Sampling Event Matrix

The matrix field on a SamplingEvent records what was sampled — for example, groundwater, surface water, or sediment. This matters for compliance because regulatory thresholds often differ by matrix: a benzene limit for groundwater may be very different from a surface water standard. When AnalyticalResults from a SamplingEvent are compared against ThresholdValues, the matrix context helps ensure the right limits are applied. Reporting a sample with the wrong matrix can result in incorrect exceedance determinations.