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Oil and Grease Filter


Oil and grease filters are devices that are designed to remove oil, grease, sediments, trash, and other debris from stormwater by passing them through a filtering device.

Oil and grease filters are most often used at gas stations, industrial sites, parking lots, loading areas, and anywhere hydrocarbons are likely to be present in large quantities. Because they generally operate underground, they are often used in retrofit applications where other management practices are not practical. In high flow situations, the volume of water may exceed the capacity of the filter chamber and stormwater may bypass the device without treatment. As a result, these practices are best used in conjunction with other management practices.


  • Widely applicable
  • Requires minimal land areas
  • Compatible with most storm drain systems
  • Can be used in retrofit applications


  • Limited effectiveness with large storm events
  • Provides little detention time
  • Does not reduce peak flows
  • Requires frequent maintenance


Oil and grease filters are proprietary devices that are available in a wide array of configurations from a variety of vendors and should be custom designed to meet the individual needs of the site. However, at a minimum, they shall be designed to treat the first ½ inch of runoff from the site and should provide sufficient volume as to ensure adequate detention time for the filtration of oil, grease, and sediment.


  • Installation should follow all manufacturers’ specifications
  • Oil and grease filters must be water tight to prevent groundwater pollution
  • Installation should provide access for maintenance activities
  • Filters may be installed off-line to prevent the capacity of the separator from being exceeded during large storm events


All maintenance activities should follow the manufacturers’ recommendations and specifications. However, additional maintenance requirements may be required and are listed below.

  • Oil and grease filters should be inspected regularly to ensure that the practice is functioning properly
  • All accumulated oil, grease, sediment and other debris should be disposed of properly

Method to Determine Practice Efficiency

The manufacturer of the device determines the efficiency of this practice. It is dependent upon several factors, including the volume of water that enters the device and that proper maintenance activities are performed in a timely manner. Due to these factors and because oil and grease filters are rated based practices and are not designed to handle a specific storm event, efficiency is dependent upon external factors that are beyond the control of the designer. As a result, the efficiency for this practice is at the discretion of the LWRD Director.