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Water: Water Quality Standards Academy

Deriving the CMC: From FAV to CMC

Aquatic Life Criteria

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Basic Course: Supplemental Topics

After the FAV is calculated, it is divided by two (a safety factor to avoid lethality) to arrive at the recommended acute criterion—that is, the Criterion Maximum Concentration. The CMC is set equal to half of the FAV to represent a low level of effect for the fifth percentile genus, rather than a 50 percent effect.

Key Point. An acute criterion is applied as a limit on the short-term average concentration in the environment. Both the acute and chronic criteria are values that are not to be exceeded more than once in 3 years. In other words, the criteria specify a magnitude, duration, and frequency to be met in order to provide protection of aquatic life.

For informational purposes only–Not official statements of EPA policy.

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