The Rossdale Water Treatment Plant (WTP) in Edmonton, Alberta is a legacy facility originally constructed in 1947 and currently supplies approximately 35% of the city’s potable water demand. Faced with accelerated projected population growth and the need for reliable long-term supply, EPCOR required a strategy to increase firm net potable capacity from 300 to 375 ML/d, a 25% increase, without greenfield expansion. The plant’s location within the North Saskatchewan River valley, combined with legacy-designated structures and an operational facility serving over 400,000 people, presented significant constraints on the scope and execution of potential upgrades. A comprehensive capacity assessment was completed through five sequential technical memoranda (TM1–TM5), each targeting a major process system: raw water intake and low-lift pumping (TM1), flocculation and clarification (TM2), filtration and UV disinfection (TM3), and reservoir conveyance and high-lift pumping (TM4). Hydraulic modelling confirmed that all four systems were capacity-constrained, with firm capacities ranging from 238 to 273 ML/d against a target gross demand of 416 ML/d (accounting for 10% in-plant process losses). Fifteen upgrade alternatives were developed spanning from targeted, internal structural modifications to full redundancy construction. TM5 integrated these findings through a structured multi-criteria decision analysis (MCDA) framework incorporating weighted criteria derived from stakeholder workshops. Five evaluation criteria were applied to quantitative risk adjustment, sensitivity analysis, and quadrant analysis, testing the robustness of rankings: operations and maintenance, constructability, capital cost, performance, and facilities siting. The analysis demonstrated that targeted upgrades to existing infrastructure consistently outperformed high-cost green field replacement or process technology upgrades. The recommended program comprises four coordinated investments: replacement of low-lift pumps and twinning influent piping to resolve the most critical bottleneck; expansion of tube settler coverage and effluent launders to increase clarification capacity; high-volume filter underdrain and media upgrades to increase filtration loading rates pending pilot confirmation; and replacement of a hydraulic restriction in the East Flume chamber to eliminate the reservoir conveyance bottleneck. The integrated strategy achieves the targeted 375 ML/d firm capacity at an estimated AACE Class 5 capital cost of $130.6M (2025 CAD). A phased implementation plan aligns capital expenditure with capacity trigger points through 2036, allowing investment to be deferred or accelerated in response to actual demand growth. This presentation presents the decision framework, key technical findings, and lessons learned from each process assessment. The methodology offers a transferable approach for utilities across Western Canada facing similar challenges: how to extract meaningful capacity gains from aging treatment infrastructure through disciplined, risk-informed investment planning rather than defaulting to costly greenfield construction.
