NYC-WTC_000232959

NYC 9/11 Public Portal Document

Following the sampling effort, more than 5,400 analytical results were individually returned from the laboratory. All results were entered into a Microsoft EXCEL spreadsheet along with the other raw data describing where and how the sample was taken. Asbestos­ in-air laboratory results were submitted calculated in concentration and were used as received. The laboratory typically submitted particulates-in-arr results as the initial and final filter weights (pre- and post-sampling weights). The total amount of material deposited on the filter and resulting concentrations for the sampling location were estimated from the laboratory results. Results for asbestos, fiberglass, and mineral components in settled surface dust were used as provided by the laboratory: percentage of material analyzed.

All of the results were reviewed as a part of normal data quality analysis. The general purpose of this quality assurance/quality control (QA/QC) review is not to pronounce the data “accurate,” but to determine whether the results are obviously affected by sampling or analytical errors. For this investigation, the reported analytical results were accepted, rejected, or used conditionally. Decisions on how to treat a data set were made primarily by comparing the measured results to information gathered from the blanks using graphs and statistical analyses.

Most of the results were used as received from the laboratory. The laboratory reported the asbestos in air results as a concentration of asbestos in the sampled location. The asbestos and fibrous glass in airborne and settled surface dust were used as received.

Results for the airborne particulate matter were rejected due to issues found during the quality assurance analysis. Variability of field blank sample weights was beyond the acceptable limits. A more thorough discussion of why the airborne particulate matter results were rejected is located in Appendix A of this report.

The XRD analysis was conducted on the air samples collected for particulate matter (PMIOO, PMIO, PM4, and PM2.5). The PM results were rejected, but the XRD results were accepted as semiquantitative. The XRD results are considered valid because the analysis method does not depend on the filter-weighing process used to determine PM concentration. The XRD mineral concentrations are based on individual mineral weight standard curves—not the weight of the dust sample collected. These standard curves are not impacted by pre- and post-sampling filter weight variability.

Minerals were not detected on the blank air samples. This indicates that sample contamination or cross-contamination did not occur during air sampling, shipping, or sample analysis. The XRD information for the air samples provided semiquantitative values (estimated values, indicated by “J”). The PMIOO and PMIO results may be potential overestimates, as the crystalline mineral size used for the standard curve is close to PM4 in size. This will result in the XRD overestimating the concentration of minerals present in the larger fractions. Similarly, the PM2.5 results may be potential underestimates of mineral concentrations.

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