SANITARY SEWER OVERFLOW MONITORING, DATA ANALYSIS AND RESPONSE PROCEDURES

The City of Edmonton, Asset Management and Public Works Department, Drainage Services has developed an Interconnection Control Strategy to eliminate or minimize the discharge of sanitary and combined sewerage to the storm sewer system, and subsequently to the North Saskatchewan River. These discharges would be defined as Sanitary Sewer Overflows in the United States. The Interconnection Control Strategy has evolved to focus on monitoring sanitary sewer to storm sewer interconnection activity. In 1997, the City implemented a comprehensive monitoring program, using virtual level gauges (VLGs) at about 180 active interconnection sites. Since 1998, the City downloads data on a weekly basis from these VLGs through remote communication technologies.Monitoring data are reviewed and analyzed in order to estimate overflow frequency and duration of overflows at these interconnections. If the site is identified as active during dry weather flow conditions, the City's operations crew is notified immediately to investigate and confirm the overflow activity. They are also required to collect water samples, release any blockages that may be found in the sewer line and report to the provincial regulator.Results obtained from the monitoring program are also utilized to quantify interconnection activity, to support sewer system assessment and for prioritization of remedial works. For the five year period between 1997 and 2001, an average of 69% of the City's interconnections were found to be inactive each year. About 29% of the interconnection sites are active each year under various levels of wet weather flow and 3% overflow on at least one occasion during dry weather.This paper presents the features of the montioring program to quantify sanitary sewer overflows. It also provides an overview of the current response procedures to interconnections with dry weather overflow, and outlines the correction and assessment work plan for interconnections.