Chapter 10 Groundwater!

Section 1 – Movement and Storage of Groundwater The Hydrosphere – the water on and in Earth’s crust. 97% of the hydrosphere is in the oceans.

70% of all freshwater is captured in the polar ice caps and glaciers. The ultimate source of all water on land is the oceans. Water evaporates from the oceans, travels as clouds, condenses and drops as precipitation.

Infiltration is the process by which precipitation that falls on land trickles in the ground and becomes groundwater. Groundwater travels through the ground and eventually returns to the surface through springs and seepage in bodies of water.

Pore Spaces – the small openings in the Earth’s crust that allows water to pass. The more pore spaces, the greater the porosity. Porosity depends on the size and variety of particles in soil.

The Zone of Saturation – the region below Earth’s surface where groundwater completely fills all the pores of a material. The upper part of the zone of saturation is called the water table.

Above the water table is the zone of aeration where the material is moist but not completely wet. Air occupies much of the pore spaces in the zone of aeration.

Water in the zones is either gravitational water or capillary water. Gravitational water travels downward as gravity pulls.

Capillary action pulls water upward to the zones and holds it there.

How deep is the water table? Depends on the location, climate, and topography. How fast does this groundwater flow? Depends on the permeability of the material. Material with large pores allows water to flow faster than material with small pores.

Some material like clay can stop the flow altogether. A layer of impermeable material that stops the flow of groundwater is called an aquiclude.

Aquifers are composed of layers of sand, gravel, sandstone and limestone. Aquicludes are made of impermeable layers of clay or shale. When these two are in contact a spring can develop.

Spring discharge can be very small or very large. Karst springs are rivers that flow out of the ground.

Sometimes the underground water emerging from a spring is warmed hot rocks under the surface. These are called hot springs.

In areas where there is a large amount of underground thermal activity a geyser can develop. A geyser is an explosive hot spring where water is vaporized and under high pressure.

Section 2 - Groundwater Weathering and Deposition Because rainwater is slightly acidic due to the carbon dioxide in the atmosphere is can dissolve certain types of rocks

The main type of rock dissolved by acid is limestone because it contains calcium carbonate. This process can create caves. Another feature created by the dissolution of limestone bedrock is a sinkhole.

A sinkhole is a depression in the ground caused by the collapse of a cave.

Limestone regions that have sinkholes are said to have karst topography. In these areas sinkholes grow and connect creating valleys.

Common structures in caves are called dripstones Common structures in caves are called dripstones. These develop as water droplets leave small amounts of calcite behind as they drip. A stalactite hangs from the caves ceiling and form gradually.

As the water drips onto the floor it forms stalagmites.

When they meet it forms a column.

Hard Water – tap water contains various dissolved solids Hard Water – tap water contains various dissolved solids. Water that contains high concentrations of calcium, magnesium, or iron is called hard water. Hard water can precipitate inside water pipes of homes and on the heating elements of appliances. It can also turn your clothes brown.

Section 3 – Goundwater Supply Wells – holes dug into the ground to reach an aquifer. The level of the well is the same as the level of the water table. As water is drawn from the well it is replaced by water in the water table.

If too much water is taken a cone of depression can be created around the well.

The difference between the original water table level and the water level in the well is called the drawdown. Too may wells can cause an overlap in the cone of depressions causing some well to go dry.

Precipitation will add water back to the aquifer in a process called recharge. Artesian well - If water reaches the ground surface under the natural pressure of the aquifer, the well is called an artesian well.

Threats to the water supply Overuse – groundwater can be pumped out faster that in can be recharged. Subsidence – when the land sinks because water has been withdrawn.

Pollution – pollution such as chemicals can spread quickly once it reaches the aquifer. Salt water intrusion – occurs along coast when water from the ocean seeps into the aquifer.

Radon – a product of the radioactive decay of uranium.