Transcript Ground Water - the Essentially Science Wiki!

What is ground water?
The Hydrologic Cycle
(emphasizing ground water flow)
Why is ground water important?
50% of drinking water in U.S. is ground water
27% of drinking water in NC is ground water
90% of drinking water in the NC Coastal Plain is
ground water
In addition, it is used for irrigation and industry
What’s an Aquifer?
A geologic unit capable of storing and
transmitting water in sufficient quantities to
supply wells.
Land Surface
Water Table
Unsaturated zone
Unconfined
Saturated zone
Aquifer
Confining
Beds
Confined
Aquifers
Aquifers (white) and confining layers (gray) in the
Coastal Plain of North Carolina
www.ncwater.org/
For water to infiltrate to form
aquifers, the soil/rocks must have…..
Porosity
Permeability
Porosity and Permeability of
Different Aquifer Types
Type of Aquifer
Porosity
Permeability
Gravel
Coarse- to fine sand
Fine-grained sand & silt
Sandstone, mod. cemented
Fractured Shale
Metamorphic Rocks
Unfractured Shale
Very High
High
Moderate
Mod - Low
Low
Low
Very Low
Very High
High
Mod - Low
Low
Low
Very Low
Very Low
Press, et.al, Understanding Earth, 4th edition
Drill rig equipped with core barrels, drill
stems and mud reservoirs
USGS Elizabethtown, NC 2003
Drill bits are designed to cut through
different materials. This one will go
through both sand and clay at depth
USGS Elizabethtown, NC 2003
Continuous cores of the rock are
collected through the drill bit in a
wireline core rig
USGS Elizabethtown, NC 2003
Preparing to set the
monitoring well casing in the
drill hole
USGS Elizabethtown, NC 2003
View of unlocked monitoring
well with its pressure cap
USGS Elizabethtown, NC 2003
How deep do you have to go to find
ground water?
Potentiometric surface:
The “head”, or the level to which water will rise in a
well
For unconfined aquifers:
Potentiometric surface = water table
For confined aquifers
Potentiometric surface relates to pressure
Potentiometric Surface
What is a “flowing well”?
Ground water comes up out of the well without
pumping
Also known as an artesian well
Typical for confined aquifers but not unconfined
aquifers
Occurs because potentiometric surface (head) is
above top of the well
Springs
Press, et.al, Understanding Earth, 4th edition
Where does ground water flow?
In general, from high elevation to low elevation
From high pressure to low pressure
Ground Water Flow
2002 Potentiometric Surface of the Upper Cape Fear Aquifer
(contour elevations in feet above or below mean sea level, contour interval = 10 feet)
Ground water Problems
List problems you can think of
related to ground water
Depletion due to over-pumping
Contamination
Salt-water Intrusion
Depletion
Relates to cone of depression developed around a well that is
pumped
Example: Kinston, NC
1920’s – artesian well flowing under own pressure
Today – pumping by industry, public water and farms has
dropped the water level 150 feet
Why is depletion in deep (vs shallow)
aquifers especially a problem?
It takes thousands of years for deep aquifers to
recharge with ground water
Ground Water Recharge