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Why we regulate
Learn what types of wastewater discharges are regulated and how
Plan review
The DNR reviews plans for municipal and industrial wastewater treatment plant construction
Discharge permits
Wastewater discharges to surface or groundwaters
Contact information
For information on Holding Tanks, contact:
Steve Smith, P.E.
Plan Review Engineer
608-266-7580

Holding tanks for non-domestic wastewater

Definition of domestic and 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 tanks

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 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. Admin. Code will be acceptable to DNR. A proposed holding tank receiving mixed wastewater will be jointly reviewed by 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 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, DSPS must obtain verification from 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 < 3,000 gallons per day DSPS (or applicable designated agent) Plan Approval
(No DNR involvment)
Domestic Generates > or = 3,000 gallons per day DSPS (or applicable designated agent) Plan Approval, but DSPS must obtain verification from 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 WDNR Plan Approved
Submit DNR Form No. 3400-185 [PDF]
Mixture of Domestic and Non-Domestic Any Size Submit DNR Form No. 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 Department 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 more than 3,000 gallons per day), should be submitted to the following address. There is no fee for the review.

Stephen Smith, P.E.
Wisconsin DNR
Bureau of Water Quality
101 S. Webster St., Box 7921
Madison, WI 53707-7921
Ph. (608) 266-7580; FAX (608) 267-2800

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 floatation).
  • 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. Admin. 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 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 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.

Last revised: Monday May 15 2017