Vaseys Paradise

Groundwater discharges from the wall of Marble Canyon to form a series of natural springs.

(Grand Canyon)

Major Groundwater Regions of the USA

Porosity= The percent void space in a rock or sediment.

It is a measure of the potential volumeof 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

Uncemented SandCemented Sand

Types of AquifersUnconfined 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).

Unsaturated Zone:Pores include both air and waterSaturated Zone:Pores filled with waterGroundwater TableUnconfined Aquifer

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 Aquiferin a Temperate Climate

During the Wet Season

During the Dry Season

Darcys LawAn equation by which the discharge (rate of flow) of groundwater can be calculated.

Darcys LawQ = A ( K x S )

Darcys Law Q = A x ( K x S ) = A x ( K x H / L )Q = Discharge

A = Cross-sectional area of flowK = Permeability (hydraulic conductivity)S = Slope of water table = ( H L ) H = vertical drop L = flow distance

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

Darcys 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

Pressure Surface Ground Surface Flowing artesian well

Artesian Well in Glacial Sands & Gravels (MA)

Perched Water Table

Formation of a Cone of Depression

The OgallalaAquifer:

Mining Groundwater

U.S. Groundwater Withdrawals: 1950-1995

Fissures and depressionscaused by ground subsidence due to overpumpingof groundwater

(Antelope Valley, CA. January 1991. 625 meters long!)

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

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. InvertedCone of depression

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