GEO EXAM II

What is hydrogeology ?

The study of groundwater, including its storage, movement, chemistry, and contamination

What is a water reservoir ?

A place where water is stored, such as an ocean, glacier, lake, aquifer, or the atmosp

Where is most of Earth’s water stored ?

In the oceans as saltwater

Where is most of earth’s freshwater stored ?

In ice caps glaciers

Why is gorundwater an important freshwater resource ?

It stores a large amount of freshwater that can supply wellsl, agriculture, and surface waters

What is the hydrologic cycle, and what drives it?

The continuous movement of water among reservoirs, driven primarily by solar energy and gravity

What is evaporation?

The conversion of liquid water into water vapor

What is condensation?

The conversion of water vapor into liquid water

What is precipitation?

Water falling from the atmosphere as rain, snow, sleet, or hail

What is transpiration?

The release of water vapor from plants, mainly through their leaves

What is infiltration?

The movement of water from the ground surface into soil or rock

What is runoff?

Water flowing over the land surface instead of infiltrating

Is water always a renewable resource?

No. Water cycles globally, but local supplies can be depleted when consumption exceeds replenishment

What is porosity?

The proportion of a material’s total volume occupied by pore spaces; it measures storage capacity

What is permeability?

How readily water can move through a material’s connected pores or fractures

Can a rock have high porosity but low permeability?

Yes. Abundant isolated pores store water but provide few connected pathways for flow

Can rock with low porosity have substantial permeability?

Yes. Connected fractures can allow water to flow through rock with little pore space

How does sorting affect porosity in the slide examples?

Well-sorted grains generally leave more open pore space; smaller grains in poorly sorted material fill gaps

How do compaction and cementation affect groundwater storage and movement?

They generally reduce pore space and restrict water flow.

How do sandstone, compacted shale, and unfractured granite generally compare?

Sandstone commonly stores and transmits water well; compacted shale restricts flow; unfractured granite has low porosity and permeability.

What is an aquifer?

A permeable body of rock or sediment that stores and transmits usable quantities of groundwater.

What is an aquitard?

A low-permeability layer that slows groundwater movement

What is an acquiclude ?

A layer with extremely low permeability that effectively prevents groundwater flow

What is the vadose zone ?

The unsaturated zone, where pore spaces contain both air and water

What is the phreatic zone ?

The saturated zone, where pore spaces are filled with water

What is the water table ?

The upper boundary of the saturated groundwater zone

How does subsurface water differ from groundwater?

Subsurface water includes water below ground in both unsaturated and saturated zones; groundwater refers to water in the saturated zone

What is a perched water table?

A localized saturated zone above the regional water table, supported by a low-permeability layer

What is groundwater recharge?

Water entering and replenishing an aquifer

What is groundwater discharge ?

Groundwater leaving an aquifer, such as through springs, streams, lakes, or wells.

What is the difference between a gaining and losing stream?

A gaining stream receives groundwater; a losing stream supplies water to the surrounding aquifer.

What is an unconfined aquifer?

An aquifer whose upper saturated boundary is the water table, without an overlying confining layer.

What is a confined aquifer?

An aquifer beneath a low-permeability confining layer, with groundwater under pressure

What is the potentiometric surface?

The elevation to which water rises in wells tapping a particular aquifer

What makes an artesian well a flowing artesian well?

Its potentiometric surface is above ground level, so water flows out without pumping

What determines groundwater flow direction?

Groundwater flows from higher hydraulic head to lower hydraulic head.

How do you calculate hydraulic head from ground elevation and well water level?

Water below ground: subtract its depth from ground elevation. Water above ground: add its height to ground elevation

What is hydraulic gradient?

The difference in hydraulic head divided by the distance between the measurement points: i = change in H / change in D

What is Darcy’s law?

Q = KA(change inH/change inD), where Q is discharge, K is hydraulic conductivity, and A is cross-sectional area.

How do hydraulic conductivity, area, and gradient affect discharge?

Increasing any one increases discharge, holding the others constant. With K in m/s and A in m², discharge is in m³/s.

What is a cone of depression?

A lowered groundwater surface around a pumping well

How can groundwater withdrawal cause land subsidence?

Removing groundwater can allow sediments to compact, causing the land surface to sink

What is saltwater intrusion?

Saltwater moving into a freshwater aquifer, often when coastal pumping lowers freshwater pressure

How does urban development reduce groundwater recharge?

Impermeable pavement and buildings reduce infiltration and increase runoff

How can artificial recharge increase groundwater supplies?

Recharge basins, trenches, and wells direct water into the subsurface

What is a sinkhole?

A surface depression or collapse formed when material moves into an undergorund opening

How can groundwater create sinkholes?

It dissolves soluble rock, creating cavities into which overlying material can sink or collapse

What is karst?

Terrain shaped by dissolution of soluble rock, commonly featuring caves, sinkholes, and underground drainage

Which rocks or minerals are especially associated with dissolution?

Limestone containing calcite, gypsum, and salt

Why are karst aquifers vulnerable to contamination?

Pollutants can move rapidly through connected fractured and conduits with limited natural filtration

What is a groundwater contamination plume?

A spreading body of contaminated groundwater that generally moves with groundwater flow

What is a water pollutant?

A substance or agent that degrades water quality or harms organisms at the concentration present

What is the difference between point and nonpoint pollution sources?

Point sources have identifiable discharge locations; nonpoint sources are diffuse and spread across an area

How are a paper-mill pipe, fertilizer runoff, and road-salt runoff classified?

Paper-mill pipe: point source. Fertilizer runoff and road-salt runoff: nonpoint sources

Why can excess organic matter pollute water ?

Microorganisms consume dissolved oxygen while decomposing it, potentially deriving aquatic organisms of oxygen

What is the difference between aerobic and anaerobic decomposition?

Aerobic decomposition uses oxygen; anaerobic decomposition occurs without oxygen and can produce methane

What is dissolved oxygen, or DO?

Oxygen dissolved in water and available to aquatic organisms, commonly measured in mg/L

What is biochemical oxygen demand? (BOD)

The oxygen microorganisms required to break down decomposable organic matter

How does adding decomposable organic matter affect BOD and DO?

BOD increases, and DO generally decreases as microorganisms consume oxygen

What is the difference between hypoxia and anoxia?

Hypoxia means low dissolved oxygen; anoxia means essentially no dissolved oxygen

What is a dead zone?

An area with oxygen levels too low to support many aquatic organisms

What does an oxygen sag curve show?

The decline and subsequent recovery of dissolved oxygen downstream of an organic-waste discharge

How can DO and BOD graphs reveal waste-discharge locations?

BOD rises at an organic-waste input, followed by a downstream DO decline; repeated changes can indicate multiple inputs

What equation describes aerobic decomposition of glucose?

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O. One mole of glucose consumes six moles of oxygen.

How do you calculate oxygen mass consumed by glucose decomposition?

Multiply glucose mass by 192/180, assuming complete aerobic decomposition. That is about 1.067 g oxygen per gram of glucose

What is eutrophication?

Nutrient enrichment of water that stimulates biological production, often causing excessive algal growth

Which nutrients commonly cause eutrophication?

Nitrogen and phosphorus

What is cultural eutrophication

Eutrophication accelerated by human nutrient inputs, such as fertilizer, sewage, manure, or phosphate detergents

What is the main eutrophication sequence?

Nutrient input → algal growth → algal death → bacterial decomposition → oxygen depletion → aquatic-organism stress or death

Why can an algal bloom eventually cause oxygen depletion?

After algae die, microorganisms consume oxygen while decomposing the accumulated organic matter

How do oligotrophic and eutrophic waters differ?

Oligotrophic waters have low nutrients and productivity; eutrophic waters have high nutrients and productivity and may develop oxygen-poor bottom waters

What are major consequences of eutrophication?

Excess biomass, reduced clarity, taste and odor problems, harmful blooms, low oxygen, and altered biological communities

What is biomagnification?

Increasing pollutant concentration at successively higher trophic levels in a food web

How do you calculate pollutant concentration and a biomagnification factor?

Concentration = pollutant mass / biomass. Factor = higher-trophic-level concentration / starting-level concentration

Which mercury compound is emphasized in aquatic biomagnification?

Methylmercury, which can accumulate at high concentrations in predatory fish

What is Minamata disease associated with?

Methylmercury poisoning, which can cause severe neurological damag

What is cadmium poisoning associated with?

Itai-itai disease, painful bone damage, softening of bones, and kidney damage

What major health effect is emphasized for lead pollution?

Damage to brain and nervous-system functions

Why is arsenic different from mercury, cadmium, and lead?

Arsenic is a metalloid, and naturally occurring arsenic in groundwater can cause widespread poisoning

How does chemical form affect arsenic toxicity?

As(III), or arsenite, is generally more mobile and toxic than As(V), or arsenate; organic arsenic is generally less toxic than inorganic arsenic

What is the capillary fringe?

The zone immediately above the water table where water rises into pores through capillary action

How does the water table generally relate to topography?

It often loosely follows surface topography, rising beneath hills and falling toward valleys

Where does water generally stand in a well tapping an unconfined aquifer?

At approximately the local water-table elevation

What is the grain-size order from smallest to largest?

Clay → silt → sand → gravel

Why doesn’t high porosity guarantee high permeability in clay-rich material?

Small pores and narrow connections can restrict flow even when substantial pore space exists

According to the slides, which two used together account for nearly 80% of U.S. freshwater use?

Agriculture and electricity generation

What are major benefits and limitations of permeable pavement?

It promotes infiltration and reduces runoff, but costs more initially, requires maintenance against clogging, and may be unsuitable for heavy loads

What is pump-and-treat remediation?

Pumping contaminated groundwater to the surface and treating it

What is natural attenuation?

Natural physical, chemical, or biological processes that reduce contaminant concentrations or harmful effects

What is an example of in situ groundwater contamination management?

Installing an underground impermeable barrier to contain contamination or control its movement

Why is the Ogallala Aquifer vulnerable to depletion

Heavy agricultural withdrawals can exceed its limited modern recharge

What is the main water-resource problem emphasized for the Colorado River Basin?

A limited water supply in a dry region faces competing demands and allocations

Why has salinity increased in the Salton Sea?

Irrigation supplies dissolved salts, and evaporation removes water while leaving salts behind.

What caused the Aral Sea to shrink, and what followed?

River water was diverted for irrigation, causing shrinkage, increased salinity, fishery collapse, and exposed contaminated lakebed dust

What human nutrient source is highlighted in the historical Lake Erie eutrophication example?

Phosphates from detergents

What can a shift from oxygen-sensitive to pollution-tolerant organisms indicate?

Declining oxygen conditions and increased organic pollution; the slides identify Hexagenia as oxygen-sensitive

How do you distinguish fold increase from percent increase?

Fold increase = new ÷ original. Percent increase =
(new - original)/original x 100). A threefold final value is a 200% increase

What produced the lead-contamination problem highlighted in Flint?

A water-source change combined with insufficient treatment allowed lead to enter drinking water from plumbing

What is the key lesson of the Bangladesh arsenic example?

Groundwater can be contaminated by naturally occurring arsenic; water from a well is not automatically safe

In the slide’s food-web example, what are the mercury concentrations and overall biomagnification factor?

lgae: \(10/1000=0.01\) mg/kg. Zooplankton: \(5/100=0.05\) mg/kg. Small fish: \(4/20=0.20\) mg/kg. Large fish: \(2/2=1.0\) mg/kg. Overall factor: \(1.0/0.01=100\)