NYC-WTC_000195194

NYC 9/11 Public Portal Document

collected. Lead was detected in all three micro vacuum samples at concentrations above (approximately four to six times) the comparison value of 25 pg/ft". Two of the three wipe samples had detectable concentrations of lead above the primary clearance criterion of 25 pg/ft2, while the third was below the primary clearance criterion.

Post P‘ Cleaning Samples - Two air samples, three micro vacuum samples and four wipe samples were collected after the first cleaning. The two air samples were below the primary clearance criterion of 1.0 pg/m^. However, at the time the results were received, «r the primary clearance criterion that was being used for comparison was the background clearance criterion of 0.1 pg^m\ not the health-based clearance criterion of 1.0 pg/m^ which was developed during the execution of this project. Therefore, additional air samples were collected after the second cleaning. w All three micro vacuum samples were below the detection limit. This indicates that the cleaning techniques used were able to reduce the elevated pre-cleaning lead concentrations that were observed in the settled dust in the areas where the samples were collected.

The results of three of the four wipe samples were below the primary clearance criterion (one sample was broken and not analyzed). The results from the first cleaning indicate that the cleaning technique was effective in removing the elevated concentrations of lead w that were observed prior to the first cleaning. Since the primary clearance criterion was met for lead after the first cleaning, no additional samples were collected for the analysis of lead, with the exception of the air samples discussed above. <« Post 2'“^ Cleaning - Two air samples were collected after the second cleaning. The results of both indicate that the samples were below the primary clearance criterion of 1.0 pg/m’. Since the primary clearance criterion was met for lead after the first cleaning, no additional samples were collected.

41 Alpha-Quartz Before Cleaning Samples - Pre-cleaning air samples were not collected.

Post P' Cleaning Samples - Two air samples were collected after the first cleaning. Both were below the detection limit.

Calcite Before Cleaning Samples - Pre-cleaning air samples were not collected.

Post P‘ Cleaning Samples - Two air samples were collected after the first cleaning. Both samples were below the detection limit.

Cristobalite 4* Before Cleaning Samples - Pre-cleaning air samples were not collected.

Post P' Cleaning Samples - Two air samples were collected after the first cleaning. Both samples were below the detection limit.

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NYC-WTC_000195271