EPA interim final report on WTC background study, April 2003

NYC 9/11 Public Portal Document

Revised May 14,2003 background Study. This required employing an estimate of average dust load in a residential dwelling, a value that can vary considerably depending on housekeeping habits. Also, the Christmann Study collected samples fi-om households that contained furniture treated with a wood preservative. This may serve to bias the results high. Finally, the Christmann Study employed a vacuum sampling method whereas the WTC Background Study collected wipe samples.

7.2.8 Comparison of Polycyclic Aromatic Hydrocarbon Concentration in Settled Dust All 80 wipe samples collected in the WTC Background Study were reported to be below the limits of detection (290 pg/m^, benzo[a]pyrene equivalents). No citations were found in the literature search for surface loading of PAHs in the indoor residential environment. Consequently, no comparison is possible with the PAH surface loading results reported in the WTC Background Study.

8.0 DISCUSSION The objective of this Study was to determine indoor baseline levels or background concentrations for a specific group of compounds that are associated with the World Trade Center collapse. These background concentrations will be used to supplement the health-based benchmarks established in the "World Trade Center Indoor Air Assessment: Selecting Contaminants of Potential Concern and Setting Health-Based Benchmarks"document and may be used as an alternative cleanup value if the health-based benchmark cannot be achieved.

The compounds of interest were asbestos, man-made vitreous fibers, lead, dioxin, polycyclic aromatic hydrocarbons, and crystalline silica. In addition to these compoimds, data were also collected for calcite, gypsum, portlandite, and total dust. A combination of air samples, microvacuum samples, wipe samples, and bulk dust samples were collected to evaluate these compounds in residential buildings and in common areas of residential buildings. The microvacuum samples were collected fi-om a variety of porous surfaces, while the wipe samples were collected fi-om a variety of hard surfaces. The data were evaluated separately for each type of sample, type of space, and each compound.

In addition, the data were evaluated for groups of similar data, such as all residential lead wipe data. The combined of analyses provided a combination of 192 background concentrations, which represents 95% upper confidence limits on the arithmetic means. Similar subsets of these 192 data points (e.g., by compound or by media.) were then qualitatively compared to determine a representative background concentration for each compound in air, bulk dust, porous materials, and hard materials. The recommended values are presented below in Table 8-1. The values presented in the table are an upper-bound statistical estimation of the true mean of the sample population. The upper-boimd confidence limit is 95%, which represents the confidence that the true mean is equal or lower to the value that is presented in the table. WORLD TRADE CENTER BACKGROUND STUDY 38

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