Phase 1 assessments preclude Phase 2 assessments. There are a number of reasons that a Phase 1 Environmental Site Assessment (ESA) is performed for commercial properties. Here are the reasons why most ESAs are performed:

1. The property is going to be purchased by an entity or person who was not previously on the title.

2. The existing property owner wants to know about and understand the toxic history of his or her property.

3. A new lender is deciding whether or not to provide a real estate loan.

4. The site owner is applying to a public agency in order to change the nature of the land use permit.

5. There is a pending partnership buyout or other principal redistribution that will affect of the ownership of the property.

6. The property is being divested.

7. A regulatory agency suspects that there are toxic conditions on the site and has mandated that a Phase 1 ESA be performed.

There are a number of variations in how a Phase 1 study is performed. These depend on the precise protocols that are utilized. However, most Phase 1 ESAs perform the following tasks:

1. An on-site visit to view the present conditions in order to evaluate any probable environmentally hazardous history on the site.

2. An evaluation of neighboring properties and their risks to the subject site.

3. To review local, state, federal, and tribal records to distances specified by AAI Standards and the ASTM 1528.

4. To interview people who have knowledge of the site's history. This could include both present and past owners, tenants, neighbors, and the site manager.

5. To examine county or municipal planning files in order to ascertain if prior permits were granted and to determine previous land usage.

6. To examine historical aerial photographs of the site and other areas in its vicinity.

7. To determine the topography of the site and drainage patterns by examination of current USGS maps.

8. To examine Activity and Land Use Limitations (AULs) and/or chain-of-title for Environmental Liens.

When a Phase i Environmental Site Assessment (ESA) determines that there is the likelihood that a site is contaminated a Phase ii Environmental Site Assessment is often undertaken. Phase ii assessments are more intrusive investigations. The investigator(s) collect original samples of groundwater, building materials, and/or soil for analysis.

Phase II Assessments quantify the values of the different contaminants that have been found on the site. The substances that are tested most frequently include pesticides, petroleum hydrocarbons, solvents, heavy metals, asbestos, and mold.