Model Testing Optimizes and Verifies Design of a 200-MGD Trench Wet well for the Sugar Creek WWTP

Charlotte-Mecklenburg Utilities (CMUD) and CDM are currently involved in the design of several treatment plant upgrades at the Sugar Creek wastewater treatment plant (WWTP) in Charlotte, North Carolina. Implementation of this project, which includes a 200-million-gallonper- day (mgd) screenings and influent pump station with dual self-cleaning trench-type wet wells, will provide CMUD with the ability to handle wet-weather flows to the plant. The primary objective of the trench-type wet well design is to minimize the accumulation of solids in the wet well, thereby reducing odors, corrosion potential, and maintenance. The pump station layout is in agreement with the configuration recommended in the latest Hydraulic Institute standard for pump intakes used for solids-bearing liquids. Due to the great importance of the continuity and reliability of the pump station to the WWTP, and because the wet well design is a relatively new and innovative approach, given its shear size, a physical model study is being developed. The objectives of the model study are to determine the existence of any adverse flow phenomena that would affect the system performance, develop the necessary modifications, and document the satisfactory performance of the pump station. In addition, an innovative inlet vortex drop structure is being designed and modeled to verify the inlet hydraulics of the three incoming sewers to the new pump station. Preliminary modeling results have been witnessed and modifications to the original design are being made. Final witness testing of the proposed pump station layout by CMUD and CDM was completed in April 2005.This paper will discuss the unique features of the pump station design, including:Hydraulics and routing of three influent sewers to the pump station including an innovative vortex type drop structureFirm pumping capacity in excess of 200 mgdPump station structural design including a depth over 30 feet below gradeMultiple wet wells for redundancy and reliability to the plantBar screens to protect the pumps with multiple units for redundancy and reliabilityA dry pit/wet pit arrangement with dry-pit submersible type pumpsA self-cleaning trench-type wet well configurationPump station modeling importance and modeling results