Chain of custody form for DEP environmental samples, 2001

NYC 9/11 Public Portal Document

aggressive technique.

The results from the two commercial units included as part of the study could not be used to evaluate existing contamination or overall cleaning efficiency, in as much as the cleaning and sampling process that was used in the commercial units differed from the cleaning and sampling process that was used in the residential units. The non-study commercial units were sampled only for post-cleaning clearance confirmation.

It should be noted that samples were collected for alpha-quartz, calcite, gypsum, tridymite, crystobalite and total dust. However, data for these parameters are not included in this document due to uncertainties in the analytical results. Another data set, asbestos micro vacuum samples, was also not included for evaluating the extent of contamination or cleaning efficiency because the results were extremely variable and did not present consistent trends, as did other data. A work group of the Interagency Indoor Air Task Force debated the inclusion of asbestos micro vacuuming in this study as a result of concerns that the results would not be relevant because, as stated in the ASTM - Standard Test Method for Micro Vacuum Sampling and Indirect Analysis of Dust by Transmission Electron Microscopy for Asbestos Structure Number Concentrations; ".. .the collection efficiency of this technique is unknown and will vary among substrates.”*’ This uncertainty, combined with the high degree of uncertainty in predicting airborne asbestos levels based on the amount in settled dust^” and the variable nature of the asbestos micro vacuum results, limited the use of this data set. Despite these concerns and the quantitative limitations of the method, micro vacuuming was used in an effort to assess the presence of asbestos.

The data sets that did not provide adequate information for determining the extent of existing contamination and the efficiency of cleaning methods, were useful, in combination with the other data sets, to address variances in the use of different sampling and analytical methods, and the use of different equipment.

5.2 Extent of Contamination

This study was designed to establish the effectiveness of a variety of cleaning methods in removing dust and associated materials related to the WTC collapse. In order to evaluate different cleaning methods, the degree of contamination prior to cleaning needed to be assessed. This was accomplished by visually observing the amount of dust in an apartment and by collecting samples prior to cleaning events.

Qualitative visual observations of the quantities of WTC dust that had been deposited into each

'^American Society for Testing and Materials. (1995/ Standard Test Methodfor Microvacuum Sampling and IndirectAnalysis ofDust by Transmission Electron Microscopyfor Asbestos Structure Number Concentrations. (ASTM Publication No. D576-95.) West Conshohocken, PA.

2°The uncertainty of predicting airborne asbestos levels based on settled dust was recently reiterated by a panel of experts that peer reviewed an EPA report that proposed a health-based benchmark for asbestos in settled dust based on utilizing a K factor approach. Specifically, the peer review panel (www.tcra.org) stated: "The panel did not endorse the asbestos settled dust benchmark because the only relevant exposure pathway for asbestos is inhalation and the K-factor methodology is, at this time, inadequate for predicting inhalation exposure from asbestos surface loading measurements." 104

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