Week 9: Groundwater

Define groundwater

Underground water that is flowing through saturated media (soil)

What is an aquifer?

Porous and permeable rocks that store enough water and transmit it at a rate fast enough to be hydrologically significant

What is an Aquitard?

Impermeable layers that hinder or prevent water movement

Define primary and secondary porosity?

Primary porosity: Pores originally formed with the rock

May decrease with burial compaction

Secondary porosity: Pores formed due to fracturing, faulting, and dissolution

How does groundwater flow?

From an area of greater head (recharge area) to areas of less head (discharge area)

Where do lakes, springs, and wetlands occur?

Where the water table is at or above ground level

What are springs? What are some characteristics of them?

Springs: Locations of natural groundwater discharge

Marked by:

Hydrophilic vegetation

Perennial wetlands

Saturated soils

Non-freezing ground

Stream flow

Define Porosity

The total volume of open space within sediment or rock

Define primary and secondary porosity?

Primary: Originally formed with the material

Secondary: Developed later from jointing/dissolution

Define permeability

The ease of water flow due to interconnectedness

What are aquifers and aquitards?

Aquifers: Porous and permeable rocks or sediment that freely transmit groundwater

Aquitards: Impermeable layers that hinder or prevent water movement

What rocks are the best aquifers and aquitards?

Aquifers:

Sandstones

Conglomerates

Unconsolidated sand and gravel

Limestone

Aquitards:

Low permeability crystalline rocks (igneous and metamorphic)

Clay rich shales or mudstones

What is a water table? What are perched water tables?

The saturated zone with water below the surface

Perched water tables: Water tables formed by aquitards

How do hot springs form?

When groundwater rises from warm rock deep in the crust or where igneous activity heats water near the surface

What are some characteristics of groundwater quality?

High quality because particulates are filtered

Clay minerals absorb certain dissolved ions

Natural groundwater may contain unwanted substances

Dissolved Ca and Mg, iron, Mg, and hydrogen sulfide and arsenic

What pollutants from human activities are released into groundwater?

Dissolved and pure organic and inorganic compounds

Dissolved metals

Pathogenic microbes

Groundwater transport pollutants away from a source

What are artesian aquifers?

They are confined to tilted aquifers

Upland recharge pressurizes the aquifer

Water rises in artesian wells to the potentiometric surface (where the water table could be)

What are issues with groundwater pumping?

Drawdown occurs (lowering of the water table)

Cones of depression also form

List some groundwater problems

Depletion

Reversing the flow direction from the cones of depression

Saline intrusion

Subsidence