Race to the Finish Line - Designing and Permitting an ARPA Grant Funded CSO Tunnel in Eight Months

Race to the Finish Line - Designing and Permitting an ARPA Grant Funded CSO Tunnel in Eight MonthsAbstractThe City of Lynchburg (the 'City'), Virginia is one of the few communities in the nation that took early actions to address its CSO issues shortly after the promulgation of the Clean Water Act. Starting in the mid-1970s the City began to address CSOs by mapping out its entire combined sewer system and identifying overflow points. The City developed its initial CSO control plan in 1989, which was then updated in 2000 and 2014. The City successfully negotiated an affordability-based Consent Order with the Virginia Department of Environmental Quality (DEQ) in 1993 and had the Consent Order reissued in 2015 for implementation of the 2014 Updated CSO Long-Term Control Plan — saving 300 million compared to the original complete sewer separation approach. To date, the City has spent 307 million on CSO controls which separated 85% of the combined sewer area, eliminated 114 of 132 overflow points, and reduced the CSO discharge volume by 93%. The City is at the final stage of the CSO program and hopes to complete the regulatory mandated program by 2028. Figure 1 shows the system maps before and after the CSO program. CSO 52 control is the largest CSO project remaining on the Consent Order and will also be the most costly single project the City has ever done. The project will reduce the CSO volume by 98% when completed. The drainage area to CSO 52 is approximately 2/3 of the City's sewer service area. The project will not only achieve the compliance of the Consent Order, but also improves the capacity of a critical interceptor (Blackwater Creek Interceptor) for future growth in the watershed, and mitigate sanitary sewer overflow risks along a highly utilized park trail. The City evaluated several alternatives including parallel interceptor, storage, sewer separation as well as the combination of the above and selected a deep tunnel option as the most feasible and beneficial alternative. The project, titled 'LYNBEYOND Blackwater CSO Tunnel, ' consists of construction of a 4, 716 feet long, 12-foot internal diameter deep rock tunnel about 65 to 120 feet below ground, two flow diversion structures and drop shafts, and a tunnel dewatering pump station. The alignment of the tunnel is shown in Figure 2. The project is partially funded by American Rescue Plan Act (ARPA) grant and therefore has a mandated complete date of December 31, 2026. In order to meet the funding schedule, the City must complete the design, obtain all the permit approvals, and close the land acquisition by the end of 2023. The City's design engineer Stantec started the preliminary engineering in December 2022 and completed the preliminary engineering report in February 2023 to meet the ARPA grant application deadline. The final design started in late March and is scheduled to be completed in early December 2023. In anticipation of the tight design schedule, the City started the geotechnical exploration program in September 2022. In less than eight months, the City worked diligently with its design team and obtained all necessary approvals and permits from the stakeholders and permitting agencies, including a blasting variance for a railroad crossing, easement with two private properties, approval for the bridge crossings, property acquisition, and all DEQ and US Army Corps of Engineers environmental permits. Understanding the private property easement has the highest schedule risk, the City selected the tunnel alignment to only cross two private properties. The tunnel was designed to allow both drill City of Lynchburg 2;SourceProceedings of the Water Environment FederationDocument typeConference PaperPublisherWater Environment FederationPrint publication date Apr 2024DOI10. 2175/193864718825159348Volume / Issue Content sourceCollection Systems and Stormwater ConferenceCopyright2024Word count19