EPA interim final report on WTC background study, April 2003

NYC 9/11 Public Portal Document

sampling method, analytical results for vacuum dust samples are not likely to reflect the total dust contained within the sampling area prior to sample collection. This practice generally will have a collection bias towards smaller, less dense particles.” Since the bias of this method is known, microvacuum samples collected for lead analysis were used for determining background loading levels.

4.1.3 Wipe Sample Collection Wipe samples of settled dust, from nonporous hard surfaces were collected fi-om each unit and analyzed for asbestos, lead, dioxins, PAHs, crystalline silica, calcite, gypsmn and total dust. The methods used for the collection and analysis of wipe . samples are summarized in Table 4-1.

Wipe sampling employs the use of a cloth-like material (e.g., gauze. Ghost Wipes'™ or baby wipes), wetted or pre-moistened with a solution and is conducted by wiping an area within a template of known size.

4.1.4 Bulk Dust Sample Collection During the development of the sampling plan and QAPP, no standard method was found for the collection of dust and particulate matter trapped in window air­ conditioner filters. EPA’s contractor TRC developed a procedure to collect this material by brushing the dust and particulate matter fi-om the filter using a disposable brush. The dust was collected into a foil-lined stainless steel bowl. If sufficient material was obtained, the sample was transferred to the appropriate sample container for shipment to the laboratory. The procedure is noted in Table 4-1 of this report.

In several cases there was not enough material on the window air-conditioner filter for all of the analyses to be conducted. An order prioritizing the analyses was established in the event of insufficient material collected. The first container was sent for the analysis of asbestos and man-made vitreous fibers (MMVF). If sufficient sample material was collected for the remaining parameters, the second container was sent for analysis of lead, crystalline silica, excite and gypsum in descending priority.

Dust and particulate matter of sufficient amount could not be collected fi-om any of the apartment air-conditioning unit filters for the analysis of PAHs and dioxins. These parameters require a large quantity of material in order to conduct the analyses.

4.1.5 Quality Control Samples Quality control (QC) samples are used to assess the sampling and analytical processes and to ensure that these processes are being conducted properly. QC samples were collected during each day of sampling. These samples included the collection of field spike wipe samples, field blanks and lot blanks. QC samples were collected for microvacuum, wipe and air samples. QC samples were not collected with the bulk dust samples due to insufficient material needed to perform the analyses. Table 4-2 provides a summary of the samples collected WORLD TRADE CENTER BACKGROUND STUDY 13

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