EPA interim final report on WTC background study, April 2003

NYC 9/11 Public Portal Document

settings similar to New York. However, there are a niunber of limitations. The CPSC Study reported on houses with ACM. The known existence of ACM in the CPSC Study homes would likely serve as a positive bias. Also the particular housing stock differed, the CPSC Study looked at individual houses whereas the WTC Background Study focused on apartments. The HEI (1991) summation of the CPSC Study did not report the frequency of non-detects or what concentration was assigned to non-detects.

7.2.2 Comparison of Asbestos Settled Dust Concentrations The WTC Background Study collected measurements of asbestos load (fibers per unit area) in settled dust by two methods: Microvacuum (ASTM D 5755-95) and wipe sampling (ASTM D 6480-99). Microvacuum sampling was performed on porous surfaces (carpets and couches) and resulted in the collection of 162 samples, while 146 wipe samples were collected on hard surfaces (ceilings, counters, walls and floors). The arithmetic mean for asbestos loading was 2,783 s/cm^ for the microvacuum samples and 37,174 s/cm^ for the wipe samples. The literature search identified a study by Ewing (2000) that reported a geometric mean of 1,000 s/cm^ for samples collected in six buildings without friable asbestos­ containing surfacing materials.

Little in the way of meaningful comparison can be made between the Ewing and WTC Background Studies. Three significant shortcomings exist. First, unlike the WTC Background Study, the Ewing Study reports a geometric, rather than arithmetic, mean. Based on the number of samples (n=28) and maximum value (210,000 s/cm^), it is evident that the arithmetic mean (calculated by EPA for the piupose of comparison) was greater (> 7,000 s/cm^) than die geometric mean (1,000 s/cm^) reported in the Ewing Study. Second, the microvacuum samples in the Ewing Study were obtained from hard surfaces, whereas the WTC Background Study used microvacuum sampling only on porous surfaces. Finally, the building type was not identified in the Ewing Study.

7.2.3 Comparison of Airborne Man-Made Vitreous Fiber Concentrations The WTC Background Study reported a mean concentration of 0.000042 s/cc (95% UCL = 0.00006 s/cc) in a sample size of 62. ATSDR (2002) reported that airborne concentrations of MMVFs in outdoor and indoor air samples usually are 0.0001 f/cc. Accordingly, the airborne concentration of MMVFs in the WTC Background Study appears consistent with background measurements reported in the literature although the cited reference is very general and does not provide sufficient information to make a detailed comparison.

7.2.4 Comparison of Man-Made Vitreous Fibers in Settled Dust or Soil The WTC background Study reported results of MMVF in bulk dust and wipe samples. Of the 24 samples collected from bulk dust, all were below the detection limit of 1%. The following results were reported for 141 wipe samples collected: frequency of detection (14/141); range (29 - 286 s/cm^) and mean of 38 s/cm^ (95% UCL = 52 s/cm^). ATSDR (2002) reports that no data exist pertaining to the WORLD TRADE CENTER BACKGROUND STUDY 35

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