VOC sampling locations table for Ground Zero area, Jan 2002

NYC 9/11 Public Portal Document

DD = [IN * HRD * C * ABS]/[BW] (3)

where DD is daily dose (pg TEQ/kg-day); IN is the inhalation rate (m^/hr), HRD is the hours/day of inhalation, C is the concentration (pg TEQ/m^), ABS is the fraction of contaminant inhaled which is absorbed (unitless), and BW is the body weight (kg). The draft Dioxin Reassessment assumes an adult body weight of 70 kg and an absorption fraction of 0.8 for TEQ exposures, both from inhalation and food consumption, and these assumptions are used here. The average daily dose (ADD) is calculated simply as the average of the daily doses over the period of exposure.

2. Exposure Scenarios The scenarios which were evaluated here include:

1) WTC worker: This individual was exposed 10 hours per day, 5 days per week, in the time period between September 12 and November 30, 2001. This time frame roughly corresponds to the time when it seemed clear that dioxin air levels were elevated according to the monitoring data. Measurements from the WTC Building 5 monitor represent the concentration to which this individual is exposed. A time-weighted average (TWA) air concentration was derived for this period. The air concentration between September 12 and September 23 (the date of the first measurement at the WTC monitor) is assumed to be equal to the September 23 measurement, and the concentration between November 8 (the last date in November for the WTC monitor) and November 30 was similarly assumed to be equal to the measurement on November 8. These seem to be reasonable assumptions since the September 23 measurement from the WTC monitor was the second highest found at 161 pg TEQ/m\ and the November 8 measurement of 5 pg TEQ/m^ reasonably reflects the downward trend of measurements at the site. Between September 12 and November 30, a TWA air concentration was derived to represent the concentration to which the workers were exposed. A TWA concentration is not the same as the simple average of concentrations measured. To derive the time-weighted concentration, concentrations were assigned to each day between September 12 and November 30. From one measurement to the next, air concentrations were assumed to linearly rise or fall. For example, if the concentration was measured as 100 pg TEQ/m^ on one day and 5 days later it was 50 pg TEQ/m\ the concentrations assigned to the intervening days were 90, 80, 70, and 60 pg TEQ/m\ The TWA concentration is then simply the average of all the concentrations assigned to days when the worker was assumed to be exposed. With these assumptions, the average TEQ concentration during this time was calculated as 60.7 pg/m\ The rate of inhalation for a WTC worker was 1.3 m’/hr. This is equivalent to the rate for a “laborer” as quantified in EPA’s Exposure Factors Handbook (EPA, 1997).

2) Office worker: This individual is exposed 10 hours per day, 5 days per week, and the exposure began on September 19, corresponding to the time when individuals were allowed back into office buildings outside of the Ground Zero site itself but in areas initially “restricted” near Ground Zero. The office worker was assumed to be exposed to air concentrations measured by the Park Row monitor. This simplistically assumes that the air concentrations within office buildings near Ground Zero were similar to air concentrations outside of office buildings this close to Ground Zero. The period of exposure was September 19 to November 30, and the same strategy to derive TWA concentrations was used as for the WTC worker. The TEQ air

DRAFT-DO NOT QUOTE OR CITE 78 October 2002

NYC-WTC_000149022