Chapter 12 - Groundwater Flashcards
Whats the % of groundwater compared to total water. So how much drinking water do we have?
- 625%
- EVEN LESS DRINKING WATER, AS WE CANT EVEN DRINK ALL GROUNDWATER
Define groundwater
water contained in pores within bedrock or regolith
- in groundwater, there is a saturated zone – most of the water is contained
- above, there is a zone of aeration(no water in pores)
- there is an area between saturation zone and aeration zone, called water table
Relative sizes of zone of aeration and zone of saturation
cm to tons of m - zone of aeration
1m to 100s of m - zone of saturation
What are outcrops of water table?
Lakes
What is the potable/usable depth of saturation (depth that we can drink groundwater). What is the max depth
Max depth/potable/usable of saturation: 750m
they lower you go, the ore minerals get dissolved in groundwater, the more salty
Does groundwater stay in its place or does it move?
Most groundwater moves several cm to meters per year
Define porosity. What does it depend on?
% of rock that is pore space
Depends on sorting and cementation
Define permeability . What does it depend on
Easy of fluid flow through porous medium
-depends on pore size + connectivity + viscosity
Rank permeability between the 3 A’s
Aquifer: high perm - carries water
Aquitard: Low perm - movement of water is retarded (slow)
Aquiclude: No perm
What is structured water?
Thin water coating on edges of pores of rocks.
-structured water’s permeability depends on the pores of rocks (big pores big permeability)
Rank permeability of
(I)sand, silt, clay
(ii)sandstone, shale, solution activity in limestone, dolostone
(I) sand - high perm silt - medium perm clay - low perm (ii) soln permeability in limestone/dolostone - very high sandstone - high shale - low (THIS ALL DEPENDS ON POROSITY)
Aquifer porosity?
High
Aquitard porosity?
medium
Aquiclude porosity?
low
Correlation of porosity and permeability?
High porosity = lots of white space beteween rocks = high permeability
Recharge and discharge areas - groundwater flow paths; Unconfined aquifers
For unconfined aquifers:
Water moves in an idealized fashion
-water frickles through ground surfaces and goes back to nearest stream
-flow velocity of water is variable: Faster at top, and the deeper you get it gets slower
Rates of velocity of water in unconfined aquifer. What about the rate of our drinking water? How do they create streams if they slow? OH WAIT THEYRE not.. nvm no spoiler
-flow velocity of water is variable: Faster at top, and the deeper you get it gets slower
Rates: shallow water takes ~1000 days for any given molecule to rain down and come back out along river system and back to ocean
if you go deeper, it can take 100 yrs, 10 centuries, to a millennia
The water we drink flows fast
-when it rains, it fills up pore space in ground water, until It gets up to surface level, then starts to create streams
Confined aquifers
Floridan aquifer (our example)
- water flows through stricted layer of rocks
- recharge and discharge,
How to tell which way groundwater flows in confined aquifer? And can you drill into ground to get fresh ground water?
Water wells are called artesian wells in this case, they may or may not flow. We basically determine the level up to which the water rises from the bottom of the well. So you drill down to the ground water, and you see how high the water rises. Then at another point a few distance away. Connect the highest the water rises from both points, and then you get a plane. This plane describes how the water flows.
What word do we use to describe a water well that may or may not flow on their own?
“Artesian”(may or may not flow) water well
When do springs appear? Do springs appear in confined, or unconfined aquifers?
In unconfined and confined aquifers, springs appear where a boundary of aquifer to aquitard intersects the land surface
TOP 10 GROUNDWATER PROBLEMS: 10 IS MOST DANGEROUS, 1 IS LEAST
Ten groundwater problems:
Problem 1: things may not stay buried / in the ground. Ex) in new Orleans, the ground water is so shallow, and it pushes things out of the ground. In coffins, that are buried in the ground, they put them on the ground so groundwater doesn’t push them out
Shallow ground water could push things out of the ground.
Problem 2: land subsidence: the ground can sink, *Structural damage to roads, buildings, bridges
problem 3: dry wells due to cones of depression in unconfined aquifers : water cannot get replenished at the same rate it is being pumped out
-to avoid these dry wells, you space the wells at a large distance, and you pump less.
Problem 4: salt contamination due to cone of ascension in unconfined aquifers
Usually happens in coastal area, the wells causes a cone of ascension which causes contact with salt water and thus contamination
at some depth the water is eventually gonna turn salty, because its beside a sea
-to fix this, you have to stop pumping, and then wait for the fresh water to come back in
Problem 5: contamination due to spills, leakage, garbage dumps
Problem 6: drying up of water well and or contamination from CBM extraction .. The wells could also be contaminated from the methane or fossil fuels they extract
Problem 7a: Drowning of salt mines - Radioactive contamination
7b: drowning of salt mines - Loss of mining operation
Problem 8: drought - non cultivated land turning into desert –> habit destruction, species migration
Problem 9: agricultural land turning desert, little or no water for agriculture and drinking
Problem 10: wars over water:
difference between confined and unconfined aquifer
unconfined aquifer: water table is upper boundary
confined aquifer:
confined aquifer: water is bound above and below by beds (deeper than unconfined)
