Water Quality and Treatment at City Snow Disposal Sites
Original article by Curtis Faucher and Kentson Yan The City of Edmonton uses five snow storage sites to manage snow that is collected from roadways and parking lots. Melt-water from the storage sites is treated using detention ponds to reduce environmental impacts. As part of Edmonton’s “The Way We Green” initiative, Transportation Services engaged the Edmonton Waste Management Centre of Excellence (EWMCE) to investigate potential improvements to the treatment efficiency in detention ponds. Curtis Faucher, a Research Engineer Intern at the EWMCE and Master of Science Student at the University of Alberta, is spearheading this collaborative project between EWMCE, Transportation Services, and the University of Alberta. The project will solve practitioner-based problems, and develop highly qualified personnel in an interdisciplinary field. The Melt-water Quality and Treatment The snow melting process is dynamic, particularly in large snow piles at snow storage sites. Salts (as measured by electrical conductivity), water, and suspended solids are released from the piles over three general phase as shown in the figure below. Figures: Variance in the quality (top graph) and quantity (bottom graph) of meltwater entering treatment ponds at Edmonton snow storage site. Phase 1: High Electrical Conductivity (Top graph) When snow piles begin to melt, the melt-water has a high electrical conductivity because of a high level of ions concentrated by freeze-thaw exclusion. Freeze-thaw exclusion occurs as ice crystals melt then reform causing impurities to move to the edges of the crystals. These impurities, such as ions, accumulate in the passing melt water as the water begins to migrate down through the snow pile. The majority of the ions are anti-icing salts that are collected with the snow. Phase 2: High Melt Run-Off Flows (Bottom graph) Higher temperatures and longer sun exposure provide more energy which increases melting rates and results in high run-off flows from the snow piles. Phase 3: High Suspended Solids (Top graph) As snow piles collapse and begin to fragment, solids such as sand and clay particles previously held in the snow are released. These solids may then be flushed out, carrying with them metals and organics that are adsorbed onto their surface. Practices for the design and operation of a typical snow storage site use detention ponds to control high water flows. These ponds also operate as a primary treatment unit to remove settleable solids. To further reduce environmental impacts, EWMCE and its partners continually investigate more robust practices for reducing electrical conductivity (e.g. ions) and suspends solids (e.g. metals and organics) from snow sites. Moving Forward In the next phase of this project, EWMCE and its partners will: (1) provide a detailed characterization of snow melt water quantity and quality (e.g. composition and settling parameters); and (2) identify any limitations of the current technologies used to meet the treatment (environmental quality) objectives. Results from this study will provide a foundation for a larger research project aimed at improving the water quality treatment of snow melt water sites in Western Canada. The knowledge gathered furthers best management practices for engineered snow disposal sites that can be used by other municipalities, especially those with similar cold climate conditions. Link to original article: Snow Melt Water Quality and Treatment at Engineered Snow Disposal Sites Further Reading: Oberts, G.L., Marsalek, J., and Viklander, M. 2000. Review of Water Impacts of Winter Operation of Urban Drainage. Water Quality Research Journal of Canada, 35 (4): 781-808. Wheaton, S.R. and Rice, W.J. 2003. Siting, design, and operational control for snow disposal sites. Water Science and Technology, 48(9): 81-92.