Vasey’s Paradise Groundwater discharges from the wall of Marble Canyon to form a series of natural springs. (Grand Canyon)

Major Groundwater Regions of the USA Puget Sound & Willamette Valley (alluvial basin) Columbia Plateau (fractured lava flows)

Porosity = The percent void space in a rock or sediment. It is a measure of the potential volume of water that can be stored in a rock.

Permeability = The ability of a material to transmit a fluid. It is a measure of how fast the fluid can travel through the rock or sediment.

Aquifer = A geologic unit capable of storing and transmitting water in sufficient quantities to supply wells.

Porosity varies with % Cement Size-Sorting Fracturing

Cemented Sand Uncemented Sand

Types of Aquifers Unconfined Aquifer - The permeable layer extends to the surface. It consists of an unsaturated zone separated from the saturated zone by the groundwater table. Confined Aquifer - The permeable layer is sandwiched between less-permeable layers (aquitards or aquicludes).

Pores include both air and water Pores filled with water Unconfined Aquifer Unsaturated Zone: Pores include both air and water Groundwater Table Saturated Zone: Pores filled with water

Water Table • The top of saturated zone of groundwater • The level to which water will rise in a hole • The level to which water will rise in an unconfined aquifer

Dynamics of an Unconfined Aquifer in a Temperate Climate

During the Wet Season…

During the Dry Season…

Darcy’s Law An equation by which the discharge (rate of flow) of groundwater can be calculated.

Darcy’s Law Q = A ( K x S )

Darcy’s Law Q = Discharge A = Cross-sectional area of flow Q = A x ( K x S ) = A x ( K x H / L ) Q = Discharge A = Cross-sectional area of flow K = Permeability (hydraulic conductivity) S = Slope of water table = ( H  L ) H = vertical drop L = flow distance

Hydraulic gradient = 1 m / 1000 m V = ( K x ( h1 - h2 ) / ( d x n ) V = (60 m/day x 1 m) / (1000 m x 0.3) 1 m Permeability = 60 m/day Porosity = 30% (=0.3) Hydraulic gradient = 1 m / 1000 m

Darcy’s Law

The recharge area of a confined aquifer is the area where rainfall enters (recharges) the aquifer. The pressure surface is the level to which water will rise in wells in confined aquifers.

Note the Difference Between: Groundwater Table: The level to which water will rise in an unconfined aquifer Pressure Surface: The level to which water will rise in a confined aquifer * * If the pressure surface is above the ground surface, the water will flow freely out of the ground. Such wells are called flowing artesian wells.

Confined Aquifer Recharge Area: Pressure Surface: Flowing where the confined aquifer is recharged by infiltration Pressure Surface: Height to which water will rise in the confined aquifer Flowing Artesian Well

Pressure Surface Ground Surface Flowing artesian well

Artesian Well in Glacial Sands & Gravels (MA)

Perched Water Table

Formation of a Cone of Depression

The Ogallala Aquifer: “Mining Groundwater”

U.S. Groundwater Withdrawals: 1950-1995

Fissures and depressions caused by ground subsidence due to overpumping of groundwater (Antelope Valley, CA. January 1991. 625 meters long!)

The Winter Park Sinkhole, Florida (Photo by Leif Skoogfors)

Saltwater - Freshwater Interface Dynamics of the Saltwater - Freshwater Interface

The thickness of the fresh groundwater floating on top of the salty groundwater is affected by the balance between groundwater recharge and discharge

If the rate of discharge increases too much (by overpumping), the saltwater will rise, causing saltwater intrusion in the well. Inverted Cone of depression

Carlsbad Caverns, NM) Stalagmite Stalactite

Some Major Features of a Karst Landscape

Subsurface Features of a Karst Landscape

Some Human Activities that Can Contaminate Groundwater

Cape Cod Sewage Plume (MA)

Detergent in groundwater (Cape Cod, MA). From abandoned military base (wastewater & sewage disposal).

(Maryland)

Hand-dug well in Sinai. Ancient river sediment.

Lancaster County, PA