Water: Water Quality Standards Academy

# Deriving the CCC: Calculation of the FCV

##### Course Navigation

- 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
- Summary
- Quiz

A three-step calculation process results in a Final Chronic Value (FCV), which is then used to derive the Criterion Continuous Concentration. These FCV calculation steps are described briefly below.

*Step 1. Calculate Acute-Chronic Ratios (ACRs).*

ACRs are calculated for each set of parallel acute and chronic tests by dividing the acute value by the chronic value. That is, ACR = AV ÷ CV. At least three species with a specified taxonomic diversity must be addressed by studies with parallel testing to calculate a valid final ratio.

*Step 2. Develop a Final Acute-Chronic Ratio (FACR).*

The geometric mean of the ACRs is then determined. That is, the ACRs are averaged to arrive at the FACR.

*Step 3. Calculate the Final Chronic Value (FCV).*

The FCV is then calculated from the Final Acute Value (FAV)—which was calculated in deriving the CMC—by dividing it by the FACR. That is, FCV = FAV ÷ FACR.

Thus, if the side-by-side tests show that, on average, chronic effects occur at one-half the concentration of acute effects, the chronic criterion will be one-half of the FAV, which is the same as the acute criterion.

A chronic criterion is applied as a limit on the 4-day 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.Key Point.