Sampling frequency for ground-water quality monitoring. Final report, May 1985-May 1989

The project was initiated to collect a benchmark water-quality dataset and evaluate methods to optimize sampling frequency as a network design variable. Ground water was collected biweekly for 18 months from twelve wells at two sites in a shallow sand and gravel aquifer in Illinois. Sampling and analyses were conducted for twenty-six water-quality and geochemical constituents with careful quality control measures to allow statistical analysis of variability in ground-water quality data. The results demonstrate that natural variability over time can exceed the variability introduced into the data from sampling and analysis procedures. Analysis of data collected during the project suggests that the collection of a long-term dataset is necessary to determine optimal sampling frequency and to identify seasonal trends in ground-water monitoring results.