Ammonia Criteria: New EPA Recommended Criteria - PUB2481

On Aug. 22, 2013, the U.S. Environmental Protection Agency finalized new water quality criteria for ammonia based on toxicity to mussels and gill-bearing snails. Missouri’s current ammonia criteria do not take these species into account. 

The adult forms of mussels seen in rivers, lakes and streams are sensitive to pollutants because they are sedentary filter feeders. They vacuum up many pollutants with the food they bring in and cannot escape to new habitats, so they can accumulate these pollutants in their bodies to a level that may ultimately prove fatal. Very young mussels, called glochidia, are exceptionally sensitive to ammonia in water. 

EPA conducted toxicity testing and, using this data, developed ammonia water quality criteria that protect young mussels. These new criteria will apply to any discharge of ammonia that may pose a reasonable potential to violate the standards. The new criteria have implications for nearly all discharging domestic wastewater treatment facilities (cities, subdivisions, mobile home parks, etc.), as well as certain industrial and stormwater dischargers with ammonia in their effluent.

When new water quality criteria are established by EPA, states must update their regulations to reflect the new criteria in order to keep their authorization to issue permits under the National Pollutant Discharge Elimination System. States may develop their own criteria, taking into account specific circumstances unique to the state, but any criteria developed by the state must be as protective as the federal recommended criteria. Ultimately, EPA must approve any water quality criteria developed by the state. The department has initiated stakeholder discussions on this topic and at this time, there is no firm target date for starting the rulemaking to adopt new standards. Part of the consideration during these discussions will include an evaluation of actual species of mussels native to Missouri and their sensitivity to ammonia.

Many treatment facilities in Missouri are currently scheduled to be upgraded to comply with the current water quality criteria. Because these new standards may require a different treatment technology than the one being considered by the permit holder to meet the existing standard, the department strongly recommends permit holders discuss the new standards with their consulting engineers.  Permit holders can also contact the department to discuss upcoming requirements. An evaluation of the capabilities of various treatment technologies is included in this fact sheet along with contact information for the department.

Ammonia toxicity varies by temperature and by pH of the water. Assuming a stable pH value, but taking into account winter and summer temperatures, Missouri includes two seasons of ammonia effluent limitations. Typical ammonia effluent limitations for a facility discharging to a stream with no dilution allowances, under the current water quality standard, are:

• Summer – 3.6 mg/L daily maximum, 1.4 mg/L monthly average      
• Winter – 7.5 mg/L daily maximum, 2.9 mg/L monthly average          

Under the new EPA criteria, where mussels are present or expected to be present, typical effluent limitations for a facility discharging to a stream with no dilution allowance would be:

• Summer – 1.7 mg/L daily maximum, 0.6 mg/L monthly average      
• Winter – 5.6 mg/L daily maximum, 2.1 mg/L monthly average          

Operating permits for facilities in Missouri must be written based on current statutes and regulations.  Therefore permits will be written with the existing effluent limitations until the new standards are adopted.  To aid permit holders in decision-making and alert them to upcoming changes, the department is including advisory language regarding the new federal criteria in permits and permit fact sheets. When setting schedules of compliance for ammonia effluent limitations, the department will take into consideration recently constructed upgrades to meet the current ammonia limitations and any other relevant factors.

For more information about this topic, contact the Missouri Department of Natural Resources, Water Protection Program at 573-751-1300.  Additional guidance is available from the U.S. Environmental Protection Agency at Aquatic Life Criteria - Ammonia.

The attached chart is not a comprehensive list of technologies. It is intended as a guide to assist permit holders in evaluating technologies and assumes facilities are designed, constructed, operated and maintained to effectively remove ammonia. Permit holders should not rely solely on this document when making treatment technology decisions. It is important to consult closely with an experienced professional engineer in selecting a treatment technology.

Wastewater Treatment Technologies

Key

A – Preferred when feasible
B – Has demonstrated capability in meeting ammonia when designed appropriately
C – Shows potential for meeting ammonia limitations.
D – Unlikely to meet ammonia limitations, or data inconclusive