West Yost is designing upgrades to increase the sewer capacity in two regions of the City of Rialto to support new development. The Sycamore Lift Station will have upgrades to increase capacity from 450 gpm to 560 gpm and the Agua Mansa Lift Station will increase capacity almost six-fold from 250 gpm to 1,470 gpm. The project included a condition assessment in order to determine the existing condition of the wet wells at each lift station and the condition and capacity of existing electrical equipment to support the expansions.
Neither lift station was equipped with flow meters, so it was difficult to determine the existing flow capacity. After reviewing past records and completing some flow monitoring, West Yost was able to narrow down the existing flows. West Yost estimated the future flow requirements by understanding the development goals and using the proposed square footages of industrial buildings and the acreage of proposed development and housing units. Once West Yost understood the needs of the development, we made recommendations in a preliminary design report.
West Yost found that a variable frequency drive (VFD) would be the most efficient approach to increase station capacity over time, even though they add capital cost to the project and increase operational complexity. West Yost estimated that it will take several years for the sewage flows to increase to their proposed flow rate at full development. Large housing developments add flow to the sewer collection system gradually, as homes are built and occupied individually, and because large housing developments are often periodically slowed by small recessions. The VFD will allow the lift station to function most efficiently without allowing sewage to sit in the wet well for a long period of time and become septic, which increases odor and sulfuric acid production.