Any piece of real estate can be the subject of a Phase I - Environmental Site Assessment. (ESA). Generally speaking, Phase I - ESAs are reports prepared for a real estate holding which identify potential liabilities associated with existing environmental contamination. ESAs typically address both the underlying land as well as physical improvements to the property. Actual sampling of soil, air, groundwater and/or building materials is typically not conducted during a Phase I ESA. The Phase I ESA is generally considered the first step in the process of environmental due diligence. The examination of a site may include: definition of any chemical residues within structures; identification of possible asbestos containing building materials; inventory of hazardous substances stored or used on site; assessment of mold and mildew; and evaluation of other indoor air quality parameters. The investigation also includes examination of potential soil contamination, groundwater quality, surface water quality and sometimes issues related to hazardous substance uptake by biota.