Hydrogeology Lab
Last Modified: 08/20/09
Aquifer: A rock body that has the capacity to transmit
"usable" quantities of water to a well.
3 Rock Types that are good aquifers:
- Sandstone
- Conglomerate
- Fractured Limestone
Aquitard: A rock body that DOES NOT transmit
"usable" quantities of water over a reasonably short
period of time. (Ex. SHALE)
Yes, these definitions are relative--what may be considered an
aquifer to one may not me considered one by someone else. A
farmer who has a well that provides 25 gallons of water a day may
consider that to be a good aquifer--it meets his needs. However,
the farmer trying to irrigate his 300 acre farm would consider it
to be an aquitard--it doesn't meet his needs.
* Up to
Hydrogeology Topic Listing *
Porosity: Void spaces in the rock body
- Primary Porosity: original porosity in the rocks (i.e.,
initial empty space between/within the particles that
make up the rock)
- Secondary Porosity: porosity in a rock derived from
external processes (i.e., fracturing, dissolution, etc.)
Permeability: How well interconnected the pores are
(how well the rock can transmit fluids)
* Up to
Hydrogeology Topic Listing *
They are also called CLASTIC AQUIFERS (Sandstones,
Conglomerates)
- Have a natural high porosity/permeability
- DIFFUSE FLOW (water flows slowly through large numbers of
thin, sinuous channels)
- Provides a good natural filter of contaminants
* Up to
Hydrogeology Topic Listing *
- Limestones don't naturally have a high
porosity/permeability
- Interconnected, solution enlarged fractures allow water
to flow through quickly (relative to the alluvial
aquifers) and in large quantities along discrete paths
(DISCRETE FLOW)
- Practically no filtering of contaminants
* Up to
Hydrogeology Topic Listing *
Recharge: The process of surface water entering the
aquifer
- Infiltration: rain or surface water soaks into the
ground over a large area--recharging an ALLUVIAL AQUIFER
- Focused: recharge to KARST aquifers along narrow
zones of interconnected fractures that are exposed at the
earth's surface
Discharge: The process by which groundwater exits an
aquifer and enters a body of surface water (such as lakes,
rivers, etc.)
* Up to
Hydrogeology Topic Listing *
Impervious cover: includes material such as concrete
that restricts the infiltration of water into the aquifer
Three Main Problems:
- It causes pollutants to concentrate on top of the cover
rather than allowing them to seep slowly into the
subsurface and become diluted.
- It increases the rate at which rain runs off the
surface-- allowing little time for pollutants to degrade
before they enter surface water bodies; it also worsens
floods
- It inhibits recharge to the aquifer (by diverting water
out of the recharge zone).
* Up to
Hydrogeology Topic Listing *
1) Tertiary Ogallala Aquifer
- an alluvial aquifer
- is in a semi-arid region--low recharge of aquifer
- overpumping is causing a net decline in water levels of
the aquifer
2) Cretaceous Edwards Aquifer
- a karst aquifer
- very vulnerable to contamination
- water flows through quickly, allowing for little dilution
or degradation of the contaminants
* Up to
Hydrogeology Topic Listing *
Back to Cory's Geology
303 Lab Home Page