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Disinfection depletion and HPC increases are other examples of water quality impacts associated with nitrification that are addressed under provisions of the Safe Drinking Water Act. The loss of disinfectant residual does not necessarily pose a direct public health threat (many systems throughout the world are operated without use of a disinfectant residual). However, disinfectant decay can contribute to microbiological problems such growth of organisms within the bulk water or accumulated sediments. The Surface Water Treatment Rule establishes maximum contaminant level goals (MCLGs) for viruses, Legionella, HPC, and Giardia lamblia. It also includes treatment technique requirements for filtered and unfiltered systems that are specifically designed to protect against the adverse health effects of exposure to these microbial pathogens. The Surface Water Treatment Rule requires that a "detectable" disinfectant residual (or HPC measurements not exceeding 500/mL) be maintained in at least 95% of samples collected throughout the distribution system on a monthly basis. A system that fails to comply with this requirement for any two consecutive months is in violation of the treatment technique requirement. Public water systems that disinfect must monitor for the presence of a disinfectant residual (or HPC levels) at the same frequency and locations as total coliform measurements taken pursuant to the total coliform regulation. Nitrite/Nitrate Formation Under the Safe Drinking Water Act (SDWA), primary MCLS have been established for nitrite -N, nitrate -N, and the sum of nitrite -N plus nitrate -N. The MCLs are 1 mg/L for nitrite -N, 10 mg/L for nitrate -N, and 10 mg/L for nitrite + nitrate (as N). The current nitrite and nitrate standards are measured at the point of entry to the distribution system so any subsequent elevated nitrite/nitrate levels resulting from nitrification within the distribution system are not identified by compliance monitoring. Nitrite and nitrate are produced during nitrification through ammonia utilization by nitrifying bacteria. According to equations (1) and (2), for every mole of ammonia -N produced, a 1 -mole equivalent of nitrite -N is produced. Subsequently, for every mole of nitrite -N produced, a 1 - mole equivalent of nitrate -N is produced. Ammonia can also be released from chloramines through a series of complex reactions. Reactions 2 through 6 in Table 2 describe five mechanisms of ammonia release presented by Woolschlager et al. (2001). According to Valentine et al (1998), the overall net stoichiometries can be used to examine the relationship between chloramine decay and ammonia production. Review of the equations presented thus far indicates that the greatest fraction of ammonia species is produced from Reaction 3 in Table 2. Prepared by AWWA with assistance from Economic and Engineering Services, Inc. 5