Influent Pipe Replacement Project
City of Stockton Department of Municipal Utilities
Kjeldsen, Sinnock & Neudeck, Inc., (KSN) was retained by Power Engineering Contractors Inc. to provide surveying and mapping services for the emergency replacement of four 36” diameter raw sewage pump discharge pipes at the City of Stockton’s Regional Wastewater Control Facility (SRWCF). The completed project allows the Stockton Municipal Utilities Department to continue providing wastewater treatment to the City of Stockton throughout the peak flows of winter without the risk of pipe failure which could flood the pump room and shut down the plant.
The enclosed dry pit pump station in the basement of the operations building is the main pumping facility at the headworks to the SRWCF and has the capacity to transport 142 million gallons of raw sewage per day, and contains four raw sewage pumps, four raw sewage pipes, the raw sewage wet well, and their associated valves and controls. The raw sewage discharge piping, constructed of steel with mortar lining, was replaced in 1991, but the mortar lining of the discharge pipes had eroded by 2007, exposing the steel pipe. The walls of the steel pipe had corroded to the point where the discharge pipes had developed pinhole leaks, prompting an urgent repair project. If any of the discharge pipes were to fail, the pump room would have flooded, and all pumps and motors submerged in sewage would stop working. The loss of the raw sewage pumps and the inability to pump sewage through the plant would result in a plant shut down. In order to minimize the down time of this critical pumping facility, each of the four discharge pipes had to be accurately prefabricated offsite and quickly dropped in place. Each discharge pipe was unique and the complex configuration required that each pipe be custom fabricated.
KSN was essential to the success of the project and the team’s ability to efficiently replace the corroded pipes in a fiscally and timely manner. KSN recognized the project to be an ideal application for 3D laser scanning technology and utilized its Leica ScanStation in addition to conventional surveying methods to create a 3D model of the existing pump room.
The discharge pipes replaced in this Project are located in the basement of the pump room, accessible solely through a small opening in the pump room ceiling. KSN survey crews began the project by establishing a six-point survey control network in the pump room which covered the first and second floors. Each control point was leveled through to ensure vertical accuracy throughout the network. KSN’s High Definition Surveying (HDS) Crew then collected a series of scans from each survey control point utilizing Leica Cyclone Software and the Leica ScanStation.
All the scans were overlapping, and fixed height backsight targets were utilized throughout the scanning process. Multiple overlapping scans and fixed height backsight targets were registered together and used to create a single 3D point cloud of the pump room, resulting in a final point cloud registration with a mean absolute error of 0.01 feet.
The process for replacing the discharge pipes called for shutting the system down in stages to minimize disruption to the plant. To accomplish this it was necessary to have the new discharge pipes prefabricated in the exact layout as the existing pipes before the replacement could begin. KSN was able to utilizing the final point cloud data to model the existing discharge pipes and provide finished AutoCAD drawings to the pipe fabricator. The fabricator was then able to create shop drawings for the fabrication of new discharge pipes as exact replicas of the existing discharge pipes quickly and accurately, and in segments small enough to fit through the access opening.
Having a complete 3D model of the existing site conditions allowed KSN to avoid mobilizing crews for additional survey requests. If additional information was required, it was quickly extracted from the registered point cloud data, minimizing impacts to the budget and schedule. The application of 3D laser scanning technology also increased the field crew’s safety, since they no longer were required to climb on the discharge pipes 30 feet above a concrete floor to take measurements.
The existing pipes were removed one at a time and the prefabricated replacement pipes slipped perfectly into place, minimizing the down time for each pump. By replacing the corroded discharge pipes, and avoiding a discharge pipe failure, normal operation of the Stockton Regional Wastewater Control Faculty continues without disastrous interruption. If a discharge pipe failure had occurred, the pump room would have flooded with raw sewage, damaging the pumps, and substantially increasing the overall cost of repairs.
KSN was able to meet and exceed the Owner and Client’s needs and delivered a quality mapping product by utilizing the best available surveying technology, keeping the project on schedule and within budget. This 3D High Definition Scanning Project earned KSN a Small Firm Engineering Excellence Honor Award in 2009 from the American Council of Engineering Companies.