Session 21B: Collection & Conveyance: Rehabilitation - Livestream
10:30am - 11:15am
Rehabilitation Analysis Of The 100-Year Old Whatcom Creek Trunk Main
Carollo Engineers, Seattle, WA; ,
The City of Bellingham’s Whatcom Creek Trunk Main was installed in 1909 and consists of large diameter, up to 3-foot wide by 6-foot tall, egg-shaped concrete pipe running along Whatcom Creek and into downtown Bellingham. The existing 6,500 foot-long trunk main includes several sections of pipe which are visible in the creek’s bed and completely exposed during the dry season. Maintenance completed by the City showed structural pipe deficiencies which compelled the City to look at the replacement or rehabilitation of the existing sewer.
Carollo Engineers was hired by the City to complete an alternatives analysis to compare viable replacement or rehabilitation options, which included open cut replacement, cured-in-place pipe (CIPP), sliplining, and epoxy coating. Each alternative was evaluated on criteria which could impact the design and construction of the preferred alternative, including hydraulic capacity, constructability, community and environmental impact, bypassing requirements, and construction costs.
To accomplish the alternatives analysis, a laser profile was performed to provide accurate dimensions, estimates of sedimentation, identification of major structural defects not previously identified, and any infiltration which could impact construction.
Each of the rehabilitation methods identified would also require the pipe to be at least partially bypassed to allow for machinery and workers to perform the pre-cleaning and rehabilitation. A bypass pumping analysis was performed using the historical rain and sewer flow data to size an appropriate temporary bypassing system.
This presentation will look at the construction of the original sewer trunk main and how the design of critical sewer interceptors has changed over time, the data and criteria required to complete the alternatives analysis, and the selected alternative. Attendees will learn what risk management aspects needed to be addressed as part of this analysis including, sewer bypass, construction footprint constraints, traffic impacts, and design requirements for non-circular pipeline rehabilitation.
11:15am - 12:00pm
Planning for Seattle’s Future – The Wastewater System Analysis Episode
1Murraysmith, United States of America; 2Seattle Public Utilities; ,
Seattle Public Utilities (SPU) is currently undertaking an ambitious effort to integrate their wastewater and drainage systems planning efforts, bridging the needs of the wastewater and stormwater systems to achieve greatest environmental and community benefit. Continual growth and development have made providing adequate capacity a challenge throughout Seattle’s history, since it requires addressing challenges such as an aging system, growing population, densification, and climate change.
SPU serves a population of approximately 747,300 spread over 84 sq-miles and operates a complex network comprised of 1,423 miles of sewers, 68 pump stations, and 86 CSO outfalls. A system-wide capacity analysis was conducted using the latest hydraulic/hydrologic (H/H) model; the results were used to identify and prioritize risk areas using input from multiple stakeholders within SPU.
A primary objective of the Wastewater System Analysis (WWSA) was to identify and understand wastewater capacity needs. Performance Thresholds were selected to achieve performance goals of providing adequate capacity in the public wastewater system, minimizing the risk of sewer backups into private property and public right-of-way. Performance parameters of 1-ft pipe surcharge, maintenance hole flooding, and hydraulic capacity limitation of above 100% of existing pipe were used under one, two, and five-year, 24-hour design storms to evaluate system performance.
The modeling results were used in conjunction with community outreach results to identify and prioritize risk areas. 384 risk areas were delineated and categorized into critical, high, medium, medium-low, and low categories. The project team investigated and categorized critical priority risk areas further to identify capacity issues, providing a framework for programmatic solutions like Inflow and Infiltration (I/I) reduction, pipe and pump station replacement, operational and connected sewer agency constraints, and any combination of issues. This presentation will provide a sound approach to future planning efforts by incorporating technical and non-technical challenges in an expanding urban environment.