Planning, Design, Construction and Performance of the Royal Avenue CSO Storage Tank in Hamilton, Ontario

The City of Hamilton, Ontario, Canada is located at the western end of Lake Ontario. Much of the City is serviced by a combined sewer system (CSS) which captures sanitary sewage and storm water and conveys them to the 409 MLD (100 MGD) Woodward Avenue Wastewater Treatment Plant (WWTP) in the east end of the City. During heavy rainfall, the capacity of the CSS and/or WWTP is exceeded and excess sewage is discharged to Cootes Paradise and Hamilton Harbour via 23 combined sewer overflows (CSOs). The City completed a Master Plan Class Environmental Assessment (EA) study to address solutions to 3 remaining CSOs in Ward One in West Hamilton, including the Ewen, Sterling and Royal sites. These CSOs discharge to Cootes Paradise, an environmentally sensitive wetland area that flows into Hamilton Harbour and ultimately Lake Ontario. The Ward One CSO Master Plan considered several alternative solutions, and identified preferred alternatives for each CSO outfall in close consultation with the community.The first component of the implementation of the Ward One CSO Master Plan was the construction of a 15,000 m3 CSO storage tank to reduce the frequency and volume, and mass of pollutants discharged into the Chedoke Creek at the east end of Royal Avenue. The facility is sized to capture over 90% of the average wet weather flow (WWF) volume entering the contributing combined sewer system (CSS) from April 1 to October 31 of each year, to achieve the 90% minimum WWF control level required by Ontario Ministry of Environment (MOE) Procedure F-5-5. On average, the CSO tank is expected to reduce existing annual CSO volumes by over 70%, and reduce the average number of CSO events to less than one per year.Some novel/key features of the project included:Extensive public consultation during the planning phase, including the establishment of a Community Advisory Committee consisting of concerned local citizens to help guide the study process and provide a focus for community-based input throughout the study.Identification and evaluation of various CSO control alternatives, including source controls (water conservation, downspout disconnection, infiltration reduction), sewer system controls (CSO regulator adjustments, sewer separation, detention storage), CSO treatment (high rate treatment), and combinations of these options.Long-term continuous modeling of the contributing CSS (30 years) to compare potential CSO control levels provided by each CSO control alternative, and to confirm the capacity of CSO control measures required to meet desired CSO control targets.Detailed review of the hydraulics of the proposed storage tank and associated conveyance elements to optimize hydraulic performance, which resulted in several improvements to the hydraulic design of the facility.Assessment of potential impacts of odor emissions from the facilities, including air dispersion modeling, which confirmed additional odor controls were not required.Relocation of existing creek crossing the tank site, including natural channel design features to permit future migration of fish and minimize erosion of the creek banks.Design and construction of deeper than normal tank, up to 12 m (39 ft) deep, in order to minimize footprint of tank and maximize distance from adjacent residences.Inclusion of maintenance bypass gate and channel to permit isolation of tank for any major maintenance/repair activities within the tank (should this ever be required).The detailed design of the Royal Avenue CSO storage tank was completed in the summer of 2005, and the facility was constructed from 2005 to 2007, at cost of approximately 9 million. The CSO storage tank has since significantly reduced the volume and frequency of sewage bypasses and the mass of pollutants discharged to Chedoke Creek and Cootes Paradise.This paper discusses some highlights of the project, including some interesting challenges addressed during the planning, design, construction, and commissioning of the facility, and discusses the actual performance of the facility since it was commissioned.