Rehabilitation of failing sanitary sewer systems is a high priority for many cities in the United States with major projects under way relining and replacing aging and failing mains.
Laterals that connect homes and commercial buildings to sewer main line pipes are an integral element of sanitary sewer infrastructure, yet the condition of laterals in most sewer systems remains largely ignored, even though failing laterals can be responsible for a significant amount of the inflow and infiltration (I&I), leakage and other problems affecting the system.
Yet, maintenance, repairs and rehabilitation of failing laterals lags far behind attention given to sewer main lines.
Several factors are responsible, with the primary reason being the position of most sewer system operators that laterals are not their responsibility, but rather that of the owners of property through which a sewer lateral provides service
For years, dig-and-replace construction was the only method available to repair failing laterals or make point repairs and often today, it still is the only option offered for making repairs, even though trenchless rehabilitation methods provide cost-effective alternatives. In addition to lack of knowledge about the benefits of trenchless lateral rehabilitation, plumbing codes in many areas do not permit their use.
The Lateral Committee of NASSCO (National Association of Sewer Service Companies) is preparing a document that will provide a comprehensive overview of lateral and main-lateral connection repair and sealing technologies.
Larry Kiest, chairperson of the committee, said a primary goal of the group’s work is to develop a document that will provide the operators of sanitary sewer systems and the general public with up-to-date information about lateral renewal and repair options.
“In an effort to seek a viable cost effective solution to one of the most significant contributors to our failing sewer infrastructure,” said Kiest, “technology providers have developed several methods to structurally repair and/or seal lateral pipes and their connection to the main sewer.
“The NASSCO Lateral Committee has agreed to develop educational information for the purpose of advancing these technologies by working with local and state governing health and plumbing boards through education to encourage these agencies to accept these technologies into the code books.”
Many member companies of NASSCO provide these products and services.
Kiest said a draft of the report was completed in January and distributed to committee members for peer reviews.
“There is an enormous amount of information that needs to be discussed and put into booklet form that is easy to understand and will provide significant education on the benefits of trenchless lateral repairs,” said Kiest. “Once the document is finalized, NASSCO will make it available to association members and the public.”
This article summarizes the content in the draft of the report about the types of resin systems and liner tubes used for rehabilitating laterals. Subsequent articles will cover installation and curing methods, sealing connections and grouting.
Types of lateral rehabilitation
The report identifies six lateral rehabilitation possibilities:
• Lining a section of a lateral;
• Lining the entire lateral;
• Repairing the lateral/main connection;
• Repairing the lateral/main connection and entire lateral by lining;
• Repairing the lateral/main connection by chemical injection; and
• Repairing the lateral/main connection and a portion of or the entire lateral by chemical injection.
All but two of these methods involve cured-in-place pipe technology while the others incorporate chemical or resin injection. Individual lateral pipes often have multiple bends, diameter changes, shifted joints, cracks, deposits and roots, creating a considerable challenge to repair or seal.
Accessibility of the lateral to perform rehabilitation is an issue because one end is located in the sewer main and the other in a building. In some cases a clean-out exists either in the building or outside of the building. Therefore, the report said, it is critical that the rehabilitation methods developed take into account existing conditions in order to provide an effective product and installation method that can be installed efficiently.
Polyester Resin Systems — Unsaturated polyester resins (UPR) are the workhorse of the CIPP industry and represent approximately 90 percent of resins used. Polyesters are versatile because of their capacity to be modified or tailored during the building of the polymer chains. The principal advantage of these resins is a balance of properties (including mechanical and chemical), dimensional stability, cost and ease of handling or processing.
Epoxy Resin Systems — The structure of epoxy resin can be engineered to yield a number of different products with varying levels of performance. A major benefit of epoxy resins over unsaturated polyester resins is their lower shrinkage, and they emit little odor compared to polyesters. Generally, epoxies have short working time with long cure times.
Vinyl Ester Resin Systems combine the advantages of epoxy resins with the better handling/faster cure, which are typical for unsaturated polyester resins. These resins are produced by reacting epoxy resin with acrylic or methacrylic acid. The resulting material is dissolved in styrene to yield a liquid that is similar to polyester resin. Vinyl ester resins typically cost two to three times more than polyester resins.
Silicate Resin Systems provide good adhesion to properly prepared, cleaned and compatible surfaces. They have similar curing issues as an epoxy where the work-time is short and the cure-time is long, yet unlike an epoxy, silicate resins are typically not suitable to external heat sources as commonly used in CIPP applications. For these reasons, silicate resins are well-suited for short liners, main/lateral connection liners or injection grouting.
Synopsis of resin systems
In most residential sewer systems, all of these resins would be suitable for a CIPP application, providing the cured-in-place pipe meets the minimum requirements as set forth in relevant ASTM standards. However, depending on the chemical makeup of the effluent, one resin may be preferred over another, and resin suppliers can recommend the correct resin for specific applications based on the type of pipe on a project.
Lining tubes typically are constructed from a needle punched felt or a knitted tube. These liners vary in density and flexibility in order to negotiate small diameter pipe, bends and to reduce pressures for inverting the liner so the tube is not overstressed. Sometimes liners stretch, but advanced technology allows both types of liner tubes to be reinforced to eliminate stretching and increase flexural properties.
Regardless of tube construction, good installation practices combined with the right material are keys to successful lining repairs. Trained and seasoned installers know how to accommodate for stretch and ensure quality control during inversion to prevent over stressing the tube and squeezing resin, critical when the liner is installed from a single access point, sometimes called a “blind shot.”
NASSCO Lateral Committee Chairperson Larry Kiest is president and chief executive officer of LMK Enterprises, Ottawa, IL.
NASSCO is a national organization comprised of several hundred members representing rehabilitation industry manufacturers and suppliers, municipalities and utility districts, engineers, and contracting firms. Ted DeBoda is executive director. NASSCO offices are in Owings Mills, MD, (410) 486-3500, www.nassco.org.
NEXT MONTH: In the May issue of Underground Construction: A summary of the committee’s draft covering installation and curing