Hillsborough County Post CIP Lining Investigation and I/I Reduction

Purpose: Hillsborough County (County), Florida, has experienced strong population growth in recent years, which has increased the demand on their existing wastewater collection system. To maximize the capacity of the collection system, the County started a comprehensive mainline cured in place (CIP) lining program. After CIP lining the mainlines, the County continued their infrastructure investigation and conducted a post CIP lining sewer inspection and rehabilitation program focused on infiltration reduction. The purpose of the post CIP program was to identify the source of lateral infiltration, public or private, and rehabilitate laterals up to the property line. Benefits of Presentation: Infiltration reduction minimizes increased wastewater flows experienced when the groundwater table is high and following wet weather events, while reducing the opportunity of sanitary sewer overflows. For gravity mainlines, infiltration is traditionally identified through the completion of Sewer System Evaluation Surveys (SSES) that include manhole inspections, flow monitoring, closed circuit television (CCTV) inspections, smoke testing and dye water testing. These assessment technologies quickly identify areas susceptible to inflow and infiltration (I/I). To identify individual laterals that were leaking post CIP lining, Electro Scan's Focused Electrode Leak Location technology (FELL) was used in combination with traditional lateral CCTV conducted in compliance with National Association of Sanitary Sewer Survey Companies (NASSCO) Lateral Assessment Certification Program (LACP) guidelines. Benefit 1 The presentation will benefit the industry by providing post CIP lining condition assessment results indicating that only lining gravity sewer mains will not reduce infiltration entering the system if tap connections and defective laterals are not sealed. Results of the investigation indicate that a comprehensive CIP lining program in a high I/I area should include the sealing of tap connections and lateral lines to the property line or cleanout. Additionally, the presentation will explain how newer technologies such as FELL can be incorporated into traditional SSES investigations to identify I/I. Benefit 2 This presentation will benefit the industry by identifying construction issues related to the repair and rehabilitation of tap connections and lateral lines utilizing chemical injection grout and full wrap CIP lateral liners. For example, Full Circle Lateral Repair Liners (FCLRL) that extended 3 feet from the mainline lateral tap connection do not require the installation of a cleanout; however, FCLRL repairs that extend more than three (3) feet require the installation of a cleanout to facilitate installation of the liner system. Benefit 3 To track the progress of this project and support the County's growing asset management program, the County developed a GIS asset registry to capture lateral tap connection points, lateral lines, and cleanouts. This presentation will explain how a GIS application was developed to collect locations of lateral line attribute data, and repair and rehabilitation information in real time. Status of Completion: As of 12/5/2023, the total project is approximately 70 percent complete. All FELL work is complete, 95 percent of the CCTV inspection work is complete, and approximately 30 of the lateral repair and rehabilitation work is complete. All construction work is scheduled to be completed in May of 2023. Conclusion: The County began post Cured in Place lining investigation work to address ongoing infiltration issues by utilizing the innovative FELL technology to identify leaking laterals in Hillsborough County's Clair Mel Area. Results of the FELL study indicated 25 percent of the sewer mains previously lined had laterals that were contributing infiltration to the system. Based on FELL infiltration rates traditional CCTV lateral inspections work was completed, which visually confirmed the presence of infiltration identified by the FELL technology. Based on CCTV inspection results, 53 percent of the lateral defects were located on the public side of the lateral and that the infiltration could be addressed by chemical injection grouting or a structural CIP liner. Overall, laterals are a significant source of infiltration entering the wastewater collection system. By sealing tap connections and lateral lines the amount of infiltration entering the system can be reduced which will maximize the capacity of the system and increase the useful life of aging infrastructure.