More than 1 million storm-water culverts that drain U.S. roadways are in need of repair. State Departments of Transportation (DOTs) have turned to cured-in-place pipe, or CIPP, as a fast and low-cost way to rehabilitate the aging systems.
The technology repairs concrete or corrugated metal culverts by lining them with plastic pipe, a patch job that’s not without risks: When the liner is installed, it can unleash an initial flood of chemical contaminants into waterways that slows but continues to leach for weeks afterward. DOTs are trying to get a grip on the environmental impact of the chemicals released and have conducted some initial studies on the scope of the problem. They have held discussions with companies that make and install CIPP on developing better construction practices and switching to alternative materials that could green up the process.
The problem first came to light in 2008 when ecologist Bridget M. Donaldson, a senior research scientist at the Virginia Department of Transportation’s Virginia Center for Transportation Innovation & Research, tested water at CIPP installation sites. Donaldson was taken aback by the levels of styrene—a component of pipe polymer resin—she found in downstream water. Even when Donaldson later studied sites that used “environmentally friendly” nonstyrenated polymer, she found levels of additional toxic chemicals in stream water that exceeded drinking water standards.
“It’s not something that was on people’s radar,” Donaldson says.
At the time, states had no standardized product test methods to screen culvert repair materials and practices or to test construction sites for environmental damage. And federal highway and environmental guidelines don’t address the issue.
“Following our initial study, numerous DOTs contacted us,” Donaldson says. “They wanted to share similar findings or request information to develop environmental safeguards.”
Upon hearing the bad news about CIPP, Virginia and other states instituted moratoriums on its use. The moratoriums were detrimental to DOTs, Donaldson says, because many of their projects involve CIPP. And companies that make and install CIPP squawked at the action because it put a damper on their livelihoods. The moratoriums were lifted after the DOTs put restrictions on and tightened inspections of CIPP installations.
“It was clear that chemical containment and cleaner installation processes were needed, and that this issue needs more attention from municipalities and the transportation community,” Donaldson says.
CIPP allows workers to repair culverts without having to close lanes of traffic or entire roadways to excavate and replace the drainage systems. The technology doesn’t compromise the performance of the existing drainage system and extends the service life by up to 50 years. CIPP was invented in the early 1970s and was first commercialized by industry leader Insituform Technologies. The installation process, originally designed for rehabilitating sanitary sewer pipelines, gradually became popular for storm-water system repair—now its largest use.
Culverts that divert storm water away from roadways are usually out of sight. But like road surfaces that develop cracks and potholes, culverts develop defects over time.
To install CIPP, workers place a wetted, polymer-impregnated flexible felt or fiberglass tube in the culvert. Then they inflate the tube with water or air pressure. The polymer is typically an unsaturated polyester resin, such as isophthalic acid-maleic anhydride-propylene glycol, that is diluted with styrene. It hardens when workers use hot water, steam, or ultraviolet light to cure the polymer via styrene cross-linking.
For hot-water curing, some 10,000 gal of 90 °C water circulates through the pipe over several hours, accumulating contaminants. According to DOT specifications, work crews are supposed to collect cure water and process it in a wastewater treatment plant. But they often release the water on-site, Donaldson adds. Steam-curing at 125 °C for a similar amount of time generates a few dozen gallons of syrupy condensate that is collected and treated as waste. The UV-curing process doesn’t generate liquid waste, but currently it’s the most expensive curing method and not often used.
Spills occur, and construction debris scatters on the ground and into streams. If not contained with adsorbent mats and cleaned up, Donaldson says, chemicals can leach from these materials into soil and water.
To expand on Donaldson’s efforts, VDOT recruited civil and environmental engineer Andrew J. Whelton, originally at the University of South Alabama and now at Purdue University, to take a closer look at CIPP’s environmental effects. CIPP activities have caused more than a dozen documented fish kills and inhibited the activity of beneficial microbes in sewage sludge of wastewater treatment plants, Whelton found. In cases where CIPP was used to patch sewer lines, odors have backed up into buildings and led to evacuations, including schools and hospitals.
“All of these incidents were preventable, but many of the infrastructure repair methods had not undergone any environmental impact testing,” Whelton says.
Whelton and his colleagues have been developing standard test methods for screening CIPP materials. The work involves conducting laboratory leaching studies to determine which chemicals can end up in stream water. They also went into the field to collect water and waste samples at CIPP installations.
Whelton’s team detected a range of chemicals in the water and steam condensate. Depending on the type of repair and materials used, these include styrene, methylene diphenyl diisocyanate, and bisphenol A monomers; methylene chloride and chloroform solvents; dialkyl phthalate plasticizers; and organic peroxide cross-linking initiators, such as Perkadox and Trigonox. Some of the compounds, such as styrene, are suspected carcinogens. And others, such as phthalates, are suspected endocrine disruptors.
In environmental chemistry, chemical oxygen demand (COD) is a common test used to indirectly measure the amount of organic compounds in water. Expressed in parts per million, COD indicates the amount of oxygen consumed when the compounds are oxidized. Whelton and his colleagues found that raw condensate from steam curing registers a COD level of 36,000 ppm. That compares with a range of 10 to 30 ppm for unpolluted streams, he notes. Although contaminant levels drop over time after CIPP installation, the researchers measured elevated CODs up to 375 ppm for up to five weeks after curing.
In addition, the condensate’s pH, 6.2, is a problem because it’s acidic relative to pH 7, which is normal in most streams. When Whelton’s team added Daphnia magna, a microscopic plankton commonly used to test the aquatic toxicity of chemicals, the organisms completely dissolved in raw condensate within a day. When the researchers diluted the condensate by a factor of 10,000, the solution killed all the Daphnia within two days (Environ. Sci. Technol. 2014, DOI: 10.1021/es5018637u).
“Preventing any release of CIPP waste into the environment is clearly important,” Whelton says. “But our data are just the tip of the iceberg in understanding the degree of engineering controls needed and how long after installation any problems might linger.”
Donaldson’s work and Whelton’s work have each culminated in VDOT reports that recommend prescreening all construction materials. They’ve also suggested that monitoring for organics, metals, pH, and other measures be conducted at installation sites before, during, and after culvert repair.
“These reports provide eye-catching information that hasn’t been available in the past,” says Mohammad Najafi, director of the Center for Underground Infrastructure Research & Education at the University of Texas, Arlington. Najafi says more data will be needed to get a fuller picture of the CIPP issue, but these early results “will have a large impact on the CIPP industry.”
Najafi adds that polymer resin producers, such as Interplastic, are developing new formulations to reduce or eliminate styrene and other problematic compounds from entering the environment. Najafi also notes that, in addition to DOTs, the National Association of Sewer Service Companies has developed a pipeline assessment and certification program to improve the quality of CIPP installations.
VDOT is now leading an initiative to pool funding with other states for additional research and mitigation efforts, Donaldson says. With miles of storm-water culverts in need of repair, CIPP technology is a necessity—but it needs appropriate safeguards, she observes. “We hope this research will continue to lead to better controls and encourage the industry to develop more environmentally friendly forms of pipe rehab.”