Ammonia nitrogen (NH3-N) is a common pollutant in domestic wastewater. It can be toxic to aquatic organisms even at low levels. Missouri’s water quality standards contain ammonia water quality criteria to protect Missouri’s aquatic life from ammonia toxicity. The Missouri Department of Natural Resources has recommended updates to the ammonia water quality criteria to ensure adequate protection of freshwater mussels and snails, which are critical to maintaining healthy freshwater ecosystems.

In some instances, small communities may lack the resources needed to install wastewater treatment technologies that reduce ammonia to low concentrations. In these instances, an ammonia water quality standards variance can provide an affordable pathway to compliance and incremental water quality improvements over time.

How does an ammonia variance work?

When compliance with water quality-based effluent limits is not feasible due to cost, an ammonia water quality standards variance provides a discharger with temporarily relaxed ammonia effluent limits. The department establishes ammonia limits based on the facility’s highest attainable condition, or HAC. The facility must then develop and implement a Pollution Minimization Plan that identifies actions to achieve the HAC during the variance period.

How long is the variance period?

The applicant should propose the ammonia variance period. The proposed period should reflect the time necessary to achieve the proposed highest attainable condition, as reflected by your Pollutant Minimization Plan. The variance and proposed highest attainable condition will be revaluated at least every five years.

For example, a facility may propose a 10-year variance term to meet their highest attainable condition. In that time, the department may evaluate them once or twice, depending on where they are in their permit cycle. At the end of the 10-year term the facility may no longer need a variance, or they could choose to reapply.  

Does your facility qualify for a variance?

Facilities currently eligible for discharger-specific variances from 2013 ammonia criteria are listed in the document linked below. Additional facilities may qualify. Facilities with insufficient information, or are listed as impact unclear, are encouraged to reach out to the department's Water Quality Standards Unit for more assistance.

Start the Process

To start the process for a variance, complete the form below. Submit the completed form and any attachments to the department according to the instructions in the form. An incomplete form may result in the form being returned.

EPA Resources

Do you need assistance?

The department will hold several open house sessions to provide assistance with variance applications. During these sessions, representatives of any domestic facility are welcome to walk in for one-on-one in-person assistance with their variance application. Online and call-in options are also available during these times. Simply join the online session and we will set you up with your own one-on-one meeting. Click on the link below for more information.

Outside of these dates, we would be happy to set up in-person or online meetings with facilities. Please contact the department's Water Quality Standards Unit to set up a time that works for you!

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Contact Information

Water Quality Standards Unit

Water Protection Program
Water Pollution Control Branch
P.O. Box 176
Jefferson City, MO 65102-0176
United States

Main
573-751-5723
Toll-free
800-361-4827
wqs@dnr.mo.gov