Not the regular Kool-Aid: How to implement a cost-effective I/I rehab plan under extreme drought conditions with significant operational challenges

The HRSD is currently implementing high-priority projects in two service areas of Portsmouth, VA, as part of the 2020 Regional Wet Weather Management Plan (RWWMP). These projects aim to cost-effectively reduce infiltration and inflow (I/I) in the gravity sewer and manholes to meet the Consent Decree's (CD) sanitary sewer overflow reduction goals. However, identifying I/I in one of the most leak-prone areas has been a significant challenge due to frequent surcharge conditions in the collection system and below-average rainfall in 2022, which has led to the lowest groundwater levels in the past five years. Figure 1 shows the history of flows, rain, and groundwater level conditions over the last 6 years. Figure 2 shows the rainfall event characterization over the flow monitoring period. The I/I hot spot area in Portsmouth, VA includes the historic district near the Naval Hospital and the area upstream of HRSD's Camden Ave. pump station. These areas have been under investigation since July 2022. Over 33 flow monitors have been deployed across these areas to characterize I/I in different parts of the system. Various sanitary sewer evaluation survey (SSES) techniques have been employed to identify the sources of I/I and recommend necessary sewer rehabilitation measures. Figure 3 shows the project area, the flow monitoring locations and sanitary sub-basin delineation and Figure 4 shows a sample of the SSES techniques applied to understand I/I in the system. Unlike most traditional I/I rehabilitation projects, HRSD's objective was not merely to eliminate I/I, but to understand the most effective way to reduce SSOs in line with the goals of the CD. This is particularly remarkable given that HRSD is implementing I/I reduction and capacity improvements on assets they do not own. This arrangement was established through a Memorandum of Agreement (MOA) with all local municipalities during the RWWMP development, aiming to achieve SSO reduction in the most cost-effective manner. Consequently, the project approach involves a comprehensive hydraulic analysis of the service areas to understand I/I behavior and determine whether capacity improvements could be a more beneficial investment for achieving the ultimate goal of eliminating SSOs for an agreed level of service. This paper will present key insights from flow monitoring and SSES investigations that could be beneficial to numerous utilities across the country. The topics covered include: -Flow Monitoring in Pre-Rehabilitation Conditions: This section discusses the effects of dry/wet weather on flow data quality, temporary blockage impacts, sewer response to mild intensity tropical events, flow evaluation under surcharge and backwater conditions, and the influence of sediment/debris/rags on flow sensors. It also covers the selection of flow monitoring equipment and the operation of vacuum-assisted sewer systems, among other pertinent observations. -Traditional SSES Applications: This part focuses on NAASCO's MACP-compliant manhole inspections, smoke testing, and main sewer line CCTV inspections conducted as per NASSCO's PACP criteria. It uses two different types of dye testing: the traditional method where dye water is supplied to a suspected area and visual observation in the sewer confirms the I/I connection, and flooding dye testing where dye water fills nearby stormwater infrastructure and a CCTV camera in the sewer looks for pipe defects where dye enters the sanitary system. The paper also discusses lateral simulated rainfall testing, which can be a cost-effective approach when dealing with private property I/I. In addition to the conventional SSES methods, HRSD is exploring two cutting-edge SSES techniques: -Distributed Temperature Sensing (DTS): This technique involves placing a fiber optic at the bottom of the main sewer lines to detect the presence and exact location of potential I/I sources along the pipe where installed. This method can be especially beneficial in narrowing down the scope of rehabilitation on private property. To visualize the useful information gathered with this technique an example plot is shown in Figure 5 during a tropical storm Ophelia in September 2023 when I/I inputs were colder than the wastewater flow in the sewer at that time -Improved In-Situ Manhole Leakage Test: This innovative technique, a spinoff from an earlier manhole leakage test called by HRSD as the 'Rocket Launcher'. This technique simulates a flooding condition on top of the manhole while maintaining a water surface elevation of 6 to 8 inches over the manhole rim in a wide area around the manhole as shown in Figure 6. The ponded, dyed water infiltrates all around the manhole, activating I/I at various points. Cameras placed within the manhole during the test record the accumulation of volume over time and observe exact I/I entry points. Unlike the previous technique, the leakage rate is calculated as the manhole fills inside while all connected pipes are plugged. Compared to other SSES methods, this new manhole leakage test provides a comprehensive quantification of leakage rates from different parts of the manhole under controlled, replicable conditions. This allows for proper prioritization of I/I contributions from manholes across different zones of the collection system. High-resolution video capture before, during, and after the test offers an excellent qualification of I/I defects inside the manhole. This can be used to identify the necessary scope of rehabilitation, saving significant capital when qualified I/I sources are grouped and full manhole surface rehabilitation is not required. The complete paper will elaborate on the utilization of flow monitoring data, the choice and order of various SSES techniques employed for the project and share some of the outcomes with their implications on the proposed rehabilitation scope of work. A compilation of quantitative and qualitative evidence from work in Portsmouth, VA will be presented to better illustrate this approach's advantages. This demonstrates that HRSD is achieving the Consent Decree's objectives while significantly reducing capital expenditure compared to the original comprehensive rehabilitation estimated by the RWWMP.