While the parent ThresholdSet carries a high-level citation, the source on an individual ThresholdValue allows for analyte-specific references — for example, noting that a particular compound's limit comes from a footnote or an updated amendment not reflected in the set's primary citation. This granularity is useful in exceedance reports where you need to cite the exact regulation that sets the standard for a specific analyte violation, rather than just the general regulatory program. For straightforward sets where all values come from a single table, the ThresholdValue source may be left blank and the set-level citation is sufficient.
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Threshold Value Source
The `source` on a ThresholdValue records the analyte-specific regulatory citation when the limit comes from a distinct sub-table or subsection.