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AA-EQS Calculation Method
How to calculate whether you comply with an annual average EQS — arithmetic mean of all readings over the calendar year.
Per Part B of Annex I to Directive 2008/105/EC: the annual average EQS is met when the arithmetic mean of concentrations measured at different times during the year at a representative monitoring point within the water body does not exceed the standard. Where monitoring frequency is lower than annual, the available measurements are still averaged. For grouped substances (e.g., PFAS sum of 25), each individual PFAS concentration is multiplied by its Relative Potency Factor (RPF) and then summed before comparison to the 0.0044 μg/L threshold.
Legal reference
Directive 2008/105/EC Annex I Part B, as amended