Modeling Aquifer Storage and Recovery and Arsenic Contamination in a Cambrian-Ordovician Aquifer System, Green Bay, WI

Aquifer Storage and Recovery (ASR) has been investigated in the Cambrian-Ordovician aquifer system in Green Bay, Wisconsin as an option to enhance the local municipality's supply capabilities. In Green Bay, the local cone of depression became so extensive that the municipal supply was switched from groundwater to surface water from Lake Michigan in 1957. In the early 2000's, an ASR system was tested using treated lake water as the injection supply. ASR was seen as a potential method for increasing the treatment plant's capacity by injecting water treated during periods of off-peak demand then recovering and distributing that water during peak demand. The project was determined to be unfeasible due to high levels of arsenic in the recovered water. The system included an injection well open to approximately 550 ft of the aquifer system, including an upper quartz and dolomite aquifer, a middle confining unit, and a lower quartzaranite aquifer. Packers installed in the monitoring well between each of these units allow for sampling from three intervals. Differences in the concentration histories for specific conductance and arsenic concentrations among these three intervals suggest that preferential flow paths are present through one or more of the formations and that the release of arsenic to the injected water is not uniform among the units. This study investigates the Green Bay ASR system using computer modeling to assess preferential flow paths and likely sources for arsenic within the local stratigraphy.