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EARTHSC 1G03 Lecture Notes - Capillary Fringe, Aquifer, Gabbro


Department
Earth Sciences
Course Code
EARTHSC 1G03
Professor
Maureen Padden

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15 GROUND WATER
Ground water: fresh water beneath the ground surface, filling pore space b/c grains in bodies of
sediment and clastic sedimentary rock, and filling cracks/crevices; roughly 1% of water on Earth
ZONES
Divided into 3 “zones” in the ground: unsaturated, water table, saturated zone
1. Unsaturated Zone: air and water fill pores collectively; surface tension causes water to be held
above water table
2. Water table: The line that divides the unsaturated and saturated zones this is also the upper
limit of the saturated zone; capillary forces create a transition zone above the WT
3. Saturated Zone: water fills the pores of rocks/sediment
ACCUMALATION:
Source of groundwater is snow and rain which percolates down to the water table (~15%).
Position of the water table depends on seasonal factors - only water in the saturated zone is
“ground water.”
Capillary fringe: transition zone where water is located higher than the water table due to
capillary effects. In rocks with smaller pore spaces (e.g. clay) we see a higher water level than
rocks with larger pore spaces (i.e. gravel).
AQUIFERS
Porosity: percentage of rock or sediment that consists of voids or opening for water to be held
High %: gravel, sand, silt, clay
Low %: glacial till, crystalline rock, shale
Permeability: capacity of a rock to transmit a fluid such as water or petroleum through pores or
fractures
Excellent: gravel, sand,
Poor: clay, glacial till, crystalline rock, shale, conglomerate
Aquifers: body of saturated rock that allows water to move through easily conglomerate, well-
sorted little cement sand stone, well-jointed lime stone. Further subdivide into:
Unconfined aquifer: access to the surface and rainfall can percolate freely into the aquifer
o Quick recharge of water
Confined aquifer: bound by low permeability beds above and below, and can only get
water from surface exposure.
o Susceptible to pollution; slow recharge of water
Aquitard: rocks that do not allow water to transfer through it easily shale, crystalline rocks
(gabbro, particular lime stone)
RECHARGING AND DISCHARGING
Recharge is the water goes into the saturated zone typically upland; discharge is where the
water comes out of the surface lakes, ponds, rivers. Groundwater generally moves from
recharge to discharge.
WATER FROM WELLS
Water wells are cylindrical holes dug or drilled into the ground penetrating an aquifer; must be
deeper to access water during dry season. Pumping results in the initially straight water table to
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