.
In the following section, we highlight three projects where CSPE liners and floating covers have been used in longer-term applications in hot, dry climates for municipal potable water storage. The profiles help to demonstrate the unique weathering ability of CSPE to withstand the elements of time, temperature, UV exposure and chemicals used for water disinfectant.
Hinkle Reservoir
- San Juan Water District
- Granite Bay, Calif.
- 62-million-gallon (235-million-l) capacity
- Potable water storage
- CSPE liner and cover installed in 1980
The San Juan Water District’s Hinkle Reservoir had a 45-mil (1.1-mm) CSPE liner and floating cover installed in 1980. The cover has a defined sump design with the flotation system installed on the bottom side of the cover. The water district initially chose an open-top reservoir with a floating cover based on the substantial cost savings versus other storage options. When the reservoir was initially reconstructed, alternatives such as steel and concrete tanks were considered. Since this was a municipal facility, both cost and performance were equally considered in the determination of the storage facility. It was determined at the time that the cost of a CSPE liner and floating cover system was approximately 60% to 80% less than alternative storage systems considered (Figure 3). This also factored in life-cycle costs for maintenance and servicing. As a result, CSPE was specified and the material was designed, fabricated and installed as one of the first-generation larger-scale floating covers. Fully extended, the floating cover spans 14 acres (5.7 ha). The Hinkle Reservoir is located northeast of Sacramento, Calif. The region is known for its hot, arid summers and high UV exposure. The winters are typically a bit cooler, wet and partly cloudy. Over the course of the year, average temperatures can vary from 35°F to 104°F (2°C to 40°C).
In 2016, when the CSPE material reached the 36-year mark, the material was tested by the manufacturer, with the results shown below in Figure 5. The material’s tensile strengths and tensile elongation properties were shown to be above the original published material specifications. Further independent third-party testing was conducted by the water district. The reservoir is currently scheduled to have a new liner and cover installed over the next couple of years. At that time, the original installed liner and cover materials will have been in service for 40 years. A key to the outstanding success of this floating cover was the regular maintenance and servicing performed by the San Juan Water District. It is believed that the Hinkle Reservoir is one of the longest-reported CSPE floating cover systems still operating.
Happy Valley Reservoir
- South Australia Water Corp., South Australia
- 26.4-million-gallon (100-million-l) capacity
- Potable water storage
- CSPE liner and cover originally installed in 1988
In the mid-1980s, South Australia Water Corp. was evaluating the feasibility of installing geomembrane liners and covers on two new 26.4-million-gallon (100-million-l) earth bank potable water storage reservoirs adjacent to the Happy Valley water treatment plant. This plant provides potable water for most of the southern Adelaide region. Ambient temperatures for the area can reach as high as 114°F (46°C) with extreme high solar exposure in the summer months. Due to its proximity to the treatment plant, higher levels of chlorine were expected at the inlet stream. Extensive research and testing were carried out during the preliminary design stage on all liner materials available at the time. Significant focus was placed on the puncture resistance, flexibility, UV resistance and long-term durability of materials. This was due to the fact that South Australia has some of the highest solar conditions in the developed world. Specific puncture resistance tests were conducted using material obtained from the site, and HDPE, CSPE, ethylene propylene diene monomer (EPDM) and butanol were all evaluated.
Following the evaluation process, 45-mil (1.14-mm) CSPE was selected as the most suitable material. Black material was selected for the liner while the cover material was black on the underside, which was in contact with the potable water, and tan on the top surface to reduce surface temperatures and provide a more aesthetic appearance (Figure 4).
The liner and cover for Storage 1 were factory fabricated off-site. The twin storages were constructed using compacted cut and fill material with an underfloor drainage system. After final surface preparation, a heavyweight nonwoven geotextile cushion layer was installed by the contractor before installation of the prefabricated CSPE liner panels. All field seams carried out on the liner were performed using CSPE adhesive. The covers were installed in the same manner. Storage 1 was completed in 1988, and Storage 2 was completed a year later. Annual inflation of the CSPE floating covers were carried out to facilitate inspection and cleaning of the liners. Three years after installation during one of these regular inflations, the cover on Storage 1 was torn open by a gust of wind, resulting in a large tear more than halfway across the cover and displacing approximately 25% of the cover area. Over the following days, the cover was manually pulled back into place and successfully repaired using the CSPE gluing process. The repairs carried out in 1991 on the cover on Storage 1 remained effective for the full remaining life of the material.
The decision to replace the CSPE liners and covers was made taking several factors into account. This included that the planned 25-year asset life had been achieved. Changes to flow were also necessary as water-quality standards had progressed over the previous 25 years, and short circuiting was an issue as the inlets and outlets were relatively close to each other.
After 26 years of service, the liner and cover on Storage 1 were replaced in 2014. While the tan top surface of the cover was stained, the CSPE material was still completely pliable and the black underside surface appeared nearly new. When the liner material was cleaned, it appeared to be in close to new condition. The 26-year-old CSPE liner and the cover material appeared to still have some life in them and were cut and reused as drop-in liners, evaporation pit liners, tarpaulins and haystack covers.
In 2016, after 27 years of service, the liner and cover on Storage 2 were replaced. The CSPE material was in the same near-new condition as in Storage 1 and was again recovered and reused in other applications. The new replacement 45-mil (1.14-mm) CSPE covers were constructed with integral CSPE baffle curtains to improve chlorine contact/residence time and eliminate short circuiting.
Upper Reservoir
- Otay Water District, Spring Valley, Calif.
- 36.7-million-gallon (139-million-l) capacity
- Potable water storage
- CSPE liner and cover originally installed in 1988
Otay Water is a water, recycled water and sewer service provider. The California State Legislature originally authorized the establishment of the Otay Water District in 1956 as a special district. Today, the district provides water services to customers within 125 square miles (323 km2) of the densely populated region of southeastern San Diego County. The district’s facilities service the water and sewer needs of customers residing in several southern communities of San Diego County down to the border of Mexico. This region has a very hot, arid climate with summer average temperatures ranging from 70°F to 100°F (21°C to 38°C). Winter average temperatures range from 45°F to 60°F (7°C to 16°C). San Diego County is known for a very high to extreme UV index most months of the year.
The original cover and liner material for the Upper Reservoir were installed in 1988 using a 45-mil (1.14-mm) CSPE. A special aqua skin color was chosen for the skin layer of the CSPE for its aesthetic. The Upper Reservoir is used as a potable water reservoir, servicing a rapidly growing population base in San Diego County. A weighted tension cable system was chosen for the cover design based on its lower maintenance cost—primarily the result of not having any surface floats or sumps required to tension the cover. It also allows the operator to use the existing hardware when replacing the cover at the end of its life, representing a measurable cost savings during replacement.
In 2018, the existing cover and liner needed to be replaced to allow for mechanical pipe and pump upgrading requirements. At the time of relining, the Upper Reservoir floating cover had been in operation for 30 years with no reported major problems encountered during its long operational life. After physically inspecting the material, both the CSPE manufacturer and the liner installer were of the opinion that it was still in overall good condition and would have functioned for a few more years. An important part of the cover longevity can be attributed to Otay Water’s regular inspection and maintenance programs and the quality design and workmanship of the original installation. The new CSPE cover system incorporated most of the existing hardware, a benefit to using the mechanical tension cable system. In terms of industry records, Upper Reservoir was one of the longest-performing CSPE floating cover projects for potable water storage in Southern California (Figure 5).
Conclusion
In the relatively short history of polymeric geomembranes, CSPE has proven to be an excellent choice of material for long-term exposed applications. The geomembrane industry has seen several products introduced and promoted into potable water storage; however, to date, no other material has consistently demonstrated the same successful long-term performance as CSPE. CSPE is backed by an industry-leading 30-year weathering warranty. It is one of the few materials that has truly passed the test of time.
Acknowledgments
Tony Barela, San Juan Water District, Granite Bay, Calif., USA
Paul Vince, WSP Engineering, Adelaide, SA, Australia
David Jaensch, South Australia Water Corp., Adelaide, SA, Australia
Bob Kennedy, Otay Water District, Spring Valley, Calif., USA
Andrew Mills, Layfield Environmental, Edmonton, AB, Canada
Doug Hilts, Hilts Consulting Group, Orange Country, Calif., USA
Bob Pitman, Burke Industries, San Jose, Calif., USA
References
Fabricated Geomembrane Institute. (2018). General information about fabricated geomembranes, University of Illinois at Urbana-Champaign, Dept. of Civil and Environmental Engineering, Urbana, Ill. https://www.fabricatedgeomembrane.com/resources/faqs.
Geosynthetic Institute. (2013). GRI test method GM 28, Geosynthetic Institute, Folsom, Pa. http://geosynthetic-institute.org/grispecs/gm28.pdf.
Mills, A. (2011). “The effects of chlorine on very low-density thermoplastic olefins.” Proc., Geo-Frontiers Congress 2011, Dallas, Texas.
Scheirs, J. (2009). A guide to polymeric geomembranes: A practical approach. 1st ed., Wiley, Chichester, West Sussex, UK.
WaterWorld. (2004). Hinkle Reservoir pioneers floating cover with 45 year lifetime (Press release). https://www.waterworld.com/articles/2004/12/hinkle-reservoir-pioneers-floating-cover-with-45-year-lifetime.html.
Wikipedia contributors. (2018). Hypalon, In Wikipedia: The Free Encyclopedia. https://en.wikipedia.org/wiki/Hypalon.
Brian Fraser, MBA, is vice president of Layfield USA in Lakeside, Calif.
Steven Roades is vice president of Burke Industries in San Jose, Calif.
Mike Neal is senior project manager of Layfield USA in Eugene, Ore.
Alex Gersch is business development manager for Layfield Australia in Adelaide, S.A., Australia.
All figures courtesy of the authors unless otherwise noted.