The collection, conveyance, and treatment of municipal wastewater constitute a vital chain of services that protects public health and the environment and enables economic activity. Designing and operating a municipal sewer system comes with many challenges, including how to manage unwanted inflow and infiltration (I/I) from stormwater and groundwater, respectively.
Rob Sowby, Ph.D., P.E., assistant professor at Brigham Young University, and Dan Jones, P.E., C.F.M., both water resources engineers at HAL, published an article titled “A Practical Statistical Method to Differentiate Inflow and Infiltration in Sanitary Sewer Systems” in ASCE’s Journal of Environmental Engineering. In it, the authors present a practical regression model that quantifies inflow and infiltration (I/I) without intensive data requirements. The required data consist of daily precipitation totals, average air temperature, groundwater peak day, and daily wastewater flows. The model was verified using South Salt Lake and other local city data.
Through the practical application of this research, wastewater professionals can prioritize I/I interventions. For example, if the model suggests high inflow, rehabilitation can focus on capping cleanouts, disconnecting roof drains and storm sewer cross connections, and sealing or replacing leaky manholes. If the model suggests high infiltration, rehabilitation can focus on grouting manholes and replacing or lining pipes. The analysis may be included as part of a sewer master plan or similar study.
Image courtesy of King County, WA. Used with permission.