Precision And Accuracy

One of the objectives of the QA or QC plan is to ensure that there is no contamination from initial sampling through final analysis. For this reason, duplicate, field blank, and travel blank samples should be prepared and analyzed.

Duplicate sampling requires splitting one field sample into two aliquots for laboratory analysis. Typically, 10% of the samples should be collected in duplicate. Duplicates demonstrate the reproducibility of the sampling procedure.

A travel blank is a contaminant-free sample prepared in the laboratory that travels with empty sample bottles to the sampling site and returns to the laboratory with the samples. Typically, two travel blanks are prepared and shipped. Travel blanks identify contamination in the preparation of sample containers and shipping procedures.

Field blanks are empty sampling bottles prepared using contaminant-free water following general field sampling procedures for collection of waste samples. These are returned to the laboratory for analysis. Field blanks identify contamination associated with field sampling procedures.

For liquid samples, all three types of the above QA/QC samples are prepared. For soils, semi-soils, sludges, and solids, only duplicate samples are typically prepared.

The field supervisor of sample collection should maintain a bound logbook so that field activity can be completely reconstructed without relying on the memory of the field crew. Items noted in the logbook should include:

• Date and time of activity

• Names of field supervisor and team members

• Purpose of sampling effort

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