Recycling wastewater for direct potable reuse by artificially recharging underground aquifers is a decades-old but increasingly popular tool in the fight against depleting water supplies. An important parameter, mandated under state law due to its connection to water quality, is the underground residence time of recharged water. Hydrogeologists primarily employ conservative geochemical tracers to quantify subsurface travel time. My research investigates multiple tracer approaches, searching for the ideal candidate to date water on the required time scale. Additional research examines gas exchange rates at the air-water interface of a subalpine stream near Lake Tahoe, part of a larger project to study groundwater/surface water interaction.