NYC-WTC_000164840

NYC 9/11 Public Portal Document

A summary of the reasons why some chemicals might not be found around the WTC is provided below. Full discussion of the reasons is provided in Appendix A.

Chemical Reason Benzene Benzene is very volatile and dissipates into ambient air quickly. This is confirmed by results of air monitoring around the WTC. PCBs All measurements of ambient PCB around the WTC work zone have been well below EPA’s screening level of concern. Chromium Levels of chromium measured around the WTC work zone have all been below the screening level. Cadmium & Cadmium was not detected in air sampling, except in one sample at Manganese a level equal to EPA’s screening level. Manganese was found in only three samples that were above EPA’s screening level. Mercury Although mercury was found once in police officers’ blood tests, the cause was determined to be canned tuna fish, not ambient air. Mercury has not been detected in any air samples taken in the WTC area. A study of indoor and outdoor WTC dust samples showed that it is unlikely that harmful levels of mercury could ever be released to the air. Particulate Ambient monitoring in the WTC area has shown that, since late Matter (PM) October, levels of PM 10 and PM 2.5 (two commonly measured inhalable PM sizes) have been below the level of concern, indicating that there is no continuing source PM entering homes and offices.

Setting Benchmarks for the Contaminants of Potential Concern (COPCs)

A tiered approach was used to evaluate the health risks posed by any contaminants that might be present in the indoor environment (air and dust). For each COPC, three levels were established:

Tier 1 Level above which aggressive clean-up action should be taken Tier 11 Level where diligent cleaning should continue, with follow-up testing Tier III Level below which the risk is negligible or no different from the every day

Each level (or “benchmark”) was established based on existing standards, where available and applicable. For example, action levels for lead in indoor air and dust were set using EPA’s National Ambient Air Quality Standard (NAAQS) and the Housing and Urban Development’s (HUD’s) standard for floors.

In cases where appropriate standards did not exist, risk-based criteria were developed using EPA risk assessment methods: for indoor air, methods described in EPA’s “Hazard Evaluation

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