Who Regulates Domestic Wastewater in Missouri?

Water Protection Program fact sheet
08/2019
Division of Environmental Quality Director: Ed Galbraith
PUB1296

The purpose of this publication is to help explain the basics of who has jurisdictional responsibility for domestic wastewater in Missouri. Different state and local agencies have responsibility for regulating domestic wastewater systesms, from a simple septic system1 serving a single family residence to a centralized wastewater collection and treatment system serving an entire community.

10 CSR 20-2.010(26) defines domestic wastewater as “wastewater (i.e., human sewage) originating primarily from the sanitary conveniences of residences, commercial buildings, factories, and institutions, including any water which may have infiltrated the sewers. Domestic wastewater excludes stormwater, animal waste, process waste, and other similar waste.”

For the purpose of this publication, “wastewater” or “domestic wastewater” shall be defined the same as “sewage” or “domestic sewage.”

Missouri Department of Health and Senior Services or Local On-site Wastewater Authority
In Missouri, the Missouri Department of Health and Senior Services or local on-site wastewater authority (commonly the county health department) have responsibility for domestic wastewater treatment systems that include:

  1. An individual on-site wastewater treatment (septic) system serving a single family residence.
  2. An individual lagoon (earthen basin) serving no more than a single family residence.
  3. An individual holding tank serving a single family residence.

The Department of Health and Senior Services or local on-site wastewater authority also have responsibility for on-site wastewater treatment systems with subsurface soil treatment or holding tanks for maximum daily flows of domestic wastewater of less than or equal to 3,000 gallons per day including:

  1. Multiple family cluster or centralized systems under the same common promotional plan and/or within the same operating location2 .
  2. Commercial facilities such as offices, motels/hotels, RV parks, theaters, restaurants3 , etc.

Copies of the Department of Health and Senior Services on-site wastewater treatment laws and regulations, as well as other resources, are available online at health.mo.gov.

Missouri Department of Natural Resources
The Missouri Department of Natural Resources is responsible for approving the method of domestic wastewater treatment in new residential housing developments, such as subdivisions, recreational developments and multiple family housing units, when they meet specific criteria. The department also approves the method of wastewater treatment for the expansion of existing subdivisions, recreational developments and multiple family housing units4 .

The department is also responsible for:

  1. All domestic wastewater treatment systems with direct point discharge.
  2. All domestic wastewater lagoons (earthen basins) other than an individual lagoon as described above.
  3. Any facility that has a maximum daily flow of domestic wastewater greater than 3,000 gallons per day.
  4. All industrial process waste. Industrial process waste is anything not defined as domestic wastewater such as waste from a brewery, a winery, a dog kennel, etc. Industrial process waste also includes stormwater.

Related publications and other resources describing permitting, approvals and exemptions are available online at dnr.mo.gov/pubs/

Calculating Maximum Daily Flows vs. Water Use Data to Determine Jurisdiction

Calculating Maximum Daily Flows of Domestic Wastewater
Table 2A-Quantities of Domestic Sewage Flows, 19 CSR 20-3.060 Minimum Construction Standards for On-Site Sewage Disposal is used to calculate maximum daily design flows when determining jurisdictional responsibility for all new on-site wastewater treatment systems.

Example 15 :
A new restaurant proposes to have 50 seats with 950 square feet of dining area and use an on-site wastewater treatment system with subsurface soil treatment as the method of wastewater treatment. Table 2A-Quatities of Domestic Sewage Flows gives a design flow for domestic wastewater generated from a restaurant at 40 gpd per seat or 40 gpd per 15 sq. ft. of dining area, whichever is greater.

Calculations:
50 seats x 40 gpd per seat = 2,000 gpd of domestic wastewater.

Or

950 sq. ft. of dining area ÷ 15 sq. ft. = 63.33
63.33 x 40 gpd = 2,533 gpd of wastewater.

Calculating the design flows based on number of seats or dining area, as described in Table 2A-Quatities of Domestic Sewage Flows, demonstrates the maximum daily design flows of domestic wastewater in this example are less than or equal to 3,000 gpd; therefore, this project falls under the jurisdiction of the Department of Health and Senior Services or the local on-site wastewater authority.

Example 2:
A new recreational vehicle park proposes 20 camping spaces with full water and sewer hookups along with a laundromat that will have two washing machines. Because of the topography within the development, the facility is proposing two separate on-site wastewater treatment (cluster) systems each with subsurface soil treatment. One system will serve 10 camping spaces, while the other system will serve 10 camping spaces and the laundromat. All of the camping spaces will be offered for lease under the same common promotional plan with both on-site wastewater treatment systems being located within the same operating location.

Table 2A-Quatities of Domestic Sewage Flows gives a design flow for domestic wastewater generated from a Travel Trailer/Recreational Vehicle Park (with water and sewer hookups) at 120 gpd per space and a design flow for a laundromat at 580 gpd per machine.

Calculations:
20 camping sites x 120 gpd per camping site = 2,400 gpd of domestic wastewater
2 washing machines x 580 gpd per machine = 1,160 gpd of domestic wastewater
Total domestic wastewater = 3,560 gpd

It should be noted that, although the facility proposes two cluster systems with subsurface soil treatment and each system can be designed to treat less than or equal to 3,000 gpd of domestic wastewater, given that all of the camping spaces are being offered for lease under the same common promotional plan and both wastewater treatment systems are within the same operating location the domestic, wastewater flows are calculated together to determine jurisdiction regardless of the number of cluster systems. Therefore, because the total maximum daily design flows of domestic wastewater are greater than 3,000 gpd, they are the department’s jurisdiction.

Determining Jurisdiction Utilizing Water-Use Data
Jurisdiction for existing domestic wastewater treatment systems can be determined using accurate and verifiable daily water-use data. The water-use data should be sufficient to reflect an acceptable period of time with respect to the nature of the facility’s use. Examples of an acceptable period of time: a full school year for a grade school – late August through early May; the reasonably accepted season for an RV park – April through mid-September; a full year for a mobile home park, etc. It is recommended that water-use records are compared with Table 2A-Quatities of Domestic Sewage Flows when justifying their use.

Although using averages based on monthly billing statements is generally not recommended, it is understood that daily water-use records are not always available. If daily water-use records are not available and monthly billing records are averaged, the period during which the facility is in use should be used to calculate flows. For example, if a public school is open Monday through Friday with minimum activities on any given Saturday, the calculations should be based on the number of week days the school is in session during the school year, minus holidays.

The Department of Health and Senior Services or the local on-site wastewater authority can accept any water-use records when determining jurisdictional responsibility and can request additional documentation as needed.

When undertaking a project that may need a jurisdiction determination prior to permitting and construction, it is important to contact the Department of Health and Senior Services or the local on-site wastewater authority early in the planning process to avoid any unforeseen issues.

1For the purpose of this publication the term “septic” will not be used except as a component of an individual on-site wastewater treatment systems, like septic tank, anaerobic treatment, etc.
2Definitions for common promotion plan can be found in 10 CSR 20-2.010(15) Definitions and 10 CSR 20-6.015(1)(B) 9 No-Discharge Permits respectfully.
3Restaurant waste is commonly referred to as high strength domestic wastewater.
4Once a development receives written approval from the Missouri Department for Natural Resources for the method of wastewater treatment they are directed to contact the Department of Health and Senior Services', On-site Wastewater Treatment Program or the local on-site wastewater authority for the permitting of the specific on-site wastewater treatment system.
5Examples given are for discussion of jurisdictional responsibility only, any other interpretation is out of the scope of this publication.