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Fig. 1. Pressures relevant to measurement of water level in (a) a conventional (nonisobaric) well and in (b) an isobaric well. In both cases, water level is measured by using a pressure transducer to measure water pressure (Pobs) at a given elevation within the well. In the nonisobaric well, water levels in the well respond to changes in atmospheric pressure (Pbar) and the pressure transducer is referenced (Pref) to atmospheric pressure. The isobaric well is sealed from the atmosphere, and the pressure transducer is referenced (Pref) to gas pressure above the water table (Psg).
