By: Imbrium Systems
Manufacturers of oil-grit separators (OGS) routinely make claims that their device will capture oil. While that sounds good on the surface, there are more facets to consider in determining whether an OGS will actually perform effectively in protecting downstream water bodies from oil contamination throughout the typical range of storm events. This includes differentiating “oil capture” from “oil retention”.
For example, let’s say an auto accident occurs during a light drizzle, and several liters of leaked oil get washed into a nearby curbside catch basin. Due to the very low intensity rainfall, and relatively low flow rate of stormwater entering the catch basin, it is possible that a good portion of the oil will be “captured” in the device temporarily. However, as a rain event (during this storm or a subsequent storm) increases in intensity, the higher flow rate and turbulent energy entering the catch basin will typically re-entrain the oil and flush it downstream. This is an example of good “oil capture” but poor “oil retention”, with the effect being inadequate protection of downstream water bodies from a major pollutant of concern.
Some OGS devices are deficient in their design, such that they do not adequately capture and retain oil during the typical range of storm intensities. Since oil is easily mobilized from a site during the early, low-intensity portion of the storm hydrograph, it is important for an OGS to demonstrate good capture of oil from low flow rate influent. And since peak storm intensities can vary widely, it is critical that the OGS demonstrate good oil retention during high flow rate influent. For these reasons, the Canadian ETV testing protocol titled “Procedure for Laboratory Testing of Oil-Grit Separators” contains provisions for assessing both oil capture and oil retention during its prescribed Light Liquid Re-entrainment Simulation test.
Stormceptor® is well-known for its effectiveness in capturing and retaining hydrocarbons, and Imbrium’s latest addition to its OGS family, Stormceptor® EFO, demonstrates best-in-class ISO 14034 ETV verified performance, with greater than 99% cumulative oil retention. This qualifies Stormceptor® EFO as the preferred treatment solution on oil hotspot sites such as roadways, parking lots, fueling stations, fast food restaurants, and convenience stores.