Ground water

  Chapter 10   Pages 238-263

Ground water focus questions

  Where does your drinking water come from?

  What factors affect ground water movement and storage?

  Is ground water an unlimited resource?  How much of the world’s water is fresh water?  How much of the world’s water is ground

water?

Ground Water Focus Questions

  How do confined and unconfined aquifers compare?

  What is polluting our ground water and how can we conserve and protect it?

NATURAL RESOURCES II: WATER RESOURCES

ANNUAL MOVEMENT OF WATER ON THE GLOBE

Where’s the Water?

-  Water on Land (Where is most of this held?)

Where does your drinking water come from?

  Ground water   In cracks and pore

spaces   Not in underground

lakes and streams

GROUNDWATER

Zones   Saturated zone = where all

the cracks and pore spaces are filled with water = ground water

  Zone of aeration = unsaturated zone = area where there is water and air in the pore spaces and cracks

  Water table = upper limit of the saturated zone

Porosity   The ability to store water

in pores and cracks.   Factors affecting it

  Particle shape -- rounded has more pore space than angular

  Sorted sediments have more pore space than unsorted

  Clay - soaks up the water slowly but holds a surprisingly large amount

Permeability

  The ability to transmit water Factors affecting it: 1.  Sizes of pores &

cracks 2.  Whether pores and

cracks are interconnected

3.  Capillarity - water is attracted to clay and resists moving

Aquifers

  Aquifers are both porous and permeable.

Unconfined aquifer

  Does not have impermeable rock above and below.

  Must be pumped out   Can be contaminated

from surface spills more easily

Confined or Artesian aquifer

  When an aquifer lies sandwiched between two impermeable layers

  Water rises in the well under pressure

AQUIFERS AND AQUITARDS

GROUNDWATER FLOW

Surface of the Water Table mimics the topography of the land surface

Ground water flow   Ground water movement

is typically feet/day but can be faster in coarse gravel or limestone

  It may take years, decades or even centuries for groundwater to move long distances through some aquifers.

  Ground-water may take only a few days or weeks to move for a short distance through loose soil.

Recharge

  Precipitation and runoff enter permeable rock and sediment to recharge the groundwater.

  Pavement prevents recharge

Gaining streams

  Are fed by ground water

Artesian Conditions

Created by the tilt of a confined aquifer

SPRINGS

Where the land surface abruptly intersects the water table

CAVES and KARST

Limestone dissolved by acidic groundwater near the top of the water tables

GROUNDWATER HAZARDS

Wells - cone of depression

  Water use can lower the water table

  In coastal areas, this can cause salt water to intrude

  Too much water use and too little recharge can lead to subsidence   The ground sinks

IS GROUNDWATER A RENEWABLE, NONRENEWABLE, OR UNLIMITED RESOURCE?

What is polluting our ground water and how can we conserve and protect it?

  Homework:   Visit scorecard.org

  Enter your zipcode   Gather information on

Dakota County 1.  Who are the top polluters? 2.  What chemicals the main

chemicals released? 3.  Where is the superfund

site and what toxins is it releasing?

4.  3 other facts of interest

  Observe the poster of nitrates in wells in the Hastings area.

  How many wells have over 10 ppm?

  Why is this unsafe?

Source for visuals

  Jim Miller, Associate Professor of Geology, University of UMD

  http://www.d.umn.edu/~mille066/teaching.htm