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Holding Tanks for Non-Domestic Wastewater

Wastewaters originating from plumbing fixtures and appliances such as sanitary (toilets), bath, laundry, dish washing, garbage disposal and cleaning wastewaters are defined as domestic wastewater. Wastewater from restaurants is also generally considered as domestic wastewater. This wastewater is typically discharged from dwellings and from commercial establishments and is commonly called sewage. Non-domestic wastewater may include wastewater from any other source including industries, food processing operations, vehicle service facilities, vehicle storage facilities, kennels, car washes and milkhouses. Mixed wastewater refers to a combination of domestic and non-domestic wastewater.

Holding tank regulations

Holding tanks of any size that are connected to a building structure by a plumbing system, and receive only domestic wastewater, are subject to Department of Safety and Professional Services (DSPS) regulations. A holding tank of any size receiving 100% non-domestic wastewater will be regulated by the DNR under ch. NR 213, Wis. Adm. Code. For most applications, however, a tank designed in conformance with SPS 384.25 and other applicable sections of SPS 383, Wis. Adm. Code, will be acceptable to the DNR. A proposed holding tank receiving mixed wastewater will be jointly reviewed by the DNR and DSPS. This procedure will include a DNR "concurrence" determination on whether the wastes can be land applied (via either surface or subsurface application) and whether a Wisconsin Pollutant Discharge Elimination System (WPDES) permit is needed, or if the wastes should be treated at a publicly owned wastewater treatment plant.

The basic design and disposal requirements for the contents of holding tanks receiving non-domestic wastewater are addressed in DNR Form 3400-185.

Although the DSPS has regulatory responsibility for holding tanks that receive only domestic wastewater, there is some DNR involvement with this review process. Any proposed domestic wastewater holding tank with a design capacity greater than or equal to 3,000 gallons per day must obtain an agreement or commitment that the wastes will be accepted at a publicly owned wastewater treatment plant in accordance with s. NR 113.07(1)(e), Wis. Adm. Code. Prior to issuing plan approvals, the DSPS must obtain verification from the DNR that such an agreement or commitment has been obtained.

Summary of Holding Tank Plan Review Requirements

Wastewater type Holding tank design Requirements
Domestic Generates less than 3,000 gallons per day DSPS (or applicable designated agent) Plan Approval
(No DNR involvement)
Domestic Generates 3,000 or more gallons per day DSPS (or applicable designated agent) Plan Approval, but DSPS must obtain verification from the DNR that there is an agreement of commitment that tank contents will be disposed of at a publicly owned wastewater treatment plant.
Non-Domestic Any size DNR Plan Approved
Submit DNR Form 3400-185 [PDF]
Mixture of Domestic and Non-Domestic Any size Submit DNR Form 3400-185 [PDF] to DNR for "concurrence" review/determination and obtain DSPS Plan Approval

For systems receiving 100% non-domestic wastewater, the owner or installer may proceed with construction immediately upon submittal of the Form 3400-185 if an approval can be granted as specified in Part IV of the form. But if Form 3400-185 specifies the inclusion of plans with the submittal (per Part III of the form), then construction cannot start until a DNR approval letter is issued. For systems receiving mixed wastewater, construction cannot commence until the DSPS plan approval is obtained in addition to Form 3400-185 for issuance of DNR concurrence.

Form 3400-185, or waste treatment agreements (for domestic wastewater holding tanks generating 3,000 or more gallons per day), should be submitted to the address below. There is no fee for the review.

Jason Knutson
Wisconsin DNR
Bureau of Water Quality - WY/3
PO Box 7921
Madison WI 53707-7921

Note: Tanks or other storage structures that are not connected to a building plumbing system, and are used for septage storage, are subject to DNR requirements for septage storage facilities under s. NR 113.12, Wis. Adm. Code.

Additional information and guidelines for holding tanks

  • Holding tanks receiving non-domestic wastewater are subject to the DNR site and design requirements of ss. NR 213.08 and NR 213.15, Wis. Adm. Code. In general, a tank designed in conformance with SPS 384.25 and other applicable sections of SPS 383, will be deemed acceptable for DNR purposes. All such tanks must have an inspection manhole, be vented, have a high-level alarm and have watertight joints. If bedrock or high groundwater are present, appropriate design provisions should be included for tank bedding and anchoring (to prevent tank flotation).
  • Holding tanks must be located in compliance with separation distances from buildings, property lines, water supply wells and service lines, and navigable waters. See Form 3400-185 or Table 383.43-1 in SPS A-383.42(2)(f), Wis. Adm. Code, for specific requirements. The setback distances in NR 213.08, Wis. Adm. Code, may apply for proposed holding tanks serving industrial facilities.
  • The size of the holding tank is the responsibility of the owner/designer and should be based on the amount of water discharged and the desired frequency of hauling.
  • The disposal of the wastewater is the most important part of the approval process. The department strongly encourages the hauling of holding tank wastewater to a municipal wastewater treatment facility. If this is not possible, disposal through hauling and land application or subsurface drainfield discharge may be granted by the DNR, but additional restrictions, including the need for additional treatment, and possibly a WPDES permit, may apply. Certain wastewaters, such as wastewater from a vehicle servicing facility, are not permitted to be disposed by land application or subsurface drainfield. If wastewater is hauled to a municipal treatment facility, no further permit, reporting or approvals from the DNR are needed, but approval for disposal to the municipality must be obtained.
  • The owner should consider use of systems or materials to limit the amount of oil, grease or other similar material from reaching the holding tank. Oil absorbent material in catch basins or other grease interceptor units may be employed.
  • If there is oil on the surface of the holding tank or solids accumulated in the bottom of the tank, they should be removed from the tank before the wastewater is pumped.
  • Hazardous wastes should not be discharged to a holding tank.



Q: Does the waste from a holding tank need to be disposed of at a publicly owned treatment works (POTW)?

A: No, holding tank waste can be disposed of at any other facility that is covered by a WPDES permit as long as the waste being disposed of complies with the WPDES permit requirements for that facility. Waste from a holding tank may also be disposed of onto approved agricultural land if done in accordance with a WPDES permit’s terms and conditions.

Q: Do I need a licensed hauler if I plan to spread the wastewater from the holding tank on my own land?

A: A licensed hauler is only required if the wastewater is being taken offsite to be treated. However, in order to land apply wastewater from a holding tank onto your own land, a WPDES permit is required.

Q: Does rainwater or snowmelt from a garage or any other area(s) where one or more vehicles are being stored need to be conveyed to a holding tank?

A: The wastewater would only be required to be conveyed to a holding tank if maintenance on or washing of vehicles and/or equipment is also occurring in the area.

Q: What should be listed for the designer on the “Small Capacity Non-Domestic Wastewater Holding Tank Plan Approval Application” if a pre-fabricated tank is being used?

A: The designer section of the application should be filled out with the information of the licensed plumber that will be installing the holding tank.

Q: If the holding tank will only be receiving wastewater seasonally or non-routinely, does the design flow rate need to be filled out on the application form, and if so, what should be put there?

A: Yes, this still needs to be filled out on the application. It should be filled out with whatever flow was used to determine the size of the holding tank that will be used.