GROUNDWATER Minerva Terrace, Yellowstone WY underground water stored in the pore spaces of rock, sediment, or soil important resource for domestic, industrial, and agricultural use important erosional agent important energy source in some areas underground water stored in the pore spaces of rock, sediment, or soil important resource for domestic, industrial, and agricultural use important erosional agent important energy source in some areas

HYDROSPHERE Oceans 97.2% Glaciers 2.15% GROUNDWATER 0.62% Other 0.03% lakes 0.009% inland seas 0.008% soil 0.005% atmosphere 0.001% streams % biosphere % Oceans 97.2% Glaciers 2.15% GROUNDWATER 0.62% Other 0.03% lakes 0.009% inland seas 0.008% soil 0.005% atmosphere 0.001% streams % biosphere %

POROSITY and PERMEABILITY Porosity the percentage of a material’s volume that is pore space Permeability a measure of the interconnectedness of pore spaces Porosity the percentage of a material’s volume that is pore space Permeability a measure of the interconnectedness of pore spaces well sorted = high porositypoorly sorted = low porosity carbonates, evaporitesmetamorphic or igneous rocks

POROSITY Unconsolidated sediment soil 55% gravel 20-40% sand 25-50% silt 35-50% clay 50-70% Rocks sandstone 5-30% shale 0-10% carbonates, dissolution 10-30% basalt, fractured 5-40% granite, fractured 10% Unconsolidated sediment soil 55% gravel 20-40% sand 25-50% silt 35-50% clay 50-70% Rocks sandstone 5-30% shale 0-10% carbonates, dissolution 10-30% basalt, fractured 5-40% granite, fractured 10%

POROSITY & PERMEABILITY Porosity sand 25-50% clay 50-70% Permeability Sand: high permeability Clay: low permeability

“Aqui-” Terms Zone of aeration pore spaces contain mostly air Zone of saturation pore spaces contain mostly water Water table the top of the zone of saturation Capillary fringe surface tension pulls water up from the saturated zone few cm’s to several meters thick

“Aqui-” Terms Aquifer: a permeable layer that transports groundwater Confined (closed) Unconfined (open) Aquiclude or Aquitard: an impermeable layer that prevents or retards the movement of groundwater

Variations in the Water Table Shape of the water table mimics the shape of the landscape Wherever the water table intersects the Earth’s surface, there is free-flowing or free- standing water (springs, ponds) Water-level in wells = position of the water table

Variations in the Water Table

Groundwater Flow Gravity moves groundwater, just as it does water in channels moves from areas of high pressure to areas of low pressure may move up to 250 m per day, or less than a few cm/day Groundwater “piles up” beneath high areas because it moves so slowly; if rainfall stopped, the “hills” in the water table would slowly flatten out.

Groundwater Flow Mapping the water table. The water level in wells coincides with the water table. A. A.The locations of wells and the elevation of the water table above sea level are plotted on a map. B. B. These data points are used to guide the drawing of water table contour lines at regular intervals (10 ft). Flow lines (dashed) are added to show water movement in the zone of saturation.

Gaining Steams/Losing Streams Gaining streams receive water from the GW system: water table above stream. Losing streams lose water to the GW: water table below stream. When losing streams are separated from the GW system by the zone of aeration, a bulge may form in the water table: rate of infiltration > rate of GW flow

Movement of GW Slope of the water table = hydraulic gradient h 1 - h 2 d Steeper slope = faster flow Greater permeability = faster flow (hydraulic conductivity K) Darcy’s Law (aquifer discharge) Q = KA(h 1 - h 2 ) d

Springs Places where groundwater flows or seeps out of the ground when percolating water reaches the water table or an impermeable layer, it flows laterally and may intersect the surface, yielding a spring Marble Canyon AZ

Artesian Aquifers “artesian” GW under pressure rises above the level of the aquifer Non-flowing Free-flowing

Artesian Aquifers

Oasis desert spring

WELLS penetrate the zone of saturation Water level in the well marks the position of the water table. Pumping water from wells causes drawdown of the water table around the well, creating a cone of depression

WELLS penetrate the zone of saturation

Hot Springs and Geysers GW is heated as it circulates at depth or near cooling magma bodies travertine, tufa sinter, geyserite

Hot Springs and Geysers

Depletion Lowering of the water table (depletion) occurs when GW is pumped out faster than it is replenished (non-renewable resource). Largest aquifer in the U.S. = Ogallala Aquifer (High Plains Aquifer)

Subsidence Subsidence of the ground surface occurs when GW is pumped out faster than it is replenished in some areas (compaction). San Joaquin Valley New Orleans, LA Mexico City

Saltwater Contamination Saltwater contamination occurs in coastal areas when GW is pumped out faster than it is replenished. Recharge wells and drainage basins help to replenish fresh GW. Orange County CA Long Island NY

Pollution Hazardous pollutants = flammable, corrosive, explosive, toxic Pollution sources: Sewer systems and septic tanks Farm wastes and fertilizers Industrial chemicals from pipes, tanks, or holding ponds Landfills A. A.Although the contaminated water has traveled more than 100 m before reaching Well 1, the water moves too rapidly through the limestone to be purified. B. B.As the discharge from the septic tank percolates through the sandstone, it is purified in a relatively short distance.

Pollution A. A.Originally the outflow from the septic tank moved away from the small well. B. B.The heavily pumped well changed the slope of the water table, causing contaminated GW to flow toward the small well.

GW Erosion Depositional features (speleothems) form as water percolates through the unsaturated zone: stalactites, stalagmites soda straws, columns Caverns form as a result of dissolution of carbonate rocks below the water table

GW Erosion Carlsbad Caverns NM

KARST Karst Topography A. A.GW percolates through limestone along joints and bedding planes. Dissolution creates and enlarges caverns at and below the water table. B. B.Sinkholes form when the roof of a cavern collapses. Surface streams may disappear down sinkholes and reappear as springs. C. C.As time passes, caverns grow larger and the number and size of sinkholes increase. Collapse of caverns and coalescence of sinkholes form larger, flat- floored depressions (solution valleys). Eventually dissolution may remove most of the limestone from the area, leaving only isolated remnants (towers).

KARST Guilin CHINA