A controlled recharge event with multiple tracers was conducted on August 30, 2010. A pool adjacent to a sinkhole was filled with approximately 13,000 L of water. The water was heated, and salt, deuterium oxide, and uranine were added. The pool was then emptied into the sinkhole, and data were collected at Freiheit Spring approximately 95 m north of the sinkhole to monitor changes in discharge, temperature, conductivity/chloride, δD, uranine, and suspended sediment. This combined trace demonstrated the feasibility and utility of conducting superimposed physical, chemical, and isotopic traces. Flow peaked first at the spring and was followed by a suspended sediment peak; then essentially identical uranine, chloride, and δD peaks; and finally a temperature peak. The initial increase in flow at the spring recorded the time at which the water reached a submerged conduit, sending a pressure pulse to the spring at the speed of sound. The initial increase in uranine, chloride, and δD at the spring recorded the arrival of the recharge water. The initial change in temperature and its peak occurred later than the same parameters in the uranine, chloride, and δD breakthrough curves. As water flowed along this flow path, water temperature interacted with the aquifer, producing a delayed, damped thermal peak at the spring. The combination of conservative and nonconservative tracers illustrates unique pressure, advective, and interactive processes.
Bibliographical noteFunding Information:
Funding for this project was provided by the Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources (LCCMR). A.J.L. is supported by a Doctoral Dissertation Fellowship from the University of Minnesota Graduate School. M.D.C. acknowledges support from the National Science Foundation (NSF) under Earth Sciences Postdoctoral Fellowship 081647. The ongoing permission of Susan, Aaron, and Matt Kolling to access their property is gratefully acknowledged.
- Heat transport
- Tracer breakthrough curve