City of Westminster's Sewer Collection System Assessment Program: A Case Study

The City of Westminster, a suburb of Denver, Colorado, determined the need to rehabilitate or replace portions of its sewer collection interceptor system. The City's collection system consists of two sewage collection basins, each with different operational concerns. In the smaller, Little Dry Creek basin, the primary concern is with capacity-related issues due to anticipated future growth. In the larger, Big Dry Creek basin, significant corrosion due to hydrogen sulfide has been observed in the reinforced concrete pipe that makes up most of its collection system interceptors. Based on these concerns with its collection system, the City sought to identify sources of high inflow and infiltration (I/I), as well as evaluate the sewer capacity and recommend a systematic approach to rehabilitate and replace portions of its sewer interceptor system. The City's objective of the program was to establish a cost-effective and prioritized list of sewer projects to ensure sufficient capacity and minimize risk of sewer failures. This paper presents the approach taken to combine pipeline condition assessment and capacity modeling with rainfall monitoring and in-pipe flow monitoring to develop a holistic solution to addressing the City's sewage collection system issues.