Wastewater pretreatment

Use of the sanitary sewer for non-domestic wastewater requires the approval of the local wastewater treatment authority. Since non-domestic wastewater is often very different from domestic wastewater, pretreatment before sewering is usually needed.

If a facility generates industrial process wastewater that comes from metal-finishing or other industrial processes covered by the EPA categories listed in 40 CFR 413 - 471 and if this wastewater is routed to the sanitary sewer system, the pretreatment form below must be provided to the MPCA directly.

Microsoft Office document icon Industrial Pretreatment Discharge to a Municipal Wastewater Treatment Facility Application (wq-wwprm7-23)

Pretreatment responsibilities of POTWs

All publicly owned treatment works (POTWs) are responsible to control their Industrial Users (IUs) to prevent interference and pass-through.

POTWs that do not have formally delegated pretreatment programs must notify the MPCA of any Significant Industrial User (SIU) within 30 days of identifying the IU as significant.

The notification should be made using the form provided and must give identifying information on the POTW and the SIU, description of SIU, characterization of discharge from the SIU, required local limits imposed on the SIU, justification of these required local limits, and a plan for monitoring the SIU. Other information may also be requested by MPCA.

POTWs must control SIUs individually and must not impose limits on the SIU that the POTW knows may allow violations of the general or specific prohibitions.

The POTW generally should impose required local limits for all SIUs, and is specifically required to do so when interference or pass-through has occurred and may reoccur. A POTW also must evaluate or reevaluate the need for, and value of, local limits if interference or pass-through occurs without a violation of a required local limit by an SIU.

The POTW must monitor SIUs for pollutants of concern, or require the SIU to self monitor. Monitoring must be representative of the SIU discharge.

The POTW must report annually on the pretreatment annual report form provided. We plan to send out forms annually to POTWs that we know have SIUs. The SIUs known to MPCA will be listed on the forms. Copies of the annual report forms are available below. The annual report form comes in four parts:

When we mail the forms to you we will include your known SIUs one the SIU Information Form.

Delegated POTWs have additional and more detailed responsibilities. A delegated POTW Pretreatment program requires substantial program development and a formal delegation process. There are currently nine delegated POTWs in Minnesota.

Responsibility to enforce pretreatment standards

All POTWs are responsible to control IUs to prevent interference and pass-through, and to control SIUs as described above.

Delegated POTWs are also responsible to enforce national categorical pretreatment standards for IUs in their systems. Elsewhere MPCA enforces national categorical pretreatment standards through the use of MPCA issued permits.

POTWs should notify the MPCA if they believe that they have IUs subject to national categorical pretreatment standards.



For assistance with pretreatment standards and requirements, contact:

Jaramie Logelin
MPCA Duluth office
525 Lake Avenue South, Suite 400
Duluth, MN 55802
Phone: 218-302-6640
Fax: 218-723-4727


IU or Industrial User is a non-domestic user of the POTW. An IU is inherently identified with a specific POTW.

Interference occurs when the POTW has a violation of its limits that is caused by an IU discharge that upsets the POTW plant and causes the violation. The pollutant limit violated can be any limited pollutant in the POTWs discharge or biosolids, but interference does require a showing of some kind of negative impact on the operation of the POTW.

National Categorical Pretreatment Standards are federal technology based standards that apply to specific categories of industrial users. They can be found in the Code of Federal Regulations, 40 CFR 405 through 40 CFR 471.

Pass-through occurs when the POTW has a violation of its limits caused by an IU discharge that passes through the POTW plant without being adequately treated. The pollutant limit violated must be a pollutant discharged by the IU, but no showing of any impact on POTW operation is needed.

SIU or Significant Industrial User is first of all an IU that has potential to impact the POTW. Additional criteria that identify an IU as an SIU are: the IU discharges 5% or more of flow or load to the POTW of any pollutant of concern, or the IU discharges 25,000 gallons per day of process wastewater.

Required local limits are limits imposed by a POTW on its IUs or SIUs that are needed to prevent interference or pass-through, as required by pretreatment rules and regulations. In addition to these required local limits, a POTW may have other local limits, that are not required by pretreatment rules and regulations. Required local limits are enforceable by MPCA, pretreatment local limits that are not required by pretreatment rules and regulations are not enforceable by MPCA.