I did Phase1 environmental reports for commercial properties. There are three categories of reports .
Phase I is a survey of the property. Kind of like a geology of the property to see what is on it and what was on it. If anything looked like it may be pr may have contaminated the property, a Phase II was recommended.
A Phase II involves drilling sampling wells and taking soil and groundwater samples. If contamination over a certain (action) level is found a Phase III is done.
A Phase III involves removing contaminated soil and or groundwater from the site.
If there is no soil contamination (or the source is removed) orcontamination is below the action level, the recommended action is to let the contamination level naturally be attenuated by dilution.