NYC-WTC_000232959

NYC 9/11 Public Portal Document

B. Potential Contaminants

The dust cloud released at the collapse of the buildings was comprised of materials that were used in the construction of the buildings (such as concrete and insulation materials). In addition to the dust cloud from the building collapse, contaminants were released in fires fed by jet fuel and the combustible materials in the buildings.

The dust contained the constituents of concrete, wallboard, and insulation. Concrete is a mixture of cement, aggregate (sand and gravel), and water. Cement contains limestone, clay, gypsum, and metals. Sometimes other minerals (such as fly ash or crystalline silica) are added to concrete to change its properties. Concrete tends to have a high pH, and if dust from the concrete was mixed with moisture, the resulting solution would tend to have a high pH. Asbestos was used as insulation in a portion of the towers. Fiberglass, a synthetic vitreous fiber, was also used as insulation in the buildings and is likely to have been used in building furnishings. Surface dust and debris containing asbestos have been found in lower Manhattan. Asbestos was detected in the personal air samplers of rescue and recoveiy workers. In addition, low levels of asbestos, fibrous glass, and the constituents of concrete and wallboard have been detected in air samples collected at the WTC site perimeter. These materials are common building components, and there are other sources of these materials in any large urban areas.

C. Monitoring in Lower Manhattan After the Collapse of the World Trade Center

The U.S. Environmental Protection Agency (EPA) and other federal, state, local agencies, and private firms have been conducting environmental monitoring in a variety of media since September 11 (some of the ambient air sampling locations are depicted on Figure 5). In November 2001, EPA tasked the IT Corporation Quality Assurance Technical Support Program contractor to evaluate the environmental monitoring data that had been collected. Through April 24, 2002, there were approximately 263,000 sample results analyzed (7). There were 605 analytics that were included in the database such as asbestos, fibers, particulates, metals, volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs). The greatest number of analytical samples was collected for analysis of total fiber concentration, asbestos fiber concentration, or the percentage of asbestos. The overall largest number of samples in the monitoring was for particulate matter. The monitoring stations for particulate matter (roof­ top locations) are a pail of the New York State Department of Environmental Conservation air quality-monitoring program. Additional stations were added after the WTC towers collapsed.

The analytical results of air samples showed decreasing concentrations that appeared to have reached pre-existing background levels by the end of April 2002 (7). Bulk dust samples were tested for asbestos, dioxins/furans, PCBs, PAHs, and metals. The levels for some of the analytics (e.g., asbestos) were relatively high; however, only a few samples obtained after mid-October showed elevated levels (7).

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