Water Beneath the Surface 6.3

There is Water Underground Pore spaces + fractures and joints = lots of openings Water collects underground

What happens when it rains? Runs off, evaporates, soaks into ground Underground water depends on: Steepness of slopes Surface materials Intensity and duration of rain Vegetation type Amount of vegetation

Where does the water in the soil go? Seeps downward until the zone of saturation Zone of saturation = area where water fills all of the open spaces in sediment and rock Groundwater is in zone of saturation

Water Table Upper limit of zone of saturation Water can be pumped Above the water table = not saturated = zone of aeration Wells can’t pump water from zone of aeration

Porosity and Permeability Flow and storage of groundwater depend on material underground Porosity = percentage of pore spaces (spaces between sedimentary particles) Permeability = ability to flow Rock can be porous and not very permeable

How does groundwater move? Twisting and turning through small openings Moves more slowly when pore spaces are smaller Too small --> water can’t move Ex: clay = high porosity but impermeable Aquifers = transmit groundwater freely Source of well water

Aquifer

Springs Spring = flow of groundwater naturally at the surface water table intersects the ground surface Hot spring = 6-9 °C hotter than the average annual air temperature

Geysers Hot spring where column of water shoots up at intervals Ex: Old Faithful Superheated water expands some water forced out at the surface Loss of water = decreases pressure Some water turns to steam Geyser erupts

Wells Hole bored into the zone of saturation Biggest user: irrigation for agriculture Must go far below the water table Cone of depression = withdraw more water than is replenished

Artesian Well Most wells need to be pumped in order to get water Artesian well = groundwater rises on its own under pressure Water in aquifer that is tilted Water can’t escape

Caverns Limestone = easily weathered by groundwater groundwater contains carbonic acid Carbonic acid weathers rock Cavern = naturally formed underground chamber Erosion forms most caverns at or below the water table in the zone of saturation Dissolving process slowly creates cavities and caverns

Caverns Stalactites = hang from the ceiling of a cavern Water seeps through cracks in the cavern’s ceiling Stalagmites = develop on the floor of the cavern Water falls from the ceiling and splatters on the floor

Karst Topography Underlain by limestone Evidence of groundwater erosion seen at the surface US = limestone Kentucky, Florida, Tennessee, soutern Indiana, Alabama Lack of streams

Sinkholes Karst areas have sinkholes = depression because groundwater has removed soluble rock Some happen gradually, some happen suddenly

Environmental Problems Land Subsidence = large amounts of groundwater have been withdrawn Groundwater supplies are finite Water pumped from wells faster than it can be replaced Ground sinks Ex: California

Groundwater Contamination Sewage from septic tanks, farm wastes, broken sewers Highly permeable means increase in groundwater contamination Fertilizers spread across land, pesticides, highway salt

What happens if groundwater is polluted? Abandon the water supply = pollutants flush out gradually Aquifer unused for years Pump out and treat polluted water Aquifer recharges naturally Prevention