By: Imbrium Systems
Think for a moment about the times you have gazed out the window of an airplane and peered down on a busy city shortly after take-off. If you’re like me, one of the most compelling urban scenes when viewed from above is the incessant stream of motor vehicles flowing down endless miles of highways and streets. Looking like so many thousands of ants on the march, the traffic paints the obvious point that modern life is highly dependent on cars and trucks. When viewed from such a distance, the scene looks innocuous, even artistic. But when scrutinized on the ground, especially through the lens of water quality, it becomes readily apparent that our dependence on motor vehicles and the liquid hydrocarbons that fuel and lubricate them has serious consequences on the health of water bodies and the aquatic life that inhabits them. Spills of oil and fuel are real dangers to the environment, with large spills having devastating impacts.
The term “oil spill” generally conjures up images of a high-profile oil tanker disaster such as the one caused by the Exxon Valdez in Alaskan waters, or the calamitous Gulf of Mexico incident involving the Deepwater Horizon drilling rig. News media showed countless images of dead fish and marine mammals, oil-soaked birds, hazmat-suited workers struggling to clean vast stretches of contaminated beach, and the forlorn faces of fishermen and tourist-dependent merchants whose businesses were hammered by the spills. However, countless smaller spills occur on a daily basis, some occasionally making the news, but the vast majority flying under the radar. Derailment of oil railcars and overturning of oil and fuel tanker trucks generally get brief mention on TV news and in newspaper articles, while the routine spills that occur in automobile accidents go largely unnoticed. But when oil and fuel make their way into a storm drain uncontained, bad news is sure to follow for the downstream creek, lake, river, or bay.
The use of an oil-grit separator (OGS) for treating stormwater runoff can be a very effective measure for preventing hydrocarbon spills from reaching downstream waterways. However, performance for oil capture and retention varies widely among the many marketed OGS devices. Most OGS devices are capable of capturing dry weather spills, but some devices have problems retaining the oil during storm events, especially during higher intensity runoff periods when influent turbulence may re-entrain and washout previously captured oil. For high-traffic sites where oil and fuel spills are more likely to occur (such as fueling stations, convenience stores, fast food restaurants, and high-accident-frequency intersections), it is important to select an OGS device that has been third-party verified for oil capture and retention. The selected device should demonstrate good performance in the “Light Liquid Re-entrainment Simulation Test” specified within the Canadian ETV protocol Procedure for Laboratory Testing of Oil-Grit Separators. Additionally, the manufacturer should provide actual video evidence of how the device captures oil during stormwater influent conditions.