Next-Gen Pumping Stations: A Case Study at Crum Creek

This project showcases the successful implementation of crucial improvements at the Crum Creek Wastewater Pumping Station (CCPS) site in Philadelphia, Pennsylvania to align with the Central Delaware County Authority's Act 537 Plan, expanding its capacity from 16 to 24 million gallons per day. The existing 1930s station grappled with frequent flood-induced damage and service outages, necessitating a complete replacement of the station. The new station boasts a trench-type self-cleaning wet well equipped with four, 300-horsepower, submersible pumps operating in a 3+1 arrangement. These pumps, fitted with variable frequency drives (VFDs), were strategically designed to meet a staggering 10 distinct design points. The unique challenges of this project lent to many lessons learned and considerations that can be applied to pumping station designs around the country. System hydraulics were one of the primary complexities of the design. The new station had to have the capability to pump into two separate force mains (Figure 1) with vastly different hydraulic conditions. The project team implemented creative solutions in programming and controls to ensure efficient pump operation under the entire operating range from 5MGD to 24MGD (Figure 2) with a simple pump arrangement of three identical pumps. Notably, the customized pump operations were devised to minimize clogging during low-speed operation by requiring a full speed ramp-up during pump initiation and shutdown. Creative thinking was also required for programming and controls to safely operate the pumps dependent on the receiving force main in order to prevent pump runout. A detailed control sequence was developed to automatically facilitate the self-cleaning process. Based on Hydraulic Institute (HI) standards, the self-cleaning cycle should be performed when influent flow is roughly half of the cleaning pump's capacity. To automate this process, a motor-operated slide gate was installed upstream of the wet well. Once the cleaning cycle is initiated, the slide gate will partially close to a position predetermined by flowrate via a feedback loop to ensure proper influent flowrate for a successful cleaning cycle. The pump station's design was based on HI 9.8 standard for a self-cleaning trench wet well. Utilizing scale physical models constructed by Clemson Engineering Hydraulics, the team was able to validate theoretical dimensions, and guide necessary deviations, including the removal of the flow splitter along the ogee spillway. Considering the controls were critical to the project's success, a 'SCADA Summit' was held at the project's construction kickoff to coordinate between the integrator, contractor, and engineer. This session proved critical for aligning perspectives, clarifying concepts, and streamlining submittals, ultimately contributing to the project's success. Throughout, a paramount focus was placed on safety. The design incorporated a bridge crane to facilitate pump and valve maintenance from above the station. The design incorporated the innovative use a parapet wall for wet well access, simplifying pump removal. At a 42-inch height above the station top slab, the parapet wall provided superior fall protection and flood protection. The wall was also a convenient place to mount pump power and control junction boxes (Figure 3). A significant challenge of the project involved the intricacies of constructability on a confined site, with existing facilities occupying over half of the available space. Innovative solutions played a pivotal role, such as a unique gravity bypass configuration that eliminated the need for costly bypass pumping, resulting in substantial savings. The gravity bypass arrangement involved installing a temporary plug in one of the parallel 42-inch gravity sewers that fed the existing station, allowing for a segment of the main to be removed on site and freeing up more space for the new station (Figure 4). Confirmed via hydraulic modeling, the plugged sewer was then allowed to surcharge upstream to a junction manhole, where it would overflow to the parallel sewer. Temporary bypass pumps were staged at the junction structure as a safety precaution during wet weather events. Other noteworthy constructability challenges included partial demolition of the existing station for a new electrical room (Figure 5), with careful considerations for equipment relocation and temporary setups to ensure uninterrupted station functionality. Once the pump station and control building were complete, flow was routed to the new station and the existing station was demolished (Figure 6). The Site was configured in such a way that facilities that were not essential for start up could be constructed once the existing station was demolished (Figure 7). The project incorporated the innovative use of lidar scanning which became a critical tool for as-builting. Using a tripod mounted Leica terrestrial scanner, the team was able to capture detailed interior and exterior views with millimeter accuracy. This data was seamlessly integrated into the original design file, enabling a precise comparison of field changes (Figure 8). From unique bypass configurations to creative programming solutions, the project incorporated innovation and creative thinking that ultimately led to its success and on-time, under-budget completion.