Chapter 11 – WATER UNDER THE GROUND

Freshwater Underground Ground water Subsurface water contained in pore spaces in regolith & bedrock

Freshwater Underground Zone of aeration Mix of air & water Zone of saturation Saturated with water Water table Top of saturated zone

Freshwater Underground How groundwater moves Porosity % of total volume of rock body or regolith made of open spaces (pores) Permeability Measure of how easily a solid allows fluids to pass through it

Freshwater Underground How groundwater moves Hydraulic gradient Change in elevation divided by distance Used to determine rate of groundwater flow

Freshwater Underground How groundwater moves (continued) Percolation Groundwater seeps downward Recharge Replenishment of groundwater Discharge Subsurface water leaves saturated zone Becomes surface water Spring Occurs where water table intersects land surface

Freshwater Underground How groundwater moves (continued) Other methods of discharge Hot springs Geysers

Freshwater Underground Where groundwater is stored Aquifer Rock body or regolith that is water saturated, porous, & permeable Aquiclude Layer of impermeable rock

Freshwater Underground Where groundwater is stored Aquifer Unconfined Confined Potentiometric surface Artesian well

Freshwater Underground Groundwater depletion Cone of depression Cone-shaped dip in water table due to pumping Groundwater mining Rates of groundwater withdrawal continuously exceed rate of recharge

Freshwater Underground Groundwater depletion (continued) Land subsidence Compaction Salt water intrusion

Freshwater Underground Groundwater contamination Contamination

Freshwater Underground Dealing with groundwater issues Enhanced recharge Conservation Other sources Desalination (i.e. distillation; reverse osmosis; electrolysis) Icebergs

Freshwater Underground Natural methods Filtration Decomposition Bacterial action Human methods Exterior treatments Dilution Chemical treatments

Groundwater in the U.S.

Groundwater in the U.S. Groundwater Mining Recharge rate vs. consumption rate Ogallala Aquifer: largest aquifer in U.S. 225,000 sq miles Found in 8 states 30,000 years of water accumulation

Ogallala Aquifer

Groundwater in Nebraska

Groundwater in Nebraska

Groundwater in Nebraska What areas seem best suited for groundwater withdrawal? Why do you think these areas are not utilized? Answer: The Nebraska Sandhills However, Crops do not grow well in sand, so the area is primarily used for ranching.

Freshwater Underground When groundwater dissolves rock Carbon dioxide + water = carbonic acid Adds acid to water in atmosphere & underground Calcite + carbonic acid = dissolution Calcite dissolves

Freshwater Underground Factors of dissolution Rock composition Extent of rock fracturing, jointing, & bedding Acidity of water Climate

Freshwater Underground When groundwater dissolves rock Karst topography Sinkholes Disappearing streams

Freshwater Underground When groundwater dissolves rock Cave Underground open space Cavern = system of connected caves Stalactites Stalagmites Columns (pillars)