Definition: Groundwater is the water found underground in the cracks and spaces in soil, sand and rock. It is stored in and moves slowly through geologic formations of soil, sand and rocks called aquifers.
- What is Ground Water?
- What is Ground Water Flow?
- Ground Water Pollution/Contamination
What is ground water?
Groundwater is water that exists in the pore spaces and fractures in rock and sediment beneath the Earth’s surface.
It originates as rainfall or snow, and then moves through the soil into the Groundwater system, where it eventually makes its way back to surface streams, lakes, or oceans. It is naturally replenished from above, as surface water from precipitation, streams, and rivers infiltrates into the ground.
Groundwater is a long-term reservoir of the natural water cycle, as opposed to short-term water reservoirs like the atmosphere and fresh surface water.
The Groundwater table is the surface of the Groundwater exposed to an atmospheric pressure beneath the surface of the saturated zone. A water table may vary in elevation.
Groundwater makes up about twenty percent of the world’s fresh water supply, which is about 0.61% of the entire world’s water, including oceans and permanent ice. Global groundwater storage is roughly equal to the total amount of freshwater stored in the snow and ice pack, including the north and south poles. This makes it an important resource which can act as a natural storage that can buffer against shortages of surface water, as in during times of drought.
What is ground water flow?
Groundwater flow is the movement of water that travels and seeps through soil and rock underground. Stored in cavities and geologic pores of the earth’s crust, confined groundwater is under a great deal of pressure. Its upper part is lower than the material in which it is confined.
Unconfined groundwater is the term for an aquifer with an exposed water surface.
Water flows across a land surface then penetrates soil and rock. Once it goes underground, the water is still moving. Groundwater flow speed depends on subsurface materials and the amount of water.
From the land surface, the water moves to the water table. Hydrologists can predict and measure the flow, as well as the level and the gradient. Problems occur as the water goes through an unsaturated zone and picks up substances, some of which are toxic.
Toxicity is dangerous because groundwater supplies are used for public drinking water. The resource also irrigates agricultural land, is used to develop urban areas and supplies rural populations with drinking water via well systems.
Some ecosystems, such as aquatic systems in arid regions and coastal margins, rely on groundwater to survive. Pollution from uncontrolled industrial and urban waste is beginning to affect aquifers.
Ground water pollution/contamination
Groundwater pollution is a very serious problem. Unlike a lot of the pollution on the surface waters, like trash floating in the bay, groundwater pollution is harder to recognize until after illness has occurred.
Groundwater, which is the water that remains under the ground and is tapped into to provide drinking water for homes is generally polluted by the activities that occur just above it. People are the number one cause of groundwater pollution. Having water samples tested regularly is the only way to be sure that the groundwater is not contaminated. Unfortunately, there are a multitude of potential groundwater pollutants that can seriously contaminate drinking water. Most ground water pollution happens because of improper disposal, use or storage of chemicals, pesticides, or substances like car engine oil.
A groundwater supply that is directly over a plot filled with animals, such as a farm environment, can be contaminated with the bacteria from animal waste, The chronic use of chemically based pollutants such as weed killer, insecticides, and antifreeze puts many home groundwater supplies at risk for contamination.
Because there are so many variables that can lead to groundwater pollution it is vital that the state of groundwater health be tested regularly.
Different causes of groundwater pollution have different warning signs. Sometimes these warning signs can be found in the water itself while other times it takes awareness of one’s surroundings to notice a problem. Being aware of potential dangers can help determine a problem should one develop. When buying or leasing a new property, residents should become familiar with the hazards that are nearby. Is there a landfill in the area or a gas station across the street? Does the property have a septic system? This type of information can help residents keep themselves safe from exposure to pollution that can enter groundwater.
The three most common causes of groundwater pollution are septic systems, residential use of pesticides or automobile chemicals, and the use of deicing salts. If deicing salts were to seep into the groundwater supply the water’s taste would become suspiciously salty. It takes a home test to determine high levels of chloride in the water itself to confirm the suspicions.
Most pesticides and other home use chemicals are either not readily detected in the water or will cause sudden illness in everything that the water is used to sustain. When plant life that is watered with pesticide polluted groundwater the plants tend to become ill and die. Animals that drink from the polluted water also become ill and may die.
Septic system pollution usually shows signs of septic system failure elsewhere. Residents are likely to find that the septic system has backed up and is creating a raw sewage flood somewhere in the yard or the surrounding property.
In most cases groundwater tests are needed to determine the level of bacteria that infiltrated the groundwater. In very rare cases the water might appear to be off color or contain an unwelcome aroma.
What is an aquifer?
Groundwater is often contained in aquifers: an aquifer is an underground water saturated stratum of formation that can yield usable amounts of water to a well. There are two different types of aquifers based on physical characteristics: if the saturated zone is sandwiched between layers of impermeable material and the Groundwater is unfed pressure, it is called a confined aquifer; if there is no impermeable layer immediately above the saturated zone, it is called an unconfined aquifer. In an unconfined aquifer the top of the saturated zone is the water table as defined above. Usually an aquifer can produce an economically feasible quantity of water to a well or spring. A saturated region that, due to lower hydraulic conductivity, does not yield a sustainable amount of water in an economic fashion is called aquitard.
Typically, groundwater is thought of as liquid water flowing through shallow aquifers, but technically it can also include soil moisture, permafrost (frozen soil), immobile water in very low permeability bedrock, and deep geothermal or oil formation water. Groundwater is hypothesized to provide lubrication that can possibly influence the movement of faults. It is likely that much of the Earth’s subsurface contains some water, which may be mixed with other fluids in some instances. Groundwater may not be confined only to the Earth. The formation of some of the landforms observed on Mars may have been influenced by groundwater. There is also evidence that liquid water may also exist in the subsurface of Jupiter’s moon Europa.
Types of aquifers found in South Africa
Most South African aquifers occur in fractured rock ranging in age from earliest Pre- Cambrian to Jurassic. Aquifers consisting of recent to Tertiary formations are restricted to coastal dune belts and unconsolidated deposits associated with rivers and Aeolian sands. The aquifer regions developed by DWS are:
Generally unconsolidated but occasionally consolidated.
Groundwater within interstices in porous medium and in basal conglomerate. Moderate areal extent.
Examples include Tertiary-Quaternary coastal deposits and alluvial deposits along river terraces.
Fissured and fractured bedrock resulting from decompression and/or tectonic action. Groundwater occurs predominantly within fissures and fractures.
Extensive in area.
Examples include sedimentary and metamorphic rocks within limited overlying unsaturated residual weathered products.
Water-bearing properties depend on fractures, joints and cavities in Namibian ages calcareous rocks.
Very limited in areal extent.
Examples included limestone and interbedded shale is particularly groundwater bearing in valleys where sizable alluvial deposits occur.
Intergranular and Fractured Aquifers
Largely medium to coarse grained granite, weathered to varying thicknesses, with groundwater contained in intergranular interstices in the saturated zone and in jointed and occasional fractured bedrock.
Occurs extensively throughout South Africa but its characteristics varies in space and time.
- Republic of South Africa, Department of Water Affairs and Forestry, 2008: A Guideline for the Assessment, Planning and Management of Groundwater Resources in South Africa, Edition 1. Pretoria.