Onsite Wastewater Treatment Systems for Non-Domestic Wastewater

• Definition of Domestic and Non-Domestic Wastewater
• Plan Review and WPDES Permit Programs
• Plan Submittal Procedures
• Additional Guidelines for Specific Types of Non-Domestic Wastewater or Facilities

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.

Plan Review and WPDES Permit Programs

WDNR authority for regulation of non-domestic (and mixed) wastewater disposal consists of two components. The Wisconsin Pollutant Discharge Elimination System (WPDES) permit program authorized by Chapter 283, Wisconsin Statutes, requires a discharge (operating) permit for all facilities that discharge non-domestic or mixed wastewater to surface waters or to the groundwater (via application to either the ground surface or into the subsurface). In addition, Section 281.41, Wisconsin Statutes., requires that WDNR review and approves construction plans for all wastewater treatment systems that treat and discharge non-domestic wastewater.

Some types of non-domestic or mixed wastewater may not be acceptable for disposal through a typical subsurface system or through application to the land surface. In these instances, the non-domestic or mixed wastewater may be collected in a holding tank and hauled to a municipal wastewater treatment facility for disposal.

A proposed wastewater system for mixed (domestic and non-domestic) wastewater with subsurface disposal will be reviewed on a case specific basis to determine if a WDNR WPDES permit will be required. If the mixed wastewater has characteristics similar to domestic wastewater, or the proposal presents minimal water quality concerns, then the proposal may be jointly reviewed by WDNR and Commerce. In this process Commerce is responsible for issuance of the plan approval and WDNR issues a “concurrence” that disposal of non-domestic wastewater to the system is acceptable, and no WDNR WPDES permit will be issued.

If a WPDES permit is determined to be necessary, an application should be made for the General Permit for “Discharging Nondomestic Wastewater to a Subsurface Soil Absorption System”. If the system does not qualify for a General Permit, the Department will issue coverage under an individual (specific) permit. If a WPDES permit is required then the facility discharge cannot commence until the permit is issued. Additional information on the General Permit, and the permit application form are available from the following link:

• General Permit for Discharging Nondomestic Wastewater to a Subsurface Soil Absorption System

Plan Submittal Procedures

The design requirements for subsurface soil absorption systems receiving non-domestic wastewater are provided in s. NR 214.16, Wis. Adm. Code. Applicable site investigation requirements are provided in s. NR 214.20. These requirements are not the same as the Department of Commerce regulations, and, in general, are intended to enable WDNR to require designs that are more protective of groundwater and public health, as may be warranted by non-domestic wastewater that may pose more of a pollution risk than typical domestic wastewater. But in situations where the wastewater is determined to be essentially equivalent to domestic wastewater, in terms of potential effects on water quality and public health, the WDNR may accept both Commerce site and design standards from Chapter Comm 83, Wis. Adm. Code.

The acceptable format and content of plans and specifications are described in s. NR 108.04(2), Wis. Adm. Code. In general, plan drawings should be numbered, cross-referenced as necessary, drawn with a suitable indicated scale, and clearly show connections and relations to elements of existing sewerage systems. The plans and specifications should provide all the necessary information for construction of the project.

An applicant may choose to provide a submittal containing preliminary or conceptual plans instead of final plans and specifications. The Department will then provide comments and advice regarding the general acceptability of a proposal or requirements for a final design.

Plan Submittals should be mailed to:

Thomas J. Mugan, Chief
Wastewater Section
Bureau of Watershed Management
101 S. Webster St., Box 7921
Madison, WI 53707-7921
Ph. (608) 266-7420; FAX (608) 267-2800

The plan submittal package should include:

• 2 Copies of a Transmittal Letter
• 3 Copies of Plans
  (Plan drawings should be legible and of suitable scale. A plan size of 11" by 17"is preferred, but a minimum size of 8 ½" by 11" and maximum size of 24" by 36" are also acceptable)
• 3 Copies of Equipment and Construction Specifications
• 2 Copies Engineering Report
• 2 Copies of Supplemental Information or Correspondence as Applicable

Content of Submittal Package:

Transmittal Letter: It is important that a transmittal letter from the owner or project designer be included with all submittal packages to ensure proper processing. The transmittal letter should clearly identify the type of submittal and include a request for Department plan approval. Any submittal that is a revision or addition to a previous submittal should be identified as such.

If not submitted directly by the system owner, the person submitting should describe their relationship to the owner. Submittals must be from the owner, or a person authorized by the owner, or the submittal must contain a letter from the owner indicating their approval.

If not submitted under the seal (or stamp) and signature of a Professional Engineer registered in Wisconsin, the transmittal letter should provide a description of the credentials and qualifications of the designer. The Department may require submittal by a Professional Engineer in some circumstances, but this is typically not required for systems treating wastewater considered equivalent to domestic wastewater.

It may also be beneficial to briefly describe any unique circumstances or special variance request in the transmittal letter.

The Plans, Specifications, and Engineering Report should include the following items:
(Note - This list is provided as a general outline and guidance. Additional or more specific information may be required dependent on project specific circumstances)

• Contact information for owner and designer, or submitter.


• A project summary description including a general project location map or plan drawing.


• A detailed description of the type of facility, or process, which produces the wastewater and the general nature of the wastewater to be discharged to the subsurface absorption system. If applicable, explain how any detrimental wastes will be segregated from the flow discharging to the absorption system.


• Site and soil information, including the expected vertical separation distance between the infiltrative surface of the absorption system and bedrock and high groundwater. Describe the information source or basis for making this determination. Include any known information on the direction of groundwater movement in the project area.


• Identify the separation distances from buildings, water supply wells, property boundaries, and water supply service pipes. Identify the location of any other existing onsite wastewater systems and paved surfaces or structures.


• Existing and projected future wastewater flow rates and the basis for these rates.


• Design information and calculations demonstrating how any necessary treatment will be provided to ensure compliance with the Wisconsin groundwater standards of ch. NR 140, Wis. Adm. Code. For wastewater that is consider equivalent to domestic quality, conformance with Commerce site and design requirements for POWTS will constitute an adequate demonstration of compliance.


• Plan drawings indicating existing and proposed collection, treatment and monitoring and control equipment. Piping should be labeled to indicate pipe content and flow direction. A schematic flow diagram including treatment units, monitoring and control devices should be included for more complex designs.


• The expected amount of septage generation and how it will be disposed.


• A draft management plan, or description of the management arrangements and practices.


• General description of the environmental features of the proposed site (identify and describe water resources and existing land use and characteristics).

Additional Guidelines for Specific Types of Non-Domestic Wastewater or Facilities

(Industrial Process Wastewater; Vehicle Repair, Maintenance and Storage Facilities; Car Washes; and Animal Kennels)

Non-Domestic Industrial Process Wastewater

Disposal of industrial process wastewater to an onsite wastewater disposal system is dependent on the ability of such a system to appropriately treat the wastewater prior to its introduction into the soil and groundwater. Normally, such systems are acceptable only for biodegradable wastewater of relatively low strength containing no toxic materials.

Non-Domestic Wastewater From Motorized Vehicle Repair or Maintenance Operations

During normal vehicle repair and maintenance activities, vehicle fluids may drip or spill or otherwise enter floor drains and sinks in service areas. These fluids, which can introduce various toxic chemicals into sources of drinking water, may include engine oil, transmission fluid, power steering fluid, brake fluid, hydraulic fluid, antifreeze, chlorinated or non-chlorinated cleaning solvents and degreasers. This would generally apply to businesses that have a floor drain or shop sink in an area where motorized vehicle service or repair work is performed or any area where the liquids associated with those activities is are stored. Such businesses typically include automobile dealerships, service stations, body shops, recreational vehicle sales and service facilities, fleet facilities, marinas, airports, railroad facilities, etc.

Under federal and state laws and regulations, discharges from any new or existing motorized vehicle repair and/or maintenance operation may not be connected to an onsite subsurface wastewater disposal system such as a septic tank/absorption field or drywell.

The owner or operator of an existing onsite wastewater disposal system that receives these types of wastes must disconnect any floor drains or other plumbing from such on-site treatment / subsurface disposal systems.

There are four alternatives an owner/operator may employ to comply with the prohibition on the discharge of wastewater from such facilities:

1. Dry Shop - Remove all floor drains and sinks from areas where service or repair work is performed. Use absorbent materials and a vacuum to collect spills and drips. Place all wastes into containers for off-site disposal following state guidelines and regulations.

It may also be possible to physically separate the sinks and floor drains in the service area where repair or maintenance activities take place from other shop areas. In this instance, the part of the shop where service and repair work is performed may be a dry shop and other parts of the facility (where there is no vehicle service performed) may be acceptable for discharge to an on-site disposal system.

2. Municipal Sanitary Sewer - connect the plumbing system to a municipal sanitary sewer. The local municipal sewer authority should be consulted to determine if they have restrictions on discharges of such wastewater into the sanitary sewers.


3. Holding Tank - connect your plumbing system to an approved wastewater holding tank and dispose of the holding tank contents at wastewater treatment facility. The holding tank could also receive domestic (sanitary) wastewater.

Non-Domestic Wastewater From Motorized Vehicle Storage

Floor drains that receive only snowmelt or rainwater drippage may be connected to a non-domestic or mixed wastewater subsurface disposal system. Water used to wash the exterior of vehicles in the vehicle storage facility may be discharged to a subsurface disposal system. Soap or detergent appropriate for use in vehicle washing should be used in these instances (do not allow waxes or other treatments to enter the disposal system).

If the wastewater discharged through the floor drains contains any material other than precipitation water drippage (e.g., salt from highway maintenance trucks, excessive solids, etc.), the wastewater cannot be discharged into the subsurface system. The Department cautions that if there is any potential for future vehicle maintenance to occur in such a facility, then approval for subsurface disposal cannot be granted. The building owner is responsible to assure that vehicle maintenance wastewater is not discharged to the system, thereby maintaining compliance with the aforementioned vehicle waste disposal regulations.

Non-Domestic Wastewater From Car Washes

The WDNR may approve the use of a subsurface disposal system for non-domestic wastewater from car washes. The disposal system may be approved by the Department on a case-by-case basis, assuring that groundwater quality is protected.

Non-Domestic Wastewater From Kennels, Stables and Other Non-Agricultural Animal Facilities

Wastewater from kennels is frequently mixed with domestic sewage from the facility. It is acceptable to discharge the wastewater from the cleaning and disinfecting of the kennel runs and from animal washing into a mixed wastewater POWTS with subsurface effluent disposal system. Solid feces from animals and any other solid bedding material should be manually collected and disposed separately / appropriately. Filters should be placed in the system to prevent excessive hair from entering the POWTS system.