1. (a) The total ammonia nitrogen (TAN) criteria and the frequency of occurrence are as follows:

   1. (1) The one-hour average concentration of total ammonia nitrogen shall not exceed, more than once every three (3) years on the average, the acute criterion as shown in the following tables:
   2. (2) The monthly average concentration of total ammonia nitrogen shall not exceed those values shown as the chronic criterion in the following table:
   3. (3) The highest four-day average within a 30-day period should not exceed 2.5 times the chronic values shown above.

2. (b)

   1. (1) For permitted discharges, the daily maximum or seven-day average permit limit shall be calculated using the four-day average value described above as an instream value, after mixing and based on a season when fish early life stages are present and a season when fish early life stages are absent.
   2. (2) Temperature values used will be fourteen degrees Celsius (14° C) when fish early life stages are absent and the ecoregion temperature standard for the season when fish early life stages are present.
   3. (3) The pH values will be the ecoregion mean value from least-disturbed stream data.

Codification Notes: This section contains the following footnote: Footnote 18 provides as follows: "Family of fishes that includes trout."