GEOL ch 14 groundwater
groundwater is __% of freshwater source to us in US, and about 70% of it goes to ___
25% irrigation
average travel rate of groundwater
4 cm per day
Which of the following defines an aquifer?
A saturated, porous, and permeable layer or stratum
Which of the following describes an artesian well?
A well in which water rises above the top of the aquifer without any pumping
Which of the following describes a disappearing (sinking) creek?
An influent stream in a karst area In karst areas, streams are very short and usually disappear into sinkholes produced by the dissolution of limestone.
Which of the following statements concerning unconfined aquifers on barrier islands and atolls is correct?
Any salt water in the aquifer will rise if the water table is lowered by pumping.
Which common rock-forming mineral or mineral group is most readily dissolved by groundwater?
Calcite
Which of the following describes the configuration of an unconfined water table around a pumping well?
Cone of depression
interaction between groundwater and streams: gaining streams and losing streams
Constitutes a basic link in the hydrologic cycle o gaining streams: gain water from inflow of groundwater through streambed -water table higher than stream surface o losing streams: lose water to groundwater system by outflow through the streamed -water table lower than stream surface o combination: can gain and lose in different sections
What happens after a geyser erupts?
Cool groundwater seeps back into the underground chambers, and the cycle starts again.
When water is pumped from a well, drawdown occurs. Which of the following is a true statement regarding drawdown?
Drawdown decreases with increasing distance from the well.
What is the relationship between drawdown and the cone of depression associated with a pumping well?
Drawdown is the distance between the original water table and the water level in the well.
How would hazardous substances such as gasoline, kerosene, ethyl alcohol, pesticides, and acids that accidentally entered a groundwater system behave?
Gasoline and kerosene would float on the water table; ethyl alcohol would dissolve and disperse in the groundwater.
Which one of the following is not a speleothem? Dripstone Stalagmite Stalactite Geyserite
Geyserite
__________ are intermittent springs that eject columns of water and steam at various time intervals.
Geysers
Name two characteristics found in all aquifers.
High porosity and high permeability
Which of the following describes the water table?
a boundary between saturated rock below and unsaturated rock above
Which of the following best describes the cone of depression?
a dimple in the water table surface due to water pumped faster than an aquifer can be replenished
well, drawdown, cone of depression
a hole bored into zone of saturation o most common methods for removing groundwater o drawdown: as water is withdrawn from well, surrounding water table is lowered o cone of depression forms around well
capillary fringe
a region where groundwater is held in pore spaces by surface tension found in the unsaturated zone
artesian well /spring -requirements
a system where groundwater under pressure rises above the level of the aquifer o water must be confined to an inclined aquifer o aquitards must exist above and below the aquifer to confine the aquifer (aquifer confined by aquitards: confined aquifer)
permeability
ability of material to transmit a fluid and depends on connectivity between pore spaces
A perched aquifer is located directly above a(n) __________.
aquitard
cavern dripstone:
calcium carbonate deposited as dripping water evaporates
Depositional features created by dripping of water over great spans of time are called ________.
dripstone
saltwater contamination caused by: can be corrected with ___ mainly an issue in ___
excessive groundwater withdrawal causes saltwater to be drawn into wells, thus contaminating the freshwater supply o can correct with recharge wells o primarily a problem in coastal areas
A(n) __________ acts as a conduit that brings heated water to the surface.
fault
Once overlying water heats to a sufficient temperature, it __________ and releases pressure on the water below.
flashes to steam
sinkholes
formed by groundwater slowly dissolving the bedrock often accompanied by collapse
hydraulic gradient hydraulic conductivity
gradient: water table slope conductivity: considers permeability of aquifer, viscosity of liquid, to determine how fast water will move through a medium
___ and differences in __ move groundwater
gravity pressure
What reservoir(s) contain(s) the next-highest percentage of Earth's freshwater after ice sheets and glaciers?
groundwater
Groundwater flows from __________.
high to low pressure areas
aquitard
impermeable layer that hinder or prevent water movement e.g. clay
mining groundwater is an issue and it is treated as a nonrenewable resource because: example:
in many places the water available to recharge the aquifer is significantly short of the amount being withdrawn e.g. high plains aquifer
The cone of depression increases the __________ near a well.
increases the hydraulic gradient
The hot spring deposits at Mammoth Hot Springs, Yellowstone National Park, are travertine. What rock probably lies somewhere beneath the hot springs?
limestone
A __________ is separated from the groundwater system by the unsaturated zone.
losing stream (disconnected)
non-flowing artesian well flowing artesian well
non-flowing: pressure surface is below ground level flowing: pressure surface above ground artesian systems can be springs, too
porosity depends on ____ of grains and how ____ they are. Poor sorting means ____ porosity means ___ groundwater
o % of pore spaces in rock/sediment o depends on size/shape of grains, how well sorted and how tightly packed o poorly sorted, low porosity, less groundwater
hot springs are ____ warmer than mean annual air temp of locality water is usually heated by ____ some warmed by ___
o 6-9°C warmer than mean annual air temp of locality o water is usually heated by cooling of igneous rock o some warmed by geothermal gradient
karst topography and common features
o a type of landscape that has been shaped mainly by the dissolving power of groundwater o features: irregular terrain, sinkholes/sinks, lack of surface drainage
geological importance of groundwater
o acts as erosional agent dissolving soluble bedrock such as limestone o serves as an equalizer of streamflow
unsaturated zone (vadose) pore spaces include __ and __ includes ___ and ____
o area above water table/zone of saturation o pore spaces include air and water o includes zone of soil moisture o includes of capillary fringe
geyser deposits
o chemical sedimentary rock accumulates at the surface o type of rock reflect chemical makeup of bedrock e.g. siliceous sinter or geyserite form from dissolved silica e.g. travertine forms from dissolved calcium carbonate
variation in water table's depth and shape
o depth varies b/c precipitation o shape is a subdued replica of surface topography
groundwater
o found in pores of soil, sediment, and bedrock fractures o largest reservoir of freshwater readily available to us o less than 1% of hydrosphere
speleothems
o general name for all dripstone features o stalactites (hanging) o stalagmites (floor)
geysers and how they work geysers are ___ in which columns of water ____ occur where ______ exist within ____ ________ rock they erupt when:
o geysers are intermittent hot springs in which columns of water erupt with force how: o occur where extensive underground chambers exist within hot igneous rock o groundwater heats, expands, changes to steam, erupts
how groundwater dissolves rock
o is acidic with carbonic acid o reacts with calcite in limestone to form calcium bicarbonate, soluble material
Darcy's Law
o measure of volume of water that flows through an aquifer, using hydraulic gradient, conductivity, cross-sectional area
how caverns are formed by groundwater where this is most active (level in ground)
o most made by acidic groundwater dissolving soluble rock like limestone bedrock o occurs at several levels, most active at/just below zone of saturation
groundwater contamination besides sewage: sinking well other sources
o sinking a well can lead to pollution: cone of depression can increase/reverse slope of water table o highway salt, fertilizers, pesticides, chemicals, industrial materials
groundwater contamination: sewage o an issue in what type of aquifers o sewage is purified in what type of aquifers
o very permeable aquifers like coarse gravel allow groundwater to travel long distances without being cleaned o sewage becomes purified as it passes through aquifer of sand/permeable sandstone
zone of saturation and water table
o where all pore spaces are filled with water o water in zone of saturation is groundwater o water table is upper limit of this zone
zone of soil moisture
o zone in which water is held by molecular attraction on soil particles in near surface o used by plants o evaporates directly back to the atmosphere
springs occur where ____ are natural ___ of groundwater can be caused by _____ (perched water table)
occur where water table intersects earth's surface natural outflow of groundwater can be caused by aqiuitard creating localized zone of saturation that is called a perched water table
To ensure a continuous supply of water, a well must do what?
penetrate well below the regional water table surface
aquifer
permeable rock strata or sediment that transmits groundwater freely e.g. sands and gravels
most groundwater gets into ground by ____
precipitation
recharge and discharge areas
recharge: where groundwater is replenished discharge: where it flows back to the surface
example of artesian system that transmits water a great distance example of artificial artesian systems
south Dakota municipal water tower
What is the name of an icicle-like speleothem that grows down from the roof of a cavern?
stalactite
Which of the following is necessary to calculate hydraulic gradient?
the distance between two wells that penetrate the zone of saturation
What characteristic of rocks and/or soil controls the ease (or difficulty) of groundwater transmission?
Permeability
What term describes the volume of voids or open spaces in a rock or unconsolidated material?
Porosity
What force pushes groundwater from pore to pore below the water table?
Pressure gradient or hydraulic gradient
Darcy's law equation
Q = KA(h1-h2) / d Q= discharge K= hydraulic conductivity A= cross sectional area of aquifer h1-h2 / d = hydraulic gradient
Which of the following materials would have the best capability to naturally remove sewage pollutants? Slightly clayey sand Well-sorted, coarse gravel Limestone with solution channels and caverns Fractured granite
Slightly clayey sand
Which of the following are specific features of karst topography? A perched water table creates springs on hillsides. Numerous artesian wells occur in a given area. Streams flow into depressions called sinkholes and continue to flow underground. Perennial, influent streams are fed by large springs.
Streams flow into depressions called sinkholes and continue to flow underground.
Which of the following statements defines the aerated, or vadose, zone?
The aerated, or vadose, zone lies above the water table.
scales of movement for groundwater
The area of groundwater flow systems vary from a few square kilometers to tens of thousands of square kilometers. Regional groundwater systems interact with deeper, larger groundwater systems
What is an unconfined water table?
The boundary between the aerated, or vadose, zone above and the saturated zone below
subsidence
The ground sinks when water is pumped from wells faster than natural recharge processes can replace it. •Example: San Joaquin Valley of California
What prevents water at the bottom of the underground caverns from boiling at the normal surface temperature?
The pressure from the weight of overlying water causes the boiling point to increase.
What can be a result of excessive groundwater withdrawal?
The water table may drop or decline in elevation.
When will a perched water table develop?
When a horizontal aquitard above the regional water table lies below an aquifer
Which of the following best describes how geysers erupt?
With a slight reduction in pressure, water in a saturated, natural conduit suddenly boils, sending a plume of steam and hot water into the air above the vent.
Where are the most extensive geothermal features in the world located?
Yellowstone National Park, United States
example of hot spring
Yellowstone' mammoth hot springs