Water levels in many open monitoring wells fluctuate in response to changes in barometric pressure. The change in water level expressed as a fraction of the change in barometric pressure is termed the barometric efficiency (BE). For a shut-in monitoring installation, the change in pore pressure divided by the change in barometric pressure is called the loading efficiency (LE). By measuring how LE or BE vary with frequency or time following fluctuations in barometric pressure, we can infer if conditions are confined, semi-confined or unconfined. In addition, specific storage and drained compressibility can be estimated from LE or BE in confined and semi-confined formations. These parameters are important for incorporating into models used to predict the impact of groundwater extractions.
Low hydraulic conductivities (K) or large monitoring well diameters increase the time for monitoring wells to equilibrate with pore pressures. These time lags may be so long that BE cannot be adequately assessed in open monitoring wells. This study shows how packers can be used to reduce time lags to enable reliable LE assessments. Two examples are presented from the Mooki River catchment, New South Wales. Estimates of BE from an open monitoring well installed in a confined, high-K formation matched shut-in LE estimates. By contrast, BE could not be satisfactorily assessed in an open monitoring well located in a low-K confining layer due to time lag. For this site, a reliable assessment of LE was made from a short, 24-day monitoring period by sealing the monitoring well with a packer. The shut-in LE response showed that conditions were confined and enabled estimation of specific storage and drained compressibility. We conclude that short periods of shut-in monitoring can enhance our understanding of hydrogeological conditions and potentially provide hydraulic parameters to improve groundwater models.