Determining an Optimal Sampling Frequency for Measuring Bulk Temporal Changes in Ground‐Water Quality

In the Data Quality Objectives (DQO) process, statistical methods are used to determine an optimal sampling and analysis plan. When the DQO decision rule for instituting remedial actions is based on a critical change in water quality, the monitoring program design must ensure that this change can be detected and measured with a specified confidence. Usually the focus is on the change at a single monitoring location and the process is limited to addressing the uncertainty inherent in the analytical methods and the variability at that location. However, new strategies that permit ranking the waste sites and prioritizing remedial activities require the means for assessing overall changes for small regions over time, where both spatial and temporal variability exist and where the uncertainty associated with these variations far exceeds measurement error. Two new methods for assessing these overall changes have been developed and are demonstrated by application to a waste disposal site in Oak Ridge, Tennessee. These methods incorporate historical data where available and allow the user to either test the statistical significance of a linear trend or of an annual change compared to a baseline year for a group of water quality wells.