Reducing Inflow and Infiltration

The Capital Regional District’s Liquid Waste Management Plan was introduced in 2009 to combat against largely preventable losses as a result of aging sewers and wastewater infrastructure being unable to cope with increased extreme rainfall events due to climate change. The plan mandated that each municipality in the region should not be exposed to peak wet weather sanitary sewer flows that exceed four times average dry weather flows. In the City of Victoria, flows were known to be above this target, making the region extremely vulnerable to the impacts of climate change and necessitating adaptation efforts. Seeking to establish and implement a plan to better control the inflow and infiltration of rainwater into the sewer system, Victoria launched an in-depth study focused on determining how stormwater was entering sanitary sewer pipes in the James Bay area. With aging sewer infrastructure in the region, extreme rain events threatened the backup of sanitary waste into homes and the discharge of untreated sewer water into the environment. Video inspections of the sewer system, smoke and dye tests, and the collection of flow monitoring data offered insights on sources of inflow and infiltration. The design phase of the James Bay project tested four different approaches to reduce inflow and infiltration, with a focus on trenchless technologies. During the evaluation phase, the reduction of stormwater in sewer pipes was measured once the rehabilitation work was completed. This comprehensive study revealed that mainline and lateral sewer rehabilitation contributed to a 60 percent reduction in stormwater inflow and infiltration. The results of the various tests conducted in James Bay helped the engineering department in Victoria to establish a long-term plan to best manage their current infrastructure and decide where to prioritize rehabilitation practice.

Understanding and Assessing Impacts

Extreme rainfall events temporarily increase demands on stormwater systems and increase the volume of rainwater flowing into streams and rivers. As climate change increases the frequency and intensity of such rainfall events, Victoria’s current stormwater infrastructure may become overwhelmed. Risks associated with these climate-related impacts include potential extensive damage from sanitary waste backing up into homes and environmental damage as untreated sanitary waste is discharged into streams and lakes. The 2012 Canadian Infrastructure Report Card noted that 40 to 50 percent of participating local governments have no data on the state of their buried infrastructure. Twenty percent of Canada’s wastewater and stormwater infrastructure was estimated to be in “fair” to “very poor” condition. Local governments likely need more than $55 billion to replace these failing systems. In Victoria, a city with several older neighbourhoods, aging sewers and wastewater infrastructure meant the City was vulnerable to the impacts of climate change, as increased extreme rainfall events would result in greater stormwater inflow and infiltration. Since the damage from such inflow and infiltration was largely preventable by proactively rehabilitating failing infrastructure, the City of Victoria identified the need to establish and implement a plan that would better control the inflow and infiltration of rainwater into the sanitary sewer system. Understanding the core issue and the City’s vulnerability to climate change, Victoria moved to the planning phase of their adaptation efforts.

Identifying Actions

A significant motivator for improvements in stormwater infrastructure in Victoria was the Capital Regional District’s Liquid Waste Management Plan. Introduced in 2009, the plan mandated that municipalities in the region should not be exposed to peak wet weather sewer flows that exceed four times average dry weather flows. Since flows in Victoria were known to be above the target, one of the first actions identified by the City was to study exactly how stormwater was entering the James Bay area—where aging sewage infrastructure was highly vulnerable to inflow and infiltration of stormwater during heavy rainfall events. The James Bay area was divided into smaller sections to isolate sources of inflow and infiltration in each section. The subsequent design phase of the project would involve the testing of various approaches to reduce inflow and infiltration based on the observations in the initial ‘planning’ phase. The different approaches to adaptation would then be tested using flow monitoring to measure their success at reducing stormwater in sanitary sewer pipes. In this phase of the project, one of the basins would be left untouched to serve as a benchmark for evaluating progress. This outlined approach sought to provide Victoria with a blueprint for future inflow and infiltration reduction programs in the City. Other objectives were related to the elimination or reduction of sanitary sewer overflows, the improvement of public safety by lowering the risk of sewer collapse, the reduction of future sewage treatment costs, and public education.

Implementation

The study of the James Bay area began by using video inspections of the sewer system, smoke and dye tests, and the collection of flow monitoring data to isolate sources of inflow and infiltration in each section of the region. In the design phase, the City tested the effectiveness of four different approaches to reduce inflow and infiltration, with a focus on using trenchless technologies. The adaptation actions that were tested included mainline rehabilitation using pipe bursting and cured-in-place pipe lining, lateral rehabilitation using pipe bursting and cured-in-place lining, manhole rehabilitation using a coating system and internal chimney seals, and stormwater inflow redirection through the elimination of cross connections. Approaches were tested individually and in conjunction with each other to determine the best way to reduce stormwater inflow and infiltration. To evaluate the effectiveness of different measures, flow monitoring was conducted to measure the reduction of stormwater in sanitary sewer pipes once the rehabilitation work was completed. Rehabilitation was conducted in three of four sub-catchment areas, with the fourth basin used as a benchmark for progress (as outlined in the “identifying actions” section). The James Bay area study collected over a year of data to cover a range of rain storm intensities and durations.

Next Steps

The results of the James Bay area study will be fundamental to informing adaptation measures in the stormwater infrastructure in Victoria for years to come. Further infrastructure rehabilitation is needed to ensure compliance with the region’s comprehensive Liquid Management Plan introduced in 2009. The City of Victoria is also committed to taking advantage of the emergence of new technologies by evaluating them through similar exercises to the James Bay area study. The approach to the study proved to be an extremely useful method of justifying rehabilitation and renewal expenditures. It is likely that similar studies will be conducted in Victoria to evaluate new approaches to reducing infiltration and inflow in the City. While specific next steps are not outlined in the case study, there is a significant emphasis on addressing long-term issues with their adaptation efforts. This indicates the City of Victoria is committed to using the results of the study to introduce proactive adaptation that prevents future damage due to aging sewers and wastewater infrastructure.

Resources

Link to Full Case Study