EPA interim final report on WTC background study, April 2003

NYC 9/11 Public Portal Document

were analyzed for portlandite. Portlandite was not detected in any sample. However, since the detection limit for the samples varied slightly, a theoretical background concentration can be calculated using the entire combined data set for all surfaces from the residential and common areas. The 95% UCL for the combined data set is 99.8 p-g/ft^, which can be used as an estimate of the background concentration of portlandite on hard surfaces.

6.3.5 Total Dust Wipe - There were nine wipe samples collected from residential areas and analyzed for total dust. Dust was detected in all nine samples with a mean concentration of 10.9 mg/ft^ The 95% UCL for this data set was 14.4 mg/ft\ which can be used as an estimate of the background concentration of total dust.

7.0 HISTORICAL STUDIES ON BACKGROUND CHARACTERIZATION 7.1 Background Literature Search Results The WTC Background Study was conducted to address the following question: What were the baseline levels for a select group of contaminants in residential dwellings in lower Manhattan had the Trade Center never collapsed? A complete set of data were not available that captured the baseline levels of WTC COPCs in the settled dust and indoor air of residential dwellings in lower Manhattan prior to 9/11/01. However, there are various sources of data that partially address the specific aim of the WTC Background Study. This section evaluates the findings of historical studies on background by way of a comparison to the methods and results of the WTC Background Study.

A search of the literature was conducted for published data on residential indoor measurements of WTC COPCs. The focus was for relevant data, collected in the past ten to fifteen years, that may be used for comparison with the measurements from the WTC Background Study. Worth noting are the multiple factors that limit the representativeness of historical studies to the WTC Background Study. They include: variations in sampling and analytical methods; characteristics of the housing stock (e.g., age, type and upkeep) and seasonal variability.

7.1.1 Residential Indoor Airborne Asbestos Measurements The literature citations on airborne asbestos measurements focused mainly on occupational environments. Some information is available for schools and other public buildings. Very few studies described measurements made in residential settings.

There are a number of analytical techniques (PCM, TEM, direct preparation, and indirect preparation), as well as different units of measurements reported in the literature for airborne asbestos concentration. HEI (1991) listed eleven different measurement units that could be encountered in the literature for asbestos fibers analyzed by TEM. Another factor to note is how the average or mean value is determined from a set of measurements. Some studies treat all samples with no asbestos structures/fibers counted as 0 s/cc or 0 free and not as a “less than” WORLD TRADE CENTER BACKGROUND STUDY 31

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