NYC-WTC_000232959

NYC 9/11 Public Portal Document

as higher than values in comparison areas above 59th Street. So although these materials are found in urban areas, perhaps due to erosion of concrete, building construction and maintenance, the estimated percentages of calcite and portlandite were larger in some areas of lower Manhattan relative to the comparison areas above 59th Street (Figures 13 and 15.)

Gypsum (hydrated calcium sulfate) is a major component of dry wall. Gypsum was found in 11 of 14 outdoor settled dust samples at levels estimated as 0.03%J to 27%J. Indoor levels of gypsum ranged from an estimated 0.07%J to 20%J in 23 of 26 common areas and from 0.05%J to 30%J in 45 of 57 residences. These estimated percentages are higher than the estimated maximum of 4%J seen in the comparison areas above 59th Street. Figure 14 shows the locations where the estimated gypsum content in settled surface dust was higher than or similar to the levels in the dust samples from the comparison areas above 59th Street. Nine residence and six common area samples had estimated levels higher than those found in the comparison areas above 59th Street. Gypsum was elevated in settled indoor dust in some areas of lower Manhattan relative to the comparison areas above 59th Street (Figure 14).

The data can also be evaluated in a nonquantitative manner by just inspecting the frequency of detects of mineral in dust for lower Manhattan and the comparison areas. As shown in Table 7, the pattern of prevalence for the minerals appears to be similar in both study areas. In other words, the minerals were detected in both locations with about the same frequency. The data imply that building materials were the source for both areas. This source was likely building materials; however, the magnitude of the impact was greater in areas closer to the World Trade Center.

3. Alkalinity of Settled Surface Dust

Several of the minerals detected in the settled surface dust samples, such as portlandite, can make the dust more alkaline, or raise the pH. Originally, the pH of all of the settled surface dust samples was to be determined. However, enough dust for this analysis was only available at two locations. Both dust samples were alkaline (pH of 8.6 and 9.8). On the pH scale of 0 (acidic) to 14 (alkaline or basic), these values are slightly alkaline. Mineral analysis of these two settled surface dust samples estimate levels of calcite (15%J, 19%J) and portlandite (6%J, 3%1) were present, respectively. These crystalline minerals along with other components of concrete would have contributed to the measured alkalinity.

C. Air

The settled surface dust results discussed previously indicate the materials present in each area sampled. Fibers and small particles within the dust may become airborne during daily activity or during periods of high activity such as cleaning. Therefore, the settled surface dust sample results are an indicator for areas with a potential for airborne contaminants.

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