13.3+Ground+Water

Lesson Objectives

 * Define ground water.
 * Explain the location, use, and importance of aquifers.
 * Define springs and geysers.
 * Describe how wells work and why they are important.

Introduction
Although this may seem surprising, water beneath the ground is commonplace. Usually ground water travels slowly and silently beneath the surface, but in some locations it bubbles to the surface at springs and geysers. The products of erosion and deposition by ground water were described in the Erosion and Deposition chapter.

Ground water

 * Ground water** is the largest reservoir of liquid fresh water on Earth.

Ground water is found in **aquifers**, porous rock and sediment with water in between. Water is attracted to the soil particles and **capillary action**, which describes how water moves through a porous media, moves water from wet soil to dry areas.

Aquifers are found at different depths. Some are just below the surface and some are found much deeper below the land surface. A region may have more than one aquifer beneath it and even most deserts are above aquifers. The source region for an aquifer beneath a desert is likely to be far from where the aquifer is located; for example, it may be in a mountain area.

The amount of water that is available to enter ground water in a region is influenced by the local climate, the slope of the land, the type of rock found at the surface, the vegetation cover, land use in the area, and water retention, which is the amount of water that remains in the ground. More water goes into the ground where there is a lot of rain, flat land, porous rock, exposed soil, and where water is not already filling the soil and rock. The residence time of water in a ground water aquifer can be from minutes to thousands of years. Ground water is often called “fossil water” because it has remained in the ground for so long, often since the end of the ice ages.

Features of an Aquifer
To be a good aquifer, the rock in the aquifer must have good:
 * **porosity**: small spaces between grains
 * **permeability**: connections between pores

This animation shows porosity and permeability. The water droplets are found in the pores between the sediment grains, which is porosity. When the water can travel between ores, that’s permeability. @http://www.nature.nps.gov/GEOLOGY/usgsnps/animate/POROS_3.MPG

To reach an aquifer, surface water infiltrates downward into the ground through tiny spaces or pores in the rock. The water travels down through the permeable rock until it reaches a layer that does not have pores; this rock is **impermeable** (**Figure** [|below]). This impermeable rock layer forms the base of the aquifer. The upper surface where the ground water reaches is the **water table**. Ground water is found beneath the solid surface. Notice that the water table roughly mirrors the slope of the land

The Water Table
For a ground water aquifer to contain the same amount of water, the amount of recharge must equal the amount of discharge. What are the likely sources of recharge? What are the likely sources of discharge?

In wet regions, streams are fed by ground water; the surface of the stream is the top of the water table (**Figure** [|below]). In dry regions, water seeps down from the stream into the aquifer. These streams are often dry much of the year. Water leaves a ground water reservoir in streams or springs. People take water from aquifers, too.

What happens to the water table when there is a lot of rainfall? What happens when there is a drought? Although ground water levels do not rise and fall as rapidly as at the surface, over time the water table will rise during wet periods and fall during droughts.

The top of the stream is the top of the water table. The stream feeds the aquifer.

One of the most interesting, but extremely atypical types of aquifers is found in Florida. Although aquifers are very rarely underground rivers, in Florida water has dissolved the limestone so that streams travel underground and above ground (**Figure** [|below]).



In Florida, ground water is sometimes not underground.

Ground Water Use
Ground water is an extremely important water source for people. Ground water is a renewable resource and its use is sustainable when the water pumped from the aquifer is replenished. It is important for anyone who intends to dig a well to know how deep beneath the surface the water table is. Because ground water involves interaction between the Earth and the water, the study of ground water is called hydrogeology.

Some aquifers are overused; people pump out more water than is replaced. As the water is pumped out, the water table slowly falls, requiring wells to be dug deeper, which takes more money and energy. Wells may go completely dry if they are not deep enough to reach into the lowered water table.

The Ogallala Aquifer supplies about one-third of the irrigation water in the United States (**Figure** [|below]). The aquifer is found from 30 to 100 meters deep over about 440,000 square kilometers! The water in the aquifer is mostly from the last ice age.

The Ogallala Aquifer is widely used by people for municipal and agricultural needs.

The Ogallala Aquifer is found beneath eight states and is heavily used.

About eight times more water is taken from the Ogallala Aquifer each year than is replenished. Much of the water is used for irrigation (**Figure** [|below]).



Farms in Kansas use central pivot irrigation, which is more efficient since water falls directly on the crops instead of being shot in the air. These fields are between 800 and 1600 meters (0.5 and 1 mile) in diameter.

Lowering the water table may cause the ground surface to sink. **Subsidence** may occur beneath houses and other structures (**Figure** [|below]).



The San Joaquin Valley of California is one of the world

When coastal aquifers are overused, salt water from the ocean may enter the aquifer, contaminating the aquifer and making it less useful for drinking and irrigation. Salt water incursion is a problem in developed coastal regions, such as on Hawaii.

Springs and Geysers
Ground water meets the surface in a stream, as shown above, or a **spring** (**Figure** [|below]). A spring may be constant, or may only flow at certain times of year.



Big Spring in Missouri lets out 12,000 liters of water per second (Left). Other springs are just tiny outlets like this one (Right).

Towns in many locations depend on water from springs. Springs can be an extremely important source of water in locations where surface water is scarce (**Figure** [|below]).



In the dry Arizona desert, Oak Creek and many other streams are spring fed.

Wells
A **well** is created by digging or drilling to reach ground water. When the water table is close to the surface, wells are a convenient method for extracting water. When the water table is far below the surface, specialized equipment must be used to dig a well. Most wells use motorized pumps to bring water to the surface, but some still require people to use a bucket to draw water up (**Figure** [|below]).



An old-fashioned well that uses a bucket drawn up by hand.

Lesson Summary

 * Ground water is the largest reservoir of fresh water.
 * The water table is the top of an aquifer below which is water and above is rock or soil mixed with air.
 * Aquifers are underground areas of sediment or rock that hold ground water.
 * An aquifer needs good porosity and permeability.
 * Where ground water intersects the ground surface, a spring can form.
 * People dig or drill wells to access ground water.

Review Questions
1. What is ground water? 2. What is the water table? 3. What are aquifers and why are they so important? 4. Replenishing an aquifer is important because it makes the aquifer a resource that can last a long time. What do you think are ways to keep the amount of water used and the amount of water replenished the same? 5. How does a well work? 6. Since ground water is largely unseen from the surface, how might you monitor how humans are affecting the amount of ground water in an aquifer?

Further Reading / Supplemental Links
Inside Yellowstone @http://www.nps.gov/archive/yell/insideyellowstone/0017oldfaithful3.htm Earth's water distribution video, University of Waikato, New Zealand @http://www.sciencelearn.org.nz/contexts/h2o_on_the_go/sci_media/video/earth_s_water_distribution

Vocabulary
water table The upper surface of ground water. subsidence Sinking of the land surface because of the extraction of ground water. spring A point on the Earth’s surface where ground water bubbles up. porosity The small holes that exist between grains in a rock or sediment. permeability The interconnectedness of the pores within a rock or sediment. impermeable Something that water cannot penetrate. capillary action Water moves from wet to dry regions in soil. aquifer A layer of rock, sand, or gravel that holds large amounts of ground water.

Points to Consider

 * Is water from a river or from a well more likely to be clean to drink?
 * Why is overuse of ground water a big concern?
 * What policies might people put in place to conserve water levels in lakes and aquifers?

Maine Connections
Maine Geological Survey: Hydrogeology
 * [|Ground Water and Development Siting]
 * [|Water, Water, Everywhere; and not a Drop to Drink!]
 * [|A Percolation Revelation]
 * [|Aquifer Maps and Maine Ground Water]
 * [|The Percolation Rate of a Soil]
 * [|Water Testing and Analysis by the United States Geological Survey]
 * [|A Measure of Maine's Water in a Typical Year]
 * [|Wetlands]
 * [|Single-Channel Seismic Graphing]

Maine Geological Survey: Ground Water & Wells

[|Virtual Tour]
 * [|virtual tour]

Field Localities.
 * [|The Freeport Basin Study: A Cooperative Investigation of Water Use]
 * [|Hydrogeology of the Bingham Water District Well]
 * [|Hydrogeology of the Governor Hill Fish Hatchery, Augusta]
 * [|Maine's Highest Yielding Well]

[|Frequently Asked Questions]

Fact Sheets
 * [|Anatomy of a drilled bedrock well]
 * [|Sand and gravel aquifers]
 * [|Sand and gravel aquifer maps - A work in progress]
 * [|Seismic refraction profiling: An important tool used in mapping sand and gravel aquifers]
 * [|Water resources in Maine]
 * [|Ground Water, Wells and the Summer of 1999]
 * [|Maine Springs]
 * [|Alkalinity: An Important Parameter in Assessing Water Chemistry]
 * [|Water well information]
 * [|Maine's Dug Wells]

Geologic Maps and Digital Data
Related Reading Ground Water Regulatory Issues
 * **ONLINE hydrogeologic map series**
 * [|Significant Sand and Gravel Aquifer Maps Online (PDF format)]
 * [|Bedrock Ground-Water Resources Basic Data Maps Online (PDF format)]
 * [|**PRINTED geologic maps**]
 * Descriptions of MGS hydrogeologic map series
 * [|Significant Sand and Gravel Aquifer Maps]
 * [|Bedrock Ground-Water Resources Basic Data Maps]
 * [|**Water Well Database**] - Downloadable database of located water wells.
 * [|An Introduction to Ground Water Hydrology] - This website contains information originally published in the first two chapters of the Ground Water Handbook for the State of Maine.
 * [|Ground Water Handbook for the State of Maine]
 * [|Bibliography of Maine Geology] - For those interested in more in-depth research, the Bibliography of Maine Geology contains more than 12,000 references related to Maine geology. The Bibliography is part of our publications search site and the results displayed will have links to online Maine Geological Survey maps and publications.
 * [|Maine Water Resources Planning Committee]
 * [|Review of Ground Water Withdrawal Regulations]

Maine Bureau of Land and Water Quality


 * [|Antifreeze information page]. Antifreeze poses perils for pets and wildlife.
 * [|AQUA INDEX: Risk Assessment of Land Use on High Yield Sand and Gravel Aquifers in Maine].
 * [|Aquifer mapping] (off-site). Information from Maine Geological Survey.
 * [|Basics of groundwater]. This page contains links to some excellent resources for information on groundwater.
 * [|Contacts]. Who does what.
 * [|Drinking Water Program] (off-site). Helps public water systems comply with the federal [|Safe Drinking Water Act] and state regulations, provides technical assistance, works with systems to protect source water areas and provides grants or loans funds for infrastructure improvements.
 * [|EGAD]. The Maine Environmental and Groundwater Analysis Database (EGAD) is designed to store site and water quality information.
 * [|Groundwater links]. Links to agencies, organizations, and more.
 * [|Groundwater quiz (for highschool students)]. Can you answer these groundwater questions?
 * [|Integrated water quality monitoring and assessment reports]. This report, also known as the 305(b) report as it is required by Section 305(b) of the Clean Water Act, summarizes water quality data collected by the DEP as well as numerous other state, federal and tribal government agencies, volunteer water monitoring organizations, and other sources.
 * [|National primary and secondary drinking water regulations](off-site: EPA). Legally enforceable standards that apply to public drinking water sources. Primary standards protect public health by limiting the levels of contaminants in drinking water.
 * [|Plumbing Control Program] (off-site). This program's mission is to minimize health and safety hazards associated with improperly installed subsurface waste water disposal systems.
 * [|Public Water Resources Map] (off-site). The Public Water Resources Map can be used to find public water supply wells and intakes, associated buffer zones, as well as land use activities (such as gasoline spills or landfills, etc) that are potential or actual threats to groundwater. Just register and login.
 * **Residential Septic System Impacts on Groundwater Quality in Maine** -- Characterization of Nitrate Concentrations in Domestic Wells at 18 Subdivisions. June, 1999. Doc. No. DEPLW1999-7. [|Executive summary]. For a copy of Part I or Part II, email.
 * [|Safe Home]. How much do you know about your drinking water?
 * [|Septic Systems: How they work and how to keep them working] (scan of an older pamphlet by Casco Bay Estuary Project and Cumberland County Soil and Water Conservation District, adapted from a Maine DEP publication).
 * [|Significant groundwater wells]. Significant groundwater wells were added to the Natural Resources Protection Act in 2007 as a regulated activity.
 * [|Source Water Protection] (off-site). Information on the program to assess the vulnerability of Maine public water supplies.
 * [|Sustainable Water Use Program] (water use). The reporting program includes separate reporting thresholds for withdrawals from rivers, streams and brooks; lakes; and groundwater.
 * [|Underground Injection Control Program]. The program protects underground sources of drinking water by regulating the subsurface discharge of both hazardous and non-hazardous pollutants through injection wells.
 * [|Water protection doesn't go on vacation]. Many camps, motels and other facilities rely on septic systems to treat wastewater. Your water use and activities will affect how these treatment systems work.
 * [|Wellwater.maine.gov]. Information for the public on contaminants in wellwater, from the Maine CDC.

[|Maine Public Health: Protect Your Groundwater]

Lesson Plans
[|Groundwater Contamination] [|Is Your Water Clean?]

Webquests
[|Water Webquest] [|Water Systems: Ground Water]

More Resources
[|EPA: Drinking Water and Ground Water] [|A Layman's Guide to Clean Water: Locating Groundwater] [|Groundwater Resources at UTexas] [|Groundwater Model Handbook - Understanding Groundwater and Using the Groundwater Model]

Videos
[|Groundwater: The Hidden Source of Life] [|Groundwater Animation]


 * Games**

[|Water Island Game] [|Water Conservation Games] [|Groundwater Games at K-12 Resources, UTexas]

some great information **[|Coolest Marketer Traffic And Conversion]**