The traditional criteria for selecting a contractor to rehabilitate a sewer line usually focuses on competitive pricing, past experience, financial solvency, qualifications of staff and skilled workers, client references, and the appropriateness and proven performance of the technology and products to be used.

  Add to that list a demonstrated sensitivity for the community relations that the job will require and you have a complete package. In fact, it might be wise to put that at the top of the list. A contractor who meets all the other qualifications and lacks an understanding of the community relations effort that is required will most certainly be an enormous liability for the municipality.

  Residents who live near and, sometimes, on top of sewer lines that must be rehabilitated are usually very willing to accept the fact that the work must be done. They just donít want it to disturb them. They want the contractor and his workers to have the stealthy qualities of a master cat burglar. Enter and leave the neighborhood without any evidence of having been there at all.

  In 1999, the city of Annapolis encountered a sewer line rehabilitation project that clearly demonstrated the need for such community relations work.

  The City needed to rehabilitate approximately 3700lf of 33-inch interceptor sewer pipe in a residential community situated on the banks of Spa Creek. The creek is a navigable estuary, which feeds into the Severn River, which in turn feeds into the Chesapeake Bay. The Spa Creek neighborhood is part of the City's Historic District, and the affluent and influential occupy its pristine homes. Most of the residences back up to the creek, which permits the homeowners to dock their prized boats immediately in their backyards.

  The line to be rehabilitated had been installed by the Works Progress Administration (WPA) in the 1930s. Not only did the WPA install a line that performed satisfactorily for more than 60 years, but it also left behind precise records making it easy to determine the exact location and configuration of the line. However, that was the last of the good news! A survey of the location showed that the line was now under one home, very near several others, adjacent to a swimming pool, and zigzagged along the shoreline creating numerous 45-90 degree bends.

  A preliminary closed circuit TV inspection confirmed what was already suspected as to the condition of the 60-year-old reinforced concrete pipe. Hydrogen sulfide damage had reduced the wall thickness in some areas from 3.75'' to less than 1''. One section had already collapsed, and it was apparent that more were imminent.

  As the owner evaluated a rehabilitation strategy, open cut methods were quickly eliminated due to the inevitable destruction to the surrounding area. Due to the geometry of the zigzagging line, slip lining was also determined to be too costly and destructive. The concept of using a purely trenchless method was quickly determined to be the best alternative considering the delicate location and the limited funds available for such a large undertaking. After the competitive bid process, the City settled on New Hope Pipe Liners, a New Jersey based company that is a leader in the burgeoning trenchless technology industry, and their National Liner CIPP Trenchless system.

  National Liner, a product of National Envirotech Group, is a premium trenchless CIPP pipeline rehabilitation system. It employs a polyester felt tube, which is saturated with a thermosetting resin. The tube consists of an inner liner of 1.5mm to 3.0mm thick polyester felt coated with polyurethane film. Multiple layers of non-woven polyester are used to develop the required thickness. The outer liner is plastic coated polyester felt. The coated inner and outer liners encapsulate the resin and protect it from contamination.

  It is installed by the standard "inversion" process. Water pressure is used to invert and expand the liner into the host pipe. Once it is in place, heat is applied to activate the resins, which harden to form a pipe within a pipe.

  More than 1.3 million lineal feet of National Liner have been installed in the US in pipe diameters ranging from 6'' to 48''. National Liner meets all the requirements of ASTM F-1216, which is the industry standard. The polyester felt liner is manufactured by Applied Felts, Inc., a leader in product quality and innovation.
 

  To minimize the inconvenience to the homeowners, Applied Felts and New Hope engineered a strategy that made it possible to install 33'' liners directly through existing 24'' diameter manholes. The strategy maximized the inversion lengths and reduced the need to set up equipment in neighborhood backyards. All the liner installation operations were performed from adjoining side streets.

  After a series of project definition meetings between City officials and New Hope Pipe Liners, a meeting was held for residents who would be impacted by the project to explain in detail the need for the work, and the innovative strategy that would be used to repair their damaged sewer lines and minimize inconvenience.

  The implementation strategy started with the design of an effective bypass pumping system to handle the 3-5 million gallons per day of flow in the 3700 feet to be rehabilitated. Because the line ran along the creek's shoreline, it was necessary to run the bypass line through backyards, between homes and boat slips. New Hope utilized the services of Godwin Pumps of America, Inc., Bridgeport, NJ, the leader in bypass pumping design and construction. Godwin was up to the task, and designed a 12'' bypass system using Godwin Dri-Prime series portable pumps. The primary pumps were electric motor driven with power supplied by the city of Annapolis by way of a power drop located at the suction manhole. The electric pumps operated quietly in the residential neighborhood eliminating the need for special sound attenuation. Emergency backup pumps with diesel engine drive were in place with an automatic start/stop float control system. A single discharge line was designed to minimize the impact of the line running through residential areas. With limited access to run the pipe along the shoreline, Godwin Pumps used 12'' X 10' length of quick disconnect style lightweight galvanized steel pipe which could be hand carried, by New Hope workers, and set in place without disruption to residents.

  While the 33'' interceptor handles most of the sewage flow from downtown Annapolis, some of the abutting residences added a minimal amount which, never the less, had to be bypassed. Small diameter electric submersibles were placed in the existing cleanouts for this task, and any service interruptions were avoided.

  Even though scheduling had to take into account a wedding, Naval Academy Graduation, and other homeowner events, the project was completed in 60 days without any serious inconveniences to the neighborhood. The new rehabilitated sewer will allow the idyllic setting of Spa Creek to remain so for the next 50+ years. This article was written by Joe Baker, Chief of Engineering & Construction for the City of Annapolis, MD.

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