EPA interim final report on WTC background study, April 2003

NYC 9/11 Public Portal Document

between different surfaces and between different spaces. Overall, asbestos was detected about twice as frequently in the common areas (26%) than in the residential areas (13%). The results from the common areas had several very high concentrations reported due to detection limits being unusually high for several samples. This might artificially increase the backgroimd concentrations and for this reason the common space data sets were not used for determining the backgroimd concentration.

Based on the residential data set, the mean concentration was higher in the ceiling samples, followed by the floor samples, then the walls, and finally the counters. The UCLs for these surfaces were within an order of magnitude with the exception of the UCL for the ceiling, which was one order of magnitude higher. However, given that the primary goal is to estimate the background concentration for a residential space, it is recommended to use the entire residential data set, which includes ceilings, counters, floors, and walls to establish a background concentration for hard surfaces. The 95% UCL for this data set is 6,192 s/cm^ and would be applicable for all hard surfaces in a residential space.

6.2.2 Man-Made Vitreous Fibers Bulk Dust - There were twenty-four bulk dust samples collected and analyzed for MMVF. All of the samples were collected from the residential spaces. The results for the twenty-four samples were below the detection limit of 1%. As all of the samples were below the detection limit and the same detection limit was used throughout the Study, the UCL for MMVF in bulk dust could not be calculated because there was no standard deviation. The data suggest that background MMVF concentration in bulk dust is 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, with forty-eight collected from residential spaces and fourteen collected from common areas. The frequency of detection for the common spaces (29%) was higher than the residential spaces (2%), however the range of detections and means were very similar. The UCL for the combined data set is the same as the UCL for the residential data set. Given that the UCLs are the same, it is recommended to use the 95% UCL of 0.06 s/L or 0.00006 s/cc.

Wipe - There were 141 wipe samples collected, with ninety-nine collected from residential spaces and forty-two from common areas. The frequency of detection was similar between the residential (9%) and the common (11%) areas, as well as the range of detections and the mean for the wipe data set for each space. Each space had wipe samples collected from hard surfaces including ceilings, counters, floors, and walls. The samples collected from the ceiling, counters, and walls in the common spaces were all below the detection limit and a UCL could not be calculated for these surfaces. All of the surfaces sampled from the residential areas had UCLs that were within a factor of three. Given that the residential data for the different surfaces were similar, as well as the data from the common areas, it is recommended to use the entire data set, which includes the residential and WORLD TRADE CENTER BACKGROUND STUDY 24

NYC-WTC_000145899