Groundwater All water present below the ground surface

Groundwater • All water present below the ground surface; the water that has infiltrated the ground

The Hydrologic Cycle

Zones of Aeration and Saturation • Zone of aeration – voids in rock or sediment are filled by air or water films on particles • Zone of saturation – voids are filled by water • Water Table – Separates these

Water Table • The boundary between the zone of aeration and the zone of saturation

Aquifers • Bodies or porous and permeable rock or sediment that are saturated with water

Porosity and Permeability • Porosity is the volume of pore space as a percent of total volume • Permeability is the ease with which fluids flow through geologic materials

Aquicludes • A geologic material or layer of very low permeability that inhibits water flow

Cone of Depression

Unconfined and Artesian Aquifers • An unconfined aquifer has a static water table and is directly exposed to the atmosphere • An artesian aquifer is confined between aquicludes

Artesian Systems • Three Requirements for pressurization: – – –

Artesian Systems • Water Under Pressure:

Groundwater Management • Managing the amount of water contained in a groundwater basin so that it will produce water in the future • Sustained yield • Specific retention

Groundwater Mining

Hydraulic Head

Gyben-Herzberg Lens

Seawater Encroachment • Invasion of coastal aquifers by saltwater • Maintaining high fresh water tables can balance the incursion of denser saltwater

Groundwater-Surface Water Interactions • Surface water and groundwater cannot be treated as separate entities; what affects one impacts the other

U. S. Use Trends • Water use increased between 1950 and 1980 • Water use declined by 10% from 1980 and 1995 – Economical use of irrigation water – Conservation – Recycling

Work Done by Groundwater • Solution of limestone and gypsum by groundwater forms caves, sink holes, etc. • Karst topography – formed by collapsing caverns

Sinkholes • Collapse of ground surface into caves

Tower Karst • End result of dissolution

Water Quality • Water purity is established by the U. S. Public Health Service • Less than 500 ppm total dissolved solids for “sweet” water

Water Pollution • Chemical, physical or biological materials that impair the current and future use of water and that be a health hazard

Residence Time • The average length of time a given substance will stay in a system, such as water in a lake or aquifer • Pollutants may reside in groundwater aquifers for thousands of years

Common Pollutants • Hydrocarbons • Carcinogenic chemicals • Fertilizers • Pesticides • Livestock manure • Gasoline