Law Department notice on WTC document preservation, Oct 2001

NYC 9/11 Public Portal Document

of dust contamination as determined through visual inspection. If a visual inspection of the residence and the building’s common spaces (including elevator shafts) revealed minimal dust accumulations (light coating), “Scope of Work A” applied. If visual inspection indicated large or significant accumulations of dust or debris from the WTC collapse in residences, portions of the residence, or the building’s common spaces, “Scope of Work B” applied. In general, “Scope of Work B” included additional cleaning of surfaces not included in “Scope of Work A.” Appendix M describes the two approaches available for residents requesting cleaning and post-cleaning testing.

A significant issue with respect to developing health-related benchmarks (or clearance standards) is the extent of prior or background contamination, particularly in urban areas. This information is needed to determine the impact of a disaster on the indoor environment. Studies have shown that these background levels can exceed concentrations that may present a greater than 1-in-1,000,000 excess lifetime cancer risk (the desired cleanup goal for the Superfund program). In the WTC case, EPA’s background study of Upper Manhattan suggests that the background concentrations for asbestos in indoor air and dioxin in settled dust were at levels that presented a greater than 1-in-1,000,000 excess cancer risk.

Concurrent with the start of the indoor cleanup, a multi-agency workgroup of Federal, State and city officials identified contaminants of potential concern (COPC) related to the WTC collapse and developed health-related benchmarks for these COPCs, including asbestos, lead, dioxin, PAHs, fibrous glass, and crystalline silica. Three of these COPCs are considered cancer causing: asbestos, dioxin, and PAHs. For each of the three carcinogens, the workgroup established a health-related benchmark that equated to an increased lifetime cancer risk of 1-in- 10,000. This means that if 10,000 people are exposed to n single COPC at the established benchmark level for 30 years, there may be one more case of cancer than if die group had not been exposed.

In September 2002, the multi-agency workgroup published these COPCs in a peer review draft entitled “World Trade Center Indoor Air Assessment: Selecting Contaminants of Potential Concern and Setting Health-Based Benchmarks,” which was peer reviewed by the Toxicology Excellence for Risk Assessment (TERA) organization in October 2002. TERA’s peer review report was issued on February 7,2003. The group’s suggestions included:

• Expanding the list of COPCs as appropriate, • More clearly explaining the methodology for selecting the COPCs, • Adding criteria to account for potential exposures through contact with dust in the risk-based screening for COPC selection, • “Adding parameters for children’s exposure, and • More fully describing the approach for considering the health effects of mixtures of COPC.

49 Report No. 2003-P-00012

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