Water Protection Program

fact sheet

Division of Environmental Quality

Director: Kyra Moore

General Information

In general, all wastewater storage, discharge and land application activities require a Missouri State Operating Permit (MSOP), which establishes applicable Clean Water Act (CWA) National Pollutant Discharge Elimination System (NPDES) requirements and terms and conditions in accordance with the Missouri Clean Water Law and regulations (MCWL).

Certain wastewater discharges have no potential to cause violations of water quality standards or other environmental harm, and in those limited instances, the MCWL allows the department to authorize a “de minimis” permit exemption. 10 CSR 20-6.015(3)(A) establishes the process for an individual or entity to seek a regulatory determination from the department regarding a de minimis source:
“Persons may apply to the department for an exemption as a de minimis source for operations that will not discharge or will have a negligible environmental impact. The department shall make a determination on a case-by-case basis. This determination shall consider the potential for releases to surface water and ground water of contaminants in concentrations exceeding background water quality levels or limitations in the water quality standards rule under 10 CSR 20-7. Testing of total and leachable concentrations of pollutants as compared to background levels in soils and/or waters of the state shall be submitted as determined necessary by the department.”

De minimis” means “pertaining to trivial things” and is a legal term for matters that are too insignificant to merit consideration. Some examples that are possibly eligible for the de minimis exemption are discharges of very small volumes with no reasonable potential; discharges that are intermittent and infrequent, with no reasonable potential; land application of a small volume of non-toxic wastewater; or discharges that contain minimal contaminant load with no reasonable potential. The department must evaluate each de minimis request separately and on its own merits. The department has significant discretion in individual cases whether or not to authorize discharges, and is not required to grant a de minimis exemption under any particular or similar circumstances.

The de minimis permit exemption can only be applied to wastewater, not stormwater, which is regulated pursuant to 10 CSR 20-6.200. (Other types of permit exemptions may apply to stormwater discharges, the most common of which is the no-exposure certification. Please see the department’s No-Exposure Certifications form.) 

Some general permits include express authorization for certain de minimis discharges if certain conditions are met.  To qualify for a de minimis authorization pursuant to a general permit, the wastewater under consideration must be of the same type and source as the general permit applicability. Authorization to discharge cannot be cross-applied to other permits.

Beneficial reuse of wastewater or wastewater treatment sludges pursuant to the Missouri Fertilizer Law (§ 266.291, RSMo.) and with a department-approved fertilizer permit exemption does not require a de minimis determination. 

Requirements to Apply

The department asks dischargers seeking a de minimis permit exemption pursuant to 10 CSR 20-6.015(3)(A) to provide the information in the table below in their submitted request. If additional information is needed, the Department will inform the applicant what is needed after review of the initial submittal. 

Requirements to Apply
Information Required Rationale for Requirement
Name, Mailing Address and Phone Number The department keeps a record of the de minimis determinations and sends a letter to the applicant with the final decision This letter is the final decision of the department, either allowing the discharge as de minimis or denying the request and asking the facility to apply for a MSOP if it does not already have one. Other options are always available, and a permit writer will assist the applicant through any recommendations made. A phone number should be supplied in the department has questions for the applicant.
Email Address The department's primary method of communication is via email. The applicant will need to provide an email address unless this is not a viable option of communication for the applicant
Location of Discharge (UTMs) or Map

The department uses UTM coordinates to determine the nearest receiving waterbody, any issues with the waterbody and general existing water quality. Streams providing permanent dilution will also be assessed and compared to the pollutants potentially discharged in the wastewater. If a map is supplied that identifies the location of the discharge, we can determine the UTMs.

Flow (Volume) The anticipated flow of wastewater must be quantified on a daily or weekly basis. Please provide the maximum expected flow and an average expected flow in gallons per minute, gallons per day or million gallons per day as appropriate.
Frequency Please disclose if the wastewater discharge will flow constantly, or it there are times when the discharge will cease. For example, the operation will only take place in the fall, in October and November, or will only operate for two sequential days a week (the weekend) for approximately four hours each day.
Duration Please disclose the duration of time that the discharge is expected to continue. This is both relevant to the department's de minimis determination and also provides the department with notice if the requested duration is perpetual. When granting a de minimis exemption for an on going activity, the department will typically provide continuous authorization, but reserves the right to establish an expiration date, before which the request should be renewed if still ongoing.
Source of Water Typical sources of wastewater are from potable sources (municipal drinking water) or pumped groundwater. Please disclose the origin of the water that ultimately leaves the facility as wastewater.
Use of Wastewater Please provide a detailed explanation of what procedures are creating the wastewater. Describe the operations and any substances or contaminants added to the wastewater stream, such as soap from employee hand-washing.
Fees There are no fees due to the department associated with requesting a de minimis determination; nor are there fees for discharging pursuant to a de minimis permit exemption.

Additional Information Which May Be Required

Sampling and Analysis of Pollutants in the Wastewater The facility may be required to obtain and have analyzed, at the facility's expense, a representative sample of the discharge for pollutants believed present.
Soil Sampling For higher volume discharges expected to soak into the ground, the department will likely require soil sampling to determine the infiltration rates and existing pollutant concentrations in the soil.
Depth to Groundwater The department may ask the facility to determine the depth to groundwater in the area. This is required in some cases to ensure the wastewater cannot impact the groundwater in situations where there are high infiltration rates due to soil type of geology.

To request a de minimis permit exemption, submit a request to that includes the above required information. For individuals without email, the request can be made through mail at Department of Natural Resources, Water Protection Program, P.O. Box 186, Jefferson City, MO 65102. A water protection program staff member will respond to the request as soon as possible. De minimis permit exemption requests with complete information can typically be processed in a short amount of time. Incomplete information can significantly delay the process. 

Nothing in this document may be used to implement any enforcement action or levy any penalty unless promulgated by rule under chapter 536 or authorized by statute.

For more information