Gas-Tracer Experiment for Evaluating the Fate of Methane in a Coastal Plain Stream: Degassing versus in-Stream Oxidation.

Methane emissions from streams and rivers have recently been recognized as an important component of global greenhouse budgets. Stream methane is lost as evasion to the atmosphere or in-stream methane oxidation. Previous studies have quantified evasion and oxidation with point-scale measurements.

Stream measurements locate thermogenic methane fluxes in groundwater discharge in an area of shale-gas development.

The environmental impacts of shale-gas development on water resources, including methane migration to shallow groundwater, have been difficult to assess. Monitoring around gas wells is generally limited to domestic water-supply wells, which often are not situated along predominant groundwater flow paths. A new concept is tested here: combining stream hydrocarbon and noble-gas measurements with reach mass-balance modeling to estimate thermogenic methane concentrations and fluxes in groundwater discharging to streams and to constrain methane sources.

A stream-based methane monitoring approach for evaluating groundwater impacts associated with unconventional gas development.

Gaining streams can provide an integrated signal of relatively large groundwater capture areas. In contrast to the point-specific nature of monitoring wells, gaining streams coalesce multiple flow paths. Impacts on groundwater quality from unconventional gas development may be evaluated at the watershed scale by the sampling of dissolved methane (CH4 ) along such streams.

Innovative environmental tracer techniques for evaluating sources of spring discharge from a carbonate aquifer bisected by a river.

Littlefield Springs discharge about 1.6 m³ /s along a 10-km reach of the Virgin River in northwestern Arizona. Understanding their source is important for salinity control in the Colorado River Basin.

Determining anisotropic transmissivity using a simplified Papadopulos method.

The straight-line method presented by Papadopulos requires a minimum of three observation wells for determining the transmissivity tensor of a homogeneous and anisotropic aquifer. A simplification of this method was developed for fractured aquifers where the principal directions of the transmissivity tensor are known prior to implementation, such as when fracture patterns on outcropping portions of the aquifer may be used to infer the principal directions. This new method assumes that observation wells are drilled along the two principal directions from the pumped well, thus reducing the required number of observation wells to two.

Gas-partitioning tracer test to quantify trapped gas during recharge.

Dissolved helium and bromide tracers were used to evaluate trapped gas during an infiltration pond experiment. Dissolved helium preferentially partitioned into trapped gas bubbles, or other pore air, because of its low solubility in water. This produced observed helium retardation factors of as much as 12 relative to bromide.