Well design to reduce barometric pressure effects on water level data in unconfined aquifers

Barometric pressure fluctuations may influence measured water levels in wells where thick vadose zones or low permeability materials overlie unconfined aquifers. Here, we present a well completion method designed to reduce the effects of barometric pressure fluctuations on measured water levels. This well configuration, called the isobaric well, seals the interior of the well from atmospheric pressure, and vents the reference side of the water level pressure transducer to the gas phase pressure above the water table. We tested the isobaric design on a well completed about 180 m below land surface in the Eastern Snake River Plain aquifer at the Idaho National Engineering and Environmental Laboratory. Water level data collected during 14 mo show more than an order of magnitude decrease in diurnal fluctuations when the well was operated in the isobaric mode. Decreasing the noise level allowed clear definition of water level trends that would otherwise have been at least partially obscured by barometric This well configuration allows direct monitoring of water changes, without the need to rely on postprocessing to mitigate barometric influences.