Earthquake papers Management and maintenance practices of storm and sanitary sewers in Canadian Municipalities E. N. Allouche, Ph.D., P.Eng. P. Freure, B.E.Sc. April 2002
ICLR Research Paper Series – No. 18
Recent events that have taken place in Walkerton, Ontario and North Battleford, Saskatchewan, have brought the issue of the state of Canada’s municipal water and wastewater systems to the forefront of public attention. Currently, most levels of government agree that there is an urgent need for the renewal of our municipal infrastructure. However, sources for the needed capital, estimated to be as much as $45 billion, are less apparent. (Sinha, 1999) Most of the funds needed will undoubtedly be generated through a combination of higher municipal taxes, higher user fees, provincial and federal grants, and low interest loans. Other efforts will focus on reducing overall costs through greater efficiency and the use of advanced technology. In particular, savings will be generated by optimizing the management and maintenance of municipal assets, developing and adopting more cost effective inspection and rehabilitation technologies, and a greater degree of integration among various construction activities.
This report focuses on the inspection, repair and management practices utilized by Canadian municipalities to maintain their buried storm and sanitary sewer systems. The report also examines several indicators of the current level of performance as well as the ability of Canadian municipalities to respond to emergency events such as natural disasters.
The results of a survey of preventative maintenance practices currently used by Canadian municipalities in managing their buried sanitary and storm sewer networks are presented. Survey results were collected from 26 municipalities of various sizes and in different geographical locations across Canada. The data collected include among others: the distribution in terms of spending per capita for new construction, inspection and rehabilitation; level of utilization of various pipe inspection and rehabilitation techniques; frequency of inspection; management of inspection data; material and diameter breakdowns; and frequency of basement flooding. The findings from the survey are compared with findings from a survey of the state-of-the-practice in sewer management of municipalities in the USA conducted by Malik et al. (1997), and a 1997 survey of the level of utilization of trenchless technologies in Canadian municipalities by Ariaratnam et al. (1999).
Analysis of the data collected reveals that Canadian municipalities spend approximately $20.00 per capita per annum on the inspection, replacement and rehabilitation of existing municipal sewer networks, an amount slightly higher than that reported for the 1996-97 construction season of $18.21 per capita (Ariaratnam et al., 1999). From this amount approximately 90% is spent on construction activities and 10% on condition assessment and evaluation. The per capita expenditure data are strongly skewed to the right (Figures 7, 8 and 9), an indication that the median value may be a better measure than the mean of the ‘typical’ level of expenditure. The data reveal a significant increase in expenditure for rehabilitation of buried infrastructure for mid-size and large municipalities in comparison to the 1996 levels.
Closed Circuit Television (CCTV) systems and smoke testing are by far the most common methods utilized by Canadian municipalities for the inspection of municipal sewer networks. Newer technologies such as sonar and ground penetrating radar have not been widely accepted in this market. The utilization of trenchless technologies by Canadian municipalities is on the rise, with 82% of municipalities using one or more pipe lining techniques in the year 2000 compared with only 66% in 1996 and 32% in 1991. Comparison of the composition of sewer networks in Canada and the USA has shown significant differences in terms of the relative weight of various pipe materials. The most common pipe material in Canadian sewers is concrete (41%) while vitrified clay is most commonly used in the USA (56%). Canadian sewers also contain larger quantities of plastic and plastic pipes (PVC/HDPE). These findings imply that research and development efforts in the USA might not fully address the needs of Canada’s municipal sewer systems.
The return period for inspection and assessment of sanitary and storm sewers in Canadian municipalities is between 25 and 30 years, which is nearly equal to the design life of many of these facilities. Computerized data management and record keeping systems are commonly used in Canadian municipalities, with 78% of respondents indicating the utilization of such systems compared to 71% in the USA. Forty-one percent of all municipalities use automated data management systems/GIS, compared with 44% in the USA. A pipe defect classification system developed by the Water Research Centre (WRC), a U.K. research organization, is commonly used by Canadian municipalities. Sixty-eight percent of all respondents use it exclusively or in combination with an internally developed system.
Basement flooding is a common event in Canadian municipalities with 42% of respondents indicating that storm surges and basement flooding occur several times each year in their jurisdictions. As for post-disaster management and recovery, only 15% of the municipalities with populations of less than 250,000 have guidelines in place for conducting post-disaster inspection of their buried municipal services. Forty-one percent of the municipalities indicated that such a post-disaster inspection would likely take more than 18 months, with only 23% being confident in their ability to accurately determine the damage inflicted on their buried networks in the aftermath of such an inspection.
The more advanced the inspection technologies and data management system that a municipality uses the greater is its appreciation of the complexity associated with a post-disaster inspection of its linear networks. When an aggregate measure of the municipality’s level of sophistication was contrasted with its anticipated level of performance, it was found that the more sophisticated the municipality the longer the anticipated post-disaster inspection is expected to take, and the higher is the predictable percentage of determinable damage caused by the natural disaster. Additionally, municipalities possessing more sophisticated data management systems are more likely to have developed guidelines for post-disaster inspection of their storm and sewer networks.
No clear correlation was observed between the frequency of basement flooding and the average annual precipitation, implying that infiltration and inflow (I/I) contributions are more significant than the base flow with respect to the creation of overflow conditions. Direct correlation was observed between the level of investment in the inspection and management of the storm and wastewater collection system and the frequency of basement flooding.