Both the ETS and the ESA are standard due diligence projects for which there are published standards issued by the American Society of Testing and Materials (ASTM).

The ETS includes an environmental database search and evaluation, site inspection, interview and limited historical research.

The ESA includes these tasks plus detailed historical research, site layout and photographic documentation and review of nearby leak files, if necessary.
The report format for the ESA is more detailed. The ESA follows a more strict layout and therefore may be more universally accepted by different lenders.

The cost of the ESA is approximately three times the cost of the ETS.