Nowadays, utilities across the United States are operating aged and declining sewer infrastructure while facing many challenges, such as climate change, population growth, and increasing regulatory pressure. Aging sewer systems also increase the occurrence of SSOs, which can cause serious water quality issues and endanger public health. Calibrated Hydraulic models are becoming a popular tool to assess the sewer's existing condition and the effectiveness of rehabilitation efforts. Hydrometeorological data is an indispensable component of hydraulic sewer characterization; however, their relationship is not always straightforward. For example, SSOs and I&I are not always caused by regional rains. In this presentation, we will show two examples of the integration of hydraulic models with rigorous analysis of hydrometeorological data to assess the previous rehabilitation methods and estimate dry and wet weather flows.
The first case study is the City of Gastonia, NC, where several projects such as flow monitoring, smoke testing, SL-RAT, sewer CCTV, sewer jetter, mapping, and weather analysis are general methods used to justify "find and fix" sewer projects. We combined the past data with sewer model RTK analysis to decipher the impact of each previous project, primarily when the initial problem still exists. A specific R-value range was proposed for the rehabilitation or installing a new sewer line to relieve areas struggling with SSOs.
Another case study is the City of Goldsboro, where the City and its sanitary sewer system are bordered by the Neuse River and several smaller tributaries. A major control point of the Neuse River watershed is the man-made Falls Lake upstream of the city. Analysis of data unraveled a strong positive correlation between dry-weather flow and R-values with groundwater depth, which was indeed affected by the river level.
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