The City and County of Denver Sanitary Sewer Master Plan (SSMP)
is a living document that evaluates Denver’s sanitary sewer capacity and level of service. It provides guidance on capacity improvement needs to maintain an appropriate level of service to residents and businesses and support the growth in the City.
North Denver Sanitary Sewer, Circa 1910-1920
Photo courtesy of Denver Public Library, Western History Collection
Sewer crew laying clay line in trench, 1923
Photo courtesy of Denver Public Library, Western History Collection
Sewer pipe sections and wooden forms, Circa 1909
Photo courtesy of Denver Public Library, Western History Collection
The City’s sanitary sewer system covers approximately 155 square miles of land area and provides services to over 730,000 people. As shown in Figure 1, the sanitary sewer system is an underground system that collects sanitary flows from residences and businesses, where it is then transported to the Metro Water Recovery’s Robert W. Hite Treatment Facility for treatment. The City-owned and operated sanitary sewer system consists of 7 lift stations, 10 miles of sanitary sewer force mains, and over 1,500 miles of gravity sewer pipe network ranging in size from 6 to 60-inches.
The City has provided sanitary sewer service for over 150 years and has conducted multiple Sanitary Sewer Master Plans (SSMPs) over the last 70 years, starting in 1950 with the most recent SSMP completed in 2023. The 2023 update is built upon the prior master plans and the current design criteria, while leveraging the advancement in hydraulic modeling to evaluate the system in a comprehensive way. It provides guidance to capacity improvements to maintain an appropriate level of service to existing and future residents and businesses in the City’s sanitary sewer system area.
Authorization
The City commissioned this master plan as an update to the 2009 SSMP to provide a digital master plan that utilizes the most up-to-date flow monitoring and hydraulic modeling practices. It provides a clear understanding of the existing level of service as well as a high-level, conceptual snapshot of the 2050 planning horizon that align with the land use and growth projections as anticipated in the City’s Blueprint Denver (Denveright) and Denver Moves Everyone plans.
Intent
This SSMP document is a high-level citywide planning tool that aims to analyze and evaluate Denver’s existing sanitary sewer flows, provides guidance on the capacity improvements to maintain appropriate level of service to residents and businesses, and support the growth in the City.
While the SSMP did not provide prioritization of the recommended improvements, it did provide the technical data required to develop projects to support the City’s data-driven decision making. Project prioritization occurs by the City during the City’s 6-Year Capital Improvement Program (CIP), which incorporate a wide variety of factors such as equity and regulatory compliance in addition to all technical data developed from the SSMP. The CIP not only considers the SSMP recommendations, but also takes other identified infrastructure needs into consideration within the City to leverage available funding in order to achieve multiple benefits when it is possible.
Figure 1. Sanitary versus Stormwater
Process
The 2023 SSMP update process began with research and data collection, identifying data quality issues for successful hydraulic model construction. Next steps included hydraulic model development, hydraulic model calibration and validation, flow projection, system performance evaluation, and the production of prioritization toolsets to guide future improvements. This resulted in a fully digital master plan that is adaptive and can be used for years to come.
Approach
The approach for this SSMP update includes the following key tasks:
Data Collection: Collection of as-builts and GIS data to support the construction of a fully dynamic hydraulic model. A flow monitoring project was conducted as part of the SSMP to monitor the flowrates in the City’s sanitary sewer system across the entire service area, capturing dry weather and wet weather flows to serve as the basis to guide hydraulic model calibration.
Hydraulic Model: A comprehensive hydraulic model was constructed to dynamically model the City’s sanitary sewer system and serve as the tool to evaluate the system performance and identify improvement needs to meet the current and future needs. The model was calibrated to the current observed flowrates to ensure the simulated flow rates is well represented across the City’s entire sewer system.
System Evaluations: The master plan evaluated the existing Level of Service (LOS) provided to residents and business across the City based on hydraulic modeling results. The master plan also evaluated how the future growth in the City (based on regional and Denver specific planning datasets) may impact the sanitary sewer infrastructure, and identified potential improvements that may be required to support the growth.
Master Plan: A comprehensive documentation of all tasks completed as part of the master planning effort, as well as digital deliverables including hydraulic models, GIS database, and numerous toolsets developed to support CIP planning.