EPA interim final report on WTC background study, April 2003

NYC 9/11 Public Portal Document

PCM - There was a higher percentage of detections in the common space areas (71%) than in the residential areas (42%) although the minium and maximum detected concentrations were the same. The UCL for the common area (0.0058 f/cc) is slightly more than twice the value for the residential area (0.0023 fZcc). This difference may not be an unusual occurrence as common areas, such as laundry rooms and hallways may contain more fibrous material, especially in laundry rooms and high traffic areas. Since the common space areas and the residential areas differ, it is recommended to use the 95% UCL for the residential spaces of 0.0023 17cc as the background value.

TEM AHERA - There was a higher percentage of detections in the common space areas (14%) than in the residential areas (4%) although the minimum and maximum detected concentrations were the same. In addition, the mean for each data set were similar. The four samples (two common area and two residential) that had detectable concentrations of asbestos were at the detection limit of 0.0004 s/cc. Since the frequency of detection was marginally different for the common space areas and the residential areas, it is recommended to use the 95% UCL for the residential spaces of 0.00024 s/cc as the background value.

TEMPCMe - There was a higher percentage of detections in the common space areas (7%) than in the residential areas (4%) although the minimum and maximum detected concentrations were the same. In addition, the mean for each data set were almost equal. The three samples (two common area and one residential) that had detectable concentrations of asbestos were at the detection limit of 0.0004 s/cc. The UCL for the common areas (0.00029 s/cc) is marginally higher than the UCL for the residential area (0.00024 s/cc). The combined data set yields a UCL that is the same value (0.00024 s/cc) as the residential UCL. Given that the residential areas and the combined data sets provide the same UCL, it is recommended to use the 95% UCL of 0.00024 s/cc as the background value.

Microvacuum - There were 162 microvacuum samples collected, with 144 from residential areas and 18 from common spaces. The microvacuum samples were collected from porous materials, such as carpets, area rugs and couches. These samples were analyzed for asbestos. The results from these analyses were quite variable between different surfaces and between the different spaces. Asbestos was detected more frequently in the common spaces (22%) and at higher concentrations (mean = 7,145 s/cm^) than in the residential spaces (4%) with a mean concentration of2,234 s/cm^. In addition, the carpets in both spaces had greater mean concentrations than the other porous surfaces (i.e., couches, chairs, and drapes). As the purpose for collecting microvacuum samples for asbestos was to determine the presence or absence of asbestos in porous items, a UCL was not calculated for this data set.

Wipe - There were 146 wipe samples collected, with 104 from residential areas and 42 from common spaces. The wipe samples were collected from hard surfaces including floors, walls, coimters, and ceilings. These samples were analyzed for asbestos. The results from these analyses were quite variable WORLD TRADE CENTER BACKGROUND STUDY 23

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