VOC sampling locations table for Ground Zero area, Jan 2002

NYC 9/11 Public Portal Document

Calculating TEQ concentrations with most congeners assigned values of one-half detection limit is not an issue when a sufficient quantity of air is drawn into the monitor, and the inability to measure the dioxin in the sample truly does signify a very low amount of dioxin in the sample. For example, congeners in the Region 2/7 samples could be quantified if they were present at concentrations higher than about 0.5 pg/m’ because enough air was drawn into the monitors leaving behind enough dioxin molecules on the monitor’s filters. The congeners in the EPA ERT samples could not be quantified unless they were present at about 5-10 pg/m’. When most of the congeners reported a non-detect in one of the Region 2/7 samples, the calculated TEQ concentration was in the range of 0.01 to 0.10 pg TEQ/m\ whereas when most of the congeners were reported as non-detect in the EPA ERT samples, the calculated concentration ranged from 0.5 to 5.0 pg TEQ/m\ As will be discussed below, typical urban air concentrations are in the range of 0.10 to 0.20 pg TEQ/m\ and these measurements come out of studies where, like the Region 2/7 samples, a sufficiently large quantity of air was drawn into the monitors.

Assigning one-half detection limit for non-detects is typical and appropriate for evaluating exposure to airborne contaminants, dioxins or otherwise. In some circumstances, this practice can underestimate the amount of contaminant in the air - i.e., when the actual concentration is just below the detection limit and above the half-detection limit value. However, in this case, it is clear based on comparison with the Region 2/7 samples and from other historical measurements around the United States, that the practice of assigning one-half detection limit to non-detects in the EPA ERT samples resulted in an overestimate of the TEQ concentration when most of the congeners in the sample were non-detects.

For purposes of analysis in this section, a limited set of the dioxin data is used. Table 4 shows reported TEQ concentrations for the WTC Building 5 EPA ERT monitor, the Church & Dey EPA ERT monitor, and the Park Row Region 2/7 monitor. These values were calculated at ND = 1/2 DL; in parenthesis for the two EPA ERT monitors is the TEQ calculated at ND = 0. The WTC Building 5 monitor had the highest concentrations, and the Church & Dey monitor was in the predominant downwind direction for most monitoring events and had the second highest measurements. The Park Row monitor began operation on October 12 and had numerous measurements through March of 2002. Figure 22 shows the location of these three monitors. The following observations are based on the data in Table 4:

The WTC and Church & Dey measurements from the first measurement day of September 23 through November 21 show unambiguous elevation, with concentrations ranging from about 10 to 170 pg TEQ/m’,

In this same time frame and for these two samplers, the influence of having high detection limits is seen in a few samples (WTC sample on 10/4: 176 pg TEQ/m^ at ND = >2 DL versus 140 pg TEQ/m^ at ND = 0; WTC sample on 10/11: 52.4 versus 9.6), but mostly, the congeners were detected and quantified, and TEQs were similar at ND = 0 and ND = DL.

The 6 Park Row measurements between October 12 and October 29 averaged 5.6 pg TEQ/m\ These measurements are consistent with the mid- to late-October measurements at Church & Dey, which is slightly off-site from Ground Zero, of

DRAFT-DO NOT QUOTE OR CITE 75 October 2002

NYC-WTC_000149019