Sampling frequency for water quality monitoring: Measures of effectiveness

摘要

Selecting the sampling frequency is one of the most important tasks in the design of a regulatory water quality monitoring program. This paper proposes two quantitative measures of the effectiveness of different sampling frequencies; these measures are intended to be used at the preliminary program design stage. The goal of the program is assumed to be the detection of violations of water quality standards. The first measure, M′, gives the expected proportion of violations that will be detected. The second, M″, is the ratio of the expected number of violated samples over the expected number of violations. Mathematical expressions for both statistics are developed. It is shown that by setting the average sampling interval equal to the average duration of a violation, the expected number of violated samples would equal the expected number of violations, since the errors caused by missing some violations and counting others more than once would tend to cancel