Monitored natural attenuation

Non-physical measurement process, carried out generally by consultants, to provide confidence that natural degradation processes in the ground or groundwater are occurring in a measurable and known way.

This would show the regulator that the buried contamination (normally oil or chemical spills to groundwater) is gradually being ameliorated by those in-ground processes, and/or is not proceeding off site to affect other receptors. It is often used post-remediation, where perhaps the contaminant source was not all removed.