NYC-WTC_000195194

NYC 9/11 Public Portal Document

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wr apartment were recorded in the initial phase of the study, prior to cleaning. Six apartments were identified as having accumulated a significant amount of dust. The remaining seven apartments were identified as having a minimal amount of dust accumulation. All of the apartments characterized as containing a significant amount of dust presented windows that had been blown in during the collapse of the WTC. The visual observations were used in an attempt to distribute the cleaning methods evenly, based on the amount of dust present.

Once the analytical results were available, it was possible to quantitatively determine differences that existed in the amount of contamination that was present in the apartments prior to cleaning. As indicated above, the pre-cleaning results for asbestos wipe sampling, lead wipe and micro vacuum sampling, and MMVF wipe sampling results from the residential units provided the most w complete data set for determining the existing contamination in apartments prior to cleaning. These four data sets were used to establish differences in contamination between apartments prior to cleaning.

The results for each data set identified above were averaged by unit, then ranked from the highest concentration t the lowest concentration, which resulted in each unit having four rankings (one for each data set). These rankings are presented in Table 9.0.

The range of the highest concentration to the lowest concentration for each compound or sample type spanned an order of magnitude. One apartment, 4B, did not contain any porous surfaces that could be sampled, therefore there were no micro vacuum samples collected. This prohibited this unit from being included in the ranking.

Once the units were assigned a ranking for each data set, the rankings for each unit were summed to create a variable called "sum of ranks". This information is presented in Table 10.0. The sum of ranks has a theoretical range of 4-48, while the observed range in this evaluation was 13-45. This indicates that there was generally an even distribution within the theoretical range, with the 4 exception of the lower end of the range, as there were no units which ranked less than 13. Therefore, the visual observations of dust generally corresponded with levels of contamination found in the dust. The results of the ranking evaluation indicates that there was a difference in the 4 degree of an average contamination for these compounds between units prior to the cleaning 4 events. 4

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NYC-WTC_000195301