EPA interim final report on WTC background study, April 2003

NYC 9/11 Public Portal Document

Revised May 21,2003

the entire data for areas skews the data set and results in a 95% UCL of 4.59 pg/tf. Alternatively, if only the residential data set is used, the calculated 95% UCL provides a value of 1.78 pg/ft^. Either value would be an acceptable background concentration for hard surfaces, however it is recommended to use the 95% UCL value of 1.78 pg/tf that was calculated using only the residential data set because of the marginal difference in the maximum detected concentration in the common areas and residential areas.

6.2.4 Dioxin Wipe - There were 114 wipe samples collected, with 80 samples collected from residential areas and 34 samples collected from common areas. The samples were collected from hard surfaces including counters, floors, and walls. The samples were analyzed for dioxin and furan congeners and the results were reported in 2,3,7,8-tetracholorodibenzo-p-dioxin (TCDD) equivalents (i.e., TEQs). Any sample which was below the detection limit for any specific congener group was assigned a value of‘A of the detection limit before calculating the TEQ, thus for the statistical analysis the reported TEQ was used without any further modifications. In addition, the TEQ yalue that was used for estimating the background concentration was the estimated maximum potential concentration (EMPC). The TEQ EMPC value uses data that indicated the detected presence of a compound above zero but did not meet all of QA/QC reporting level criteria.

The frequency of detection between the residential areas (23%) and the conunon areas (20%) were similar, as were the range of detections, means, and UCLs. The similarity between the data sets for the residential areas and the common areas permits the use of the entire data set for estimating the background concentration. The 95% UCL calculated from the entire dioxin data set is 0.693 ng/m\ which can be used as an estimate of the background dioxin concentration on hard surfaces.

6.2.5 Polycyclic Aromatic Hydrocarbons Wipe - There were 113 wipe samples collected, with 80 samples collected from residential areas and 33 samples collected from common areas. The samples were collected from hard surfaces including counters, floors, and walls. The samples were analyzed for 23 PAH compounds, of which seven of the compounds are used to calculate a toxicity equivalence factor (TEF). The analytical results indicate that none of the 23 PAH compounds were detected and the TEF for each sample would be equivalent to 290 pg/m^. The detection limit was the same for each sample that was analyzed, therefore a UCL cannot be calculated for the residential or common area data sets due to not having a standard deviation. The data suggest that the background concentration of PAHs on hard surfaces is less than the detection limit of 0.25 pg (i.e., 250 pg/m^) for individual PAHs or 290 pg/m^ for the calculated TEF.

WORLD TRADE CENTER BACKGROUND STUDY 26

NYC-WTC_000145901