Quality Assurance And Quality Control

Groundwater sampling requires a quality assurance and quality control (QA/QC) plan which is designed to minimize sources of error in each stage of the sampling process, from sample collection to analysis and reporting. The QA/QC plan should include procedures and requirements for chain-of-custody, sample storage and holding time, use of quality control samples, instrument calibration, sample analysis, laboratory validation, documentation, and record keeping.

A chain-of-custody must be filed and maintained from the moment the sample bottles are released from the laboratory until the samples are received by the laboratory. The samples must be stored in conditions that preserve their integrity. Some samples require acidification to a specified pH or cooling to a specified temperature. In addition, the recommended maximum holding time for the analyte of interest should not be exceeded. Required holding times can range from hours to days as shown in Table 9.15.1.

The purpose of quality control samples is to detect additional sources of contamination in the field or laboratory that might potentially influence the analytical values reported in the samples. Examples of quality control samples include trip blanks and field blanks.

Trip blanks consist of a set of sample bottles filled at the laboratory with laboratory demonstrated analyte-free water. Trip blanks travel to the site with the empty sample bottles, at a rate of one per shipment, and back from the site with the collected samples to simulate sample handling conditions. Contaminated trip blanks indicate inadequate bottle cleaning or blank water of questionable quality.

Field blanks serve the same purpose as trip blanks but are also used to indicate potential contamination from ambient air or sampling instruments. At the field location, an-alyte-free water is passed through clean sample equipment and placed in an empty sample container for analysis. Therefore, by being opened in the field and transferred over a cleaned sampling device, the field blank can indi-

0 0

Post a comment