EPA interim final report on WTC background study, April 2003

NYC 9/11 Public Portal Document

common spaces. This data set provides a 95% UCL of 52 s/cm^ as a backgroimd concentration for MMVF on hard surfaces.

6.2.3 Lead Bulk Dust - There were nine bulk dust samples collected from residential spaces and analyzed for lead. There were no bulk dust samples collected from the common areas. Lead was detected in all of the bulk samples ranging from 44 mg/kg to 242 mg/kg with a mean concentration of 126 mg/kg. The 95% UCL for this data set was calculated as 186 mg/kg. This UCL is recommended to be used as a background concentration for lead in bulk dust.

Air - There were forty-six air samples collected, with thirty-two samples collected from residential areas and fourteen collected from common areas. Only one sample, collected from a residential area, had a concentration of lead that was detectable and the lead concentration was equal to the detection limit. However, as the detection limit for the common areas and residential area samples varied slightly, a theoretical background concentration can be calculated for the common area because the range of detection limits permits a standard deviation to be calculated. The results indicate that the frequency of detection is similar between the residential areas (3%) and the common areas (0%), as well as the mean concentration. The UCL for each space is similar, 0.027 pg/m’ for common areas and 0.032 pg/m’ for the residential area, therefore it is recommended to use the entire data set, which includes the common area and residential area, to calculate a background concentration. The 95% UCL for the entire data set, which should be considered the calculated background concentration, is 0.03 pg/m\

Microvacuum - There were 144 microvacuum samples collected, with 114 collected in residential areas and 18 collected in common areas. The microvacuum samples were collected from porous materials including carpets, couches, chairs, and drapes. The frequency of detection for all of the microvacuum samples collected in the residential areas (8%) was similar to the samples collected in the common areas (6%), as were the ranges, mean, and calculated UCLs for the data sets for each space and each surface. Given the similarity between the data sets, both between spaces and between surfaces, it is recommended to use the entire microvacuum data set for estimating the backgroimd concentration of lead in porous surfaces. This yields a 95% UCL of 1.98 pg/ft^ for the background concentration of lead in porous surfaces.

Wipe - There were 114 wipe samples collected, with 80 collected in residential areas and 34 collected in common areas. The wipe samples were collected from hard surfaces including counters, floors and walls. The frequency of detection between the residential areas (49%) and the common areas (53%) for all of the wipe samples from each areas are similar, as are the range of detections and means, with the exception of the maximum detected concentration on the floor in the common area, which was about five times higher than the residential area. Although the data sets are very similar for both the spaces and surfaces, the inclusion of the maximum value for the floor in the common area of 49.2 pg/ft^ in WORLD TRADE CENTER BACKGROUND STUDY 25

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