GROUNDWATER GROUNDWATER Groundwater is subsurface water that fully

GROUNDWATER

GROUNDWATER Ø Groundwater is subsurface water that fully saturates pore spaces of bedrock. Ø 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) Ø The source of groundwater is rain and melt water infiltrating and percolating through fractures/pores in soil and bedrock. l 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 km 3 for groundwater Ø Surface water – 160, 000 km 3 Ø Extraction of groundwater measured in ‘acrefeet’ (the amount of water that covers one acre of land, one foot deep) Ø California extracts 17 -20 million acre-feet (maf) per year Ø The Ogallala Aquifer in central United States produces 110 maf per year (317 billion gallons of water per year) Ø

GROUNDWATER USAGE

WHO USES GROUNDWATER? Ø Almost all humans will use groundwater – either directly pumping it into their own cistern or through major metropolitan water transportation systems.

Where is Groundwater Stored? Ø Groundwater is stored in rock bodies called aquifers. l Ø A good aquifer provides both storage and transmittal of groundwater Characteristics of aquifers: l Porosity • The number and size of pore spaces, fractures, joints, in bedrock • Provides Storage for groundwater l Permeability • The connectedness of pore spaces, fractures, joints in bedrock • Provides Transmittal for groundwater

What Bedrock makes a Good Aquifer? Ø Any bedrock with both good porosity and good permeability l Unconsolidated sedimentary rock • The San Fernando Valley floor, for example l l Sandstones Fractured igneous rocks (basalt) or jointed limestone

POROSITY and PERMEABILITY POROSITY PERMEABILITY

What if bedrock only has good porosity or only permeability? Ø Bedrock with good porosity but poor permeability are call aquicludes or aquitards Ø These types of bedrock may store water, but cannot transmit it. l l l Unfractured igneous rock Metamorphic rock Bedrock with high amounts of clay • Shales, claystones, mudstones, siltstones

What Is An Unconfined Aquifer? Ø An unconfined aquifer has little to no overlying sedimentary layers. l Ø 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? Ø Confined Aquifers are usually sandwiched between two non-permeable layers. Ø 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 Ø Largest Artesian well in United States is the Big Spring in Missouri l 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 Ø The Vadose Zone: Zone of Aeration l l Ø The Phreatic Zone: Zone of Saturation l l l Ø 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 l l 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 Ø

LOS ANGELES GROUNDWATER BASINS

San Fernando Valley/San Gabriel Valley Groundwater

San Francisco Area Groundwater

Ventura County Groundwater

GROUNDWATER MANAGEMENT CHALLENGES Ø Laws Ø Water Table Depletion Ø Ground Subsidence Ø Contamination

Laws on Groundwater Usage Only two states of USA have no laws regarding the use of groundwater: Texas and California Ø The only requirement for the water to be of “beneficial use” Ø Recent attempts in California’s Legislature to regulate groundwater have been met with strong resistance from many groups: farmers, municipalities included Ø l Most recent ‘water bill’ passed has some restrictions, but groundwater still not regulated

GROUNDWATER WITHDRAWALS

WATER TABLE DEPLETION Ø Water table depletion can be the result of natural droughts as well as human activity Ø 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 Ø Over pumping groundwater can result in the sinking of overlying layers. Ø 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 Ø Groundwater contamination comes in several ways l l l 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 Ø Pesticides Ø Insecticides Ø Herbicides Ø Fertilizers Ø 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