Chapter I 7 Underground Water Global distribution of

Chapter I 7 Underground Water

Global distribution of water • • • Oceans Glaciers Groundwater Lakes Atmosphere Rivers 97. 2% 2. 15% 0. 61% 0. 001% 0. 0001%

The Distribution of Water on Earth

The water cycle • The continuous movement of water on, above and below the earth’s surface is called the water cycle OR hydrologic cycle.

The water cycle • Processes: – Evaporation – Transpiration – Precipitation

Dry Period: Dam Streams bring in small amounts of water… and carry away small amounts. Wetlands

Wet Period: Dam Streams bring in large amounts of water… which is stored… and slowly released during dry periods. Wetlands

Average U. S. Annual Precipitation

Water • Atmospheric water: vapors • Surface water: rivers. Lakes, oceans • Subsurface water: groundwater

Distribution of underground water • 2 zones – Unsaturated zone: vadose zone – Saturated zone – Separated by Water Table

Underground materials • Underground materials may either contain water or they may be dry. • In order to contain water, they have to be porous and permeable.

Underground materials • Porosity: is a measure of the material ability to hold water. • Permeability: capacity of a material to transmit water.

Porosity varies with % Cement Sorting Fracturing

Porosity Varies with % Cement MORE POROUS Noncemented Sand LESS POROUS Cemented Sandstone

Porosity Varies with Sorting MORE POROUS Well Sorted Sand LESS POROUS Poorly Sorted Sand

Porosity Varies with Fracturing MORE POROUS Fractured Shale LESS POROUS Unfractured Shale

Porosity and Permeability of Different Aquifer Types Type of Aquifer Porosity Permeability Gravel Coarse- to fine sand Fine-grained sand & silt Sandstone, mod. cemented Fractured Shale Metamorphic Rocks Unfractured Shale Very High Moderate Mod - Low Low Very High Mod - Low Low Very Low

Aquifers • Any geologic material which can yield water in significant amounts. • Aquifers must be porous and permeable. • Any geologic material which cannot hold and transmit water is called Aquiclude.

Types of aquifers • 2 types – Unconfined aquifer – Confined aquifer

• Unconfined aquifer: no confining layer on top of the saturated zone

Unconfined Aquifer Unsaturated Zone: Pores include both air and water Groundwater Table Saturated Zone: Pores filled with water

• Confined aquifer: the saturated zone is capped by a confining layer.

• Good aquifers include; – Unconsolidated deposits – Sandstone – Conglomerate – Jointed limestone

• Good aquicludes are; – Shales – Granite – Marble

Springs • A spring forms where underground water flows naturally onto the land surface. • A spring occurs when water table intersects the land surface.

Groundwater erosion and deposition • Depending on the chemical environment, water erodes the material over which it moves. • Later on the eroded material is deposited at another location.

Groundwater erosion and deposition • Erosional features: – Caves – Sinkholes – Karst topography

• Caves: underground chambers large enough for humans to enter into it. –Speleothems: calcite deposits formed by dripping water from cave ceiling.

Two types of speleothems: • Stalactites: pendants of calcite hanging from roof ceiling • Stalagmites: cone-shaped bodies of calcite formed on cave floor.

Mammoth Cave, KY

• Sinkholes: depressions formed by the collapse of a cave roof. • Karst topography: an area underlain by numerous caves and sinkholes.

Subsurface Features of a Karst Landscape

Dishman Lane collapse, Bowling Green Ky. Feb. 2002

Depositional features • Petrified wood • Geodes • Concretions

• Petrified wood: organic material is replaced by silica.

• Geodes: partly filled bodies of silica having crystals of quartz or calcite.

• Concretions: calcite or silica carried by groundwater can replace original material such as shells, bones or twigs.

High-temperature underground water • Hot springs: water temp. is higher than 37º C. – Water gains heat from hot igneous bodies – Water may also be heated through deep circulation.

• Geysers: type of hot spring that periodically erupts hot water (100º C) and steam. • Eruption may be regular as in Old Faithful geyser…. 79 mins. 45 -105 mins • Irregular eruptions are common. Ranging from days to weeks.

Water enters the ground by infiltration Hydrothermal Systems Hot Springs: form when heated groundwater reaches the surface Geysers: form where a Heated water begins to rise complicated plumbing system allows steam pressure to be built up, causing intermittent eruptions

• Hot water deposits: calcite deposited in the form of travertine.

Geothermal energy • Electric power can be generated from the hot water and steam from a hot spring. • San Francisco Geysers field. 2000 MW. Mostly used for room heating.

Water Contamination • Water is considered contaminated when it is harmful to human use. • Sources of water contamination: – Agricultural activities – Human wastes – Industrial effluents

• Agricultural Activities – Herbisides – Pesticides – Fertilizers – Animal wastes – Slaughter houses

• Human wastes – Household garbage – Septic tanks – City landfills

• Industrial wastes: – Heavy metals from industries – Mine wastes – Radioactive wastes

Remediation • Natural remediation • Site selection – Yucca Mountains, Nevada • Sealing landfills: – Geosynthetics, geotextiles – Clay blankets