EPA interim final report on WTC background study, April 2003

NYC 9/11 Public Portal Document

The recommended values were determined using two priorities:

as first priority, a combined data set, using both the residential and common areas and all samples from a specific media (e.g., settled dust) to achieve a larger sample size, was used unless the data from the separate areas were determined not to be similar’, in which case the second priority was used;

the second priority used the data set for the residential areas for all samples from a specific media, as the residential data sets had the second largest sample size and this data set would reflect the background concentration within a residential apartment.

6.2 Results and Development of Background Concentrations The following sections present a summary of the analytical results, the background values calculated, and a discussion that addresses the strengths and weaknesses for the asbestos, MMVF, lead, dioxin and PAH data sets, as well as the corresponding background value that was derived for each analyte, matrix, type of space, and type of surface. The statistical results and calculated UCLs are reported in Tables 6-1 through 6-3.

6.2.1 Asbestos* Bulk Dust - There were three bulk dust samples collected and analyzed for asbestos. All three samples were collected from the residential spaces. The results for the three samples were below the detection limit of 1%. Due to the small sample size and the results all being below the detection limit, the UCL for asbestos in bulk dust could not be calculated. The data suggest that background asbestos concentrations in bulk dust are less than 1%, however, the confidence in this statement is limited due to the small sample size.

Air - There were sixty-two air samples collected, forty-eight in residential spaces and fourteen in common spaces. Each of the samples were analyzed using Phase Contrast Microscopy (PCM), Transmission Electron Microscopy (TEM) AHERA, and TEM Phase Contrast Microscopy equivalents (PCMe) methods.

’The frequency of detection, range of detection, mean and calculated UCL for the residential and common area data sets were qualitatively compared to determine if they were similar. If any of the parameters were identified as not being similar, the second priority was used.

’For this study, the term structure and fiber are used interchangeably, although there are mineralogical nuances and counting rules that make these two terms technically different. In general, the analyses that were completed represent fibers, however for ease of comparison to the AHERA asbestos standard in a sister study, the term structure was adopted for all asbestos TEM analyses.

WORLD TRADE CENTER BACKGROUND STUDY 22

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