In January 2010, the Illinois EPA placed a monitor on the roof of Manuel Perez Jr. Elementary School to sample ambient air concentrations of lead in the area. Air samples at the Perez monitor were collected once every six days and typically showed lead levels well under the new, more protective National Ambient Air Quality Standard. However, periodically there were elevated lead readings at the monitor (elevated in 11 of the approximately 60 samples taken in 2010).
The National Ambient Air Quality Standard is based on an average of three months of readings. Although most of the readings in 2010 were well below the standard, four elevated samples between November 2010 and January 2011 caused the three-month average to be greater than the National Ambient Air Quality Standard.