GROUNDWATER DELINEATION BETWEEN STACKED KARST AQUIFERS USING STABLE ISOTOPES ON THE KAIBAB PLATEAU, GRAND CANYON

Stable Isotope end member mixing analyses of the regional carbonate Redwall-Muav aquifer (R aquifer) and Coconino (C aquifer) were used to evaluate the hydrogeologic properties of the C aquifer. This research continues to improve the understanding of how the C aquifer influences groundwater flow to the underlying R aquifer. Groundwater on the Kaibab Plateau flows between the shallow C aquifer and deep R aquifer and then discharges from springs on the North Rim. R aquifer isotope end member mixing have indicated a direct connection with the C aquifer; a perched aquifer 300 m above the R aquifer. New and increased sampling at both C and R aquifer springs were conducted to better isolate summer (rain) and winter (snow) precipitation isotopic signatures. Kaibab Plateau isotope research is important because the municipal water supply for Grand Canyon National Park is from a spring issuing from the R aquifer. Stable isotope ratios of and δD have been successfully applied to select R aquifer springs to determine seasonal contribution from recharge areas on the Kaibab Plateau. Discharge monitoring at R aquifer springs and dye tracer studies have established greater lateral connectivity between recharge areas and R aquifer springs. Precipitation on the Kaibab Plateau likely recharges directly into C aquifer storage and then undergoes significant, lateral groundwater flow until intercepted by vertical faults and fractures connected to R aquifer springs in Grand Canyon.