Significant Industrial User Permit Information

What is a Significant Industrial User?

A Significant Industrial User (SIU) is defined by the US Environmental Protection Agency (EPA) as an industrial user that discharges process wastewater into a publicly owned treatment works (POTW) and that:

  1. Discharges an average of 25,000 gallons per day or more of process wastewater to the POTW (excluding sanitary, noncontact cooling, and boiler blowdown wastewaters); or
  2. Contributes process wastewater which makes up five percent or more of the NPDES permitted flow limit or organic (BOD, TSS, or ammonia) capacity of the POTW treatment plant; or
  3. Is subject to Categorical Pretreatment Standards under 40 CFR Part 403.6 and 40 CFR chapter I, Subchapter N, Parts 405-471; or
  4. Is found by the City, DWR, and/or EPA to have the potential for impact, either singly or in combination with other contributing industrial users, on the wastewater treatment system, the quality of sludge, the system's effluent quality, or compliance with any pretreatment standards or requirements.

Does my facility need a SIU permit?

Documents and links to references are provided for informational purposes to assist you in determining if a SIU Permit is needed.  Please contact the Water Resources Compliance Manager with any questions and for guidance before completing any permit applications.


Amy Varinoski
Industrial Pretreatment Coordinator

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