Groundwater and Wells

Well is a hole bored into the zone of saturation and is the most common way of removing groundwater.

Two types of wells:

1) Surface Wells

2) Artesian Wells

Reference: Tarbuck and Lutgens text Pages 109 - 113

Groundwater and Wells In order to study wells, we must first investigate two terms Aquifer and Aquiclude.

1) Aquifer

permeable and porous layers of sediment and rock in which water can move freely. Groundwater

can be stored in these layers (reservoirs).

2) Aquiclude

impermeable layers such as clay and shale that slow down or prevent water movement.

Groundwater and Wells

Aquifer

Groundwater and Wells In order to study wells, we must first investigate two terms Aqiufer and Aquiclude.

Aquifer Types

1. Unconfined – shallow aquifers at Earth’s surface, usually made of sand and gravel, no capping impermeable layer (aquiclude). Form surface wells.

2. Confined – deep bedrock aquifer (sandstone, limestone) “sandwiched” between two impermable layers - aquicludes (shales). Form artesian wells.

Confined Aquifer The Dakota Aquifer System

Unconfined Aquifer

Unconfined Aquifer

Perched Aquifer in an Unconfined System

Surface Wells Wells act as reservoirs in which groundwater is stored.

Some uses of water from wells are; irrigation of farmland, industrial purposes, and drinking water.

Wells can exist in different rock types that exist under certain conditions. Wells are commonly found in

Sedimentary rock.

Groundwater Wells

permeable sandstone

Fractured Granite

Surface Wells Wells act as reservoirs in which groundwater is stored.

Some uses of water from wells are; irrigation of farmland, industrial purposes, and drinking water.

Water levels in wells are controlled by the position of the water table. The level of the water table depends on;

1) Season (wet season and dry season)

2) Water withdrawal

Surface Wells

Water table drops during the dry season and rises during the wet season. For this reason surface wells must be bored deep within the zone of saturation.

Shallow wells may run dry if water table drops.

1) Season (wet season and dry season)

Surface Wells

When water is pumped from the ground faster than it can be replenished, the water table drops in that area and a Cone of Depression results.

Cone of depression is often found in areas where water is pumped for industrial uses and irrigation of farmland.

2) Water withdrawal

Lowering of the Water Table

Artesian Wells

In artesian systems groundwater rises above the level where it was initially encountered.

Two conditions must exist:

Water Recharge

Permeable Aquifer

Impermeable Aquiclude

Water Table (Pressure Surface)

1) Water must be within an inclined aquifer (Blue area) where one end is exposed at the surface where it can receive water.

2) Impermeable layers (aquicludes) exist below and above the aquifer to prevent the water from escaping.

Artesian Wells

When the aquiclude above the aquifer is tapped (a hole drilled through), the weight of the water above will cause the water to rise up through the aquiclude where it tries to reach the water table or pressure surface.

Same principle as a raised garden hose with a hole.

Water Recharge

Permeable Aquifer

Impermeable Aquiclude

Water Table (Pressure Surface)

Flowing Artesian Wells

groundwater in confined system is under enough pressure that no well pumping is needed!!!

The Dakota Aquifer System

Aquiclude

Aquiclude

Confined Aquifer The Dakota Aquifer System

Springs

Sample Problem

With the aid of diagrams, explain the effect of a drought on the water table.

Answer:

Water table lowers during a drought (dry season) because the rate of withdrawal is greater than the rate of recharge. Groundwater will move out of the ground and in to streams and ponds.