EPA permit requirements for Class VI injection wells explicitly include incorporating a Testing and Monitoring Plan to optimize protection of USDWs – Underground Sources of Drinking Water. The regulatory requirement is for periodic monitoring of groundwater quality above the confining zone that may result from injection fluid movement through the confining zone. Testing and monitoring plans usually implement an antidegradation strategy. Take sufficient background data to characterize the statistical distributions of groundwater quality parameters before operation. Then the same water quality parameters are sampled periodically during and after injection and compared to the background. Any statistically significant increases over the background are investigated as a possible result of injectate migration above the confining zone.
To make the detection monitoring program more robust, there is a tendency to increase the number of well/parameter pairs in the monitoring network. This is done by adding additional wells to decrease well spacing and by adding monitoring parameters to make sure that nothing gets missed. Paradoxically, this tendency decreases the statistical power of the groundwater monitoring network by increasing the sitewide false positive rate (i.e., the number of false positive detections increases, often to an unreasonable degree). Each apparent statistically significant increase involves a costly investigation with greatly increased complexity. In this talk, we examine the sitewide false positive rate for sitewide groundwater monitoring networks and its relationship to the number of well/parameter pairs and discuss how hydrologic and geochemical knowledge and characterization can be used to build a more robust and cost-effective groundwater monitoring plan that is protective of USDWs near Class VI injection wells.