Chapter 14Groundwater

Noteworthy Information

Factors that affect the amount of groundwater that seeps into the ground:

• type of rock or soil

• climate (dry climates, water evaporates)

• topography (mountainous regions water runs

off the rocky slopes)

• vegetation (slows flow and removes water)

• land use (pavement does not allow water to

enter the ground)

Factors that affect porosity of rock:

• particle shape (round vs. angular)

• sorting (well-sorted vs. poorly-sorted)

Factors that affect permeability of rock:

• particle size (small vs. large)

• sorting (well-sorted v.s poorly-sorted)

Distribution of Groundwater

Vadose

Phreatic

• A rock can have a number of pores that are not

connected to each other. (Pumice, Scoria)

Zone of Aeration

Water Table

Zone of Saturation

Impermeable Layer

Factors that determine the water tables

distance from the surface:

• amount of rainfall

• time between rains

• season

• slope of the ground

• thickness of soil

• climate

• human activity

What is an ordinary well?

• a well drilled into the permanent water table

What is a perched water table?

• water that collects on an impermeable layer

above the water table

Springs may result from a perched water table

Rollie’s Well

• The best aquifers are made of:

uncemented sands and gravels, sandstones

• Magma or cooling pluton is the heat source for geysers, fumaroles, and hot springs 100 F+ (strong sulfur smell)

• Geothermal gradient is the heat source for most Eastern U.S. warm springs (mild sulfur smell)

GeyserEruptionSequence

Deep Circulation of Groundwater

geothermal gradient10 C/km or 1.5 F/100ft

Warm Spring

What percentage of the drinking water in the United States comes from groundwater?

• 50 %

What problems have humans created for the groundwater supply?

• Using the groundwater faster than it can be replenished by nature.

• Polluting the groundwater supply

Problems that develop due to the over use of groundwater.

• The water table drops

• Saltwater intrusions

• Subsidence

How does groundwater become polluted?

• Pollution is carried by water seeping through the soil.

Formation of a cone of depression in the water table

Discharge exceeds recharge

Saltwater contamination due to excessive well pumping

Wildwood Crest

List a few examples of groundwater pollutants.

• Oil from roads

• Nitrates from soil fertilizers

• Pesticides applied to plants

• Farm wastes

• Sewage from septic tanks

Well design requires knowledge of local geology

What is the difference between hard water and soft water?

• Hard water contains large amounts of dissolved ions from minerals.

• Soft water contains very few ions from minerals.

Why is artesian water generally harder than ordinary groundwater?

• Artesian water travels farther and may be warmer than ordinary water, so it can dissolve more mineral matter.

Artesian Well Model

Hydraulic head and urban water supplies

Just like an artesian, saves money

List some states that have Karst Topography?

• Alabama, Florida, Tennessee, Indiana, Virginia,

Pennsylvania, Georgia, Missouri, South Dakota

and Wyoming.

What is Karst Topography?