When the lithological characteristics include complete water-resistance or the aquiclude
lay under the hard rock stratum, forming a floor of "rigid upper layer and soft lower layer," the damage of mining would have a shallow depth, and the height of the confined water permeation was low, which is the most favorable condition for coal mining above confined water.
Jensen et al., "Paleozoic-aged brine and authigenic helium preserved in an Ordovician shale aquiclude
," Geology, vol.
The frozen layers act as special regional aquiclude
or aquitard layers and block or weaken the hydraulic connections between the surface water and groundwater, which make the hydrological cycle complex [4, 14-16].
According to the pregeological investigation, as the mudstone is relatively an aquiclude
, the underground part of the sandstone layer forms confined water; thus, multiple boreholes emit groundwater.
Shueib Formation this formation acts as an aquiclude
between Hummar and Wadi As-Sir Aquifers in the groundwater basin with a thickness of about 200 m, mainly consisting of marl and marly limestone (Mc Donalds, 1965).
The Pliocene consists of interbeded red brown clay, Paleonile (Madamoud Formation), which acts as an aquiclude
for the overlying Quaternary aquifers.
The small capacity to store excess water in the clay-rich sediments, together with low hydraulic conductivity, suggests that an increase in the capture of rainfall by zero-tillage cropping without greater water use (and productivity) could result in either an increase in deep drainage and the rate of discharge into shallow aquifers, or near-surface saturation and waterlogging should the clays behave as an aquiclude
Hydraulic testing has identified a 450 m thick aquiclude
having remarkable underpressuring, possibly due to Cenozoic erosion and glaciation, and ultra-low permeability with horizontal K measurements on the order of 10-14 m/s (i.e.
The terms aquifer, aquiclude
, and aquitard are relative in a carbonate sequence because of variability in bedding, jointing, and fracturing.
A thick or extensive aquiclude
can and does exclude further penetration of salt water under such circumstances.
 report four main hydraulic problems historically encountered in ATES systems: loss of permeability due to pumping, loss of recoverable heat to the aquifer, leakage along the well casing, and hydraulic fracturing of the upper aquiclude
due to injection pressures.
A dense silty clay layer of low permeability particularly at 0.7-0.9m depth acts as an aquiclude
, restricting water movement to a deeper subsurface water.