GROUNDWATER
GROUNDWATER
 Groundwater
is subsurface water that fully
saturates pore spaces of bedrock.
 The rate of movement of groundwater is
gravity driven, varying between 0.6 inches
per day (in sandstones) to several inches
per year (in granites)
 The source of groundwater is rain and
melt water infiltrating and percolating
through fractures/pores in soil and
bedrock.

Groundwater can range in age from recent to
ancient
• Some groundwater is thousands of years old
GROUNDWATER MOVEMENT
AND SOURCES
How much groundwater is there?





Estimates of up to 4 million km3 for groundwater
Surface water – 160,000 km3
Extraction of groundwater measured in ‘acrefeet’ (the amount of water that covers one acre
of land, one foot deep)
California extracts 17-20 million acre-feet (maf)
per year
The Ogallala Aquifer in central United States
produces 110 maf per year (317 billion gallons
of water per year)
GROUNDWATER USAGE
WHO USES GROUNDWATER?
all humans will use groundwater –
either directly pumping it into their own
cistern or through major metropolitan
water transportation systems.
 Almost
Where is Groundwater Stored?

Groundwater is stored in rock bodies called
aquifers.


A good aquifer provides both storage and transmittal
of groundwater
Characteristics of aquifers:

Porosity
• The number and size of pore spaces, fractures, joints, in
bedrock
• Provides Storage for groundwater

Permeability
• The connectedness of pore spaces, fractures, joints in
bedrock
• Provides Transmittal for groundwater
What Bedrock makes a Good
Aquifer?
 Any
bedrock with both good porosity and
good permeability

Unconsolidated sedimentary rock
• The San Fernando Valley floor, for example


Sandstones
Fractured igneous rocks (basalt) or jointed
limestone
POROSITY and PERMEABILITY
POROSITY
PERMEABILITY
What if bedrock only has good
porosity or only permeability?
 Bedrock
with good porosity but poor
permeability are call aquicludes or
aquitards
 These types of bedrock may store water,
but cannot transmit it.



Unfractured igneous rock
Metamorphic rock
Bedrock with high amounts of clay
• Shales, claystones, mudstones, siltstones
What Is An Unconfined Aquifer?

An unconfined aquifer has little to no overlying
sedimentary layers.


There is no confining layer of clay or other
impermeable sedimentary layers
The largest unconfined aquifer in the United
States is the Ogallala Aquifer which extends
from Texas through Oklahoma, Kansas,
Nebraska and North Dakota, plus parts of
Wyoming, Colorado and New Mexico.
UNCONFINED AQUIFER
OGALLALA AQUIFER
What is a Confined Aquifer?
 Confined
Aquifers are usually sandwiched
between two non-permeable layers.
 The confining layers provide pressure on
the aquifer, allowing the groundwater to
rise to the surface under its own energy –
no pumping required: Artesian Wells
 Largest Artesian well in United States is
the Big Spring in Missouri

Produces 300-400 million gallons of water/day
CONFINED AQUIFER
ARTESIAN WELLS
Decorative Waterwheel placed
over original Artesian Wells in
SFV (Sportsman’s Lodge)
Historic springs exist many
places along Ventura
Boulevard.
This is why the Spaniards
established California's first
highway, El Camino Real,
along this long used pathway.
Photo in Archives of The
Museum of the San
Fernando Valley -2008 Photo by Gerald Fecht
Big Spring, Missouri
AQUIFER ZONES

The Vadose Zone: Zone of Aeration



The Phreatic Zone: Zone of Saturation




This is the upper zone of an aquifer
Between each pore space and within each joint or fracture, both
air and water can be stored
This is the lower zone of an aquifer
Between each pore space and within each joint or fracture, only
water is stored.
Represents the zone within the aquifer designated as ‘true
groundwater’
Water Table




This is the upper limit of the Phreatic Zone within an aquifer
This is the boundary between the Vadose and Phreatic Zone
Depth of water table determined by wells – they will fill to the
level of the water table
Lakes, springs, streams are ‘surface expressions’ of the water
table
VADOSE AND PHREATIC
ZONES
Phreatic zone
DIAGRAM OF AN AQUIFER

California
Statewide Aquifers
LOS ANGELES GROUNDWATER BASINS
San Fernando Valley/San
Gabriel Valley Groundwater
San Francisco Area
Groundwater
Ventura County Groundwater
GROUNDWATER MANAGEMENT
CHALLENGES
 Laws
 Water
Table Depletion
 Ground Subsidence
 Contamination
Laws on Groundwater Usage

Only two states of USA have no laws regarding
the use of groundwater: Texas and California
 The only requirement for the water to be of
“beneficial use”
 Recent attempts in California’s Legislature to
regulate groundwater have been met with strong
resistance from many groups: farmers,
municipalities included

Most recent ‘water bill’ passed has some restrictions,
but groundwater still not regulated
GROUNDWATER WITHDRAWALS
WATER TABLE DEPLETION
 Water
table depletion can be the result of
natural droughts as well as human activity
 Over-pumping wells can result in
temporary and permanent lowering of the
water table
NORMAL CONDITIONS FOR
WATER TABLE
CONDITIONS FOR WATER
TABLE DEPLETION
DRAWDOWN EFFECT AND
CONE OF DEPRESSION WITH
RECOVERY
DRAWDOWN – NO RECOVERY
lowered
GROUND SUBSIDENCE
 Over
pumping groundwater can result in
the sinking of overlying layers.
 Groundwater acts to ‘buoy’ up overlying
sedimentary layers – remove the water
and all the pore spaces, fractures, and
joints can collapse
SUBSIDENCE
Picture from the San Joaquin Valley
showing the amount of land
subsidence since 1925 due to
aggressive groundwater pumping
SUBSIDENCE IN CALIFORNIA
SUBSIDENCE IN CALIFORNIA
SUBSIDENCE IN TEXAS
Subsidence in Venice, Italy
Parts of Venice have sunk more than
23 cm (approximately 9.2 inches)
causing concern
CONTAMINATION
 Groundwater
contamination comes in
several ways






Landfills and septic tanks
Agriculture
Industrial
Urban
Toxic wastes
Salt water intrusion
SOURCES OF CONTAMINATION
LANDFILL CONTAMINATION
Hazardous Wastes in Landfill
GAS TANK CONTAMINATION
Septic Tank Contamination
Groundwater
AGRICULTURE CONTAMINATION
 Pesticides
 Insecticides
 Herbicides
 Fertilizers
 Animal
Waste
AGRICULTURAL
CONTAMINATION
INDUSTRIAL CONTAMINATION
San Fernando Valley/San Gabriel
Valley Groundwater contamination
TCE –
Trichloroethylene
– a degreaser for
cleaning metal
San Francisco Area Groundwater
Basin Contamination
Arsenic used in
gold processing;
many northern
California rivers are
contaminated; even
rivers used for
municipal water
supply
SALT WATER INTRUSION