Significant Industrial Users (SIUs)

Significant Industrial Users (SIUs) are sources of industrial wastewater that, by federal definition, require a specific level of regulatory attention. This attention consists of periodic sampling and inspections of the SIU by the pretreatment program, as well as the issuance of specialized discharge permits. These permits stipulate self-monitoring and reporting requirements as they apply to: 

  • Effluent limitations
  • Hazardous materials management
  • Record keeping
  • Reporting schedules
  • Sample collection
  • And more

SIU Criteria

An SIU is defined as an industrial user that meets any one of the following criteria:

  • Is subject to Categorical Pretreatment Standards under 40 CFR 403.6
  • Discharges an average of 25,000 gallons per day or more of process wastewater to the city's sanitary sewer (excluding sanitary, noncontact cooling and boiler blow-down wastewater).
  • Contributes a process waste stream which makes up 5% or more of any design or treatment capacity (i.e. allowable pollutant load) of the wastewater treatment plant receiving the indirect discharge.
  • Is designated as such on the basis that the industrial user has a reasonable potential for adversely affecting the operation of the city's treatment plants or collection system, or for violating any pretreatment standards or requirements.

Additional Information

Each SIU connected to the city's sanitary sewer system is required to obtain a discharge permit. Please check the Forms, Applications and Regulations section of our website for application and reference documents.