Chapter 14: Groundwater

Chapter 14.1

Water in the Ground – a.k.a groundwater – water stored in the ground

Porosity – the percent or a materials volume that is pore space Factors that effect porosity Roundness – the rounder the material the more porosity Sorting – round materials that are of the same size leaves larger pore spaces Pebbles alone have more pore space than a sand and pebble mix

Permeability – rate at which liquids pass through the pore space Factors that effect permeability Larger the grain the more pore space Pebbles more pore space than silt or clay – small and lay flat clay is impermeable Cracks (fissures) in rock Granite is nonporous however if cracks develop water can pass through

The Water Table Water will travel down through the ground until it hits an impermeable layer (shale) It will then be stored in the permeable rock above (sandstone) The surface (top) of the zone saturated rock is the water table Zone of aeration is above the water table

Capillary fringe (water rises because the water molecules are attacked to soil particle) occurs between the zone of saturation into the zone of aeration Water table depth is effected by rainfall, time between rains, seasons slope of ground thickness of soil Humid areas At surface Deserts Hundreds of meters below surface

Ordinary Wells and Springs Ordinary well – drilled by people – contained water up to the level of the water table They must reach below the lowest level to which the water table is likely to fall Spring – occurs where a hillside meets the water table

Artesian Formations A permeable layer of rock surrounded by two impermeable layers trapping the water Layers are exposed in the mountains and the permeable layer may transport the water 100’s of miles (aquifer) Impermeable layer is usually shale (cap rock) On artesian wells water may come to surface on its own due to pressure (picture p. 304)

Heated Groundwater Hot springs – evidence of sub surface heat due to great depth or magma Mud pots – sticky sputtering hot springs Geyser – a hot spring that will shoot columns of water Old faithful in Yellowstone Fumaroles – steaming vents

Chapter 14.2

Conserving Ground Water 50% of the drinking water in the U.S. comes from ground water

Water Budget Income is rain or snow spending includes use, evaporation and runoff Surplus – rainfall is greater than the need for moisture and the soil water storage is filled Deficit – the need for moisture is greater than the rainfall

Ground Water Conservation Overuse – many areas ground water is being used faster than replenishment In coastal areas sea water may mix with the ground water if the water table gets too low Subsidence of land caused by the overuse of ground water causing the ground to be compacted Retention ponds and pumping water into the ground helps to replenish Ground water pollution, oils from roads, fertilizers, pesticides, farm waste, septic tanks and salt from roads

Chapter 14.3

Ground water Geology

Minerals in ground water Rainwater has almost no dissolved minerals in it however it may have dissolved gases (CO2) It dissolves minerals as it passes through the ground carrying it in solution Calcium (most common) along with iron causes water to be hard, which cause soap to form scum instead of suds. Artesians are usually the hardest because they are warmer and travel further.

Mineral Deposits by Ground Water – caused by the cooling or evaporation of water Geyserites – mounds of silica around geysers Petrified wood (fossils) – mineral matter that replaced organic matter Cement to bind sediments together Silica, calcite and iron are common cements

Mineral Springs – a spring with a high concentration of mineral matter

Caverns – formed in limestone, dissolved by carbonic acid in ground water Stalactites – deposits hang from ceiling Stalagmites – deposits on floor

Karst Topography – an area filled with sinkholes Sinkhole ponds, lost rivers and underground drainage