Determining Groundwater Residence Times of the Kaibab Plateau, R-Aquifer using Temperature, Grand Canyon National Park, Arizona

Water discharging from the R-aquifer of the Kaibab Plateau at Roaring Springs is the sole water supply for Grand Canyon National Park's staff and nearly 5 million visitors per year. Snow melt and large summer monsoon rainfall events infiltrate the Kaibab Plateau through sinkholes, faults, and fractures. Infiltrating water travels hundreds of meters vertically downward before entering the well-developed karstic R-aquifer comprised of the Redwall Limestone (Mr), the Temple Butte Formation (Dtb), and Muav Limestone (Cm). The R-aquifer is a very complex assemblage of lithologies governed by structural and chemical controls. The purpose of this study was to gain a better understanding of 1) residence times for R-aquifer waters using natural tracers, 2) determine the degree of karstification of the Kaibab Plateau, 3) determine the best sampling times for a dye tracer study.;Instrumentation to measure stage, temperature, and conductivity were deployed at five R-aquifer springs, one C-Aquifer spring in Grand Canyon, and one sinkhole on the Kaibab Plateau. The length of data collection varied at each site for various reasons, but included portions of hydrologic responses between 2011 and 2014. Hydrograph interpretation techniques were used to determine groundwater residence times and properties of the R-aquifer. Residence times of event based discharge are very quick (<2) days for a deeply buried karst aquifer. Any effects of changes in land use or climate change will be seen very quickly at R-aquifer springs. An interpretation of LiDAR data determined that the Kaibab Formation, atop the Kaibab Plateau, contains a sinkhole density of up to 3-5 per km2, and faults and fractures which funnel snowmelt and monsoon events into the groundwater systems. A hazardous material release, catastrophic fire, or change in land management, could compromise the quantity and quality of water for municipal use at Grand Canyon National Park. Streams that derive their source from the R-aquifer and are habitat for endangered species could also be impacted.;This study was performed to improve understanding of the R-aquifer system and to provide a foundation for future scientific investigations. To better constrain contributing areas and residence time of the springs of the Grand Canyon, well-planned qualitative and quantitative dye tracer studies would prove invaluable. Further monitoring of the R-aquifer system and implementation of techniques outlined in this study will help insure water quality and quantity for Grand Canyon National Park.