CONCRETE PIPE Sizing a Stormceptor As new developments continue to place an emphasis on reducing non-point source pollution, and protection of our waterways expands to further limit the accumulation of sediment, oil/grit separators will continue to play an important role in project design. Most municipalities or provincial jurisdictions outline the minimum performance criteria for oil/grit separators. In Alberta, AENV specifies a minimum 85% TSS removal target, while the City of Calgary has recently developed an oil/grit separator checklist that outlines more specific criteria. Distinguishing the benefits and drawbacks of one oil/grit separator compared to another can be difficult, and a better understanding of the technologies available is often required to make an informed decision. Each Stormceptor system is sized using PCSWMM for Stormceptor, a continuous simulation model based on US EPA SWMM. The program calculates hydrology from up-to-date local historical rainfall data and specified site parameters. With US EPA SWMM’s precision, every Stormceptor unit is designed to achieve a defined water quality objective. The TSS removal data presented follows US EPA guidelines to reduce the average annual TSS load. Stormceptor’s unit process for TSS removal is settling. The settling model calculates TSS removal by analyzing: • Site parameters • Continuous historical rainfall, including duration, distribution, peaks • Interevent periods • Particle size distribution • Particle settling velocities (Stokes Law, corrected for drag) • TSS load • Detention time of the system What Information Is Needed? At a minimum, a contributing drainage area and estimated site imperviousness is required as a basis for Stormceptor sizing. This differs from the sizing approach of many competitors, where flow rates dictate design. Stormceptor utilizes PCSWMM modeling software, available for download at, to predict unit performance based on site specific factors and particle size distribution. Within the City of Calgary, the requirements of the Oil/Grit Separator Checklist dictate that the manufacturer perform the sizing recommendation, as many default variables within the PCSWMM model must be edited to match the outlined criteria. This checklist is a relatively new requirement in the permit approval process, and is expected to evolve over time. Please refer to this eManual for additional information on oil/grit separator sizings in the City of Calgary. PAGE 26 LAFARGE PIPE eMANUAL