Chain of Custody Form Instructions for WTC Building Sampling

NYC 9/11 Public Portal Document

General Notes on Quality Assurance/Quality Control Procedures

Quality assurance/quality control (QA/QC) procedures are used to ensure the precision, accuracy, completeness, representativeness, comparability, and method detection limit of the results. The co­ located samples and blanks are a primary means of assessing each of the data quality indicators. Comparing the results of two co-located samples provides information on the precision of the results as a whole. Comparing sample results to their associated blanks can help identify some potential errors in accuracy. Comparing the results received to those expected and necessary to draw conclusions about the data can help in understanding the completeness and reliability of the results. Comparability can be assessed by looking at the results taken from different sampling locations of the same building—or from different buildings for the same type of location. The reviews are generally qualitative and provide a qualitative assessment of how well the data actually represents the sampled location.

The method detection limit is a more quantitative review. It is accomplished by calculating the lowest result the analytical method can accurately identify. It is based on an analysis of the blank samples and is specific for the sampling/analysis method. Reliable information can only be obtained from sample results with method detection limits significantly lower than the average value of the results and significantly lower than any comparison values to which the sample results will be compared.

The analytical results of the concentration of airborne particulate matter were provided by the laboratory as the initial weight of the filter prior to the sampling event and the final weight of the filter after the sampling event. The concentration of the particulate matter was calculated by dividing the weight of the material collected on the filter by the volume of air drawn through the filter by the pump using the following formulas.

Weight Gain of Filter = Final Weight - Initial Weight

Sample Volume = Average Pump Flow Rate x Sample Collection Time

Average Air Sampling Pump Flow Rate=(Presampling Flow Rate + Postsampling Flow Rate) + 2

Concentration = Weight Change Sample Volume

Airborne Particulate Matter Sample Results

Each area that was sampled for airborne asbestos was also sampled for airborne particulate matter (PM). The sample results from the PM measurements did not meet the data QA/QC objectives. A variety of statistical and graphical analyses were performed on, and with, the measured results in an attempt to identify the cause and extent of inconsistencies of the measured results. A subset of the measured results that are not potentially affected by these inconsistencies were not identified. Therefore, the entire data set describing airborne particulate matter concentrations was rejected. In addition, the specific cause of the inconsistencies was not identified. The following information explains why the airborne particulate matter results were rejected.

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