Industrial Pretreatment Program Frequently Asked Questions (FAQ's)

1. Do you have any examples of IPP plans that have been developed that could be e-mailed to me?

A good place to start would be EPA's pretreatment webpage, which has links to a lot of guidance material.  See the following link:

Look for the "Local Limits" hyperlink for their local limits guidance document.  You should also see Michigan's Part 23 Rules (R 323.2303 is specific to local limits, see 4(b) especially), which would cover this facility and has minimum requirements for local limit studies.  A link where you can search for the Part 23 Rules is located at:,9429,7-135-3313_3683_3721---,00.html.  This webpage also has links to other IPP information.

There is a model ordinance,, that may be helpful in reviewing the current SUO to see if it meets minimum IPP requirements (contained in R 323.2306 (a)). 

For guidance on writing an Enforcement Response Plan (ERP), click on:  You should find a document entitled, "Guidance for Developing Control Authority Enforcement Response Plans," which includes a model ERP.

2. When a required parameter from an SIU comes back over limit, why are they required to retest and submit the results within 30 days?

The purpose of the resample requirement is for the SIU to demonstrate that they have addressed the cause of the noncompliance and returned to compliance.

3. Can a low second result bring the average of the two down to below limits, and hence, nullify non-compliance?

The additional in compliance sample result may have the added benefit of helping the SIU stay out of significant noncompliance. It could bring the monthly average into compliance, if the SIU has to comply with a monthly average.  Remember, if only one sample is taken in a month it must meet the monthly average, as well as a daily maximum

4. Can a user collect multiple samples at the end of the month in hopes of offsetting a high sample?

No.  Samples taken are reported as being representative of the discharge over the period.  If several samples are taken to represent a month where one result is high, then it would be reasonable to expect that same level of monitoring each and every month.

5. What is the difference between an SIU and a CIU?

An industrial user (IU) will be classified as a significant industrial user (SIU) if it meets any of the following:

(A) Is subject to categorical pretreatment standards under 40 CFR 403.6 and 40 CFR chapter I, subchapter N;

(B) Discharges an average of 25,000 gpd or more of process wastewater to the POTW (excluding sanitary, noncontact cooling, and boiler blowdown wastewater);

(C) Contributes a process wastestream that makes up 5 percent or more of the average dry-weather hydraulic or organic capacity of the POTW treatment plant;

(D) Is designated as such by the POTW on the basis that the IU has a reasonable potential for adversely affecting the POTW's operation or for violating any pretreatment standard or requirement [in accordance with 40 CFR 403.8(f)(6)].

A categorical industrial user (CIU) is an SIU [see (A) above], but an SIU is not always a CIU.  Categorical users have specific limits and requirements that are determined by the Federal government.  States and local governments can develop requirements that are more restrictive, but not less restrictive.

6. What types of prohibitions or discharge controls can be developed at communities served by the stabilization lagoon treatment process?

Municipalities should develop language in their Sewer Use Ordinance which prevents hazardous conditions in their collection sewer, and prevents the introduction of pollutants that would undermine facultative bacteria treatment efficiencies. Prohibition language should follow the condition in the NPDES authorization to prevent the introduction of hazardous wastes into the waste treatment system. Discharge controls should be provided for waste streams that may undermine treatment performance. Common waste streams such as grease and oil can be minimized by adding structural control language in the Ordinance which requires separators at generating facilities. Maximum allowable headworks loading can be identified that restrict conventional pollutants to (allocated) design limits or oil discharges to no greater than 100 micrograms per liter in the treatment lagoon. The requirements in the Ordinance can then be used to monitor discharges from significant industrial users.

7. How can local limits be developed that will achieve water quality standards (WQS) in the wastewater treatment plant (WWTP) discharge?

Ideally, the basis of a local limit is the establishment of individual percent removal efficiencies through monitoring of influent and effluent quality at the WWTP. The allowable headworks loading (AHL) is calculated using the pollutant loading from either NPDES limits or derived from the most restrictive water quality criteria in R323.1057 (Rule 57), divided by the fraction of the pollutant not removed by the WWTP.  However, some pollutants may not be detected in the influent and others may not be sampled and analyzed. When monitoring does not identify WWTP removal efficiencies, the values in Appendix R of EPA's Local Limits Development Guidance, July 2004, may be used for specific treatment processes to identify the fraction of the pollutant not removed by the WWTP. Finally, dilution values with no credit for treatment may be utilized to determine the "removal" efficiency from the actual flows at the WWTP.  Local limits are derived from the most restrictive AHL and take into account measured background loadings of pollutants (domestic, commercial, and non-SIU wastes), loadings from hauled wastes, and a safety factor.  A minimum 10% safety factor should be applied to the allowable headworks loading for toxic pollutants.

There are other media considerations such as biosolids land application standards when developing maximum allowable headworks loading (MAHL) to account for all environmental standards.  The most restrictive of these will the basis for the local limit.  This can be different for each pollutant.

8. Why is a Sewer Use Ordinance important?

"The Sewer Use Ordinance (SUO) forms the foundation for the POTW's oversight of a facility.  Including appropriate language in the SUO in order to establish appropriate legal authority over a myriad of areas that may apply is the key.  Examples of items to consider may include but not be limited to the following: authority for conducting inspections; ability to establish local limits, ability to limit or control the discharge; ensuring adequate access to the facility and monitoring locations; monitoring requirements and reporting requirements; enforcement provisions; fees and surcharge, etc."

9. What should a municipal WWTP with an IPP be requiring from the SIUs using a contract lab with regard to their QA/QC practices and policies?

As a general statement, since the data is required under the authority of an NPDES permit, it must meet the same standards as the municipal WWTP for its NPDES, as described in Part II.B.  These same requirements are also in the Part 23 Rules, R 323.2309 (6)(c) and (d).  That means that they have to use EPA-approved test methods (40 CFR Part 136) and have a QA/QC program that includes equipment calibration.  The same recordkeeping requirements apply.

Further, under the Clean Water Act and regulations, 40 CFR Part 122.41(e) requires permit holders to "operate and maintain all facilities and system of control..." and states that "proper operation and maintenance also includes adequate laboratory controls and appropriate quality assurance procedures."

There is nothing wrong with having an in-house laboratory, but they have to have the same QA/QC requirements as a contract laboratory if the samples are to be used for compliance purposes.

10. Do I have to collect data each year for my IPP annual report, and where is this requirement stated?  My Additional Monitoring Requirements only require four monitoring events in a 5-year period.

Permittees are required to monitor the WWTP influent, effluent, and biosolids for all "pollutants of concern" or POCs (i.e. all parameters for which you have local limits) each year under the IPP requirements in their NPDES permits (subpart o.11.)  The results are reported in their IPP annual reports.

For many IPP Control Authorities, there are two sets of overlapping monitoring requirements in their NPDES permits.  Some permittees have "Additional Monitoring Requirements," usually in Part I.A.2. of their permits, where they are required to monitor the WWTP effluent for various potential pollutants (whole effluent toxicity, hardness, metals, VOCs, acid-extractable compounds, and base-neutral compounds, etc.) in four months specified in the permit.  The results are reported in their NPDES application.

The requirements are different but overlap; therefore, if a permittee conducts sampling for its Additional Monitoring Requirements, the permittee has likely addressed its IPP-required effluent sampling, although influent and biosolids monitoring for POCs would still be needed.  Also, there is one year with no Additional Monitoring Requirements permit cycle, usually the year that the application is due.  For that year, to meet the IPP monitoring requirements, permittees need to conduct influent, effluent, and biosolids monitoring for all POCs.

11. What can we do to protect the Publicly Owned Treatment Works (POTW)?

Even if a community is not required by the state to develop and implement an IPP, they may have industrial discharges that could negatively impact processes at the publicly-owned treatment works (POTW) that could cause them to violate an NPDES limit.  State and federal pretreatment regulations require the community to protect the POTW against pollutants that may interfere with the treatment processes or pass-through to Waters of the State.*  Communities are encouraged to have the following basic protections in its local ordinance:

  • A general prohibition against the discharge of pollutants that may cause pass-through or interference.  Pass-through may occur when a pollutant is discharged in quantities in excess of what the POTW can normally treat or if the POTW's treatment capabilities have become impaired by the discharge of pollutants that have caused interference.  Interference may be caused by either excessive quantities of compatible pollutants or by the discharge of a toxic pollutant that destroys or impairs the biological organisms that are an integral part of the treatment process.
  • Prohibitions against specific wastewater characteristics that can contribute to pass-through, interference, or cause problems with the collection system.  At a minimum, the following wastewater characteristics should be prohibited:  corrosive discharges that have a pH below 5; discharges that may result in the presence of toxic vapors or fumes; or discharges that may create a potential for fire or explosions.  The POTW may also want to prohibit excessive discharges of petroleum oil and other mineral-based oils; viscous substances that may obstruct the system; heat-containing discharges that could destroy biological organisms at the POTW; and trucked wastes, except as permitted by the POTW.
  • Local limits established to control excessive discharges of compatible pollutants that could overload the POTW and cause an upset resulting in NPDES or groundwater discharge permit violations.  These limits should be based on the POTW's design capacity and take into account unregulated sources of compatible pollutants such as residential and commercial sources.  The remaining capacity may be used to develop limits for local industry.
  • Legal authority to halt a discharge, and levy fines for violations and the ability to seek reimbursement for all costs associated with a violation, including the costs of monitoring, investigations, treatment, repairs and other remedial activities, enforcement activities, legal fees, damages to the POTW or the environment, and fines incurred by the POTW. 

In addition to these sewer use ordinance protections, communities will also need the following:

  • Procedures by which local industries are identified and their discharges characterized. 
  • Time for community staff to become familiar with nondomestic users and enforce local requirements (i.e. sewer use ordinance).  Local leaders should be briefed about any problems with nondomestic users and their effect on the POTW. 

If an industrial user is identified, please be aware that generally there is a change in discharge language and reporting obligations in permits that would need to be addressed.

* Technically the Federal IPP regulations only address impacts to waters of the US, and the state rules cover waters of the state which includes waters of the US and other surface water, as well as groundwater.

12. Selecting an IPP consultant

A municipality can develop or modify its own pretreatment program using existing guidance, but often find that task is daunting and time consuming.  A consultant may be hired to assist with development, but please understand that the municipality is ultimately responsible for the submission.

EGLE is unable to provide recommendations of specific consultants, but offers the following tips and advice.

When selecting a consultant to assist you with development and/or implementation of your IPP you should consider the following:

  • Who do you have in-house?  Some municipalities have staff that are qualified and have the time to develop an IPP, but most hire a consultant to do the work for them.
  • Is the consultant qualified?  In other words, is the consultant familiar with state and federal IPP regulations (including categorical standards if applicable) and does the consultant have experience in the IPP area you need help with (local limits, permit writing, procedures, ordinance development, etc.)?
  • Check references:  Did the consultant provide approvable documents for submittal?  Was work done on time?  Was the municipality satisfied with the quality of the service provided?  A highly qualified consultant should have IPP experience working with industrial challenges similar to what your municipality is facing. 
  • How many IPPs have they set up or helped modify?  For what specific communities have they worked?  Were the communities similar to yours?  Talk to other communities with IPPs as to which consultants they have worked with and their experience with that firm.
  • Will the consultant adapt his/her standard service/product to address the specific circumstances and needs of my municipality?  A cookie-cutter approach to IPP is not recommended.
  • Do you need a contractor to administer your IPP?  Be sure to ask the same kinds of questions about their experience implementing an IPP (e.g. writing permits, conducting inspections, enforcement, etc.) and their ability to respond on a timely basis to routine as well as emergency situations.  Remember that ultimately, your municipality is responsible for IPP implementation.