A New Approach to Monitoring Groundwater/Surface Flow Relationships, Using 222Rn and SF6

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The measurement of natural 222Rn and deliberately introduced SF6 can be used to accurately detect and quantify groundwater delivery to stream flow. Experiments, involving the simultaneous measurement of 222RN and SF6 will be conducted in the Santa Fe River in Florida. The detection of anomalously high levels of 222Rn in the stream will permit the identification of locations of groundwater input. The observed variations between SF6 and 222Rn will be used to determine accurate gas exchange rates, which are needed to estimate the groundwater component of surface discharge. The rate of gas exchange, which can be expressed as a reaeration coefficient, is also a determining factor in assessing water quality in a stream. Thus, the measurement of 222Rn and SF6 together will yield another geochemical technique for assessing the water quality of aquatic systems. Measurements of the D/H and 180/160 ratios in water samples collected from the Sante Fe during a 222Rn survey following a major precipitation event when the difference between the precipitation derived surface runoff and the well integrated groundwater component is maximized will provide an independent check on estimates of groundwater delivery based on the 222Rn data. The proposed research will benefit hydrologists and water resource managers by establishing a powerful new geochemical technique for examining the interconnections between groundwater and surface flow. In addition, the research will provide a hydrologic and water quality data base not easily obtained by conventional methods.