USEPA’s New Criteria for Ammonia in Freshwater Streams
In August of 2013 US EPA published its national recommended ambient water quality criteria for the protection of aquatic life from the toxic effects of ammonia. See, 78 FR 163, August 22, 2013. The 2013 criteria is the latest in a long history of US EPA ammonia water quality criteria recommendations that began as far back as 1976. Prior to the August 2013 recommendation, the most recent recommendation regarding ammonia criteria was US EPA’s 2009 “Draft” criteria that provided for a standard of 19 mg/L Acute (1-hour average), and 0.91 mg/L Chronic (30-day rolling average). The 2013 final recommendation is for a 17 mg/L Acute, and 1.9 mg/L Chronic criteria. Importantly, the published criteria are based on ambient stream conditions at a pH of 7 and temperature of 20 oC.
The impact of US EPA’s new criteria will not be felt by NPDES permit holders until the state agencies incorporate the standard into each individual state’s water quality standards. Once each state incorporates the new criteria, it will be implemented as part of newly issued and reissued NPDES permits held by wastewater dischargers that discharge to streams for which effluent limits are required to meet water quality standards. Most typically, ammonia water quality based effluent limits (WQBELs) will be a factor on streams where mixing zones are unavailable. Those streams are most often lower-flow streams, but sometimes include larger streams where restrictions on mixing zones might otherwise exist (such as where there are other, close proximity, down-stream point sources).
For dischargers with a WQBEL for ammonia in their permits, the ability to meet the limit may be dependent on the demonstrated pH and temperature of the receiving stream. Both a higher pH and a higher stream temperature will result in a more restrictive permit effluent limit. Cold water fisheries such as West Virginia’s designated “trout streams” use a lower ambient stream temperature for purposes of calculating the ammonia WQBEL which should result in a less restrictive effluent limit than a limit calculated using warm water fishery ambient temperatures. That said, designation as a cold water fishery like a trout stream carries may result in other significantly more restrictive effluent limit “baggage” that should be carefully evaluated.
US EPA’s final recommendation regarding the ammonia criteria will likely result in a further downward “ratcheting” of effluent limits for many dischargers on streams where mixing zones are not available as the criteria becomes part of the state’s water quality standards. US EPA has recognized that the more restrictive WQBEL will be an additional burden on dischargers and has recommended that states consider adoption of “flexibilities” in application of the new criteria. Flexibilities mentioned by US EPA include recalculation procedures for site-specific criteria derivation, variances, dilution allowances, revisions to designated uses, and compliance schedules.
As a practical matter, permit holders should begin taking steps now to prepare for implementation of the new criteria. Interested parties should work with local policy makers and agencies to ensure that the flexibilities suggested by US EPA are adopted by the states. Investigating the potential cost for additional treatment, and the socioeconomic impact of new permit limits will be helpful in working with policy makers and politicians. Finally, permit holders should begin collecting appropriate data to argue for a less restrictive ammonia WQBEL.