WTC environmental health assessment draft, May 2002

NYC 9/11 Public Portal Document

Minerals in Settled Dust

Tier Action Gypsum and Calcite Level Portlandite Level Calcium Sulfate Level I Aggressive cleaning. If 10,000/z/m’ 2000/yn?- 10,000 /z/m’ levels persist, take additional action to reduce exposure. n Maintain recommended 3300 Az/m’ 660 M/m’ 3300 Az/m’ cleaning methods. Consider additional monitoring in No further action 1000 200Az/m’ 1000 Az/m’

General approach for air screening levels:

Tier I is set at the TLV reduced by a factor of 10 to account for some of the uncertainty in predicting when the material may become irritable to sensitive populations.

Tier III which is intended to be protective over a long-term exposure is further reduced from Tier 1. The additional uncertainty factor of 10 may address irritant effects after prolonged exposure; and round the clock exposure, as well as additional consideration of sensitive populations.

Tier 11 would be the range between Tiers I and DI.

Settled dust:

Compare all minerals to loadings found in the background areas as ug/cm^. Any increased mineral loading should be addressed as Tier ll.

Dust pH should also be determined. Any dust exhibiting a pH greater than background or 8.5, which ever is higher, should be considered an irritant and addressed as Tier n.

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CONFIDENTIAL, CITY_21MC100_003423806 SUBJECT TO PROTECTIVE ORDER NO. 2, SEPT. 2008

NYC-WTC_000176177