Which zone is groundwater located

Recall that water is flowing in pores where there is friction, which means it takes work to move the water. There is also some friction between water molecules themselves, which is determined by the viscosity. Water has a low viscosity, but friction is still a factor. All flowing fluids are always losing energy to friction with their surroundings. Water will flow from areas with high energy to those with low energy. Recharge areas are at higher elevations, where the water has high gravitational energy.

It was energy from the sun that evaporated the water into the atmosphere and lifted it up to the recharge area. The water loses this gravitational energy as it flows from the recharge area to the discharge area. In Figure The water table is higher under the recharge area 90 m and lower at the discharge area 82 m. Imagine how much work it would be to lift water 8 m high in the air.

That is the energy that was lost to friction as the groundwater flowed from the top of the hill to the stream. The situation gets a lot more complicated in the case of confined aquifers, but they are important sources of water so we need to understand how they work. As shown in Figure The red dashed line in Figure If we drill a well into the unconfined aquifer, the water will rise to the level of the water table well A in Figure But if we drill a well through both the unconfined aquifer and the confining layer and into the confined aquifer, the water will rise above the top of the confined aquifer to the level of its potentiometric surface well B in Figure This is known as an artesian well , because the water rises above the top of the aquifer.

In some situations, the potentiometric surface may be above the ground level. This is known as a flowing artesian well. In this unsaturated zone , there usually is at least a little water, mostly in smaller openings of the soil and rock; the larger openings usually contain air instead of water.

After a significant rain, the zone may be almost saturated; after a long dry spell, it may be almost dry. Some water is held in the unsaturated zone by molecular attraction , and it will not flow toward or enter a well. Similar forces hold enough water in a wet towel to make it feel damp after it has stopped dripping. Date Taken: approx.

Skip to main content. Search Search. Artesian systems are desirable because they result in free flowing artesian springs and artesian wells. Changes in the Groundwater System When discharge of groundwater exceeds recharge of the system, several adverse effects can occur. Most common is lowering of the water table, resulting in springs drying up and wells having to be dug to deeper levels. If water is pumped out of an aquifer, pore pressure can be reduced in the aquifer that could result in compaction of the now dry aquifer and result in land subsidence.

In some cases withdrawal of groundwater exceeds recharge by natural processes, and thus groundwater should be considered a non-renewable natural resource. Water Quality and Groundwater Contamination Water quality refers to such things as the temperature of the water, the amount of dissolved solids, and lack of toxic and biological pollutants. Water that contains a high amount of dissolved material through the action of chemical weathering can have a bitter taste, and is commonly referred to as hard water.

Hot water can occur if water comes from a deep source or encounters a cooling magma body on its traverse through the groundwater system. Such hot water may desirable for bath houses or geothermal energy, but is not usually desirable for human consumption or agricultural purposes.

Most pollution of groundwater is the result of biological activity, much of it human. Among the sources of contamination are: Sewers and septic tanks Waste dumps both industrial and residential Gasoline Tanks like occur beneath all service stations Biological waste products - Biological contaminants can be removed from the groundwater by natural processes if the aquifer has interconnections between pores that are smaller than the microbes.

For example a sandy aquifer may act as a filter for biological contaminants. Agricultural pollutants such as fertilizers and pesticides. Salt water contamination - results from excessive discharge of fresh groundwater in coastal areas. Geologic Activity of Groundwater Dissolution - Recall that water is the main agent of chemical weathering. Groundwater is an active weathering agent and can leach ions from rock, and, in the case of carbonate rocks like limestone, can completely dissolve the rock.

Chemical Cementation and Replacement - Water is also the main agent acting during diagenesis. It carries in dissolved ions which can precipitate to form chemical cements that hold sedimentary rocks together.

Groundwater can also replace other molecules in matter on a molecule by molecule basis, often preserving the original structure such as in fossilization or petrified wood Caves and Caverns - If large areas of limestone underground are dissolved by the action of groundwater these cavities can become caves or caverns caves with many interconnected chambers once the water table is lowered.

Once a cave forms, it is open to the atmosphere and water percolating in can precipitate new material such as the common cave decorations like stalagtites hang from the ceiling , stalagmites grow from the floor upward , and dripstones, and flowstones. Sinkholes - If the roof of a cave or cavern collapses, this results in a sinkhole. Sinkholes, likes caves, are common in areas underlain by limestones.

For example, in Florida, which is underlain by limestones, a new sinkhole forms about once each year, gobbling up cars and houses in process. Karst Topography - In an area where the main type of weathering is dissolution like in limestone terrains , the formation of caves and sinkholes, and their collapse and coalescence may result in a highly irregular topography called karst topography Factories and underground storage tanks are a source of groundwater pollutants.

If a tank with a water soluble liquid leaks the liquid travels down to the water table. It then dissolves in the groundwater. These pollutants flow as a plume along with the groundwater. They can pollute wells and surface water fed by the groundwater along the plume path. If the liquid that leaks is less dense than water, it floats on top of the groundwater table. Some of the liquid will evaporate, traveling upwards to the surface in the form of vapor fumes.

Some of the liquid will dissolve and travel as a plume in the groundwater. If the chemical is not very soluble in water the major part of the liquid will float on the groundwater and flow along with the groundwater.

Liquids that are denser than water sink through the groundwater until they reach an aquitard. They then move along the top of the aquitard along with the groundwater.

Cemeteries are another source of pollution for groundwater.