EPA Special Investigative Audit Report, WTC Site, Nov 2001

NYC 9/11 Public Portal Document

WTC North Tower Center site.

Correlation coefficients between benzene and toluene, benzene and 2-butanone, and benzene and chloromethane at the WTC North and South Towers were calculated to describe the similarity or difference in the air concentrations with time using data from September 19"' through November 12'\

Benzene Correlation Coefficients with Toluene, 2-Butanone, and Chloromethane at WTC North and South Towers

sMi’a; ." -V -Toluene 2 1), e Chlorotncthanc WTC North Tower Center 0.9424 0.8418 0.2069 WTC South Tower (Location 1) 0.9493 0.9373 0.9263

Correlation coefficients near one (1.0) indicate that the compounds are changing at the same time and in proportion to benzene. Compounds of similar chemical classes might be expected to change at the same rates. At the WTC North Tower Center, the correlation between benzene and 2-butanone (0.8418), compounds of different chemical classes, is less than the correlation between benzene and toluene (0.9424). Benzene and chloromethane are poorly correlated at the WTC North Tower. Low correlation coefficients indicate different trends for each compound. The correlation between benzene and all three compounds is nearly equivalent at the WTC South Tower site which suggests similar sources of these compounds or a sampling site where the concentration of the four compounds is increasing and decreasing at the same time.

Regression analysis has also been performed for benzene at the WTC sites to describe any increasing or decreasing trend in concentrations. The results of the regression analysis is listed below.

Benzene vs Time Regression Analysis for WTC North and South Tower Sites Units; ppb/day

Site' X coefficient (slope) std error in x coefficient WTC North Tower Center 236 442 WTC South Tower (Location 1) 58.2 183

For both WTC Tower sites, the positive x coefficient indicates an apparent increase in benzene concentration. The large standard eiror in the calculation from both sites, however, indicates high variability and considerable uncertainty. At this time, the high error in the calculation indicates that any trend is very uncertain.

The X coefficient (slope) regression calculations are consistent with the linear fit lines in Figure 3. Both fitted lines indicate an increase in benzene concentration at the WTC North and South Tower sites. The recent high value for benzene of 180,000 ppb on November 8‘'’ for the

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