GROUNDWATER

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GROUNDWATER
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GROUNDWATER

• Groundwater is subsurface water that fully
  saturate 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
  granitics)
• The source of groundwater is rain and melt water
  infiltrating and percolating through
  fractures/pores in soil and bedrock

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GROUNDWATER MOVEMENT AND SOURCES
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How much groundwater is there?

• Estimates of up to 4 million km3 for groundwater
• Surface water 160,000 km3
• Extraction of groundwater measured in acre-feet
  (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)

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GROUNDWATER USAGE
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WHO USES GROUNDWATER?

• Almost all humans will use groundwater either
  directly pumping it into their own cistern or
  through major metropolitan water transportation
  systems.

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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

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What Bedrock makes a Good Aquifer?

• Any bedrock with both good porosity and good
  permeability
• Unconsolidated sedimentary rock
• Sandstones
• Fractured igneous rocks (basalt) or jointed
  limestone

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POROSITY and PERMEABILITY
POROSITY
PERMEABILITY
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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

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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.

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UNCONFINED AQUIFER
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OGALLALA AQUIFER
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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

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CONFINED AQUIFER
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ARTESIAN WELLS
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Decorative Waterwheel placed over original
Artesian Wells in SFV (Sportsmans
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
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Big Spring, Missouri
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AQUIFER ZONES

• The Vadose Zone Zone of Aeration
• 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
• The Phreatic Zone Zone of Saturation
• 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

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VADOSE AND PHREATIC ZONES
Phreatic zone
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DIAGRAM OF AN AQUIFER
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• California
• Statewide Aquifers

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LOS ANGELES GROUNDWATER BASINS
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San Fernando Valley/San Gabriel Valley Groundwater
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San Francisco Area Groundwater
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Ventura County Groundwater
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GROUNDWATER MANAGEMENT CHALLENGES

• Laws
• Water Table Depletion
• Ground Subsidence
• Contamination

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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 Californias 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

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GROUNDWATER WITHDRAWALS
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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

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NORMAL CONDITIONS FOR WATER TABLE
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CONDITIONS FOR WATER TABLE DEPLETION
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DRAWDOWN EFFECT AND CONE OF DEPRESSION WITH
RECOVERY
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DRAWDOWN NO RECOVERY
lowered
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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

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SUBSIDENCE
Picture from the San Joaquin Valley showing the
amount of land subsidence since 1925 due to
aggressive groundwater pumping
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SUBSIDENCE IN CALIFORNIA
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SUBSIDENCE IN CALIFORNIA
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SUBSIDENCE IN TEXAS
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CONTAMINATION

• Groundwater contamination comes in several ways
• Landfills and septic tanks
• Agriculture
• Industrial
• Urban
• Toxic wastes
• Salt water intrusion

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SOURCES OF CONTAMINATION
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LANDFILL CONTAMINATION
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GAS TANK CONTAMINATION
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Septic Tank Contamination
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AGRICULTURE CONTAMINATION

• Pesticides
• Insecticides
• Herbicides
• Fertilizers
• Animal Waste

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AGRICULTURAL CONTAMINATION
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INDUSTRIAL CONTAMINATION
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San Fernando Valley/San Gabriel Valley
Groundwater contamination
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San Francisco Area Groundwater Basin Contamination
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SALT WATER INTRUSION