This PowerPoint file contains information about ground water in Minnesota. The

presentation includes information on occurrence, quality, and quantity of ground

water resources in Minnesota.

Minnesota’s Ground Water1. Abundant supplies of high quality ground

water underlie most of Minnesota.2. Ground water provides drinking water for

three-fourths of us.3. Ground water feeds our lakes and rivers.

4. Ground water is used to irrigate our crops.Photo United States Geologic Survey

1. Igneous and metamorphic rock aquifers2. Sedimentary rock aquifers3. Glacial sand and gravel aquifers

Minnesota’s ground water systems are a function of the state’s geology. There are three basic type of aquifer

in Minnesota.

• The entire state is underlain by igneous and metamorphic bedrock. In places, such as northeast Minnesota, this bedrock is at the land surface, while in other places, such as southeast Minnesota, it is hundreds of feet below the ground.

Photo Institute on Lake Superior Geology

Photo Stearns County, Minnesota

Hard Rock(igneous and metamorphic)

Igneous and metamorphic rocks are used as aquifers only when sedimentary rock and glacial

aquifers are absent. These areas (pink on map) occur primarily in

northeastern Minnesota.

Ground water moves in the spaces between rocks

Photo Stearns County, Minnesota

Characteristics of Hard Rock Aquifers

• Water occurs in cracks (fractures) in the rock.• These rocks resist fracturing and hold little

ground water.• These aquifers yield low quantities of water.• The water quality of these aquifers depends on the

type of rock. Generally they have few dissolved chemicals because the rocks resist weathering, but concentrations of some metals such as iron and manganese can occur at levels of concern.

• Wells are expensive to drill because the rock is hard to drill through.

Much of southern Minnesota (areas in green) was once covered by a sea, leading to the formation of sedimentary rocks (sandstone, limestone, shale)

Sedimentary Rock

Sedimentary rock aquifers, shown in

green, occur primarily in southern and extreme western

Minnesota.

St. Peter sandstone in St. Paul. Ground water

flows through both cracks in the rock and in small pore spaces in

the rock.

Photo North Dakota State University

Characteristics of Sedimentary Rock Aquifers• Useable quantities of ground water occur in

fractures and pore spaces of the rocks.• Limestone and sandstone are easily weathered and

can hold large amounts of ground water.• These aquifers yield large quantities of water.• Except for Cretaceous bedrock, the water quality

of these aquifers is generally good. Aquifers usually have few dissolved chemicals, but if they are close to the land surface they may be vulnerable to contamination.

• Wells are expensive to drill because the rock is hard to drill through.

The last glaciers covered most of

Minnesota between 11,000 and 13,000 years ago. Glacial

advances, shown by arrows in the

diagrams, came from both the northwest

and northeast. Glacial melt water formed many large lakes,

shown in grey in the diagrams.

Glacial Deposits

The map shows shallow glacial aquifers in Minnesota. These occur in outwash plains, along

rivers, and in old lake beds. Deeper, buried glacial aquifers cover the entire state except for

the Arrowhead region and small areas in central and

Southwest Minnesota.

Characteristics of Glacial Aquifers• Useable quantities of ground water occur in pore

spaces of sand and gravel.• These aquifers can hold large amounts of ground

water and yield large quantities of water.• The water quality of these aquifers varies. When

aquifers are close to the land surface, they have few dissolved chemicals but may be vulnerable to contamination. When aquifers are far below the land surface they are more protected but may have high concentrations of dissolved chemicals, including some such as arsenic that can represent a health concern.

• Wells are not as expensive to drill.

This map shows the location of six

ground water provinces in

Minnesota. A province is an area

where the characteristics of the ground water

system are similar.

In Province 1, sand aquifers are usually >100 feet thick. Sandstone and limestone

aquifers yield large quantities of water.

Aquifers in agricultural areas often have high

concentrations of nitrate and pesticides may be

present in low concentration. Low

concentrations of fuel oils and industrial chemicals are

often found in shallow aquifers from urban areas.

In Province 2, small isolated sand and gravel aquifers occur more than 100 feet below the land surface.

Deeper sedimentary rock aquifers provide moderate to good quantities of water. Aquifers are generally safe

from contamination but may have high

concentrations of dissolved chemicals, such as calcium.

In Province 3, sedimentaryrock aquifers provide large quantities of water. When these aquifers are close to the land surface they are

vulnerable to contamination. In these aquifers, nitrate is often

present at high concentrations and pesticides are often

detected. Sand aquifers generally occur only along

rivers.

In Province 4, sand aquifers are thick and yield large

quantities of water. When these aquifers are near the land surface, they may be

vulnerable to contamination. In

agricultural areas, shallow ground water often has

detectable concentrations of pesticides and high

concentrations of nitrate. Bedrock aquifers yield low to moderate quantities of water in areas where sand

aquifers do not occur.

In Province 5, sand aquifers are isolated and occur more than 100 feet below the land

surface. In areas where these are not present,

bedrock aquifers provide low to moderate quantities

of water. Aquifers are generally not vulnerable to contamination except sand

aquifers located along rivers. Ground water often contains

high concentrations of dissolved chemicals, such as

calcium and sulfate.

In Province 6, igneous and metamorphic rocks occur at

or near the land surface. Ground water occurs in

fractures and faults in this rock. Quantities of available

water are small. Water quality varies with type of rock. Concentrations of

dissolved solids are usually low but concentrations of

iron, manganese and boron can be high.

Ground Water Quality in Minnesota is generally good. The primary ground water

quality concerns in Minnesota are:

• Naturally-occurring– Arsenic– Boron

• Human sources– Nitrate– Pesticides– Fuel oils– Industrial chemicals

Arsenic in Ground Water

• Exceeds the drinking standard in about 15% of private wells in Minnesota

• Primary source is from geologic materials (naturally-occurring)

• The map shows areas where concentrations are high in sand aquifers

Boron in Ground Water

• Exceeds current drinking standard in about 5% of private wells in Minnesota

• Primary source is from geologic materials (naturally-occurring)

• The map shows areas where concentrations are high in aquifers (primarily bedrock)

Nitrate in Ground Water• Exceeds the drinking

standard in about 3% of private wells in Minnesota

• Primary sources are fertilizer in agricultural areas and septic systems in some urban areas

• The map shows areas where concentrations are high in bedrock (green) and sand (blue) aquifers and often above standards in sand aquifers (red)

Pesticides in Ground Water

• Limited data exist for occurrence of pesticides in ground water.

• In vulnerable aquifers in agricultural areas, pesticides or pesticide breakdown products have been found at low concentrations in more than 50% of sampled wells. The percentage in all sampled wells is much lower (see upper right figure).

• There is very little data for urban areas.

Pesticide sampling

locations – MN Dept.

Agriculture

Minnesota Department of Agriculture

Fuel Oils in Ground Water• Leaking tanks; often

at gasoline and storage facilities

• More than 15000 throughout Minnesota

• New leak detection systems help prevent new sites from occurring

• These chemicals often break down in ground water

Underground tanks containing gasoline or other liquids often leak contaminants into

soil and ground water.

Minnesota Pollution Control Agency

Industrial Chemicals in Ground Water

• Many sources, including paints, dry cleaners, industrial solvents, metals

• More than 1000 sites across Minnesota• Chemicals often persist in ground water and

many are highly toxic

Minnesota Pollution Control Agency

Ground Water Quantity• As population

grows, our water consumption increases

• Some areas will experience water shortages

• Some lakes and rivers will be affected by ground water pumping

0

50

100

150

200

250

1985 1990 1995 2000 2003

Water used for drinking has increased over the past 20 years. We now use more

than 225 billion gallons of water each year.

In some places in Minnesota, we are seeing water level declines in wells due to pumping at rates that exceed the ability of the aquifer to replenish itself

Minnesota Department of Natural Resources

The areas most vulnerable to limited supply are in Southwest Minnesota, in the Moorhead area, and in

some locations in the Twin Cities Metro Area.

• The area in pink shows the extent of reliable bedrock aquifers. Locations in the Metro Area outside the pink shading may have water supply concerns.

• In Southwest Minnesota and in the Moorhead area (blue), localized aquifers are the only reliable sources of ground water.

Other Water Quantity Issues• Well interference –

pumping one well may interfere with the ability to pump a nearby well

• Surface water drawdown –pumping of ground water may lower water levels in lakes, rivers, and wetlands

Wetland vegetation and ecosystems, such as that found in calcareous fens (above), are particularly sensitive to changes in

water levels that may accompany nearby pumping of ground water.

Minnesota Department of Natural Resources

Additional Sources of Information• http://www.dnr.state.mn.us/groundwater/index.ht

ml• http://www.pca.state.mn.us/water/groundwater/g

wmap/index.html• http://www.health.state.mn.us/divs/eh/water/index

.html• http://www.mda.state.mn.us/appd/ace/maace.htm• http://www.geo.umn.edu/mgs/lcmr.htm