On July 17, 2009, we sent two PAM air samples to the lab as part of the Quality Control/Quality Assurance program as a check on both field and lab procedures. The check on the sample storage and lab procedures is called a Lot Blank, and it is run every time a new box of sample cassettes are opened to see if the cassettes were contaminated or if there is contamination at the lab. The check on the field procedures is called a Field Blank, and it is to check the field techniques/practices. For the Field Blank, the sample cassette goes through the same procedures as if it were a regular sample. The inlet/outlet caps are taken off, it is attached to the PAM sampler unit, and the flow meter, and then the caps are put back on and it is put in a plastic bag. The difference from a regular sample is that it is not run for a prolonged period of time as the samples are, so there is no calculated volume of air run through it. We only get the amount of lead in the cassette and not a concentration.

Because the field and lot blanks are not actual samples exposed to the work area, you would expect that they would have results below the detection limit (i.e. no contaminant on them), as we have seen in these types of samples since the PAM sampling started. However, both the results on the Lot Blank and Field Blank from 7/17/09 were above the detection limit, which means that there are questions regarding how much lead was actually in the samples that were run during the time period from July 17th to July 23rd when the blank contamination was identified. The important news is that the blank contamination would cause us to think that there was more lead in the air during this time period, not less, so all of the normal precautions to control dust were followed during this time. Also, work activities during this period were mainly with clean materials until the afternoon of July 22nd when grading work in the Containment Area began. The hi-volume air samplers were run on the 23rd also which will tell us what happened on that day as well.

In response to these results, in order to determine what may have caused the blank results to be above the detection limit, Gould/AGC did the following: 1) opened a new box of cassettes and sent in a new Lot Blank; 2) conducted an internal audit of procedures; 3) sent in the three samples that were put on the flow meter after the field blank on July 17, 2009; and 4) collected a field blank for each working day from July 24 through July 30, 2009, and sent them in to the laboratory for analysis. The testing of the field and lot blanks all were below the detection limit indicating that whatever caused the elevated result on July 17, 2009 was a random event and not indicative of a widespread contamination problem. The audit identified several “housekeeping” items to follow to reduce the chances of the contamination happening again. (Click here to read a summary of the audit.)