Groundwater Flashcards
Aquifer
The temporary storage of infiltrating precipitation with slow release to lakes and streams
Vadose Zone
Area close to the surface where pore spaces are filled with a mixture of water and air
Phreatic Zone
Depth where all pore spaces are saturated
Aquitards
Low porosity and conductivity, provide protection for aquifers from surface contamination
Gaining stream
Water table above base of stream, baseflow recharges stream
Losing stream
Water table below base of stream
Perched aquifer
Infiltrating water becomes trapped and cannot flow out
Seepage face
Aquifer-aquitard contact outcrops at cliff face, causes groundwater to seep out
Artesian well
Water table level sits above ground surface, flows out of ground naturally
Groundwater well
Hole drilled into ground to target an aquifer
Well screen
Outer casing that allows water to flow into well while filtering out large particles
Groundwater head
Level to which water would rise in an infinite straw that is open to just that aquifer
Piezometric surface
Contours of constant head within an aquifer
Dupoit-Forchheimer Flow
Parabolic head profile in an unconfined aquifer assuming steady state conditions
Drawdown
Change in head compared to an original pre-pumped state
Hantush-Jacob Solution
Semi-confined aquifer with leakage, modelled by extra parameter, c, characterising the hydraulic resistance of the confining layer
Moench-Neuman Solution
Model of delayed yield in unconfined aquifers
Well yield
Maximum volume rate over a specified time period that introduces a drawdown no larger than Hmax
Calculating the drawdown due to more than 1 well
Use the principle of superposition since Theis solution is linear
Pump test with lateral flow barriers or a recharge source
Place an image well to model the effect of the flow boundary/recharge
Using an image well for a lateral flow barrier
Place image well at equal distance from the lateral confinement as the pumped well
Drawdown at observation well is the sum of the image well and the pumped well
Pump rate changes from x to y from time a to b
Drawdown is the sum of head due to x till time b, and the head due to (y - x) for time (b - a)
Wellbore skin
Transmissivity reduction due to water level dropping more than expected
Rorabaugh Method
Step-rate test to quantify transmissivity reduction using estimates from a pumping test
Driven well
Pipe with pointed steel tip driven into ground to break through pebbles and layers of hard material
Drilled well
Drill rig used to excavate hole, then casing and screen is placed.
Well casing
The tubular components used in the construction of water wells
Well screen intake
For wells in unconsolidated formations, prevent the pump from being clogged with aquifer material
What is the maximum desirable screen entrance velocity related to?
Hydraulic conductivity of aquifer material
Well screening for confined aquifers
Entire thickness of aquifer
Well screening for unconfined aquifers
Lower one-third to one-half of the saturated thickness
Why are longer screen lengths preferable?
Higher pumping rates per unit drawdown
Common groundwater pump
Vertical turbine pump
Grouting
Protection between well casing and borehole to prevent polluted surface water from contaminating the aquifer
Performance assessment of groundwater wells
Pumping rate per unit drawdown
Goal of wellfield design
Meet total pumping demand using as few whiles as possible while being constrained to a maximum drawdown
Time of travel
Distance from a well where it will take a certain time for contaminants/water to reach the well
