Application of intrawell testing of RCRA groundwater monitoring data when no upgradient well exists.

A statistical quality control approach to detect changes in groundwater quality from a regulated waste unit is described. The approach applies the combined Shewhart-CUSUM control chart methodology for intrawell comparison of analyte concentrations over time and does not require an upgradient well. A case study from the U.S. Department of Energy's Hanford Site is used for illustration purposes. This method is broadly applicable in groundwater monitoring programs where there is no clearly defined upgradient location, the groundwater flow rate is exceptionally slow, or where a high degree of spatial variability exists in parameter concentrations. This study also indicates that the use of the Data Quality Objectives (DQO) process can assist in designing an efficient and cost-effective groundwater monitoring plan to achieve the optimum goal of both low false positive and low false negative rates (high power).