GEOL ch 14 groundwater

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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


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