Groundwater & Aquifers | FracFocus Chemical Disclosure Registry
For a stream to lose water to groundwater, the water table must be below the elevation of the stream-water surface in the vicinity of the stream. If the water table. Jan 8, Groundwater is any freshwater that lies beneath the surface of the Earth. The " unsaturated zone" above the water table (the greenish area). Apr 25, Most of the world's water is saltwater contained mostly in the oceans that cover the earth. Only about percent of the total global water is fresh.
Some of the world's largest aquifers — vast underground reservoirs of groundwater — are found in regions with these porous bedrocks. Groundwater can also be found in regions where the bedrock is made of denser material — such as granite or basalt — if that bedrock has been cracked or shattered.
Groundwater & Aquifers
Dense, impermeable material like clay or shale can act as an "aquitard," i. Through water might move through such material, it will do so very slowly if at all. When an aquifer is confined beneath an aquitard layer, the pressure on the groundwater can be enough to force the water out of any well that's drilled into that aquifer.
Such wells are known as artesian wells. Groundwater can be trapped beneath the Earth's surface for millions of years. Groundwater quality While surface water quality varies due to erosion, runoff, pollution, plant matter, animal waste and other possible contaminants, groundwater quality is generally more stable. And because it usually moves slowly through rock, groundwater is filtered of many contaminants, including some bacteria and viruses. These factors make groundwater an important drinking water resource.
This does not mean, however, that groundwater can't be contaminated: There are many cases worldwide where important groundwater resources and drinking water supplies have been ruined by saltwater intrusion a particular problem in coastal areasbiological contaminants such as manure or septic tank discharge, and industrial chemicals such as pesticides or petroleum products.
And once groundwater is contaminated, it's notoriously difficult to remediate.
Groundwater: water that has penetrated the earth's surface
In addition to concerns about groundwater quality, the overall volume of groundwater in aquifers is also a serious environmental issue. Groundwater is a finite resource, and even large aquifers can be drained of much of their water, especially during droughts, when aquifers aren't recharged by precipitation. This scenario has repeated during subsequent droughts.
When that happens, the well "runs dry" and no water can be removed until the groundwater is recharged — which, in some cases, can take hundreds or thousands of years. Lowering the water table also decreases the water flow into lakes, rivers and streams. The importance of preserving groundwater resources is underscored by the number of places that depend on groundwater for drinking water, industrial uses and other needs.
Texas gets almost 60 percent of its water from groundwater; in Florida, groundwater supplies more than 90 percent of the state's fresh water.
- What is Groundwater?
- How do groundwater and surface water interact?
The spaces, or pores, between grains of sand, soil or rocks are only partially or not at all filled with water in the unsaturated zone, while the spaces are completely filled with water in the saturated zone. The water table delineates the boundary between these two layers.
A thin layer just above the water table is called the "capillary fringe. The depth of the water table varies depending on the composition of the land, from zero in swampy areas to more than 25 meters feet deep.
Some water tables intersect with lakes and rivers and are modified by them. Water tables are not flat or horizontal: Groundwater Flows Precipitation, such as rain, enters streams and lakes and percolates into the ground.
Drawn downward by gravity, the water starts to fill the empty or partially empty spaces in the soil or between rock particles. When the infiltrating water reaches the water table and the saturated zone, it starts to move horizontally with the groundwater. Groundwater in the saturated zone flows from higher to lower elevations.Extreme groundwater intrusion, because of rain and high groundwater, solved
Unlike the water flow in streams and rivers, groundwater moves very slowly. Movement in sandy or gravelly soil may be millimeters per day, and in clay the movement may be even slower. Sciencing Video Vault Factors Affecting Groundwater Velocity The major factors affecting the velocity of groundwater flows are porosity, the number of available open spaces in soil or rock; permeability, the interconnectivity of the pores; and hydraulic gradient, the slope of the water table.