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February 17, 2010

EPA issued new draft ammonia water quality criteria for public comment on December 30, 2009. Since 2004 when EPA announced that it was reevaluating the criteria, NACWA has closely followed EPA’s review of new ammonia toxicity information and highlighted the need for implementation flexibility. The new criteria values depend on the presence of freshwater mussels. Where mussels are present in the receiving water, the new criteria are much more stringent than EPA’s 1999 criteria; where mussels are absent, the acute and chronic criteria change only slightly from the 1999 values. NACWA’s Water Quality Committee is reviewing the draft criteria and will be developing comments by the March 1 deadline. NACWA is asking members to provide any comments on the new criteria by February 17, 2010, so they can be included in the Association’s comments.

Overview of the Draft Ammonia Criteria

The new criteria, which are for freshwater only (the saltwater criteria are not affected), are divided into two sets of acute and chronic values, based on whether freshwater mussels are present. New scientific information on the toxicity of ammonia to freshwater mussels led EPA to initiate its revision of the criteria. The new toxicity data were expected to result in more stringent criteria and NACWA, in addition to raising technical concerns regarding the new mussel data, highlighted the need for implementation flexibility, recommending that EPA only apply the new criteria values in waters with freshwater mussels.

As expected, the new criteria values where mussels are present are much more stringent than the 1999 ammonia criteria (Note: Not all states have adopted the 1999 criteria; the old1984 criteria were more stringent and may be closer to these new values). The draft criteria document is available on EPA’s website. The acute and chronic criteria concentrations are expressed as functions of temperature and pH, such that values differ across sites, and differ over time within a site. As temperature decreases, invertebrates including mussels, become less sensitive to ammonia, but below a particular temperature threshold fish become the most sensitive to ammonia.

Acute Criteria: At pH=8, where freshwater mussels are present, the criterion concentration ranges from 1.90 mg N/L at 30° C to 9.81 mg N/L at 0° C. At pH=8, where freshwater mussels are absent the criterion concentration ranges from 3.29 mg N/L at 30° C to 9.99 mg N/L at 0° C.

Chronic Criteria: At pH=8, where freshwater mussels are present, irrespective of whether fish early life stages are present or absent, the criterion ranges from 0.186 mg N/L at 30° C to 0.817 mg N/L at 0° C. When freshwater mussels are absent, the values range from 1.33 mg N/L at 30° C to 2.32 mg N/L at 0° C at times when fish early life stages are present, and from 1.33 mg N/L at 30° C to 5.87 mg N/L at 0° C at times when fish early life stages are absent.

As illustrated in the table below, the criteria at a pH of 8 and temperature of 25 degrees C change in the following way: the acute criterion (in total ammonia nitrogen) changes from 5.6 mg/L in the 1999 criteria to 2.9 mg/L, and the chronic criterion (in total ammonia nitrogen) changes from 1.2 mg/L to 0.29 mg/L. 

NACWA Satisfied with Improvements in Underlying Toxicity Data

NACWA met July 8, 2009, with officials in EPA’s Office of Science and Technology (OST) to discuss the agency’s work to draft the revised criteria. During the meeting, EPA indicated it was relying less on the data with which NACWA had raised concerns but that other, more reliable data had confirmed the sensitivity of certain freshwater mussels to ammonia levels in water. Since soliciting more input from NACWA in 2007 on the Association’s concerns over the new mussel toxicity data, the Agency has worked to bolster the scientific basis for revising the criteria. In 2008, OST formed a workgroup with EPA Office of Research and Development experts to discuss specific technical data issues related primarily to the larval and juvenile stages of freshwater mussels and developed position statements on how those data would be considered in aquatic life criteria derivation. Those position statements were peer-reviewed and used as the basis for a draft criteria reassessment document. NACWA nominated two experts to participate in the peer review process of the reassessment document last year and is generally satisfied that most of the Association’s previous concerns have been addressed.

Implementation Issues

Throughout the criteria development process, NACWA has focused on the ability of clean water agencies to implement the criteria. In particular, NACWA has pointed out the need to account for site-specific considerations of the species present, the relationship between temperature and mussel toxicity, seasonality, and exposure frequency and duration in criteria implementation.

As noted, EPA has addressed one of NACWA’s top implementation concerns with the bifurcated criteria based on whether freshwater mussels are present. However, no details are provided in the criteria document as to how this determination (whether mussels are present) will be made. EPA notes in the criteria document that based upon the literature, it appears that many states in the continental United States have freshwater mussel fauna in at least some of their waters. Presumably, EPA will now begin work on a criteria implementation document that will explain how it envisions the new criteria should be implemented. NACWA will confirm the timeline for this work with EPA.

Again, NACWA is asking members to provide any comments on the new ammonia criteria by February 17, 2010, so they can be included in the Association’s comments.