minnesota ground water · characteristics of sedimentary rock aquifers • useable quantities of...
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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
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