A formal evaluation of the extent of contamination at a location such as a gasoline station, where contamination resulting from leaks or spills is suspected. 

Federal underground storage tank regulations require that site assessments be made in certain circumstances. Site assessment is required when groundwater monitoring or soil monitoring is to be used as a method of release detection. The site assessment studies are normally conducted by hydrogeologists and involve measurement of contaminants present in the soil and groundwater, soil permeability and groundwater movement.