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EPA interim final report on WTC background study, April 2003

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Interim final report from EPA Region 2 detailing a background study of environmental conditions at the World Trade Center site.

NYC-WTC_000145869–000146029

Folder label: “INTERIM FINAL April 2003

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NYC 9/11 Public Portal Document

Revised May 14,2003 surface sampled are not similar between the residential and common areas. Since the primary focus of this Study was to determine background concentrations for residential areas, it is recommended to use the data set for the residential spaces to estimate the background concentration. The mean concentrations from each of the surface types in the residential data set are similar, varying by less than a factor of two, therefore it is recommended to use the entire residential data set, which includes the results from the counters, floors, and walls. The 95% UCL for this data set is 79.6 pg/tf • This value can be used as an estimate of the background concentration for alpha-quartz on hard surfaces.

6.3.1.2 Cristobalite Bulk Dust - There were nine bulk dust samples collected from residential areas. These samples were analyzed for cristobalite. There were no bulk samples collected from common areas. None of the samples detected cristobalite above the detection limit. However, since the detection limit for the samples varied slightly, a theoretical background concentration can be calculated. The 95% UCL for cristobalite in bulk dust is 4.69% and this value can be used as an estimate of the background concentration.

Air - There were forty-six air samples collected with thirty-two collected from residential areas and fourteen collected from common areas. The samples were analyzed for cristobalite. Cristobalite 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 from the residential and common areas. The 95% UCL for the combined data set is 9.3 pg/m^, which can be used as an estimate of the background concentration of cristobalite in air.

Wipe - There were 114 wipe samples collected with eighty samples collected in residential areas and thirty-four in common areas. The samples were collected from hard surfaces including counters, floors, and walls. The samples were analyzed for cristobalite. The frequency of detection for the residential areas (0%) and the common areas (3%) were similar, as were the range of detection and mean concentrations. Based on the similarity of the data sets between spaces and between surfaces, it is recommended to use the entire data set, combined for surfaces, to estimate the background concentration. The 95% UCL from this data set provides a value of 103.7 pg/ft^ as an estimate of the background concentration of cristobalite on hard surfaces.

6.3. J.3 Tridymite Bulk Dust - There were nine bulk dust samples collected from residential areas. These samples were analyzed for tridymite. There were no bulk samples collected from common areas. None of the samples detected tridymite above die detection limit. However, since the detection limit for the samples varied slightly, a theoretical background concentration can be calculated. The 95% UCL for tridymite in bulk dust is 4.69%, and this value can be used as an estimate of the background concentration. WORLD TRADE CENTER BACKGROUND STUDY 28

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