(12) + (13) Groundwater Flashcards
(29 cards)
1
Q
Groundwater
A
- Water that lies beneath ground surface
2
Q
How does it get underground?
A
- Rain and snowfall: percolation into the ground under the influence of gravity
- 15% of precipitation ends up as ground water
o Big variations locally and regionally - Porosity decreases with depth
o More cement in sediment rock closes pores
o Weight of overlaying rock closes pores
o Igneous and metamorphic rocks have low porosity
3
Q
Where is groundwater stored?
A
- Fills pore space between grains in sediment and clastic sedimentary rocks
- Fills cracks in all types of rocks
4
Q
Porosity
A
- Measures rocks ability to hold water
- Porous vs nonporous
5
Q
Permeability
A
- Measures capacity of rocks to transmit fluid through pores and fractures (flow)
- Permeable vs impermeable
6
Q
Terms to know
A
- Saturated zone
- Water table (top of saturated zone)
- Vadose zone (unsaturated zone)
7
Q
Water Table
A
- Level of water table = elevation of ponds, lakes, rivers, etc.
- Mimics topography (not always flat)
- Subdued
8
Q
Water table and seasons
A
- Fluctuates
- Dry seasons: water flows out of saturated zone into springs and rivers
- Wet seasons: water table recharges
9
Q
Surface rivers and groundwater
A
- Gaining streams o Streams receive water from saturated zone o Stream surface = water table o Rainy seasons - Losing streams o Channels above water table o Water percolates down into the water table o Drier climates
10
Q
How groundwater moves underground
A
- Slow movement (compared to surface streams)
o Typical mm/day to cm/day
o Can take up to millennia for water to resurface - Influenced by..
o Slope of the water table
o Permeability
11
Q
Aquifer
A
- Highly permeable
- Saturated with water
- Unsuitable area is called aquitard
12
Q
Good Porosity
A
- Gravel
- Clay
- Sometimes Sandstone
- Sometimes Limestone
13
Q
Bad Porosity
A
- Till
- Shale
14
Q
Good Permeability
A
- Gravel
- Sometimes Sandstone
- Sometimes Limestone
15
Q
Bad Permeability
A
- Clay
- Till
- Shale
16
Q
Confined Aquifers
A
- Separated from surface by an impermeable bed
- Completely filled with water
- Under pressure
- Slow recharge (maybe no response to seasons)
- Also called artesian aquifer
17
Q
Unconfined Aquifers
A
- Exposed to surface
- Only partly filled with water
- Rapidly recharged (precipitation)
18
Q
Artesian system
A
- Must have aquitards above and below aquifer (to confine)
- Must have recharge area
19
Q
How do we find groundwater?
A
- Well: penetrates aquifer in saturated zone
o Usually must be pumped
o Artesian well: well in which water rises above the aquifer (under pressure)
20
Q
Springs
A
- Where water flows naturally from rock onto surface of the land
21
Q
Why do we need to protect groundwater?
A
- Widely used source of drinking water
- Can be contaminated
- It’s heavily used (needs to recharge)
22
Q
Contaminators
A
- Human Activity
- Minerals
- Soil and Rock
23
Q
Contamination: Human Activity
A
- Pesticides, herbicides
- Fertilizers
- Heavy metals, toxics (landfills and other garbage)
- Animal, plant and human waste
o Bacteria, viruses, parasites - Gasoline
- Acid mine drainage
- Radioactive waste
24
Q
Contamination: Minerals
A
- Naturally occurring minerals may be toxic
25
Contamination: Soil and Rock
- Depends on permeability and composition
o Humus and clay are good filters
- Depends on what the contaminant is
o Some can’t be filtered
26
Heavy use of GW
- Regional water table will drop
- Ground subsides
- Wells dry
- Ruin aquifers
- Groundwater flow can reverse
o Contamination can result: Saltwater, sewage
27
What if water table rises?
- Flooded basements
| - Mass wasting (lubricant and weight)
28
Groundwater – not just H2O
- Presence of dissolved ions
29
Features formed by GW
- Caves, sinkholes (limestone), karst topography
o Caused by solution
- Petrified wood, concretions, geodes
o Formed by mineral precipitation by groundwater
- Hot springs
- Geysers
