Forwarding WTC air monitoring scope for final review, Aug 2002

NYC 9/11 Public Portal Document

Pt. 763, Subpt. E, App. A 40 CFR Ch. I (7-1-00 Edition) may be considered complete without com­ centration on the blank fil­ paring the Inside samples to the outside sam­ ters that is less than or equal to 70 s/mm^ and ples. EPA is permitting this initial screening the average airborne asbestos concentration test to save analysis costs In situations measured Inside the abatement area is not where the airborne asbestos concentration is statistically higher than the average air­ sufficiently low so that It cannot be distin­ borne asbestos concentration measured out­ guished from the filter contaminatlon/back- side the abatement area as determined by ground level (fibers deposited on the filter the Z-test. The Z-test Is carried out by calcu­ that are unrelated to the air being sampled). lating The screening test cannot be used when vol­ umes of less than 1,199 L for 25 mm filter or 2,799 L for a 37 mm filter are collected be­ cause the ability to distinguish levels sig­ nificantly different from filter background Is z reduced at low volumes. The Initial screening test is expressed in 0.8 (l/n, ♦ structures per square millimeter of filter be­ where Yi Is the average of the natural loga­ cause filter background levels come from rithms of the inside samples and Yo is the sources other than the air being sampled and average of the natural logarithms of the out­ cannot be meaningfully expressed as a con­ side samples, ni is the number of inside sam­ centration per cubic centimeter of air. The ples and no is the number of outside samples. value of 70 s/mm^ is based on the experience The response action is considered complete if of the panel of microscopists who consider Z is less than or equal to 1.65. one structure in 10 grid openings (each grid Note; When no fibers are counted, the cal­ opening with an area of 0.0057 mm^) to be culated detection limit for that analysis is comparable with contaminatlon/background inserted for the concentration. levels of blank filters. The decision is based, 2. If the abatement site does not satisfy ei­ in part, on Poisson statistics which indicate ther (1) or (2) of this Section C. the site must that four structures must be counted on a be recleaned and a new set of samples col­ filter before the fiber count Is statistically lected. distinguishable from the count for one struc­ ture. As more Information on the perform­ D. Sequence for Analyzing Samples ance of the method is collected, this cri­ It is possible to determine completion of terion may be modified. Since different com­ the response action without analyzing all binations of the number and size of grid samples. Also, at any point in the process, a openings are permitted under the TEM pro­ decision may be made to terminate the anal­ tocol, the criterion is expressed in structures ysis of existing samples, reclean the abate­ per square millimeter of filter to be con­ ment site, and collect a new set of samples. sistent across all combinations. Four struc­ The following sequence is outlined to mini­ tures per 10 grid openings corresponds to ap­ mize the number of analyses needed to reach proximately 70 s/mm^. a decision. B. Sample Collection and Analysis 1. Analyze the inside samples. 2. If at least 1,199 L of air for a 25 mm filter 1. A minimum of 13 samples is required: or 2,799 L of air for a 37 mm filter Is collected five samples collected inside the abatement for each Inside sample and the arithmetic area, five samples collected outside the mean concentration of structures per square abatement area, two field blanks, and one millimeter of filter is less than or equal to 70 sealed blank. s/mm^, the response action is complete and 2. Sampling and TEM analysis must be no further analysis is needed. done according to either the mandatory or 3. If less than 1,199 L of air for a 25 mm fil­ nonmandatory protocols In Appendix A. At ter or 2,799 L of air for a 37 mm filter is col­ least 0.057 mm^ of filter must be examined on lected for any of the inside samples, or the blank filters. arithmetic mean concentration of structures per square millimeter offilter Is greater than C. Interpretation of Results 70 s/mm^, analyze the three blanks. 1. The response action shall be considered 4. If the arithmetic mean concentration of complete if either: structures per square millimeter on the a. Each sample collected Inside the abate­ blank filters Is greater than 70 s/mm^, termi­ ment area consists of at least 1,199 L of air nate the analysis, identify and correct the for a 25 mm filter, or 2,799 L of air for a 37 source of blank contamination, and collect a mm filter, and the arithmetic mean of their new set of samples. asbestos structure concentrations per square 5. If the arithmetic mean concentration of millimeter of filter is less than or equal to 70 structures per square millimeter on the s/mm^: or blank filters is less than or equal to 70 s/ b. The three blank samples have an arith­ mm^. analyze the outside samples and per­ metic mean of the asbestos structure con- form the Z-test.

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NYC-WTC_000139319