A Trenchless Approach to Lift Station Elimination

摘要

Initially in 2004, the City of Garland, Texas, approached Freese and Nichols, Inc. (FNI), about decommissioning a small lift station that was becoming a maintenance problem for the City staff. The City did not want to expend effort or funds into rehabilitating or replacing the lift station; it has preferred to eliminate lift stations, if possible, throughout the City. FNI conducted a study of the lift station service area, the gravity collection system in proximity of the lift station, and the topography of the immediate area surrounding the lift station site. The results of the study determined that it would require trench cuts in excess of 50-feet to install a gravity line by open-cut methods to the downstream system, and at the time the trenchless technology was not advanced enough to install a gravity wastewater line at grade for the lengths required for connecting to the existing collection system. FNI recommended to rehabilitate or replace the lift station due to the excessive expense and risk involved in attempting to run a new gravity line to eliminate the lift station. The City opted to wait, and attempted to maintain the existing lift station. Fast forward to 2014. The City of Garland contacted FNI to reinvestigate the same lift station and collection system. After 10 more years of use and maintenance, the lift station was even more of a problem for the City maintenance staff. FNI reviewed the 2004 study and determined that improvements in trenchless technology capabilities made it feasible to install a new gravity line at grade. The new line would enable the City to eliminate the lift station and connect the existing collection system to the service area of the existing lift station. This project would require over 3,500 feet of pipe to be installed by trenchless methods on a grade of approximately 0.01 ft./ft. grade. The project was successfully installed and was put in service in the Spring of 2016 as designed. Now that trenchless technologies are making it more feasible to eliminate lift stations, this paper will give utility owners a greater understanding of what trenchless installation entails and what to consider when making that decision. The paper will show the audience how the City of Garland team researched, designed and constructed the project. It will describe the installation options that the project team explored, the precautions they took during design, and the measures they implemented to minimize risks. The paper will also discuss construction issues and challenges that trenchless projects may encounter, as well as lessons learned and other guidance for utility owners.