Special Investigative Audit #14 Draft, WTC Site, Nov 2001

NYC 9/11 Public Portal Document

WTC North Tower Center reversed the line from a decreasing trend seen through November 7t''. The regression slope listed in above was also negative before the November 8t'' result was entered in the calculation. Fitted lines to describe trends should be used with caution, especially when highly variable data like the WTC VOCs are evaluated.

Outside the WTC sites and immediate vicinity, VOC concentrations are much lower or undetected (<20 ppb). The benzene concentrations at the WTC sites and surrounding Lower Manhattan sites are listed in Table 3. The highest benzene in air concentration at sites other than the WTC sites reported to date was 11,000 ppb on September 26t'' at the Liberty and Trinity site. Compared to the WTC North and South Tower sites, however, relatively few VOC results are available for other Lower Manhattan sites. On November 8t'' when the benzene concentration at the WTC North Tower site was 180,000 ppb, the highest air concentration of benzene reported to date, the concentration of benzene at the WTC South Tower (Location 1) was 1100 ppb, the WTC-Austin Tobin Plaza-Work Zone Location 2 concentration was 85 ppb, and the concentration of benzene at Murray St, between West St & North End Ave, was <20 ppb.

The relatively low concentrations detected outside the WTC North Tower site may be the result of quick dispersion of the gas, ground level sampling sites below the dispersing gases, or other wind factors. On October 6t'', the benzene detected outside the WTC sites was 44 ppb at the North Park South of Pier 25-Rockefeller Park site which is approximately 700 times lower than the WTC North Tower value of 31,000 ppb on October 6t''. The styrene concentration on October 6th at the Pier 25-Rockefeller Park site was 78 ppb which is approximately eighty-five (85) times lower than the WTC North Tower concentration of 6,700 ppb observed on that date. On October 11th when the styrene concentration was at its maximum of 180,000 ppb at the WTC North Tower site, styrene was not detected at the Pier 25-Rockefeller Park site (<20 ppb).

As one example of the sample results and information available in the NYC Response database concerning VOCs, a summary of the information for benzene is as follows:

• A total of 259 samples were collected between September 15' and November 13t" and analyzed for benzene. The media collected include 238 air samples, 14 drinking waters, 4 minican samples, and 3 Personal Air Monitoring (PAM) samples.

The benzene air samples were collected between September 16t'' and November 13t" from various WTC sites and Lower Manhatten locations (the Lower Manhatten monitoring sites for benzene are shown in Attachment 2, Figure 2). Many of the air samples were collected at "Ground Zero" sites including the WTC North Tower, WTC South Tower (Location 1), and WTC Austin Tobin Plaza (Location 2). Others were collected away from WTC, including at North Park South of Pier 25 (Rockefeller Park).

• The methods of analysis for air samples were predominantly identified as by gas chromatography/mass spectrometry (GC/MS). Also identified were EPA Methods TO-14 and TO-15. Nearly all of the air samples were analyzed in a mobile laboratory, the EPA Trace Atmospheric Gas Analyzer (TAGA) bus.

• Of the 238 air samples, 207 were reported in units of ppb, ranging from an MDL of 0.66 ppb

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