Groundwater Notes

Groundwater Overview

  • Groundwater refers to the water found beneath the Earth's surface, which comes from precipitation that has seeped through the ground.

Precipitation and Groundwater

  • Precipitation can become:

    • Runoff: Surface water that flows into rivers and streams.

    • Groundwater: Water that is absorbed into the soil and rocks below the surface.

Key Facts about Groundwater

  • The Earth's water supply is finite but constantly recycled.

  • Only 0.76% of the total water supply is usable groundwater.

  • Groundwater age can range from a few years to tens of thousands of years.

Groundwater in the United States

  • Approximately 25% of precipitation becomes groundwater.

  • It would take 10 years of rain to replenish the groundwater stores in the U.S.

Groundwater Withdrawals (1950-2005)

  • A significant increase in groundwater withdrawals has been observed from 1950 to 2005.

  • Categories include saline and freshwater withdrawals.

Groundwater Characteristics

Definition of Groundwater

  • Groundwater is the water located in the zone of saturation beneath the surface.

  • The water in the ground is primarily found in geological formations that can store and transmit water, known as aquifers.

Zones of Groundwater

  1. Zone of Saturation: All openings in the soil and rock are filled with water.

  2. Zone of Aeration: The layer above the zone of saturation where openings are filled with both air and water.

  3. Water Table: The boundary between the zone of saturation and the zone of aeration.

  4. Capillary Fringe: A layer that allows groundwater to move upward towards the surface through capillary action.

Comprehension Checks

  • Zone of has all voids filled with water (Answer: Saturation).

  • Zone of has both air and water filling voids (Answer: Aeration).

Porosity and Permeability

  • Porosity: A measure of how much water soil or rock can hold within its spaces.

  • Permeability: A measure of how interconnected the spaces are and how easily water can flow between them.

    • Permeable: Allows water to pass through (e.g., sandstone, cloth).

    • Impermeable: Does not allow water to pass through (e.g., plastic, clay).

Comprehension Checks on Permeability

  • If a rock layer does not allow water to pass through, it describes the rock layer’s permeability.

Aquifers

  • Aquifer: A subsurface layer of rock or soil that can hold a usable amount of groundwater. Groundwater is found in the zone of saturation, not in an underground lake or river.

  • Types of aquifers:

    • Confined Aquifer: Sandwiched between two impermeable layers.

    • Unconfined Aquifer: Has an impermeable layer below but not above.

Comprehension Check on Aquifers

  • Which option does NOT describe an aquifer? (Answer: An underground lake).

Groundwater as Drinking Water

  • Groundwater serves as a primary source of drinking water.

  • Extraction methods include:

    • Wells: Structures used to access groundwater.

    • Wastewater Treatment: Also known as recycled water, primarily used in urban areas to purify and reuse water.

    • Processes in Wastewater Treatment:

    1. Grit Tank

    2. Bar Screen

    3. Clarifier

    4. Aeration Tank

    5. Settling Tank

    6. Digester

    7. Incineration and landfill.

Summary

  • Groundwater is a vital resource, and understanding its characteristics, zones, and importance in water supply is crucial for sustainable management and consumption.