Hydraulic Modeling and Improvement of a Sanitary Sewer Collection System

This paper presents a cost-effective procedure approach to evaluate and improve sanitary sewer collection systems. The City of Sapulpa, Oklahoma is required to improve its wastewater collection system in Basins N02/N04 in order to reduce the frequency of sanitary sewer overflows (SSOs) experienced during periods of heavy rainfall. The Sapulpa collection system N02/N04 basins are analyzed in order to identify the optimum combination of rehabilitation and capacity enhancement needs to cost-effectively minimize wet weather overflows. This is accomplished by identifying particular lines that do not have sufficient capacity to convey anticipated flows, identifying the capacity enhancements needed so that the system will have sufficient capacity, estimating the cost of the capacity enhancements, and identifying areas where collection system rehabilitation and Inflow and Infiltration (I&I) abatement would likely yield significant results. The capacity analysis is performed by constructing an InfoWorks CS hydraulic model of the collection system, calibrating it to reflect actual system performance, analyzing it at the current design conditions, and using the model results to size capacity enhancement interceptors. Based on the hydraulic modeling results, three alternatives are developed to address these SSOs. The advantages and disadvantages of these alternatives are also discussed with estimated conceptual construction costs. Alternative 3 with I&I reduction is recommended because of cost-effectiveness, prolonged life of the collection system, reduced operation and maintenance cost of both wastewater collection and treatment systems. The proposed project consists of sanitary sewer evaluation and survey (SSES) and sewer rehabilitations of Basins N04 and the southeast part of Basin N02, gravity interceptor upgrade, and a new lift station and force main leading to the Sapulpa Wastewater Treatment Plant. A Gantt chart is also provided to depict the milestone dates and the work to be performed.