PNNL

Abstract

This chapter illustrates application of a powerful intra-well testing method referred as the combined Shewhart-CUSUM control chart approach, which can detect abrupt and gradual changes in groundwater parameter concentrations. This method is broadly applicable to groundwater monitoring situations where there is no clearly defined upgradient well or wells, where spatial variability exists in parameter concentrations, or when groundwater flow rate is extremely slow. Procedures for determining the minimum time needed to acquire independent groundwater samples and useful transformations for obtaining normally distributed data are also provided. The control chart method will be insensitive to detect real changes if a preexisting trend is observed in the background data set. A method and a case study describing how a trend observed in a background data set can be removed using a transformation suggested by Gibbons (1994) are presented to illustrate treatment of a preexisting trend.