New rehabilitation trenchless technologies introduced to the water and wastewater industry over the last 10 to 15 years have met with varying degrees of success. With aging infrastructure exceeding 50 years on average in the U.S., the useful life of existing components are reaching their limits. Rehabilitation technologies show promise in extending the operation life of critical assets and can be economically feasible.
A recent field research study by scientists at the U.S. Environmental Protection Agency (EPA) demonstrated and evaluated key emerging technologies on performance and cost, specifically two commercially available in-situ trenchless lining systems:
- Semi-structure spray-on lining
- Structural cured in place pipe lining (CIPP)
To assist water and wastewater utilities in the proper selection and implementation of these emerging technologies, analyses were based on specific metrics, including:
- Determine whether consistent design methodology and specifications were in place and easily implemented.
- Determine whether current QA/QC procedures were adequate.
- Technology assessments to determine the best technology for the specific rehabilitation.
- Technology feasibility metrics to measure each technology’s limitations, impacts to operating condition of the pipe or structure, and failure modes.
- Technology complexity metrics to determine the adaptability and benefits for small to medium-sized utilities and the level of training required for installations and maintenance.
- Performance metrics on stated vs. actual (met design specifications, impact to hydraulic performance and long-term performance).
Additionally, cost and environmental metrics were evaluated.
Water Asset Management Challenges
Certain technical challenges exist across all water utilities today. Some systems comprise a variety of pipe materials, which may require different rehabilitation strategies. Water pipeline inspection is notoriously difficult and expensive regardless of substrate, site conditions or rehabilitation technologies in use.
As with any working infrastructure, there is always a need to return a system to service at full operational capacity in a minimal amount of time, while minimizing the need for excavations. Lastly, there is a limited number of installation contractors for these new technologies, and utilities are reluctant to try new technologies with too few, or inexperienced installers.
Findings: Semi-Structural Spray-On Lining
This technology utilizes an internally spray-applied lining, which provides both corrosion mitigation and structural improvements. The demonstration was performed in August 2010 in Somerville, New Jersey.
Technology evaluation metrics concluded that this technology was still emerging since it had been used at only eight sites in North America, with difficulties similar to problems faced in the New Jersey evaluation site. Similar issues occurred in at least two other locations.
The total duration for cleaning, drying, inspecting and coating a 500 ft. (150m) section was approximately 11 hours (on average, if the bypass and access pits were already in place). This does not include the additional site preparation time that was required at the Somerville, NJ site due to cleaning issues that were rectified through the use of a drag scraper.
The technology did not perform in an acceptable manner to act as a Class III semi-structural lining, which must have sufficient thickness to resist buckling. The QA/QC plan for the demonstration was successful in discovering the liner failure during hydraulic testing, prompting the water utility owner to request a visual inspection.
Also, laboratory testing revealed that the liner installed in the field did not meet the design specifications, which is discussed in the technology performance metric. The cause of the incomplete chemical reaction of the product materials was hypothesized to be the effect of humidity in the environment, which led to increased moisture in the compressed air used to drive the spinner head that sprays the material on the pipe wall during the installation. This excess moisture is believed to have resulted in a liner material with a shorter polymer chain length and significantly reduced flexural modulus.
The testing performed by the research team, although not definitive, suggested that several differences existed in the composition of the control versus field samples, but the polymer chain length could not be verified since the design properties are proprietary. The manufacturer hypothesized that the excessive moisture caused the base material to hydrolyze, meaning that water basically blocked the complete reaction from occurring between the base and the activator.
This outcome led to the conclusion that the product chemistry was not robust enough for use in typical in situ conditions and the subsequent discontinuation of sale and distribution of the product.
Findings: Cured in Place Pipe Lining
This technology utilizes an internally placed flexible lining material, which provides both corrosion mitigation and structural improvements. Its demonstration occurred in September 2010 in Cleveland, Ohio.
The evaluation metrics showed that the technology was emerging since it had been used at more than 20 sites in the U.S., with several water utility owners expressing their willingness to use the technology in the future. The outcome of the technology evaluation is described in the technology evaluation metrics, most notably:
- The emerging technology was used at less than 30 sites in the U.S.
- This technology shows improvement over traditional rehabilitation using cement mortar lining (e.g. Class IV fully-structural solution versus Class I non-structural solution).
- Some data are available, but long-term tests are ongoing and the method track record spans 10 years.
- Each water utility owner contacted cited positive results and a willingness to use the product again.
The study article indicated additional technologies are to be evaluated by the EPA demonstration and evaluation program in the future.
To date, the application of new technologies is limited and water and wastewater utilities are reluctant to implement new technologies without clear and concise performance data from sources other than manufacturers and installers.
The EPA demonstration and evaluation program for innovative rehabilitation technologies conducts critical assessments and actual field test installations to provide needed information on which evaluated technologies provide the best engineering alternative along with benefit to cost. The program operates under the EPA’s Office of Research and Development.
This program should be expanded and funded to independently evaluate more emerging technologies, thereby allowing utilities a larger basis for selection and evaluation of needed infrastructure upgrades in the future.