NYC-WTC_000195194

NYC 9/11 Public Portal Document

5.7 Sampling Methods

Several types of sampling methods (air, micro vacuum, and wipe samples) were used in this study to determine the contaminant concentrations before and after cleaning events. An assessment was made to determine if one of these sampling methods could be used as a surrogate, which would allow only one type of sample for one compound to be used to assess if an indoor space required additional cleaning. As the amount of contamination present after a cleaning event was the most important factor for determining if a surrogate test could be used, only the post-cleaning data was used for this particular assessment.

The post-cleaning data that was collected indicated that it was necessary to conduct eleven additional cleaning events (9 second cleaning events and 2 third cleaning events) due to either a health-based benchmark being exceeded or samples that could not be analyzed. As presented in Table 14.0, air samples collected for asbestos and analyzed using PCMe accounted for the majority (82 percent) of the additional cleaning events. These additional cleaning events were conducted because the filters were overloaded with particulate matter and could not be analyzed. In comparison:

lead would have resulted in a total of four additional cleaning events (36 percent), although three were based on wipe samples and one was based on a micro vacuum sample; MMVF air samples resulted in three additional cleaning events (27 percent); silica resulted in one additional cleaning even t(nine percent); and PAH and dioxin wipe samples results in zero additional cleaning events.

This indicates that the testing methodology associated with PCMe asbestos air sampling is very sensitive to particulate matter and that an indoor environment needs to be relatively clean of particulate matter to achieve valid PCMe results. Based on the compounds and testing methods chosen, the data suggests that using asbestos air samples as an indicator for additional cleaning is the most sensitive of the testing methods, as it results in the largest percentage of additional cleaning events. In addition, it is conservative in nature because the asbestos air sampling with PCMe analysis may indicate that additional cleaning events need to be conducted even if no contamination is present above health-based benchmarks, simply because of excess particulate matter. For example, there were five instances where the sampling results for the other compounds indicated that the unit met the health-based benchmarks, which would indicate that no additional cleaning was necessary; however, because the asbestos air samples could not be analyzed due to the filters being overloaded with particulate material, the unit was cleaned again.

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