No Easy Way: Challenges Faced in Designing a Large Sewer Interceptor in a River Corridor

The Metro Wastewater Reclamation District (District) in Denver, Colorado, is currently constructing a new wastewater treatment plant, referred to as the Northern Treatment Plant (NTP), to serve the north suburban Denver metropolitan area. As part of the NTP program, the District is also constructing a new interceptor to convey wastewater to the NTP site. The new interceptor is referred to as the South Platte Interceptor (SPI). Designing a large sewer interceptor through an urban corridor is always challenging, however, because the SPI alignment was required to parallel the South Platte River, a unique set of technical issues had to be addressed. The paper/presentation will focus on the following three technical challenges and the engineering analysis performed in preparing the design to address them: (1) Where the interceptor must be installed adjacent to meandering river bends, it must be either protected from erosion or further meandering of the river must be prevented. (2) Where the interceptor parallels gravel pit lakes adjacent to the river, construction activity must not impair the ability of those lakes to collect and store water. (3) Construction dewatering adjacent to a river can have a high potential for construction claims. The geotechnical exploration program and dewatering specifications must be structured to minimize the District's risk exposure. As a result of early identification of the technical challenges and the collaborative efforts of pipeline designers, technical experts, and District staff, solutions were developed that satisfied all of these challenges and allowed the project bids to come in below budget. This paper/presentation will describe the challenges that were faced and discuss the range of solutions investigated and incorporated into the design.