Water: Water Quality Standards Academy
Introduction: Two Criteria Specifying Concentration-Related Thresholds
- Listing Impaired Waters and Developing TMDLs
- Monitoring & Assessment
- NPDES Permit Program
- Human Health Ambient Water Quality Criteria
- Aquatic Life Criteria
- EPA's Role
- Two Concentration-Related Criteria
- Steps in Deriving the Criteria
- Prioritizing Chemicals
- Collecting Effects Data
- Assessing Acute Effects Data
- Calculate the GMAVs
- Rank the GMAVs
- Calculate the FAV
- From FAV to CMC
- Factoring in Water Characteristics
- CCC Approach Based on Available Data
- Assessing Chronic Effects Data
- CCC Calculation of the FCV
- FCV to CCC
- Criteria Review Process
- Site-Specific Criteria
Basic Course: Supplemental Topics
Key Point. For a given chemical, aquatic life criteria specify limits for the magnitude of a concentration, the duration (period of time) over which the concentration is averaged, and the frequency of exposure to the concentration.
Acute and chronic criteria for aquatic life addressing magnitude, duration, and frequency are expressed with two terms:
- Criterion Maximum Concentration (CMC). An estimate of the highest concentration of a material in ambient water to which an aquatic community can be exposed briefly without resulting in an unacceptable adverse effect. This is the acute criterion.
- Criterion Continuous Concentration (CCC). An estimate of the highest concentration of a material in ambient water to which an aquatic community can be exposed indefinitely without resulting in an unacceptable adverse effect. This is the chronic criterion.
Key Point. CMCs and CCCs are usually derived for both freshwater and saltwater organisms. Thus, EPA guidelines for a particular chemical can include four criteria.
Nationally recommended criteria are expected to protect aquatic organisms from unacceptable effects assuming the following default exposures:
- Acute = Exposure to a 1-hour average concentration of the chemical does not exceed the criterion more than once every 3 years on average.
- Chronic = Exposure to a 4-day average concentration of the chemical does not exceed the criterion more than once every 3 years on average.
Learn More. As an example, the published freshwater and saltwater aquatic life criteria for diazinon. Proceed to the Learn More Topic. » (Note: This link launches a pop-up window.)