Groundwater and Aquifers Quiz

Groundwater

• Groundwater is a vital freshwater source found at varying depths underground, but is limited by the amount extractable and its quality.
• An aquifer is a rock formation containing usable groundwater. A good aquifer needs both porosity (open space to hold water) and permeability (connected spaces for water flow).

Porosity and Permeability

• Porosity is the percentage of open space in a rock. Primary porosity is the space between grains, while secondary porosity is from fractures or dissolved spaces.
• Permeability is the connectivity of the open spaces in a rock, allowing water to move. Well-sorted sediments have higher porosity.
• Compaction and cementation during rock formation reduce porosity. Clay-rich shales often have high porosity, but poor permeability due to poorly connected pores, limiting water flow.

Aquifers

• Aquifers are rock layers with sufficient porosity and permeability that allows both water containment and movement.
• For aquifer suitability, pores must be at least partially filled with water and permeable for water transmission. Potable water is also a requirement for drinking water aquifers.
• Aquifers can vary significantly in size and scale.

Groundwater Flow

• Infiltration or seepage of surface water first enters the unsaturated (vadose) zone, where pore spaces are not completely filled with water.
• Water pressure in this zone is less than atmospheric pressure.
• The capillary fringe is below the vadose zone, saturated with water, but fluid pressure is still less than atmospheric.
• The saturated (phreatic) zone sits below the capillary fringe, with fully saturated pore spaces where water pressure is equal to or higher than atmospheric pressure.
• The water table is the boundary between the zone of saturation and the unsaturated zone.
• Wells are conduits that extract, measure, or add water to aquifers.

Discharge

• Discharge areas are where the water table or potentiometric surface intersects the land surface.
• Discharge areas include springs, flowing wells, gaining streams, and playas in arid regions.

Groundwater Mining and Subsidence

• Groundwater mining occurs when water extraction exceeds recharge, leading to declining groundwater levels and potentiometric surfaces.
• Reduced spring and stream flow and subsidence can result.
• In these situations, groundwater is akin to a mine, with depletion over time.

Water Contamination

• Water contamination can result from natural features (mineral-rich formations) or human activities (agriculture, industries, landfills, and sewage).
• Contamination can be categorized as organic and inorganic chemicals, or biological agents.

Remediation

• Remediation refers to cleaning up contaminants.
• Techniques include biological remediation (bacteria), chemical remediation (reactive barriers), and physical remediation (pump-and-treat).
• Point source pollution comes from specific sources (like waste disposal sites), while nonpoint is from dispersed sources (like lawn fertilizers).

Karst

• Karst landscapes form from dissolution of soluble bedrock like limestone, creating features like sinkholes, caves, and disappearing streams.
• Groundwater dissolving limestone results in these karst features.