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Industrial Pretreatment Permits

What is Pretreatment?

Beneath the streets of every city and many smaller communities, a system of sewers and pumps conveys wastewater away from homes, factories, offices, and stores. This disposed water, which may contain a variety of domestic, commercial, and industrial wastes, flows through the sewers to a wastewater treatment plant. There, pollutants are removed and the cleansed water is discharged into an adjacent water body, such as a river, bay, lake or ocean. The residues of the treatment process (biosolids) are either used productively as a soil conditioner or disposed of as a solid waste.

Industrial plants are only one of many sources of wastewater discharged into municipal sewers. But the wastewater discharged by industry is often contaminated by a variety of toxic or otherwise harmful substances not common to other sources - the by-products of industrial processes such as cyanide from electroplating shops and lead from the manufacturing of batteries. These wastes can pose serious hazards. Because sewage collection and treatment systems have not been designed to treat them, industrial wastes can damage the sewers and interfere with the operation of treatment plants, or pass through the systems untreated, resulting in contamination of nearby water bodies and increase the cost and environmental risks of sludge treatment and disposal.

The undesirable effects resulting from the discharge of industrial wastewater into municipal sewers can be prevented. Industrial plants, using proven pollution control techniques, can remove pollutants from their wastewaters before discharging them into the municipal sewage treatment system. This practice is known as "pretreatment".

National Pretreatment Standards

The federal government has developed national regulations or "standards" that restrict industrial pollutants discharged into sewage systems. Individual POTWs must impose limitations (via Sewer Use Ordinance) that may be stricter than the national standards, but cannot allow less stringent levels of control. The national pretreatment standards consist of two sets of rules, prohibited discharge standards and categorical pretreatment standards.

Prohibited Discharge Standards

The National Prohibited Discharge Standards forbid certain types of discharges by any sewage system user (40 CFR 403). The standards apply to all industrial/commercial system users whether or not they are covered by categorical pretreatment standards.

The general prohibitions forbid pollutants to be discharged into the sewage system if they pass through the POTW untreated and cause the POTW to violate its NPDES permit, or if they interfere with POTW operations (including sludge disposal).

Categorical Pretreatment Standards

Categorical Pretreatment Standards are pollution control regulations for specific industries. The standards regulate the level of pollutants in the wastes discharged into the sewage system from an industrial process. Each categorical standard covers one industry category and assigns specific end-of-process limits for the process wastestreams covered by that specific category.

Additional Standards

In addition to applicable pretreatment standards, an industrial user shall comply with an effluent limitation more stringent than the applicable pretreatment standard that is necessary to prevent interference in the POTW receiving the discharge or violation of a state or federal water quality standard that is applicable to the state waters ultimately receiving the discharge from the industrial user after discharge from the POTW.

Pretreatment Cities

There are currently 47 Pretreatment Cities [PDF] in Indiana that run federally delegated local pretreatment programs. If you are discharging process wastewater to one of these city POTWs, you must apply for a discharge permit through that local program. Each program does its own permitting, inspecting, sampling and enforcement. The POTW shall control through permits or another control mechanism, the contribution to the POTW from each Significant Industrial User [40 CFR 403.8 (f)(iii)]. U.S. EPA and IDEM oversee each program by performing occasional audits.

All Other Industries in Indiana

All categorical dischargers not located in a federally delegated pretreatment city must apply to IDEM for an Industrial Wastewater Pretreatment (IWP) permit and must meet the specific requirements in an issued permit. Any Significant Industrial User must also apply for a discharge permit although the industry may not fall under a specific category. A Significant Industrial User is one that:

  • discharges an average of 25,000 gallons per day or more of process wastewater to the POTW (excluding sanitary, noncontact cooling and boiler blowdown wastewater);
  • contributes a process wastestream which makes up 5% or more of the average dry weather hydraulic or organic capacity of the POTW treatment plant;
  • or has a reasonable potential for adversely affecting the POTW's operation or violating a Pretreatment Standard [40 CFR 403.3(t)].

To apply for an Industrial Wastewater Pretreatment permit, if you are unsure if your industry needs to be permitted, or for questions concerning this program, contact IDEM.


  • Application for Industrial Wastewater Pretreatment (IWP) Permit (available on the IDEM Agency Forms page)
    • All IWP permit applicants are required to submit the Application for Industrial Wastewater Pretreatment (IWP) Permit (50271) and Identification of Potentially Affected Parties (49456) State Forms.
    • If the industry requires an IWP permit from IDEM and a pretreatment system will be used at the facility, a Construction Permit will be required for most new or modified treatment systems. For additional information contact the Office of Water Quality Facility Construction and Engineering Section.
  • Notification of Transfer of Industrial Wastewater Pretreatment (IWP) Permit [PDF]

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