- Water beneath the Earth’s surface in sediment and rock formations. Groundwater - Water beneath the Earth’s surface in sediment and rock formations.

Introduction Most of the water useful to humans cannot be seen but it exists beneath the ground. When it rains some water flows into lakes, rivers, or streams but most is absorbed by the ground. Groundwater fills in the spaces between rocks, sediment and soil beneath the Earth.

Properties of Materials that Allow Them to Absorb/Store Water. Porosity: The percentage of the total volume of a rock that has spaces (pores). Permeability: The ability of rock or soil to allow water to flow through it.

Porosity In the top box the materials are packed very tightly together therefore not allowing much water to be stored in between. The bottom box shows an area with high porosity. This is because the materials are loosely packed allowing for more water to be stored.

Permeability Materials like gravel, sand, and limestone are considered very permeable because they permit the flow of water. Impermeability: Materials such as clay or granite because they have low porosity, are considered impermeable because they do not allow the flow of water.

Permeability/Impermeability As you can see from the picture, the layers towards the top are much more permeable then the layers toward the bottom.

What is the Water Table Zone of Aeration: Pore spaces that contain mostly air. Zone of Saturation: Pore spaces that contain mostly water. Water Table: Top of the zone of saturation.

Water Table Continued As you can see the area to the left of the river is saturated with water. We call this area the zone of saturation. The area above the height of the river is unsaturated. We call this unsaturated area the zone of aeration. The boundary line between the zone of aeration and zone of saturation is called the water table.

Water Table

Water Table Questions 1) What factors affect the level of the water table? 2) In your own words, briefly explain porosity. 3) Explain what type of rocks allow for the most water to be stored in between them. Give a specific example. 4) Explain what is meant by the zone of aeration. 5) What is different between the zone of aeration versus the zone of saturation? 6) Which of the following rocks is the most permeable? a) Gravel b) Sand c) Clay d) Granite 7) The term used for water moving down through the different layers of ground is? 8)

Aquifers An underground formation that contains groundwater is called an aquifer. The water table forms the upper boundary of an aquifer.

Aquifers Continued From the previous picture you can see that the potentiometric surface is an imaginary line that runs from the top of the water table, the length of the aquifer. An artesian borehole (or well, think of these as a well for your house) is considered to be flowing if the opening of the well is below the potentiometric surface. If it is not below the potentiometric surface then a person would need to put a pump down their well to get water to run into their house.

Aquifer Recharge A aquifer can be recharged (have water added to it). An unconfined aquifer can be recharged anywhere along the aquifer because it has permeable material above it. A confined aquifer can only be recharged at an opening where water can flow in. This is due to the impermeable layer above the aquifer. In the picture on the next slide this is illustrated.

Recharge in an Aquifer

Types of Aquifers There are two types of aquifers Confined and Unconfined Unconfined aquifers do not have an impermeable layer overlying and protecting the aquifer. Instead, the layer above the aquifer consists of highly permeable material, such as sand or gravel. Because surface water and contaminants can pass readily through the layer above the aquifer to the water table, an unconfined aquifer is more susceptible to contamination.

Types of Aquifers Confined aquifers In a confined aquifer, groundwater is sandwiched by impermeable layers of material (such as fine silt or clay) called aquitards. The surface aquitard prevents the passage of contaminants into the aquifer. As such, confined aquifers are often good sources of drinking water. However, confined aquifers are not completely protected and may still be vulnerable to contamination at their recharge area, which may be located far away and exposed.

Aquifer Questions Write a definition for aquifer. Explain the difference between a confined aquifer and an unconfined aquifer. Which type of aquifer would be better to drill a well into? In an unconfined aquifer, the layer above the aquifer consists of what type of material? Give two example of materials that would make up an aquitard. Why is a confined aquifer better to draw water from then an unconfined aquifer? Explain what the potentiometric surface is. Another name for an artesian borehole is? Explain a circumstance when a person would need a pump down their well to draw water into their house. Explain the difference between how a confined aquifer is recharged as compared to an unconfined aquifer.

Wells A hole that is dug or drilled to reach groundwater. We dig wells because groundwater may be a more reliable source of water than surface water in parts of the world. As water travels down through layers of soil and rock it gets purified, which is great for drinking water.

Wells Continued The height of the water table changes depending on the season. Wells are drilled well below the water table to prevent the well from drying up during the hot summer months.

Wells….. Groundwater storage is like a bank account. The balance falls when withdrawals exceed deposits. Nature makes deposits through rainfall or other forms of precipitation, and withdrawals through leakage of groundwater to streams and the ocean. Our wells represent further withdrawals. If total withdrawals exceed deposits, we deplete our groundwater storage.

Wells….

Cone of Depression When water is drawn up through a well it creates a cone of depression.

Cone of Depression Continued As you can see from the picture, when a well is pumped heavily it lowers the water table. When this happens other wells in the area that may not be dug as deep can dry up.

Well Questions What is a cone of depression? What is meant by a deposit when it comes to groundwater supply? Nature make withdrawals from groundwater storage through ________ of groundwater into streams and rivers. If there are more withdrawals than deposits to groundwater storage what happens? The height of the water table changes with the __________. Give an example situation in which a well might dry up. What is a well? Why do humans drill wells over using surface water? What happens to water as it travels down through layers of material into an aquifer? What is the benefit of this happening? What is a possible situation that could arise from a well being pumped to heavily in one particular area?