WTC environmental health assessment draft, May 2002

NYC 9/11 Public Portal Document

Tier II Level where diligent cleaning should continue, with follow-up testing Tier ID 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 Handbook: A Guide to Removal Actions” were used; for dust, EPA’s “Wipe Sample Assessment” guidance was used. The risk-based criteria reflect the most current toxicity criteria (slope factors and RfCs) on EPA’s Integrated Risk Information System (IRIS), which is a regularly updated, online database that reports chemical toxicity reference values and information.

Individual sampling results that exceed benchmark values should not be interpreted to represent the occurrence of an adverse health effect. Rather, such information indicates the need for careful monitoring and the assessment of longer-term data trends for evaluation against appropriate health criteria. That is, most of the screening levels have been developed to account for continuous one-year average exposure durations. Because these screening levels assume continuous exposure for an extended duration, the average of the measured concentrations is more appropriate for evaluating risk than an individual measurements. Consequently, miscellaneous individual values above the screening level may not necessarily be indicative of potential for concern.

Developing Risk-Based Criteria for Indoor Air

For carcinogenic compounds, the benchmarks were set so that a local resident’s lifetime risk of developing cancer from exposure to WTC-related contaminants for a certain amount of time would be only one-in-ten-thousand greater than the resident’s normal risk without this exposure (in risk assessment terms, the excess lifetime cancer risk was set at E-04). The amount of time that residents and office workers were exposed to WTC-related contaminants is unknown. To be conservative, the Tier I action level was chosen to be protective of a resident who may have been exposed to WTC-related contaminants for one year. The Tier IH no-action-needed level was chosen to be protective of a resident who is exposed to WTC-related contaminants for 30 years (which is the upper-bound estimate for residency in one dwelling). The 30-year and 1-year exposure durations reflect an apportionment between child (20% of total exposure duration) and adult (80% of total exposure duration) receptors. Because children have comparatively greater (as a function of body weight) respiration rates than adults, the benchmark levels developed are marginally more stringent than values that would otherwise be derived by direct application of IRIS-verified Unit Risk values.

3

CONFIDENTIAL, CITY_2IMCl00_003423791 SUBJECT TO PROTECTIVE ORDER NO. 2, SEPT. 2008

NYC-WTC_000176162