Data qualifiers are used in lab reports to indicate a problem or irregularity with the analytical result. The most common qualifiers are shown here; most labs also will use footnotes to explain the qualifiers they have used.
J: The number is an estimated concentration because something in the sample interfered with the analysis.
U: The contaminant was not detected at a concentration greater than the detection limit.
UJ: The contaminant was not detected, but the detection limit is estimated because of interference from something in the sample.
R: The data are unusable. Resampling and reanalysis are necessary for verification.
What is fenceline monitoringFenceline (or perimeter) monitoring is the use of monitoring technology to measure the ambient air concentration of a specific chemical at the property line of a manufacturing site (e.g., petroleum refinery, chemical plant).
IOL Fenceline Monitoring Article