BACKGROUND

In 1999 the Environmental Protection Agency (EPA) updated the Ambient Water Quality Criteria for Ammonia. Colorado voted to adopt similar standards in June 2005. The San Juan/Gunnison basin will be updated in June of 2006. All other basins will be updated at an emergency rulemaking session in March of 2007.

With the new standards, Colorado has changed the method by which discharge limits are calculated. The Colorado Ammonia Model is being replaced with the AMMTOX model.

The AMMTOX model is more sophisticated than its predecessor, taking into account the presence of Salmonids and early life stages (ELS) of various aquatic species as well as using information from up and downstream dischargers to model cumulative effects on a given reach of stream. One of the largest changes, however, is that AMMTOX will set standards based upon total ammonia concentrations rather than limiting itself to the more toxic, un-ionized ammonia.

WHAT IT ALL MEANS

The new model will have significant impacts on some utilities. Utilities who discharge to warm water streams can expect their ammonia limits to be ratcheted down, although cold water dischargers may see their limits relaxed.

For utilities who are already nitrifying, the new standards will probably mean little. Most of these utilities already discharge ammonia below their current limits, and many of those who do not, have the capacity to.

significant process changes, such as switching from a lagoon system to a mechanical treatment plant. The changes in the standard will affect utilities when their permit is renewed, at which time a compliance schedule can be negotiated to meet the new standards.

WHAT YOU CAN DO

Begin planning for the change immediately. Data collection may save a number of utilities. Without adequate data, default values for stream temperature, pH, the presence of ELS and Salmonids, and other parameters are used to determine effluent limits. These default values are designed to be conservative and may be overkill for a specific reach of stream. Richard P. Arber Associates can assist in data collection, and can run the model to determine what the new discharge limits will be.

If a utility anticipates that it will not be able to meet the new standard, they have several options. The first is to begin design and construction of a new plant or upgrade. Facilities that need more than 5 years to upgrade can apply to the Water Quality Control Division for a temporary modification for their stream segment. Another option is to request a site-specific ammonia standard during the March 2007 hearing; however, this requires extensive data collection on the presence of aquatic life, pH, temperature, and ammonia in the stream.