New Insights From Water-Level Responses to Barometric-Pressure Fluctuations

Hydrologists have long recognized that changes in barometric pressure can produce changes in water levels in wells. The relationship between barometric pressure and water level has traditionally been characterized using the barometric efficiency (BE), the ratio of the change in water level to the change in barometric pressure head.  Although BE has proven to be an effective means of characterizing short-term responses of a well to a change in barometric pressure, the barometric response function (BRF) is a more effective means for characterizing longer-term responses. The BRF, which can be determined through a regression deconvolution procedure that is readily programmed in Excel, characterizes the water-level response over time to a step change in barometric pressure, essentially BE as a function of the time since the imposed load. We have extended earlier work to show that the BRF can be utilized to glean important insights into semi-confined aquifer systems. The form of the BRF indicates the degree of aquifer confinement, while a comparison of BRFs from different wells sheds light on aquitard continuity. We have developed a new approach for estimating aquitard K using BRF type curves and have verified the approach with results from a four-day pumping test. We will demonstrate the power of the BRF using field data from a series of Kansas Geological Survey monitoring sites. We will also assess the impact of well construction on BRFs from semi-confined aquifers. The BRF is a promising tool for gaining important insights into site hydrostratigraphy through passive monitoring of water levels and barometric pressure, and can often be a cost-effective supplement to a conventional pumping test for assessing aquitard properties.