Industrial Pretreatment Program

Helping businesses capture pollutants at the source to protect people, wastewater infrastructure, and the environment.

Working with Business

The Wastewater Department is charged with making sure that harmful substances aren't discharged into our sewer system. Our Industrial Pretreatment Program is set up to talk to businesses and identify things that can be a problem.

The City has a Pretreatment Ordinance that allows us to condition or deny businesses from discharging some substances into the sanitary sewer—substances that create safety hazards, damage structures, interfere with treatment plant operations and processes, or that can't be removed and pass through into biosolids or with the effluent into the Spokane River.

The Pretreatment Program's first step is to survey businesses to determine whether they have the potential to discharge anything other than domestic wastewater. The information gathered by the survey is used to determine what the business has to do and informs us about what is in the wastewater system. We can also help businesses to avoid any accidental spills. The information is also reported annually to the Washington State Department of Ecology.

Business owners should understand the regulations that apply to their wastewater discharge, and comply with applicable regulations and standards. Let's take a look at what's required.

Domestic Dischargers

Businesses that discharge wastewater only from restrooms or hand sinks are considered Domestic Dischargers. They are responsible for ensuring that no Prohibited Discharges are introduced to the sewer system from their facility. This level of normal domestic use is not regulated.

Minor Industrial Users

Businesses that discharge wastewater containing nondomestic pollutants must abide by Prohibited Discharge Standards and follow industry-specific Best Management Practices (BMPs) to keep their wastewater as clean as reasonably possible.

BMPs can prevent the release of pollutants that can damage the sewers or the treatment plant, cause the plant to release pollutants that violate its Permit, or endanger wastewater personnel.

For example, restaurants that do not properly maintain their grease interceptors can cause grease clogs in the sewer resulting in sewer backups into streets or basements; auto repair shops that do not properly dispose of used solvents can cause an explosion hazard in the sewer or at the plant headworks; and car wash operations that use acidic cleaners and do not properly neutralize their wastewater prior to discharge can cause acid damage to the sewers.

Significant Industrial Users

The City of Spokane requires all Significant Industrial Users to obtain a Wastewater Discharge Permit.

A Significant Industrial User is:

  1. A user subject to categorical pretreatment standards as defined by the US Environmental Protection Agency. These processes by their nature generate pollutants that, if unregulated, can disrupt treatment processes, pass through the plant unchanged and pollute the river, or create hazardous conditions in the sewer or treatment plant.
  2. A user that:
    1. Discharges an average of 25,000 gallons per day or more of process wastewater to the sewer (excluding sanitary, noncontact cooling and boiler blow down wastewater); or
    2. Contributes a process waste stream which makes up 5 percent or more of the average dry weather hydraulic or organic capacity of our treatment plant. “Organic capacity” means the capacity of the treatment plant to treat wastewater as opposed to the “hydraulic capacity” or capability to accept and handle fluids; or
    3. Is designated as such by the plant's superintendent because it has a reasonable potential to cause an adverse effect on the plant's operation, adverse impact on the City's ability to comply with its operating permit, cause the plant to violate any pretreatment standard or requirement, or because of other regulatory control needs. (Source: 40 CFR §403.3(v))

Pretreatment program staff scientists inspect such permitted businesses, sample their wastewater discharges, and work with them to protect the environment, the wastewater treatment plant, and personnel.

Direct Dischargers

Any industry that discharges wastewater directly to a river or other surface water (Direct Dischargers) must apply for and comply with a Discharge Permit from the Washington State Department of Ecology.

Fats, Oils & Grease

Fats, Oils, and Grease (FOG) are a particular problem for our wastewater system. Oily, greasy waste, often from restaurants and commercial kitchens, that gets into a sink or drain that goes into the sewer can build up and cause sewer blockages. In fact, FOG is the number one cause of such blockages, as it solidifies on the walls of sewer pipe.

Simple ways of reducing the amount of FOG going down your drains include:

  • Display FOG information in the workplace—see our printable FOG poster (PDF 520 KB).
  • Collect used oil and grease for recycling or disposal in solid waste.
  • Scrape dishes into a trash bin, not the sink.
  • Prevent spills. When spills happen, clean up with disposable materials (paper towels, kitty litter, spill kit), don't wash the oils down the drain.
  • Clean and cover outdoor recycling areas.
  • Hire a waste-hauling or recycling service to regularly pump out your interceptor.
  • Keep records of cleaning and service to track how often grease traps need to be maintained.
  • Don't connect dishwashers to the grease system.
  • Train staff to keep FOG out of pipes.

What about grease traps?

Every food preparation establishment is required to have a grease trap or interceptor. There are three types: passive grease traps that are usually located under the sink and must be cleaned out by hand; automatic grease traps that continually skim grease off and deposit it in a removable reservoir; and grease interceptors that are large volume devices, usually located outside, under the ground and must be pumped out by a grease hauler.

These devices are very important but they can't do the job alone:

  • Traps vary in efficiency, some remove only 85 percent of FOG.
  • Passive grease traps should be cleaned out weekly.
  • Automatic grease traps should have their collection reservoirs emptied daily.
  • Grease interceptors need to be pumped out regularly, on a schedule determined by how quickly they fill. When over 25% of the interceptor is full of grease the interceptor loses effectiveness; at 50% the interceptor lets most of the FOG flow through into the sewer.
  • Keep records in a log (PDF 16 KB) of when traps and interceptors are cleaned out and how full they are each time. This way you can know how often they need to be maintained.
  • The less FOG that goes down the drain, the less frequently the traps need to be cleaned out.

Dental Wastewater

Dental Wastewater Discharges

Dental practices that discharge waste material into the City of Spokane sanitary sewer system must be in compliance with the City's discharge limits and Environmental Protection Agency (EPA) regulations.

On July 14, 2017, the EPA promulgated new regulations for dental offices in the Code of Federal Regulations, 40 CFR Part 441. Dentists must:

  • Install an amalgam separator(s) that meets the requirements in the Approved Amalgam Separator document, and maintain it according to the manufacturer's recommendations
  • Follow the required policies in the Dental Office Best Management Practices document
  • Submit a One-time Compliance Report to the City of Spokane Industrial Pretreatment Program:
    • By 10/12/2020 for existing offices
    • Within 90 days if the office is new or transferred to a new owner after July 14, 2017

Who needs to submit a compliance report?

All dental practices, both exempt and non-exempt, must submit a One-Time Compliance Report.

Disposal of mercury amalgam

Information about the safe disposal of materials containing mercury may be found at:

Update your practice's contact information

Is yours a new dental office - or have you recently relocated your office within the City of Spokane Wastewater Treatment Facility service area? Please contact us at 509.625.4600 so we can determine whether or not you must submit a One-time Compliance Report.

The Industrial Pretreatment Program staff know that this new reporting process is complex. Please contact us at 509.625.4600 if you have questions and we will be happy to assist you.

SMC Update

No updates to report at this time.

Documents for Public Comment

There are currently no documents available for Public Comment.

Documents for Businesses

Best Management Practices

Wastewater Surveys


Contact Information


Industrial Pretreatment Program
Riverside Park Water Reclamation Facility
4401 N. Aubrey L. White Parkway
Spokane, WA 99205-3939

Office Hours:
Monday – Friday 7:30 a.m. to 4 p.m.

Report Spills to Sewer Immediately
509.625.4600 and 509.625.7900

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