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What is an SIU?

Relevant definitions are found in N.J.A.C. 7:14A-1.2 within the NJPDES Regulations, including the following:

"Significant indirect user"* or "SIU" means...

  1. Any user in the State including, but not limited to, any significant industrial user* as defined in 40 CFR 403.3(t) but excluding municipal collection systems, who discharges wastewater into a local agency where:

    i. The user is subject to Categorical Pretreatment Standards under 40 CFR 403.6 and 40 CFR Chapter I, Subchapter N;

    ii. The user's average volume of process wastewater** exceeds 25,000 gallons per day;

    iii. The amount of BOD, COD or Suspended Solids in the industrial process wastewater discharge exceeds the mass equivalent of 25,000 gallons per day of the domestic waste of the affected local agency;

    iv. The volume of industrial process wastewater in the discharge exceeds five percent or more of the average daily dry weather flow of the local agency;

    v. The user's discharge of process wastewater contributes, five percent or more of the daily mass loading of any of the pollutants listed in N.J.A.C. 7:14A-4, Appendix A Tables II through V;

    vi. The user is designated as an SIU by the control authority on the basis that the user has a reasonable potential for adversely affecting the local agency's operation;

    vii. The user is designated as an SIU by the control authority on the basis that the user has been in violation of any Federal, State, or local pretreatment standard or requirement, including, but not limited to, significant noncompliance as defined in 40 CFR 403.8(f)(2)(vii); or

    viii. The control authority determines it would be consistent with the intent of the Pretreatment Act or State Act to require a permit*** for the indirect user; and

  2. Any user in areas of the State in which the Department is the control authority where:

    i. The user is determined to be a hazardous waste facility that received a permit in accordance with N.J.A.C. 7:26-12;

    ii. The user's discharge consists of landfill leachate, which is either pure, treated, or diluted; or

    iii. The user's discharge consists of 25,000 gallons per day or more of process wastewater and/or polluted ground water which is pumped from the ground in order to decontaminate an aquifer...

Notes on the definition of SIU

*Historically, the terms "Significant Indirect User" and "Significant Industrial User" have been used interchangeably. EPA defines "Significant Industrial User" in 40 CFR 403.

**For this purpose, process wastewater includes any wastewater generated by a commercial or industrial activity and any watewater which comes in contact with it before it enters the public sanitary or combined sewers or POTW treatment works. It does not include domestic sanitary wastewater or non-contact cooling water reaching public sewers through a separate sewer connection.

***Some delegated POTWs require additional classes of users to obtain permits.



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Last Updated: February 6, 2023