The surface of most silicate mineral grains has a slight negative charge due to imperfections in the mineral structure. Water H2O is a polar molecule. This means that while it has no overall electrical charge, one side of the molecule has a slight positive charge the side with the two hydrogens , compared to a slight negative charge on the other side.
Water is strongly attracted to all mineral grains and water within that bound water layer a few microns around each grain is not able to move and flow along with the rest of the groundwater.
In the lower diagrams shown here, the bound water is represented by dark blue lines around each grain and the water that can move is light blue. We have now seen that there is a wide range of porosity in geological materials and an even wider range of permeability. Groundwater exists everywhere there is porosity. However, whether that groundwater is able to flow in significant quantities depends on the permeability. An aquifer is defined as a body of rock or unconsolidated sediment that has sufficient permeability to allow water to flow through it.
Unconsolidated materials like gravel, sand, and even silt make relatively good aquifers, as do rocks like sandstone. Other rocks can be good aquifers if they are well fractured. An aquitard is a body that does not allow transmission of a significant amount of water, such as a clay, a till, or a poorly fractured igneous or metamorphic rock.
An aquifer that is exposed at the ground surface is called an unconfined aquifer. An aquifer where there is a lower permeability material between the aquifer and the ground surface is known as a confined aquifer , and the aquitard separating ground surface and the aquifer is known as the confining layer. Figure Figure 1 shows an example of an aquifer system in the lower Portneuf River valley.
The diagram represents a cut-away perspective view of this system of multiple aquifers and is greatly exaggerated in its vertical scale to show some of the details.
Several different aquifers occur in this valley. In the northern valley beneath Chubbuck and north Pocatello multiple confined aquifers are stacked on top of one another and separated by aquitards made of clay; the aquifers tapped by Chubbuck's municipal wells are in the fractured basalts of the eastern Snake River Plain. In the southern valley Portneuf Gap to Red Hill the upper surface of the unconfined aquifer is the water table.
How Does an Aquifer Work? An aquifer is filled with moving water and the amount of water in storage in the aquifer can vary from season to season and year to year.
Ground water may flow through an aquifer at a rate of 50 feet per year or 50 inches per century, depending on the permeability.
But no matter how fast or slow, water will eventually discharge or leave an aquifer and must be replaced by new water to replenish or recharge the aquifer.
Thus, every aquifer has a recharge zone or zones and a discharge zone or zones. Figure 2 is a simple cartoon showing three different types of aquifers: confined, unconfined, and perched. Recharge zones are typically at higher altitudes but can occur wherever water enters an aquifer, such as from rain, snowmelt, river and reservoir leakage, or from irrigation.
Discharge zones can occur anywhere; in the diagram, discharge occurs not only in springs near the stream and in wetlands at low altitude, and also from wells and high-altitude springs. Nonetheless, groundwater can still be transmitted through it joints and fractures. Sandstone can be very large since beds of sandstone can spread over extended areas.
Many of the sandstone aquifers in the United States are embedded in shale and siltstone. As a result, the water in these aquifers are considered to be in confined condition because the surrounding rock is impermeable. Limestone is the most common type of carbonate-rock aquifer.
Many of them begin as deposits in former marine environments, where the sediments lithify and compact. The cracks and joints in limestone are generally made as the rock slowly dissolves in slightly acidic water, leaving places for groundwater to flow. Sometimes caverns are formed that hold water and extend for thousands of feet. Often, the crevices and joints in limestone form a connecting network, further enhancing water flow.
The yellow layer is very permeable and would make an ideal aquifer. But permeability of clay is very poor. Rocks that make up good aquifers not only have pores, but pores that are interconnected. These connections allow the groundwater to flow through the rock. Sandstone: Fine-grained rocks such as sandstone make good aquifers. Dolomite : This type of rock can easily be dissolved by slightly acidic water. Read this article to learn about the following four types of aquifers , i.
Groundwater is everywhere beneath the soil surface and can be ever-present in many places if allowed to recharge. Even in dry conditions, it maintains the flow of rivers and streams by replenishing them, providing a valuable substitute for precipitation. If the aquifer is shallow enough and permeable enough to allow water to move through it at a rapid-enough rate, then people can drill wells into it and withdraw water.
Excessive pumping can lower the water table so much that the wells no longer supply water—they can "go dry. Aquifers come in two types which are shown below: unconfined and confined. Unconfined aquifers are those into which water seeps from the ground surface directly above the aquifer. Depending on its permeability, aquifers can gain water at a rate of 50 feet per year to 50 inches per century. They have both recharge and discharge zones. A recharge zone usually occurs at a high elevation where rain, snowmelt, lake or river water seeps into the ground to replenish the aquifer.
Call a water divination expert or practice the technique yourself. Water divination is also known as dowsing and utilizes two L-shaped or Y-shaped rods or twigs to detect water below ground.
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