The lead result from a PAM sample collected during working hours from the Site perimeter between the Containment Area (CA) and Sulphur Creek on November 17, 2008, had a result of 1.011 ug/m³.  While this number is not above the Site’s action level or the current National Ambient Air Quality Lead Standard quarterly average of 1.5 ug/m³, the level was higher than expected due to its location on the Site perimeter and the limited activities that occurred in the vicinity.  Furthermore, in October 2009, USEPA will lower the National Ambient Air Quality Lead Standard from 1.5 µg/m³ to a rolling three-month average of 0.15 µg/m³.  To assess what might have caused the higher than expected result, further investigation was conducted. 

Initially, samples from the two working days before and two working days after November 17^th were sent in to the laboratory for analysis.  A sample collected on November 19, 2008, from the same location had a result of 1.339 ug/m³, also higher than expected.  In response to these results, additional samples were sent in for analysis and an investigation into sampling procedures took place.   

The only activity in the vicinity of the Sulphur Creek perimeter PAM on November 17, 2008, was the transport and spreading of woodchips in the CA. The CA was saturated due to rain events and although the PAM sample was not collocated with a dust monitor, there were no exceedances recorded for the day on any of the dust monitors at the Site.  A dust monitor had not usually been run in that location during the day because the area is not downwind of any Site activities, but since November 20, 2008,  a dust monitor has been run in that location during both working and non-working hours.  On November 19, 2008, contaminated soil from an excavation area in the North Woods and from construction of a diversion berm was placed in the CA (over 200 yards from the dust monitor location). 

The cause and source of the elevated lead levels identified in the PAM samples have not been definitively determined.  It does not appear that they would be related to Site operations since operations in the vicinity of the sampler were limited and did not involve extensive handling of contaminated materials.   It is thought that a likely cause for the elevated levels may have been the procedures used in preparation, placement and handling of the sample cassettes, particularly the removal and replacement of the plugs. Since AGC performed an audit of the procedures and identified possible cross-contamination issues, subsequent results have not shown elevated levels since November 19, 2008.  It appears that the procedural changes have been effective, and changes to Site dust control or construction operations are not warranted.