Ground Water

Ground water is water found beneath the ground surface. –It occupies the pore space between grains in bodies of sediment and sedimentary rock, and – fills cracks and crevices in all types of rock. –Ground water can also be written as groundwater or ground-water

Porosity and Permeability A.__________: The percentage of an Earth material's volume that has openings 1.Factors affecting porosity: a)___________: Generally, if the particles are rounded and sorted, particle size does not affect the porosity. As particles become unsorted the porosity decreases due to the smaller particles filling in the pore spaces Porosity Particle Size

b) ________________: Loosely packed soils have a higher porosity than more compact soils. As packing increases, the pore spaces become smaller. Particle Packing

c)____________: As the angularity of particles increases, porosity decreases. This is because the particles will fit together more effectively. Particle Shape

B.______________ 1.Factors Affecting Permeability: a) Particle _____: As particle size increases, permeability __________ The ability of an Earth material to transit a fluid through pores and/or fractures. This is often expressed as a rate (cm/sec.). Permeability Size increases

b) Particle _______: As particle shape becomes more angular, permeability ___________. Shape decreases

c) Particle ________: As particle packing decreases, permeability _________. Packing increases

2.____________ Materials A material that is impermeable will not allow fluids to move through it. Impermeable Shale Impermeable

3. __________ Permeability: A rock that is otherwise impermeable may permit fluids to move through cracks that have developed due to weathering (ie. limestone, granite). As a result not all permeable rocks have high porosity. Secondary

4. _________Infiltration Depth The depth to which fluids can move through permeable material is 3,000 m (3 km). At this depth confining pressure compresses the rock and closes pores and cracks. Maximum

5. Porous Earth Material Can Be Impermeable Not all porous Earth materials are permeable. For example, clay has high porosity –Because of its very small particles size, its permeability is so low that it is considered to be impermeable. ClayImpermeable clay liner for a landfill

Porosity and Permeability

Aquifers Any body of saturated rock or sediment through which water can move easily is referred to as an aquifer. ❑ Aquifers are porous and permeable

Subsurface Zones 1._____________________: The region in which all pore spaces are filled with water. 2._____________________: The upper limit (“top”) of the zone of saturation. It follows the surface topography. 3._____________________: Zone above the water table in which air occupies the pore spaces.  Water is present, on thesurfaceof the soil or rock particles.  Also called vadose zone 4. ________________: This is the zone above the water table in which water moves upwards from particle to particle due to adhesion and cohesion. Zone of Saturation Water Table Zone of Aeration Capillary Fringe

Adhesion and Cohesion Result from the Polar Properties of the Water Molecule

Cohesion The attraction of one water molecule for another Due to the polar charges of water molecules

Adhesion Water molecules are attracted to other types of molecules such as minerals in rock and soil because they also have charges. –Also attracted glass, metal, or plant leaves Adhesion forces are stronger than cohesion forces.

Capillarity and Particle Size a) Capillarity increases as particle size decreases. b) Generally, the capillary fringe is not more than one meter thick.

5. ________ Water Table The top of a body of ground water separated from the main water table beneath it by a zone that is not saturated. It may form as ground water collects above a lens of relatively imermeable shale with a more permeable rock, such as sandstone. Seepage from a spring in CA Perched

Movement of Ground Water  Water in the zone of saturation moves downward following the slope of the water table  The water table follows the surface topography

B. ___________Aquifers 1.Recharged rapidly by precipitation 2.Partly filled with water 3.Gravity wells yield water by pumping Wet Season Water Table and wells are high Springs and Wells flow readily Dry Season Water table and rivers are low Some springs and wells dry up Unconfined

Local Water Table The water level in a gravity well will be the water table A lake’s surface will be the water table.

Aquifers and Well Quality Even though the shale has high porosity, it has low permeability The saturated region of the sandstone is the aquifer

Aquifers and Well Quality Crystalline rocks (igneous and metamorphic) and some types of limestones are not good aquifers because they are not very porous Wells must intersect fractures to obtain water.

The Effect of a Pumping Well on the Water Table

C. ___________ Aquifers (Artesian Aquifers) 1.Separated from the surface by an ________________confining bed (often shale or clay) called an ____________ 2.Completely filled with water under pressure 3.Recharged slowly through the confining bed 4.May have no response to seasonal changes in precipitation Confined Aquitard (impermeable) impermeable aquitard

5. ______________ Drilled into confined aquifers and have water that rises under its own pressure Common in South Dakota but also present on Long Island The name is derived from the Arois region of France (artesien in old French) where these wells have been used for centuries. Artesian Wells

Artesian Wells in the Dakota Sandstone Will this well be a flowing artesian well? Water level in the well Confined Water Table

Flowing Artesian Wells Artesian well in S. Dakota Early 1900’s Dakota Sandstone Montana

D. _______ : Water flows natural onto the land surface. Can occur where the water table intersects the land surface. Can also occur – in caverns, along fractures –along faults –or rock contacts that intersect the land surface Springs

Natural Springs Spring from a limestone cavern Jasper National Park, Alberta, Canada Spring seeping from the ground at a contact between shale and overlying sandstone in southern Utah

Climate and Streamflow Climate influences the relationship between stream flow and the water table.

1.________Streams a)Rainy climates b)The stream’s surface coincides with the water table. c)Water from the zone of saturation flows through the streambed and banks that are below the water table Gaining

2. ________Streams a)Drier climates b)Water is lost to the zone of saturation. c)The stream channel lies above the water table. d)Water lost from the stream can cause a rise in the water table. As a result, in a desert the nearest water source may be below a dry streambed Losing

Effects of Ground Water Action Caves, Sinkholes, and Karst Topography

Solution of Limestone Forming Caves Great Onyx Cave, KY

Howe Caverns, NY

Carlsbad Caverns, NM

Stalactites

Karst Topography Regions characterized by sinks, lost rivers, underground drainage, caves and caverns. Limestone bedrock Named after the Kars region of Yugoslavia Also found in United States (Cumberland Plateau of Kentucky and Tennessee, Shenandoah Valley of Virginia, and Florida).

Karst Topography in the U.S. Cumberland Plateau of Kentucky and Tennessee, Shenandoah Valley of Virginia Florida)

Sinkholes Winter Park, Florida 1980

Karst Topography Timaru, New Zealand West Virginia, USA

Mammoth Caves KY

Hot Water Underground

1. ___________ Circulation near a magma chamber Circulation near hot, cooling igneous rock Yellowstone Park, WY Japan Hot Springs

2.________ Geysers Hot springs that periodically erupt hot water and steam

Geyserite Cone (Sinter) Travertine terraces

Yellowstone National Park

Geothermal Energy

Geothermal Power Plants Geothermal Power Plant The Geysers, CA

U.S. Geothermal Resources

Other Effects of Groundwater Geodes Found in some limestones Petrified wood Wood replaced by silica Concretions Precipitation of cementing material around an organic nucleus such as a leaf or a tooth Amorphous silica Amethyst crystals

Groundwater Pollution Sources Pesticides

Groundwater Pollution Sources Household Garbage

Groundwater Pollution Sources Animal Waste

Groundwater Pollution Sources Industrial Toxic Waste

Contaminant Plumes A plume of contaminated water will spread out in the direction of groundwater flow.

Density of Pollutants Affects Flow

Effects of Bedrock

Pumping Wells Causes or Aggravates Groundwater Pollution A pumping well steepens the water table near a landfill Velocity of groundwater flow increases. Contaminants are drawn into the well.

Pumping Wells Causes or Aggravates Groundwater Pollution Pumping can reverse the slope of the water table. Direction of groundwater flow changes, contaminating the well.

Pumping Wells Can Cause Saltwater Intrusion Along Shorelines Pumping thins the freshwater lens Saltwater is drawn into the well

Groundwater Mining Can Cause Land Subsidence Subsidence of 9 m in 52 years near Mendota, San Joaquin Valley, CA Signs on the pole show positions of the land surface in 1925, 1955, and 1977 Subsidence has been reduced to less than a meter since the late 1970’s as a result of –Reduced groundwater pumping –Use of surface water for irrigation