2021 Trenchless Technology Project of the Year Rehabilitation Runner Up: Front Street Interceptor Cleaning
The 2021 Trenchless Technology Project of the Year for Rehabilitation Runner Up is the Front Street Interceptor Cleaning project completed by Compliance EnviroSystems LLC (CES), Doetsch Environmental Services and Cambridge Construction Management Inc.
This project is part of the SARP10 – or Sewer Assessment and Rehabilitation Program – a 10-year initiative to improve the entire sanitary sewer system in Memphis, Tennessee. The SARP10 team implements the program through a series of condition assessment and construction rehabilitation projects and is expected to spend approximately $250 million over the program’s life.
The objective for this unique project was to clean three surcharged segments of the 105-year-old Front Street Interceptor, which were heavily impacted by sewer debris. The CES Doetsch team’s goal was to remove solids and sludge from approximately 4,000 ft of the 30-in. diameter, 60- to 90-ft deep interceptor, with minimal disruptions to traffic and surrounding areas. A 6,000 ft-long reach reel with a double hose high-pressure cleaning operation was used and one set-up to alleviate traffic disruptions in downtown Memphis throughout the project’s life.
The depth, narrowness and constant surcharge conditions made manned entry into the manholes a safety concern; however, the CES Doetsch team could clean remotely due to our long-reach capabilities, eliminating the need for manned entries. CES has been fortunate to have successfully worked on every phase of the SARP10 Program since its inception in 2013, bringing its experience and capabilities to assist SARP10, Black & Veatch Corp., the entire program management team, and the historic City of Memphis on this sewer evaluation program.
Why Project is Outstanding
The CES Doetsch team used a cleaning system capable of three to four times that of a conventional sewer cleaner to remove approximately 400 tons of debris in 300 calendar days. The high-pressure vacuum and Hydraulic Power Unit generated enough head to remove densely compacted debris and large items of sanitary sewer trash. In addition, the project required cleaning on reverse grade (a lower position), as opposed to a standard system with flow and gravity. With a classic combination jetting/vacuum machine, the water propels the cleaning nozzle up the line. If the nozzle is too small, the material is thrown behind and goes to each side or makes a small pile behind the nozzle and then spills over. Like when shoveling snow or working in a garden, a shovel has a capacity. When the ability of the shovel is reached, the material will fall off. To increase the shovel capacity, the team used a larger shovel, or in this case, a larger ‘aqueous shovel.’ The custom large-diameter cleaning equipment and the process is designed to remove debris in a pipe of this size and under surcharge conditions. The CES Doetsch team customized the cleaning process for this project based on data from divers and our experience with large diameter sewers. The changing or unknown water flow velocities of the sewer system required frequent modifications that depended on the conveyance of the water to remove the material.
The increased water flow and pressure allowed a 200-lb nozzle to propel through the sewer generating a giant ‘aqueous shovel’ that effectively moved more debris in the large diameter Front Street Interceptor. A purpose-built apparatus launched the cleaning head nozzle under the water flow into the upstream direction — the device road on a rail fastened to the fabricated extraction tube. The crew utilized a relay system to shorten the travel distance of the nozzle. The CES Doetsch team used step cleaning to monitor the amount of debris pulled back on each step to maximize the carrying capacity of the nozzle and allowed for more thorough removal of loose debris in the pipe, leaving no residual remains behind. The process for extracting the debris was also unique as it took place at the bottom of a vertical manhole. The primary process used an air supply under the water at the bottom of the extraction tube to remove large debris. The secondary process consisted of a hydraulic submersible pump to remove finer material.
Project Owner: City of Memphis, Tennessee
Engineer: Black & Veatch Corp.
Contractor(s): Compliance EnviroSystems, LLC (CES), Doetsch Environmental Services, and Cambridge Construction Management Inc.
Value of Trenchless Project (US$): $4,487,950