Site Assessments can be separated into three "phases" of assessments: Phase I, Phase II and Phase III. A Phase I level of assessment is strictly a outside look of a property or particular site. This phase involves a compliance literature review and a property overview to determine evidence of actual site and potential site contamination. Phase I assessments may be used as a stand-alone document to make informed financial decisions on a particular property. It is not necessary to conduct a Phase I assessment if the level of or evidence of contamination is determined.

The Phase II level of assessment is undertaken if evidence of contamination and in some cases, evidence of non-compliance is discovered. This level of assessment involves field sampling of the site and analysis of the samples to determine the extent and degree of contamination. This type of assessment is more time consuming, more costly and can be disruptive if undertaken in an active operating area. The degree and ultimate cost of the Phase II assessment will depend on the type and identity of the suspected contaminants, parameters to be sampled for, size of the area and the environmental factors to be sampled (air, water, soil, plants, animals). Should a Phase II be required a Phase III (Remedial Investigation), level of assessment is usually undertaken.

The Phase III level of assessment involves the establishment of a remediation plan and can be conducted separately if the contamination level is previously determined. This level usually means the selection and supervision of a suitable and experienced remediation company. The degree of remediation will depend on the level of contamination and the levels at which the contamination must be remediated to.