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FOG is of two types: (1) of petroleum or mineral origin (nonpolar FOG); (2) of animal or vegetable origin (polar FOG).

Nonpolar FOG

The limit: the King County limit for nonpolar FOG is 100 milligrams per liter of discharged wastewater. Nonpolar FOG can harm the biological phase of sewage treatment where microbes are used to break down wastes.

Oil/water separators: Industries use oil and water separators to pretreat wastewater containing nonpolar FOG. Plans for separators must be approved by King County Industrial Waste (KCIW). However, KCIW has approved requests from certain local sewer utilities to allow them to approve oil/water separators. Information on plan submittal and installation guidelines is available in the Oil/Water Separator Fact Sheet prepared by KCIW.

Free-Floating Polar FOG

This kind of FOG can block sewer lines. King County rules require

  • Dischargers to minimize free-floating polar FOG
  • That dischargers not add agents to emulsify free-floating polar FOG

Wastewater should not be discharged if someone can see polar FOG floating on the surface or adhering to the sides of storage containers. There should be less than 0.25 inches of free-floating polar FOG in a sample, as described in the Sampling Procedure. (See help box.)

FOG control plan

King County may require companies discharging polar FOG to complete a FOG control plan. The goal of the FOG control plan is to implement reasonable and technically feasible controls of free-floating polar FOG. The basic components of the FOG control plan should include:

  1. A written policy articulating management and corporate support for the plan and a commitment to implement planned activities and achieve established goals.
  2. A description of the facility type and a summary of the products made and/or service provided.
  3. Quantities of FOG brought into the facility as raw product, amounts contained in products, and quantities discharged to the sewer.
  4. Schematics of process areas illustrating drains and discharge points connected to the sewer.
  5. A description of current reduction, recycling, and treatment activities.
  6. Identification of a full range of potentially feasible reduction opportunities.
  7. A description of the reduction or control opportunities selected for implementation, process(es) affected, and estimated reductions to be achieved.
  8. Specific performance goals and implementation schedule.


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