Environmental lab report distribution, May 2002

NYC 9/11 Public Portal Document

Diojun

Tier Action Dioxin (settled dust) Dioxin (indoor air) Screening Basis Screening Basis Value Value I Aggressive >70 ng/m2 Risk-based >0.03 ng/m3 Risk-based cleaning. If levels screening level screening level persist, take for residential for residential additional action to setting (E-04 x 1 setting (E-04 x reduce exposure. yr) 1 yr) n Maintain 2 ng/ni2 (or 2 ng/m2 is risk­ 0.001 ng/m3 (or 0.001 ng/m3 is recommended backgroimd) based screening background) to Risk- based cleaning methods. to 70 ng/m2 level for 0.03 ng/m3 screening level Consider additional residential setting for residential monitoring (E-04 X 30 yr) setting (E-04 x 30 yr) m No further action <2 ng/m2 (or Determination of <0.001 ng/m3 Determination background) local background (or background) of local background

The inputs to the dose equations were based on the exposure assumptions that NYSDOH used in assessing office buildings in Binghamton, NY, and the proposed cancer slope factor for dioxin. In addition, the Tier I and III benchmarks equate to a lifetime exposure level which is approximately 1/10 of that which results fi-om current dietary intake of dioxin (65 pg/d). It is thus reasonable to assume that any lower level of exposure would result in an inconsequential reduction in the current risk levels experienced by the general U.S. population.

NYC background would also be an important consideration in determining the appropriate longer-term value. Propose selecting the longer-term value on the basis of a 10-4 risk level or NYC background, whichever is higher.

NYC-WTC_000162230