Sewer Separation in Downtown Kansas City: A Balancing Act

Kansas City Water Services (KC Water Services) owns and operates a collection system consisting of approximately 2,200 miles of sanitary sewers and 600 miles of combined sewers. This paper focuses on the design and construction of a sewer separation project in one of the oldest watersheds in Kansas City. The project is part of the City's Overflow Control Program (OCP) and is included in the City's Consent Decree (CD) for reducing the volume of combined sewer overflows (CSOs). The accomplishments, challenges, and lessons learned during this project are applicable to CSO communities looking for a straightforward, practical, cost-effective approach to public and private sewer separation. The Turkey Creek Sewer Separation project area is approximately 35 acres in size and is located on the south edge of downtown Kansas City. The project area contained combined, sanitary and storm sewers ranging in size from 8-inches to 36-inches, more than 70 commercial and residential properties, and significant vehicle traffic along Main St. In addition to these challenges, the Kansas City Transportation Authority (KCATA) is extending the City's streetcar line on Main St. The extension impacted several utilities in the congested Main St corridor, including sewer system. The original sewer system in the area drained to a Diversion Structure (DS306). During dry weather flows would exit DS306 through a 12' interceptor sewer that flowed by gravity around Washington Lake and on to the Turkey Creek Pump Station. During wet weather when flows exceeded the capacity of the 12' flow would overflow into a 30' interceptor that discharged into George Washington Lake (Combined Sewer Outfall W006). The City's Consent Decree required elimination of CSOs at Outfall W006. To meet this challenge, Tetra Tech performed an evaluation of both the public and private sewers in the area and worked with the City's Smart Sewer Program (SSP) team to complete the following tasks: - Complete a detailed condition and hydraulic analysis of the existing combined sewer for use as either a storm system or as a sanitary system. - Identify deficient storm sewer structures and surface features that contribute to storm-event related drainage problems in the project area to decrease the risk of localized ponding for future streetcar extension. - Develop conceptual recommended solutions, costs, and schedule to address deficiencies identified in the sanitary and storm systems. - Complete preliminary and final designs for new separate storm and/or sanitary systems based on recommended solutions. - Evaluate opportunities for additional infrastructure improvements within the project area. - Utilize high-level sustainability approaches to meet Envision credit requirements. In addition to the public sewer evaluation, a series of private property investigations were included in the scope. Tetra Tech investigated each commercial property in the area (50 total). The goals of these investigations included: - Locate the private sanitary and stormwater service lateral(s) for each building on the property. - Determine the connectivity between the private laterals and public sewer through visual observation, dyed water testing, CCTV and push camera technology. - Identify direct and indirect inflow sources (e.g., buried downspouts, parking lot drains, sump drains, etc.) connected to private service laterals that may require separation. - Interview property contact (e.g., owner, tenant, operations manager) to identify any specific drainage issues and potential logistical issues during future construction phase. - Conduct a visual inspection of sanitary sewer and storm drainage features on the property and noted their locations on a field sketch. Each commercial property was classified based on whether the sanitary and storm flows were already separated or if the property required internal or external plumbing work to fully separate sanitary and storm flows. Properties requiring separation were also assigned a degree of difficulty to achieve full separation (easy, medium, difficult) and a high-level cost estimate was prepared for each property requiring separation to gauge cost-effectiveness of the performing separation work. The residential properties of the project area were evaluated by a partner KC Water Program, Keep Out the Rain KC, which completed a similar investigation of each property and determined cost-effective separation methods. Tetra Tech's final sewer separation plan included new public sanitary and storm sewers, private sewer separation at nine (9) properties, removal of Diversion Structure DS306, installation of a permeable paving system in areas prone to ponding water, and rehabilitation of public manholes and sewers using a combination of methods, including cured-in-place pipe (CIPP), open cut point repairs, and pipe bursting. Rather than building an entirely new storm or sanitary sewer system, the design team focused on re-using existing infrastructure wherever possible and converted the existing combined sewers to either sanitary or storm based on condition and hydraulics. This approach allowed to site specific decisions to drive project outcomes. Re-purposing existing infrastructure saved Kansas City ratepayers by not having a one size fits all approach to design and construction. Re-using existing sewers allowed the project to be completed by the consent decree deadline and facilitated the construction sequencing with the adjacent Main Street Streetcar Extension Project.