In 2001, the City of Chicago conducted a background study investigating certain polycyclic aromatic hydrocarbon (PAHs) concentration levels within City limits. This study was conducted in consultation with the Illinois EPA to determine background concentrations for some common PAHs in urban areas, which were to be used in conjunction with the Illinois EPA’s Tiered Approach to Corrective Action Objectives.

PAHs come from a variety of sources, but primarily from the combustion or burning of fuels. Generally, any burning of an organic material such as coal, oil or wood will generate PAHs, and the existence of these chemicals is common throughout our society. Planes, automobiles, coal heating, forest fires, and power generation have all greatly contributed to the existence of these chemicals.

Background concentrations are generally considered to be the level or amount of a chemical found in common areas not associated with a particular contaminant release. Parks, roadways, residential yards, non-industrialized properties, etc., are typical background areas. The definition from Tiered Approach to Corrective Action Objectives (TACO) is:

“Area Background” means concentrations of regulated substances that are consistently present in the environment in the vicinity of a site that are the result of natural conditions or human activities, and not the result solely of releases at the site. [415 ILCS 5/58.2]

These background concentration levels have been incorporated into the Illinois EPA’s cleanup standards, the Tiered Approach to Corrective Action Objectives.