Back to glossary
BDL (Below Detection Limit)
When a laboratory measurement is too low to be precisely quantified — regulatory guidance requires substituting half the limit of detection for compliance calculations.
Below Detection Limit (BDL) or Below Quantification Limit (BQL). When a substance is present below the analytical instrument's detection threshold, the measured value cannot be reported as zero. Standard regulatory practice under EU guidance is to substitute ½ × LOD (half the limit of detection) for compliance calculations. This approach is the default in AquaCompliance, but site administrators can configure an alternative substitution method (zero or full LOD) in site settings.
Legal reference
EU Water Framework Directive technical guidance, CEN/ISO analytical standards