NPDES Pretreatment Program in Iowa

Industrial treatment facility.

Beneath the streets of every city, a system of sewers and pumps conveys wastewater away from homes and businesses. This wastewater can contain domestic, commercial, and industrial wastes. The sewer and pump systems that convey wastewater are known as municipal sanitary sewers, and wastewater flows through sewers to a wastewater treatment plant. There, pollutants are removed and the cleansed water is discharged into a nearby waterbody. The residues of the wastewater treatment process (once called sludges, now known as biosolids) are either used productively as a soil conditioner or disposed of as a solid waste.

Industrial facilities are one of the sources of wastewater discharged to municipal sanitary sewers. Industrial wastewater often contains toxic substances and it can pose serious hazards.

Because municipal sewage treatment systems are not designed to treat industrial wastes, these wastes can damage sewers and interfere with treatment plants. Industrial wastes can increase the costs and risks of biosolids treatment and disposal, and can pass through municipal systems untreated, resulting in contamination of waterbodies.

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

Below is a list of potential problems that can arise from the disposal of industrial wastes.

  • Toxic industrial pollutants may pass through the treatment plant, polluting a receiving water body and threatening aquatic life and human health.
  • Industrial wastes may interfere with treatment plant operation, rendering treatment of other wastes less effective.
  • Industrial wastes containing high levels of toxic metal or organic compounds can contaminate biosolids, making disposal options more expensive and limited.
  • Industrial wastewater can corrode the pipes and equipment in the collection system and at the treatment plant.
  • Highly volatile wastes can explode, causing considerable damage.
  • Some wastes may interact to produce toxic gases, posing health hazards to sewer and treatment plant workers.

For questions regarding pretreatment, please contact Ben Hucka at 515/725-8406 or

National Pretreatment Standards

National pretreatment standards are uniform national requirements that restrict the level of pollutants in the wastewater from industries. These national standards consist of two sets of rules: "categorical pretreatment standards" and "prohibited discharge standards".

Categorical pretreatment standards: specific requirements for different industries, organized by type of industry. For example, the categorical standard for the iron and steel industry limits pollutants in wastewater discharged by any firm in that industry.

Prohibited discharge standards: prohibit any discharge to municipal sewer systems of certain types of wastes from all sources. For example, discharge of wastewater with pH lower than 5.0 is forbidden, since it may corrode the sewer system.

Local Pretreatment Programs - Overview

Local pretreatment programs are established by municipalities based on the National Pretreatment Program. The framework for the National Pretreatment Program is contained in EPA's General Pretreatment Regulations. States that have NPDES authority, like Iowa, are required to develop state pretreatment programs for EPA approval. States can be granted pretreatment authority by demonstrating that their program meets all federal requirements. Iowa was delegated pretreatment authority by EPA in 1982.

In a state with pretreatment delegation, large publicly owned treatment works (POTWs) with a design flow more than 5 MGD and smaller POTWs with significant industrial discharges must establish local pretreatment programs. These local programs may impose more stringent discharge requirements (local limits) to prevent disruption of the sewage treatment system or biosolids, or to prevent adverse environmental impacts.  Local pretreatment programs must be approved by the delegated state.

In Iowa, the following cities have local pretreatment programs: Ames, Boone, Burlington, Cedar Falls, Cedar Rapids, Clinton, Council Bluffs, Davenport, Des Moines, Dubuque, Fort Dodge, Fort Madison, Iowa City, Keokuk, Marshalltown, Mason City, Muscatine, Ottumwa, Sioux City, and Waterloo.

Local pretreatment coordinators contact information: Iowa Pretreatment Coordinators

If a POTW does not have an approved local pretreatment program, the national pretreatment standards are enforced by the state. Industries in cities that have not established a local pretreatment program often need to establish a Treatment Agreement with the city. For more information regarding treatment agreements between cities and industries, see the Treatment Agreements page.

Local Pretreatment Program Elements

To gain approval for a local program, a POTW must prepare several documents for state review. These documents must meet the requirements for local pretreatment programs in 40 CFR 403 and must contain the following elements:

  • Building Blocks: Local pretreatment programs require legal authority, an industrial discharger database, professional staff, and funding.
  • Effluent Limits: Effluent limitations that enforce federal standards and protect local interests must be established for the industrial users.
  • Implementation Activities: POTWs must undertake activities to implement their effluent limits, including notification, permit administration, inspection, monitoring, and enforcement.
  • Information Handling and Public Access: Local pretreatment programs must allow the public to access information and comment on the program.

For more information on each of the local pretreatment program elements, see the discussion below.

Local Pretreatment Program Building Blocks

A local pretreatment program must have four building blocks to succeed. These building blocks are:

Legal Authority - A POTW must have the legal authority to implement a local pretreatment program based on state law and local ordinances. State law authorizes municipalities to regulate industrial users of municipal sewage systems, and a municipality can establish a local ordinance for its program. The legal authority granted by state and local law must authorize the POTW to:

  • limit the pollution levels in wastewater discharges from industrial users;
  • enforce national pretreatment standards;
  • implement local limits;
  • issue industrial pretreatment permits;
  • inspect and monitor permitted industries; and
  • take enforcement action against violators.

Industrial User Information Base - A POTW must develop a comprehensive database that records pollutant levels in wastewater samples to allow for the automatic detection of violations. Industrial user databases can be used to determine the source of problems, calculate local limits, and plan for expansions.

Staffing - A local pretreatment program requires adequate staff for monitoring, inspections, laboratory analysis, technical and legal assistance, and program administration. The required personnel depend upon the size of the sewage district, the number of industrial users, and POTW policies.

Funding - Funding for a local pretreatment program may be included in a POTW's budget or recovered by industrial user fees or charges. Fees can be based on the POTW services used by an industry, the flow from an industry, or the pollutants discharged by an industry.

Local Pretreatment Program Effluent Limits

A POTW must develop effluent limits for each industrial facility covered by the local pretreatment program. The effluent limits may consist of federal standards, local limits, or both. Industrial facilities must comply with federal prohibited discharge standards and applicable federal categorical standards. The POTW may establish local limits more stringent than, or in addition to, the federal standards for some or all of its industrial users.

To identify the need for and the nature of local limits, a POTW must determine if any public health or environmental problems will exist even with full enforcement of the federal pretreatment standards. This determination will address:

  • Interference - Will the pollutant load remaining after implementation of federal standards interfere with the sewage treatment system? Analyze a POTW's susceptibility to problems and its history of breakdowns.
  • Biosolids Contamination - Will any industrial pollutants contaminate the POTW's biosolids? Determine the amount of contaminants from industrial waste in the POTW's biosolids and analyze the residuals for each biosolids disposal method.
  • NPDES Permit Violations - Will the pass-through of any pollutants cause an NPDES permit violation? Determine if pollutants from industrial waste will pass through the POTW in quantities sufficient to cause a permit violation.
  • Surface Water Impacts - Will any of the pollutants that pass through the treatment plant adversely affect the receiving waterbody? Determine if pollutant pass through could substantially impact the receiving waterbody.
  • Worker Safety - Will any of the pollutants create a safety hazard for POTW employees? Review the design and operation of the wastewater collection and treatment systems and the chemical composition of the POTW's inflow to determine if the industrial pollutants will create a worker hazard.

If the answer to any of the above questions is "yes," a POTW must establish local limits. Local limits are established as follows:

  • determine the maximum concentration of each pollutant in the incoming industrial wastewater that will not cause the problems listed above, then
  • calculate the maximum pollutant loading from each industry that can be allowed without exceeding the maximum concentration of pollutants arriving at the treatment plant.

The calculations must consider the level of pollutants already present, the chemical decomposition of pollutants, and the need to accommodate future industrial growth.

Local Pretreatment Program Implementation Activities

To implement the effluent limits established in their local pretreatment programs, POTWs must undertake the following activities:

Notification - Industrial facilities in cities with local pretreatment programs must be notified of the applicable effluent limits. The effluent limits are incorporated in a pretreatment permit issued by the POTW to the industrial facility.

Permit Administration - POTWs must ensure that industries comply with their pretreatment permits. To ensure compliance, a POTW will specify effluent limitations and identify sampling locations for each industrial facility. Industries will be required by the POTW to submit monitoring reports at least twice per year.

Inspections & Monitoring Visits - POTWs must inspect and informally visit permitted industrial facilities. Discharge volume, discharge toxicity, violations, complaints, or suspected hazardous materials can be used to determine the timing of inspections and visits. The POTW must conduct both regular and unannounced visits to collect samples.

Enforcement - If an industrial facility violates its pretreatment permit, the POTW will take enforcement action after verifying the violation. Once a violation is confirmed, the violating facility will be required to comply within a specified period. If compliance deadlines are not met, the POTW may initiate civil and/or criminal proceedings.

Local Pretreatment Program Information Handling and Public Access

A local pretreatment program is a public service to protect the public health and environmental quality of a community. Public support depends on public's ability to participate in and access information on the local pretreatment program. The POTW must hold meetings and work with industries and the community to define the objectives and benefits of the local program. When local limits are developed or revised, all interested parties must be notified and invited to comment.

In general, all information collected by a POTW on industrial discharges is available to the public and to government agencies. However, if an industry demonstrates that trade secrets would be divulged, records can be labeled as confidential and withheld from the public. Nevertheless, effluent data is always available to the public. In addition, POTWs must inform the public whenever a significant violation occurs, and must annually publish the names of industries that significantly violated the pretreatment standards during the previous year.