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Introduction To Groundwater Concepts Important Concepts - - PowerPoint PPT Presentation
Introduction To Groundwater Concepts Important Concepts - - PowerPoint PPT Presentation
Introduction To Groundwater Concepts Important Concepts Hydrologic Cycle Aquifers Hydraulic Conductivity Head Gradient Drawdown Capture Earths Freshwater Resources 97% of Earths water exists as salt water Of the remaining
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Earth’s Freshwater Resources
97% of Earth’s water
exists as salt water
Of the remaining
water (3%):
69.6% glaciers,
permafrost, and snow
30.1% subsurface water <1% rivers, lakes,
swamps, wetlands, atmosphere
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Earth’s liquid fresh water resources
Michigan 500 mi3
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Precipitation on land
Infiltration
Groundwater flow Surface discharge Evaporation from land Moisture over land Precipitation to Ocean Evaporation from ocean
Surface runoff
GW Recharge Precipitation
Snow melt
GW Discharge
The Hydrologic (Water) Cycle
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Water Resources
“We forget that the water cycle “We forget that the water cycle “We forget that the water cycle “We forget that the water cycle and the life cycle are one” and the life cycle are one” and the life cycle are one” and the life cycle are one”
- Jacques Cousteau
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The Nature of Underground Water
Water table
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Water table
The Nature of Underground Water
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The Subsurface Can Be Divided Into Two Zones
A = The Unsaturated Zone B = The Saturated Zone A B
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The Water Table
…the boundary between the unsaturated (aerated) and saturated zone
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The Unsaturated Zone
Zone between the land surface
and the water table.
Subsurface material has pore
spaces between grains.
In the unsaturated zone these
pore spaces are occupied by both air and water.
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Saturated Zone
Zone underneath the water
table
All pore spaces are filled
completely with water
The water flows both
horizontally and vertically
This is groundwater
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Groundwater
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16.1 The Nature of Underground Water
Aquifer Aquiclude Perched water
table
Springs
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Groundwater
Groundwater is present in the pores and fractures in geologic formations (“Aquifers”) below the land surface – NOT RIVERS. Precipitation is the source
- f groundwater recharge.
Groundwater moves through the pores and fractures in geologic formations toward surface water, other watersheds, or pumping wells.
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Underground Rivers
They Do Exist, But……
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Important Concepts
Hydrologic Cycle Aquifers Hydraulic Conductivity Hydraulic Head Hydraulic Gradient Drawdown Capture
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Aquifers
Definition: A
geological unit which can store and supply significant quantities of water.
Depends on local
geology.
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GW Flow Through Pores
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Michigan Aquifers
Principal aquifers in Michigan by sediment/rock type:
Glacial (a.k.a. ‘glacial drift’)
Sand and Gravel
Bedrock (a.k.a. ‘rock’)
Sandstone Limestone and/or Dolomite Igneous & Metamorphic (Western U.P.)
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SE MI Area…
Aquifer Vulnerability
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SE MI Area…
Aquifer Vulnerability
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Michigan Bedrock Geology
Michigan Basin
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Hydrogeologic Cross Section
Lake Huron
Georgian Bay
Lake Michigan Lower Peninsula
- f Michigan
Wisconsin Canada
Oil & Gas Saline H2O/Brine
Glacial Deposits
Potable GW
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Bedrock Aquifers
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Michigan Bedrock Aquifers
“Good” “Not an Aquifer” “Marginal Sedimentary” “Marginal Crystalline”
* Saline GW/Brine at depth
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SW Michigan Bedrock Wells
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Public Supply Bedrock Wells
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GLACIAL DRIFT THICKNESS
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GLACIAL DRIFT THICKNESS SE Michigan
0 - 20’
MONROE LENAWEE WAYNE WASHTENAW OAKLAND MACOMB
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Michigan Glacial Drift Aquifers
“Good” “Not an Aquifer”
“Unconfined aquifer overlying bedrock – limited data”
“Thin overlying bedrock”
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SE Michigan Glacial Drift Aquifers
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Wells
Lassie, go get help!
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Groundwater Utilization
Wells
Artificial openings
dug or drilled below the water table to extract water
drawdown of water
table
cone of depression
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DRILLED WELL COMPONENTS
BOREHOLE CASING GROUT BEDROCK WELL OPEN HOLE IN BEDROCK AQUIFER
NO CASING IN ROCK BOREHOLE
WELL CAP or SEAL
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DRILLED WELL COMPONENTS
WELL CAP or SEAL BOREHOLE CASING GROUT SCREEN SCREENED WELL
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Well Screens
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Important Concepts
- Hydrologic Cycle
- Aquifers
- Hydraulic Conductivity
- Head
- Gradient
- Drawdown
- Capture
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Hydraulic Conductivity a.k.a. “Permeability”
Measure of rate at
which water can move through aquifer material
Wide range in values
due to number and size
- f pores and fractures
and how well they are connected
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Fractured Rock Coarse Sand Gravel Unfractured Rock Clay- Shale
HYDRAULIC CONDUCTIVITY RANGE Low
Silty Sand- Sandy Clay
High
Fine Sand
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Sources of Hydraulic Conductivity (K) Data
Site specific aquifer tests Estimated from well capacity data in
WELLOGIC
Use estimates based on sediment
descriptions from well log records
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K from Site Information/Tests
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K from Capacity Tests
Static
water level
Pumping
water level
Length of
test
Estimated
pumping rate
Estimated K
may be good if data good
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K from Lithologic Descriptions
Description of
sediment or rock
Thickness GWIM - Each
material (sand, clay, etc) is assigned a unique K.
Estimated K
appears to be reasonable.
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Important Concepts
Hydrologic Cycle Aquifers Hydraulic Conductivity Head Gradient Drawdown Capture
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GW Flow Direction
GW wants to move from a point of high
hydraulic head (elevation) to low hydraulic head (elevation) in the direction of steepest hydraulic gradient… IMPORTANT CONCEPT
Hydraulic Head (“GW Elevation”) Hydraulic Gradient (“Slope”)
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Hydraulic Head
Depth to water (a.k.a. static water level or “SWL”) Land Surface Elevation (LSE)
Hydraulic Head =
LSE - SWL
900 ft – 20 ft = 880 ft
Water Table
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Where does the head information come from?
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Ground Surface Elevation and Location
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Static Water Level (SWL)
Ground Surface – SWL = Head ft AMSL
Example: 929 – 85 = 844 ft AMSL
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Important Concepts
Hydrologic Cycle Aquifers Hydraulic Conductivity Head Gradient Drawdown Capture
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Heads and Hydraulic Gradient
Elevation Datum - Sea Level
Land Surface
Well 1 Well 2 Hydraulic Head1 Hydraulic Head2
GW Flow
Hydraulic Head1 Hydraulic Head2
>
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Gradient
Elevation Datum - Sea Level
Land Surface
Well 1 Well 2 Hydraulic Head1 Hydraulic Head2 Hydraulic Head1 Hydraulic Head2
- Distance
Distance
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Groundwater Movement
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Land Surface – Gradients and Divides
Elevation Contours Topographic Gradient Topographic Divide
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GW Elevation Surface – Gradients and Divides
Remove Land Surface to Expose Water Table
GW Flow GW Flow GW Divide GW Divide
GW Elevation Contours
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Cannon Twp - water table map with GW flow directions
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Important Concepts
Hydrologic Cycle Aquifers Hydraulic Conductivity Head Gradient Drawdown Capture
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Drawdown from pumping
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Important Concepts
Hydrologic Cycle Aquifers Hydraulic Conductivity Head Gradient Drawdown Capture
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Capture
Capture – GW within Aquifer that
flows toward and is removed by pumping well.
Extent of Capture NOT THE SAME
as Extent of Drawdown. *ANOTHER IMPORTANT CONCEPT*
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Extent of Capture vs Drawdown Cone
Drawdown Cone Extent
- f
Capture
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Wellhead Protection Area = WHPA = Area of Captured GW
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Wellhead Protection
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