Hydrogeology•Mr. Mike Dvorin

•Muir Middle School

Expectations

■ E4.1A – Compare and contrast surface water systems (lakes, rivers, streams, wetlands) and groundwater in regard to their relative sizes as Earth’s freshwater reservoirs and the dynamics of water movement (inputs and outputs, residence times, sustainability).

■ E4.1B – Explain the features and processes of groundwater systems and how the sustainability of North American aquifers has changed in recent history (e.g., the past 100 years) qualitatively using the concepts of recharge, residence time, inputs, and outputs.

■ E4.1C – Explain how water quality in both groundwater and surface systems is impacted by land use decisions.

Expectation 1

■ E4.1A – Compare and contrast surface water systems (lakes, rivers, streams, wetlands) and groundwater in regard to their relative sizes as Earth’s freshwater reservoirs and the dynamics of water movement (inputs and outputs, residence times, sustainability).

The world’s water supply consists of 97% ocean water and only 3% freshwater.

Breaking down that 3% (that is freshwater), 66% is held in glaciers.

World’s Freshwater

Sources

Other sources of freshwater (in order of abundance) include:

1.Groundwater

2.Freshwater Lakes

3.Wetlands

4.Rivers

Distribution of Water

While every land mass on Earth contains water, the problem is that freshwater is not evenly distributed. Desert areas have very limited fresh water resources, while rain forests can have as much as 30 feet of rainfall in a year.

The Water CycleINPUTS:

Precipitation is the source of fresh water virtually everywhere on Earth. Precipitation is usually in the form of rain or snow.

The precipitation that strikes the Earth may be either:

1) soaked into the Earth (saturates the soil and recharges groundwater), or

2) run off into water bodies found on the surface (the ocean, lakes, rivers, streams, etc.).

*Runoff recharges lakes

*Saturation recharges aquifers

Residence TimeResidence time for water is the average amount of time a molecule of water will remain in a reservoir of water (the average age of the water in a location). Residence time will vary from thousands of years for water stored in ice caps, glaciers, and permafrost to around a week for biospheric and atmospheric water.

Residence time (longest to shortest): groundwater, lakes, wetlands (swamps), rivers

Freshwater Sustainability

Sustainability of freshwater refers to the ability of humans to manage our water supply so it doesn’t decline or disappear. We must consider water usage and water conservation methods.

Expectation 2

■ E4.1B – Explain the features and processes of groundwater systems and how the sustainability of North American aquifers has changed in recent history (e.g., the past 100 years) qualitatively using the concepts of recharge, residence time, inputs, and outputs.

GroundwaterGroundwater occurs almost everywhere beneath the land surface. Although surface water is currently the most commonly used water source, groundwater provides about 65% of the drinking water in the United States.

GroundwaterAs groundwater moves downward past the soil zone, two important concepts determine how far and how fast the water moves.

Porosity is a measure of pore spaces between the grains of a rock or of cracks that can fill with fluid. The quantity of water a rock will hold depends on its porosity.

Permeability is a measure of how easily water moves through pore spaces. If liquids move easily, the rock material is said to be permeable. If liquids do not move (or at least not very easily, the rock material is said to be poorly permeable or impermeable.

AquiferAn aquifer is a geologic formation that is permeable enough to allow groundwater to be withdrawn by pumping wells or flow to a spring. Sand and gravel make some of the most productive aquifers. Sandstone and limestone sedimentary rocks can also be good aquifers.

Recharge

Groundwater can be replaced or “recharged.”

How?

Nature will recharge the groundwater through rainfall (or melting snow) infiltrating or percolating into the ground.

What’s your problem?

It has to do with sustainability.

US Population Growth

1910 Population

United States Principal AquifersU.S. population has grown from just over 90 million citizens in 1910, to just over 306 million today.

In addition to surface water, these are the principal U.S. aquifers that are providing fresh water to our growing population.

Sustainability of N.A. AquifersLet’s use the High Plains Aquifer (also called the Ogallala Aquifer) to discuss the sustainability of North American aquifers. This aquifer covers 174,000 square miles, underlying parts of 8 states. This is one of the nation’s most important agricultural areas. Extensive groundwater withdrawals have been made, exceeding the recharge rate. The result has been a lowering of groundwater levels and a shortening of residence time.

The blue areas show an increase in groundwater levels. Diversion of surface waters for irrigation can allow the groundwater to recharge.

Wherever population, agricultural, and/or industrial growth has occurred, groundwater aquifers may be suffering from more water withdrawal then recharge.

InputsAn important input for our groundwater system is amount of precipitation an aquifer will possibly receive each year. Precipitation is not distributed evenly throughout the United States. As shown by this “annual precipitation map” many portions of the central and western United States have low precipitation amounts.

Outputs – A.I.RExcessive removal of groundwater is major problem. Water usage for growing populations (residential), irrigation needs of the nearby agricultural community, and water for industrial use are the leading causes of groundwater removal. The more a local area develops or is converted into agricultural land, the greater the demand for water.

Acronym Alert!

Expectation 3

■ E4.1C – Explain how water quality in both groundwater and surface systems is impacted by land use decisions.

Water Quality - Groundwater

Saline water surrounds much of the groundwater of the United States, either laterally along the seacoasts or deep beneath aquifers. Fresh water is less dense than saline water and tends to naturally separate by floating on top of saline water.

However, when fresh groundwater is withdrawn, the boundary between fresh and saline groundwater moves (intrudes) into the space formally occupied by the fresh groundwater. This is called salt-water intrusion.

Salt-water intrusion is already a problem in parts of California, Florida, Georgia, New Jersey, and South Carolina.

Water Quality - GroundwaterAs you can see from the picture below, shallow unconfined aquifers are more vulnerable to contamination than water in deeper confined aquifers. Confined aquifers are generally protected by layers of relatively impermeable materials that impede the movement of contaminated water from the land surface. Contaminates such as nutrients, pesticides, and bacteria have been found in groundwater. Groundwater contamination is extremely difficult to reverse in part due to the slow rate at which water moves through aquifers.

Ann Arbor Groundwater QualityGroundwater beneath the city of Ann Arbor is currently contaminated by the probable carcinogen 1,4 dioxane. This chemical was used as an industrial solvent by Pall Life Sciences’ (PLS) predecessor, Gelman Sciences. Between 1976 and 1985, wastewater containing 1,4 dioxane was sprayed on their lawns and stored in unlined lagoons. The chemical seeped through soil and rock layers and into the groundwater and began to spread. Its physical properties allow it to spread rapidly with groundwater. Disposal of this chemical in this way was stopped in 1986.

Water Quality – Surface SystemsA variety of factors can impact the water quality of our lakes, rivers, streams, and wetlands.

Industrial pollution is often poured directly into our water system. Toxic chemicals and oil spills are a couple of examples in this area.

Agricultural pollution often results from water runoff that spills directly into our water system. Fertilizers, pesticides, and animal waste bacteria are all examples in this area.

Laws and Regulations■ Clean Water Act – a 1977 amendment to the Federal Water

Pollution Control Act of 1972 that regulates discharges of contaminants into the waters of the United States.

■ Safe Drinking Water Act – a 1974 law established to protect the quality of drinking water in the United States.

■ Resource Conservation and Recovery Act – a 1976 law that gave the EPA the authority to control hazardous waste from the “cradle to grave”.

■ Comprehensive Environmental Response, Compensation, and Liability Act – a 1980 law that provides Federal funding to help clean up uncontrolled or abandoned hazardous waste sites as well as accidents, spills, and other emergencies. Referred to as the “Superfund”. The government can force companies to pay to clean up their mess.

Groundwater & Aquifers

• Groundwater fills the open spaces in rocks, sediment, and soil beneath the surface

• Groundwater is animportant source foragricultural, industrial, and residential use.

Introduction…

Acronym Alert!

Groundwater and theHydrologic Cycle

■ Groundwater is about 30% of the world’s fresh water.

■ Groundwater comes from precipitation percolating through soils and sediment. (recharge)

■ Streams, lakes, and snowmelt also contribute.

What Properties of Earth’sMaterials Allow Them to Absorb

Water?■ Porosity = the percentage

of a material’s volume that is pore space

■ Permeability = the measure of the ability of water to flow through

■ Aquifer = permeable layer that transports water

What is the Water Table?• 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

Distribution ofGroundwater

How Does Groundwater Move?

■ Gravity moves groundwater, just as it does water in channels… it flows downhill!

What Are Water Wells?■ Water percolates

into a drilled or dug hole when the zone of saturation is penetrated■ pumping can create

a cone of depression lowering of the water table

■ is a major problem in some areas

Why do

farms

have

wind

mills?

Lowering theWater Table

■ Occurs primarily when groundwater is used faster than is replaced by natural processes

■ the Ogallala aquifer is used for agriculture

■ water is being used at up to 100 times its recharge rate in some areas

■ NOPE!

Tonight’s HW!!!

■ Review Questions 1-4 on Page 295Complete sentences

Did you notice that we started with a picture of a happy baby…. And ended with a mad baby! Ha!