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80 Cards in this Set
- Front
- Back
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What proportion of the Earth's water is fresh water? What proportion of that freshwater is groundwater? |
2.5% of the total water on earth is fresh, and 0.8% of that is fresh groundwater (30% of all freshwater is groundwater) |
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Define "Aquifer" |
An Underground layer of water-bearing permeable rock (or rock fractures/unconsolidated material) from which groundwater can be extracted to make a well. |
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Define "Aquitard" |
A bed of low permeability along an aquifer. |
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What is a Confined Aquifer? |
An aquifer that sits between two aquitards |
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What is an Unconfined Aquifer? Are unconfined aquifers good sources of groundwater? |
Unconfined aquifers are not surrounded by 2 Aquitards. They MUST contain the water table. Surficial/Unconfined Aquifers are poor sources of groundwater because they are easily contaminated by surface stuff (like manure) |
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Comment on Clay-sized particle's permeability and porosity. |
Clays have very poor permeability. Clays have high porosity because many clays have water in their chemical structure, AND the gaps between clay-sized particles are so small water is drawn into them by capillary action. So their effective porosity is low, their absolute porosity is high. |
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Define "Perched Aquifer" |
A layer of saturated soil above an aquitard,below which there is a layer of unsaturated soil. |
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Differentiate between K and k as mesureable quantitites |
K is a measure of hydraulic conductivity, and is a function of k, the density and viscosity of the fluid and the acceleration due to gravity. measured in m/s, not equal to velocity. k is the intrinsic permeability and is dependant on the shape and size of the fluid conduit, largely a function of the material. measured in m^2 |
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Given a Soil type, name 3 ways we can estimate k. |
Hazen's or Shepherd's method, given A plot of (% finer by weight) VS (grain size) Look it up in Freeze and Cherry |
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Describe how Hydraulic conductivity would change given a chiange in grain size |
K increases with increasing grain size. |
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What does REV stand for and why is it relevant. |
The REV is the Representative Elementary Volume, or the volume across which a property can be effectively averaged; basically a measure of the scale from which we can extract an accurate measurement of a quantity. so like, the REV for a sample where you're measuring grain size is ideally larger than that of the grains. |
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Comment on what makes a soil Heterogenous and anisotropic |
A soil that is heterogenous has properties that vary in space, and an anisotropic soil has properties taht vary with direction of measurement. |
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What does pressure depend on in terms of a water column |
P=rho*g*d; so the depth in the water column, the acceleration due to gravity and the density of the fluid. |
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If you dig a big hole in the ground what happens to the water level when the area is covered by a low pressure zone? |
The water will spill out of the hole, due to a lower atmospheric pressure. |
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Define: Bollard |
Steel pipes that surround a monitoring well and protect it form like, cars and stuff. don;t know if we even need to know this nonsense. |
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What does the bernoulli equation state, and what assumptions does it make |
total energy is constant at all times along a flow path, assuming an incompressible fluid and a closed system. Constant (h)= z + (P/{rho[w]*g}) + (V^2/2g) Hydraulic head= elevation+ pressure head+ velocity head |
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Gradient in Hydraulic head is a _______ quantity Hydraulic head is in the _____ direction as groundwater flow |
Gradient in hydraulic head is a vector quantity Hydraulic head is in the opposite direction as groundwater flow |
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Define AMSL |
Above mean sea level- a measure of height off of a standard, worldwide datum. |
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A well is assumed to have a head of h, assuming the water in it is fresh. how does h change if the fluid is denser than water? |
Hydraulic head will INCREASE in a denser fluid. |
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Forces in the body of a fluid are ___________. Forceson the surface of the interface between fluids are __________. |
Forces in the body of a fluid are equal (Effectively). Forces on the surface of the interface between fluids are unequal. |
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What physical phenomenon accounts for the imbalance of forces on the surface of a droplet (meaning, What physical phenomenon accounts for interfacial tension?) |
The curvature of a droplet; this minimezes the energy and balances the forces here. APPARENTLY :/ |
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Capillary pressure= ______ pressure - ______ pressure by convention If it's not between air and water, this pressure is called _________ ________ |
Capillary pressure= air pressure - water pressure by convention.
If it's not between air and water, this [pressure is called interfacial tension. |
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As radius of a drop decreases, Capillary pressure at the interface _______. |
As radius of the drop decreases, Capillary pressure at the interface increases. (P_c= [2*sigma*cos(theta)]/r)) |
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As the radius of the tube decreases, Capillary Pressure ____________, Capillary rise ________.
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As the radius of the tube decreases, Capillary Pressure increasers, and Capillary rise increases. |
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What is a tensiometer? What happens if you insert it below the water table. |
A ceramic tube, allows us to measure the waterpressure in the soil regardless of whether it’s positive or negative. If you insert it into the soil at the water table, the water will wet the tube to th same height. if you inser tit below the water table, the water will rise higher than the bend in the tube. |
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Hydraulic head is a measure of ________ per unit____________. |
Hydraulic head is a measure of water energy per unit weight. |
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Can groundwater flow from High pressure to low pressure? |
Yes, assuming the high pressure zone has a higher head than the low pressure zone due to the elevation or velocity components of hydraulic head |
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Differentiate between Q and q |
Q: Flow/ Discharge, a measure of the Volume rate of water flow that istransported through a given cross-sectional area. (given By Darcy's law) q is the Darcy flux, a measure of discharge per UNIT area. |
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Kxy is the Hydraulic conductivity in the ____ direction due to a gradient in the ____ direction. |
Kxy is the Hydraulic conductivity in the x direction due to a gradient in the y direction. |
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Consider an empty pipe with Darcy flux q. what happens to the velocity if it's filled with a sand? |
Asuming q stays the same, v must increase as porosity decreases. |
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How can we construct a potential field with reference to grounwater? How can ∇h be calculated from this data set? |
A potential field in any region can be described my measuring hydraulic head at a large number of points and countouring the resulting set of data set Contours are called equipotentials.
∇h be calculated by using contours and drawing a line perpendicular to the equipotentials and measuring along that line, taking care to recall that is opposite to flow. |
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In a _________ ________ system, the flow lines and equipotentials cross at 90 degrees. |
In a homogenous Isotropic system, the flow lines and equipotentials cross at 90 degrees. Equipotentials are parallell to constant head andperpendicular to no-flow boundaries |
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What are the 4 boundaries with reference to Flow nets? |
> No flow- water cannot flow across it > Constant head- an equipotential! > Water table- water cannot cross it > Boundaries in Soil type (differences in K) |
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If equipotentials cross a boundary from a high K to a low K, what happens to the distance between them? |
Q=-KA(ΔH/ΔL); since K decreases, in order increase K , ΔL must increase. |
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On a graph that plots Suction head (-P_c) VS Saturation of water, how can we tell which soils are poorly sorted? |
Poorly sorted soils will have steep slopes. As Sw decreases (Water is sucked out,) it takes stronger and stronger suction to remove the water from the messy soil. Well-sorted samples require less suction to remove the same amount of water |
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On a graph that plots Suction head (-P_c) VS Saturation of water, how can we tell grain size? |
Curves with greater grain sizes will plot higher up because it takes much more pressure to force water out of a smaller grain size due to teh stronger capillary forces in small pore throats. |
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Why is determining K of a soil through testing in lab not all that useful? What other types of tests can be done? |
because K varies in space throughout teh subsurface, so taking a small plug of a giant aquifer will most likely NOT produce a measureent with an REV. PUMPING TESTS- require monitoring wells (there are many methods) SLUG tests- require one monitoring well. |
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Generally, what do pumping tests assume about the nature of the test they are running and the subsurface? (there are 7 points). THEIS made these 7 assumptions when determining his methods to calculate K. |
THEIS's 7 assumptions i. Horizontal, confined aquifer of constant thickness that is homogeneous and isotropic ii. The aquifer has an infinite areal extent and no boundaries
iii. Natural groundwater flow in the vicinity of the pumping well isnegligible iv. The aquifer is perfectly confined (the overlying soil iscompletely impermeable and doesn’t leak any extra water into the system) v. The flow towards the well is radial, and thus there are novertical components to flow
vi. The initial h distribution is uniform |
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In a system with multiple wells withdrawdowns that overlap, the drawdown at any point in the area of influence of several pumpingwells is equal to the ____ of _______ from each well. This is valied in a ______ aquifer. |
In a system with multiple wells with drawdowns that overlap, The drawdown at any point in the area of influence of several pumping wells is equal to the SUM of DRAWDOWNS from each well in a CONFINED aquifer. |
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Pumping water into the ground causes the water table to _____. |
Pumping water into the ground causes the water table to "mound upwards". |
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Two monitoring wells are located at the same distance from a third. the first well is pumping water IN at a reate of Q, while the second is pumping water OUT at a rate of Q. what is the drawdown measured at the 3rd well? |
Assuming everythign taht Theis did, the drawdown is 0, sicne the well pumping water in in will increase the drawdown just as mucha s the well popping out will decrease it. |
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What will the drawdown cone look like if a monitoring well is pumping near an infinitely large lake? |
[Draw it]; basically the drawdown will still increase but the drawdown cone will like, start at the border of the lake |
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What will the drawdown cone look like if ONE side of the aquifer is leaky but teh other isn't? |
[Draw it]; The drawdone cone will be less drawn down on the side where the aquifer is leaky. |
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What will drawdown look like if the aquifer is bounded on on side by a really large impermeable boulder) |
[Draw it]: basically the drawdown will be much higher on the side with the boulder |
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The Cooper-Jacob method of hydraulic testing is less overbearing to use than the Theis method. it only works for small values of ___ and large values of ____. To check if these values are the right size, you can solve for ____ and check to see if it is less than ____. |
The Cooper-Jacob method of hydraulic testing is less overbearing to use than the Theis method. it only works for small values of *r* (distance to well where pumping test is occuring) and large values of *t*. To check if these values are the right size, you can solve for *u* and check to see if it is less than 0.01. |
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Based on this image of a Cooper-Jacob plot, what could cause the graph to dip up towards the y-axis like plot B? what could make it dip down towards the x-axis like plot A? |
If the data dipsdown towards the time axis like A, it means one of 3 things: the system is at asteady state, the system is not fully confined, free water is present in thesystem (there’s LESS drawdown than there should be). if it looks like B, thereis MORE drawdown than there should be, and this implies that there is animpermeable boundary nearby preventing a constant drawdown. |
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Why would we use a Slug test as opposed to a pumping test? |
It's much less tiem consuming and require less infrastructure (only require one well) |
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Compare the relative scale of measurement for K of a permeameter test, a slug test and pumping tests. |
The scale of measurement from least to greatest is permeameter-slug test-pumping test |
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What is the only surefire method to remove a contaminant from a groundwater system? (this is a rude question) |
Wait- the solution to pollution is dilution. as time geos to infinity, concentration goes to 0. |
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Why do contaminant plumes spread out in porous media? |
Partially due to tortuosity- manydifferent paths water can take through media Flow through the middle of a porethroat is FASTER than the speed close to the edge; can split up solute as itpasses through Heterogeneity in different layers-variants in K layers will affect velocity of the groundwater |
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Dispersivity is a function of...? |
Dispersivity is a function of The groundwater velocity, a dispersivity coefficient and teh diffusion. ALSO diffusion is usually entirely negligible. |
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Differentiate between a conservative and a non-conservative compound |
FIX MEEEEE |
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List the 6 possible sources of contamination and give an example each |
Sourcesdesigned to discharge substances- like fertilizer (or what we USED to design landfills to do) Sources designed to store/treat/ and/or disposeof substances- tailings pond Sources designed to retain substances duringtransport (pipelines) Sources discharging substances as a consequenceof unplanned activity (like literally breaking the law and dumping benzene in a lake) Sources providing a conduit for contaminatedwater to enter aquifers (like fracked shale "aquitards") Naturally occurring sources- like Arsenic in Yellowknife- also be aware tat this can be exacerbated by human activity |
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Define "Contaminant" |
**ANYSUBSTANCE** that at a given location at a given time that exceeds a givencriterion |
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We discussed 7 potential types of chemicals that could constitute a contaminant- what are they, and give examples of each. |
Inorganic compounds- Nitrates, H, Pb,Cl- (in drinking water) Organic- gasoline constituents (historicaland today), pesticides, industrialliquids Radionucleides-U, Ra Pharmaceuticals- ibuprofen, microbeads! Microorganisms-Bacteria, virus Disinfectants- Chlorine and chlorinedioxide Byproductsof disinfectants- chlorite, bromate, thihalomethanes |
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Define LNAPL and DNAPL. |
LNAPLis Lighter-than-water non-aqueous phase liquid DNAPL is Denser-than-water non-aqueous phase liquid Since they are non-aqueaous phase liquids, thyeyare NOT dissolved in the water (they descend like a blob of molasses and VERY slowly dissolve in water) |
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Give an examples of an LNAPL and DNAPL |
DNAPL- PCB oils, Chlorinated solvents like tri- and tetrachloroethylene and creosote LNAPL- Benzene, gasoline, heating oil and kerosene Benzene and creosote can act as DNAPLs sometimes too |
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WHY areTHE ARMS ON AN DRAINAGE/IMBIBITION curve different? |
Recall P_c= 2*IFT*(cos[theta])/r The contact angle between the interface of an advancing fluid and a retreating fluid is differenct snap-off;when you turn off the flow, you get blobs of oil that are left behind becausebubbles form in pore throats By-passing; pressure that is high enough willforce water through all pathways, but upon leaving it might only take the pathof least resistance and so oil might be trapped. Even water flushing throughthe system will go through the path of least resistance and miss NAPL-filled pathways |
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The amount of non-wetting phase residual which gets trapped in a porous medium is a function of the ______, the _____, and the maximum achieved non-wetting phase __________ __ ________. The amount left over is anywhere between __ to __% |
The amount of non-wetting phase residual which gets trapped in a porous medium is a function of the medium, the fluid, and the maximum achieved non-wetting phase saturation on drainage. The amount left over is anywhere between 5 to 50% |
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FI you are forcing a non-wetting phase into a soil, which of the following situations will require LESS entry pressure? Poorly sorted VS well-sorted sand Sand VS silt |
A poorly-sorted sample tends to have a LOWER entry pressure than a well-sorted one, (and its imbibition/drainage curve may be step-wise as well) A smaller grain size means a HIGHER entry pressure. |
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What is the difference between entry and displacement pressure? |
Entrypressure- the at which a non-wetting phase can FIRST can enterthe soil. The DISPLACEMENT pressure- the pressure required to make thenon-wetting phase form a connected pathway |
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What does stage 1 of a DNAPL spill look like? |
**Active source** the DNAPL spills downwardsthrough soil and pools on low permeability layers, creates vapors above thewater table and dissolves into the groundwater and plumes sideways into themoving water |
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What does stage 2 of a DNAPL spill look like? |
Sourceis OFF- DNAPL still pooled/stuck in top of low-Permeability areas. now weare moving back down along the imbibition curve. DNAPL may have travelled into rockfractures |
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What does stage 3 of a DNAPL spill look like? |
Vaporous phase present in the unsaturated layer.SOME residual, non-dissolved DNAPL phase present in phreatic zone. DNAPL poolson top of low K layers and some diffused into the rock matrix and layers of low K |
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What does stage 4 of a DNAPL spill look like? |
No NAPL left in the unsaturated layer, just vapourous phase. SOME DNAPL left pooled on top of low K layers but no residual remaining, (has also Diffused into layers of low K, at rates of cm/yr). NO DNAPL left, all dissolved phase |
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What does stage 5 of a DNAPL spill look like? |
Backdiffusion from low K areas (rock matrix and clay lenses) back into GW asdiffused phase and desorption. |
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What does stage 6 of a DNAPL spill look like? |
No more contaminant left. unattainable except for literally removing all of the rock and replacing it, so unattainable on human timescales. |
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What kind of well is best used to screen a contaminant plume? (this is a mean question) |
Use multiple monitoring wells! that way you can constrain concentration with depth and not just get an average concentration profile |
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Generally, the BODY of a rock isentirely ______, so the fractures are much better ______ for contaminantes (areas of very high ________). However, thebulk rock contains almost all of the ______! |
Generally, the BODY of a rock is entirely impermeable, so the fractures are much better conduits for contaminants (areas of very high permeability). However, the bulk rock contains almost all of the porosity! |
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Consider a dissolved contaminant entering a system of rock fractures. How far will teh water go relative to the contaminant phase? |
The water will infiltrate MUCH farther than the contaminant as the contaminant will diffuse into the rock in all directions away from the fracture |
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Why is spilling a DNAPL onto a limestone outcrop so much worse than onto a prous medium? |
The fracture densiy of a limestone is much lower, so the oil will travel MUCH farther in the limestone because the flow-through volume is smaller |
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What are the three ways we can produce water from a soil? |
Drain the pores of an unconfined aquifer In a confined system, water will expand due to a drop in pressure In a confined system, the soil structure can collape |
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Compare and contrast dispersion and dispersivity |
NO CLUE, HONEY. I'll ask. |
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What is the only way to compeltley remove water from a sample of porous medium? why is this? |
Heat it up until it boils off; if you force air and more air into soil, there will always be a residual phase of water stuck in the soil (P_c will increase indefinitely but stauration will stay the same) |
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If we pump from the blue soil, what actualsaturation of water (S_y) can we remove from it? what is the *theoretical* maximum saturation you could extract? |
0.3 (distance from asymptote where P_c increases but saturation dowesnt drop to the originial saturation) The theoretical maximum saturation you could extract is the porosity of the soil. for some reason saturation here i think is represented by "theta" |
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Explain what occurs when soil structure collapses that would cause water to be forced out? |
The pressure suddently drops, and the water expands but cannot compress as effectively as air, so it is forced out of the pore space. |
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Storativity is the ______ of water released from a _____ of ____ per unit decline in _____ _____ in the aquifer, per unit _____ of the aquifer. |
S= bS_s + S_y Storativity is the volume of water released from a volume of soil per unit decline in hydraulic head in the aquifer, per unit area of the aquifer. it is unitless. Recall that hydraulic head is a measure fluid energy per unitweight |
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Define "Specific yield" |
the Volume of water that we can pull out of an aquiferby desaturating it; in a confined aquifer, this value is zero! AKA "Drainable porosity) |
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In a Hvorslev slug test, what parameters are plotted on the x- axis? |
(H- h)/(H- h_o), or the RECOVERY WHERE H is the hydraulic head before teh slug test even begins, h_o is the hydraulic head the instant the water is added or removed, and h is the hydraulic head that varies with time as the test progesses) |
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In a Hvorslev slug test, what do each of the parameters mean? given that K=r^2*ln[(L/R)] What tow parameters have to have a ratio greater thanf 8 for the test to be valid? |
r is radiusof the well
L is thelength of the screen R is theradius of the sand pack/casing T_o is the time when revoery=0.37 (time when (H- h)/(H- h_o)=0.37) |
