A method to estimate groundwater depletion from confining layers

Abstract

[1] Although depletion of storage in low-permeability confining layers is the source of much of the groundwater produced from many confined aquifer systems, it is all too frequently overlooked or ignored. This makes effective management of groundwater resources difficult by masking how much water has been derived from storage and, in some cases, the total amount of water that has been extracted from an aquifer system. Analyzing confining layer storage is viewed as troublesome because of the additional computational burden and because the hydraulic properties of confining layers are poorly known. In this paper we propose a simplified method for computing estimates of confining layer depletion, as well as procedures for approximating confining layer hydraulic conductivity (K) and specific storage (S s ) using geologic information. The latter makes the technique useful in developing countries and other settings where minimal data are available or when scoping calculations are needed. As such, our approach may be helpful for estimating the global transfer of groundwater to surface water. A test of the method on a synthetic system suggests that the computational errors will generally be small. Larger errors will probably result from inaccuracy in confining layer property estimates, but these may be no greater than errors in more sophisticated analyses. The technique is demonstrated by application to two aquifer systems: the Dakota artesian aquifer system in South Dakota and the coastal plain aquifer system in Virginia. In both cases, depletion from confining layers was substantially larger than depletion from the aquifers.Citation: Konikow, L. F., and C. E. Neuzil (2007), A method to estimate groundwater depletion from confining layers, Water Resour.

Water Intrusion in the Chesapeake Bay Region: Is It Caused by Climate-Induced Sea Level Rise?

“…The aquifer-system compaction is caused by high groundwater withdrawal rates that have lowered water levels [26]. As shown in Figure 4, groundwater withdrawal rates in the region increased sharply in the 20th century as modern pumping technology was widely adopted [7]. The many decades of increasing groundwater withdrawals have caused groundwater levels to decrease across the Chesapeake Bay region.…”

“…Most land subsidence in the U.S. is caused by human activities, with groundwater withdrawals responsible for about 80 percent of land subsidence in the U.S. [7]. Causes of subsidence that are most relevant to the Chesapeake Bay region include aquifer-system compaction caused by groundwater withdrawals and glacial isostatic adjustment.…”

“…Although groundwater is withdrawn primarily from the aquifers (sandy layers), most compaction occurs in confining units and clay lenses, the relatively impermeable layers sandwiched between and within the aquifers [9]. The compression of clay layers is mostly non-recoverable, meaning that, if groundwater levels later recover and increase, then the aquifer system does not expand to its previous volume and the land surface does not rise to its previous elevations [7]. It has been estimated that 95 percent of the water removed from storage in the Virginia Coastal Plain aquifer system between 1891 and 1980 was derived from the confining layers [10].…”

A Semi-Analytical Solution for Large-Scale Injection-Induced Pressure Perturbation and Leakage in a Laterally Bounded Aquifer–Aquitard System

“…In addition, the applications of these analytical solutions have been extended to analyze pumping-induced leakage into the pumped aquifer from the aquitards and through the aquitards from neighboring aquifers (Hantush, 1964;Cheng and Morohunfola, 1993;Butler and Tsou, 2003;Zhan and Bian, 2006;Konikow and Neuzil, 2007). For example, Zhan and Bian (2006) presented a semi-analytical solution for the leakage rate and volume over the entire time domain, with closed-form analytical solutions for late steadystate conditions, by focusing on the leakage through aquitards of no storativity.…”

Delayed drainage of aquitard in response to sudden change in groundwater level in adjacent confined aquifer: Analytical and experimental studies

“…water resources stored in aquitards are considered to be small. In reality, significant sources of groundwater are stored in aquitards and can be used for water supply and depleted [1]. The non-zero permeability of an aquitard has been demonstrated through laboratory measurements [2][3][4] and regional groundwater flow modeling [5]; permeability values vary over a large range from 10 -15 to 10 -23 m 2 [6].…”