Quality assurance sample design for large and small environmental water quality surveys; a look at the past and future

Abstract

During the National Surface Water Survey, implemented by the U.S. Environmental Protection Agency from 1984 to 1986, very large (> 1700 lakes) and relatively small (< 150 lakes) surveys were conducted. In the National Surface Water Survey a large commitment was made to quality assurance with a total of 546 performance audit samples, 426 field duplicate samples, and 365 field blanks being analyzed, all of which were double blind to the analyst. The following conclusions can be drawn about the effectiveness of various quality assurance samples in defining data quality: use of field blank data for defining the lower limits of detectability is controversial generating data of limited use. Field duplicate pair samples provided conservative estimates of precision when compared to the precision estimates provided by natural audit samples. Natural audit samples were useful for determining accuracy and precision of the measurement process, but were difficult to obtain in optimal analyte concentration ranges. Synthetic audit samples were plagued with preparation and instability errors. The trend in acid deposition studies today is toward long‐term, smaller scale studies involving multiple agencies with limited resources.

Keywords:

• Quality assurance
• lake surveys
• acid deposition
• performance audit samples
• precision
• accuracy