Groundwater Lecture Notes

Recording of Lecture on Groundwater

  • Introduction

    • Apology for not being present in person.

    • Announcement: Bonus assignment unlocking this afternoon for extra points on exam number four.

Overview of Groundwater

  • Focus on natural resources, starting with groundwater.

  • Importance in hydrology, the study of water.

    • Water is crucial for survival of living organisms.

    • Lack of water can lead to death.

Hydrologic Cycle

  • Description of the hydrologic cycle.

    • Basic stages:

    • Evaporation from oceans.

    • Condensation into rain in the atmosphere.

    • Precipitation falling to the ground.

    • Water movement in rivers/lakes or infiltration into groundwater.

    • Both paths eventually returning water to oceans.

  • Water Reservoirs:

    • Ocean: Over 1,300,000 units of water (largest reservoir).

    • Glaciers: Over 26,000 units (second largest).

    • Importance of glaciers for water supply when melted.

    • Groundwater: Over 15,000 units (third largest).

    • Much larger than surface water supply in rivers and lakes (178 units).

Groundwater Formation

  • Sources of Groundwater:

    • Precipitation falling on land can either:

    • Become runoff simple water that runs off the surface off the ground (blue arrows in the diagram) to stream/rivers.

    • Become infiltration (yellow arrows) which soaks into the ground and forms groundwater.

Infiltration Process

  • Conditions for Infiltration:

    • Porosity: Measure of open void spaces below ground that hold water.

    • Represented as a percentage of total volume (e.g., 10 acres down to 30 feet).

    • Types of Porosity:

      1. Intergranular Porosity:

      • Spaces between sediment grains.

      1. Intragranular Porosity:

      • Small pores in sediment that hold large amounts of groundwater.

      1. Fracture Porosity:

      • Cracks in rock layers that can hold water.

      1. Vuggy Porosity:

      • Openings created by dissolution that store groundwater.

Factors Affecting Porosity

  • Sorting: Uniformity of grain size.

    • Well-sorted materials have high porosity due to space between evenly sized grains.

    • Poorly sorted materials have lower porosity since smaller grains fill in gaps.

  • Cementation: Degree to which sediments are cemented together.

    • Poorly cemented = high porosity; well-cemented = low porosity.

Permeability

  • Definition: Capability of water flowing through interconnected pore spaces.

    • High permeability means water can flow freely; low permeability (e.g., mudstone) can trap water.

Aquifers

  • Terminology:

    • Water Table (WT): Boundary between saturated zone (below) and unsaturated zone (above).

    • Unsaturated Zone: Contains air in pores; also known as aeration zone or vadose zone.

    • Saturated Zone: All pore spaces filled with water; known as phreatic zone.

  • Aquifers Definition:

    • Layers of loose sediments or rock containing a usable groundwater supply.

    • Key properties for aquifers include high porosity and high permeability.

    • Wells: Must be drilled below the water table to reach saturated zone.

Types of Aquifers

  1. Unconfined Aquifers:

    • No layer interrupting infiltration from the surface.

    • Able to replenish easily with precipitation.

    • An aquitard beneath restricts flow deeper.

  2. Confined Aquifers:

    • Sandwiched between two aquitards; less accessible for recharge.

    • Water pressure can create an artesian well if drilled correctly.

  3. Perched Aquifers (or perched water tables):

    • Develop above an aquitard in a slope; smaller water supply.

    • Economically advantageous for drilling due to lesser depth.

Balancing Water Supply

  • Recharge and Discharge:

    • Recharge: Water added to aquifer through infiltration.

    • Discharge: Water leaving the aquifer either naturally or through pumping.

    • Aim for balance between recharge and discharge for sustainability.

Problems with Imbalance

  • Excessive Recharge:

    • Can lead to water table rising, causing potential flooding and health issues from contaminants.

  • Overdrafting: Taking out more water than is replenished.

    • Consequences:

    • Cone of Depression: Area where the water table drops around a pumping well.

    • Subsidence: Lowering ground level due to loss of support from water in pore spaces.

    • Saltwater Intrusion: Saline water from coastal areas can enter freshwater aquifers.

Case Study: Love Canal

  • Location near Niagara Falls, New York.

  • Early History: Abandoned canals from early 1900s, later used as chemical waste dumps by a factory during WWII.

  • Development in 1960s: Population boom led to housing developments over these toxic sites.

  • Health Problems: Residents experienced unusual health issues, including high birth defect rates.

  • Investigation and Emergency Declaration: In 1978, the President declared an emergency due to contamination after the water table rose with high precipitation, drawing chemicals into homes.

  • Impact: Resulted in the Superfund Act for cleaning contaminated sites and ongoing legal battles regarding accountability.

Conclusion

  • Reminder of the vital importance of groundwater management and implications of contamination and resource imbalance.

  • Encouragement to remain aware of water supply sustainability and safety.