EVT: GEOL350 Final Flashcards
Hydrology
study of freshwater (surface and groundwater) in the environment
Hydrogeology
study of how freshwater moves through soil, sediments, and rocks
where is water stored (3)
- glaciers
- plants
- groundwater
why study groundwater? (3)
- drinking water
- industrial and commercial uses
- maintains stream flow
driving force of the hydrologic cycle
water/solar radiation
major components of hydrologic cycle (4)
- evapotranspiration
- condensation
- precipitation
- storage
what is the equation for porosity
n = (Vpores/Vtotal) x 100 = Apores/Atotalx100
porosity symbols and units
symbols: environmental - n, oil and gad - Ø
units: %
types of porosity in consolidated material (3)
- primary
- secondary
- vesicular
what is primary porosity
‘depositional or original porosity,’ formed on surface of Earth when sediments deposited
what is secondary porosity
‘induced porosity,’ forms in rock after lithification (sed) or crystallization (ign,met).
types of secondary porosity (2)
- Solution
2. Fracture
What is solution porosity
Secondary porosity that forms in rocks after dissolution by an acid. Ex., seen in MgCO3 and CaCO3 when dissolved by H2CO3.
what is solution porosity called in carbonates
vuggy porosity
what is fracture porosity
Secondary porosity that is typically formed by breaking of the rock under stress.
What is a fissure
It is a special fracture porosity only found in basalts. It happens due to the differential cooling of volcanic rock.
What type of porosity is found in clastics? (Ex., sandstone)
Intergranular porosity
What influences porosity in unconsolidated sediments? (3)
- Particle arrangement (cubic vs. face centered)
- Grain shape
- Grain size distribution (sorting)
Why do clays and shales tend to have higher porosity
It is due to their platelet shape which allows for greater compressibility.
Why do unconsolidated sediments have greater porosity than rocks?
No cement means more volume in between particles which is space to hold water.
Why is porosity of sand and silt approximately the same
Porosity is not affected by particle size
why is there such a large range in porosity in a sed/rock group? (4)
- Particle arrangement
- Grain size distribution
- Grain shape
- Fracturing
What is karst limestone
Limestone that is above ground.
Why is porosity greater in karst limestone than in limestone/dolomite?
karst limestone is above ground and more exposed to weathering and dissolution. this results in the formation of caverns and sinkholes.
what affects permeability (2)
- pore throat diameter (Dpt)
2. sorting
what is the main contributing factor to permeability
pore throat diameter (Dpt)
permeability: symbols and units
symbols: k
units: m2 or d
how to estimate ravg for permeability equation (based on grain size distribution) (2)
- well sorted = measure and average the size of all grains
2. poorly sorted = rsmallestgrains = D10
darcy’s law
describes volumetric flow rate of groundwater through a cross sectional area of porous sediments or rock
Q (what, units)
specific groundwater flow (m^3/s)
q (what, units)
specific discharge (m/s)
i (what, units)
hydraulic gradient (unitless)
K (what, units)
hydraulic conductivity (m/s)
Darcy’s law equations states (4)
- Q ∝ △h
- Q ∝ 1/△l (due to friction)
- Q ∝ k ∝ K (aquifer composition)
- Q∝ A
Groundwater flow and direction are influenced by (2)
- hydraulic conductivity
2. hydraulic gradient
Hydraulic conductivity is influenced by (2)
- rock properties
2. fluid properties
when calculating K, what assumptions made about fluid properties (2)
- fresh water only
2. constant T and P
Hydraulic Gradient
describes the path flow the Q (volumetric flow rate) will take
Major driving forces of groundwater flow (2)
- gravitational force (z/elevation head)
2. pressure force (h/elevation of water column)
Head creates _____ ______ in an aquifer
Internal pressure
P = N
kg/m x s^2
specific discharge/darcy’s flux (def/eqn)
determine flow velocity through a media. q = v x n (open tube: n=1, porous media n=%)
an aquifer’s quality is determined by it’s (2)
- storativity
2. transmissivity
transmissivity (def/eqn/units)
a measure f how much water transmitted horizontally through saturated part of an aquifer. T = b x K. units = m^2/day, gal/ft x day
storativity eqn and def
S = Ss x b
“Storage coefficient,” volume of water that will be absorbed or expelled from storage per unit surface area per unit change in hydraulic head
Specific Storage (symbol/def/units)
Ss. Amount of water per volume of a formation that is stored or expelled per unit head. m^-1 or 1/m.
why are units for specific storage m^-1 (1/m)?
Ss = vol h2o/ area x head = m ^3/ m^3 x m = 1/m
specific storage equation
Ss = pw x g (α x n x β) α is the compressibility of the mineral matrix, β is the compressibility of water.
why is water stored or expelled from an aquifer? (2)
- compressibility of water and mineral grains
2. fluctuations in the water table (unconfined)
Compare storativity in confined and unconfined aquifers
Confined: S = Ss x b, average S <0.005, S due mainly to compressibility of mineral matrix. As water is withdrawn from aquifer it remains 100% saturated.
Unconfined: S ≈ Sy, avg S 0.02 - 0.3, S due mainly to fluctuations in the water table
facies change
changes in depositional environment within a single rock unit
types of spatial variability (2) and what it is based on
- homogeneous
- heterogeneous
based on whether or not geological properties (K, n, degree of cementation) vary by location
What geological features influence heterogeneous spatial variability?
ign/meta and carbonates:
- layering
- fractures
- facies change
- thickness
- porosity in carbonates
Types of directional variability (2) and what it is based on
- isotonic
- anisotonic
based on whether or not geological properties are dependant on direction of measurement.
Causes of anisotropy (3)
- imbrication (like dominoes)
- clays
- basalts (Kh (interflow zones)»_space; Kz (columnar jointing))
bulk hydraulic conductivity is based on and differences between two
based on whether the layers/beds are in a series or parallel to each other
parallel: Kb most influenced by most permeable bed
series: Kb most influenced by least permeable bed, Kb varies with direction
types of soil classification systems (4)
- unified
- wentworth
- engineering
- USDA triangle
what is unified soil classification system?
- universally accepted
- gravel and sand is 2mm (same as wentworth)
gravel | sand | silt/clay |
what is wentworth soil classification system?
- used for clastics/ sed rx
- 2mm seperates sand and gravel
gravel ——> conglomerate, breccia
——2mm——–
sand ——> sandstone
—- 1/16 mm ——-
mud ———> siltstone, shale
—- 1/256 mm ——
what is engineering soil classification system?
% grains descriptor 30-50 and - 20-30 -y, -ey 12-20 some - 5-12 little - >5 trace -
write them in order of decreasing %
what are the three points of the USDA triangle
100% clay
△
100 % sand 100% silt
what must be included when describing soil in field (10)
- primary (GRAVEL)
- secondary (gravel)
- color
- moisture
- coarse - density
- fine - consistency
- original geologic formation
- foreign material
- odour
- presence of contaminants
what is the difference between describing fine and coarse sand in the field?
coarse is based on density while fine is based on consistency
what type of soil field analyses available? (2)
- jar test
2. eyeballing
Examples of eye balling measurements (3)
- boulders - basketballs
- fine sand - icing sugar
- fine gravel - pea
how to do a soil jar test (3 steps)
- shake up and let settle
- measure each layer thickness
_________
mud ------ silt ------ sand ------------------ 3. find % to plot on USDA triangle layer b/total b x 100
what type of lab analysis available for soil? (3)
- sieve analysis
- hydrometer
- atterberg method
what property of a soil determines which lab analysis done?
grain size: coarse (sieve analysis) vs. fine (hydrometer)
what are the standard sieves used in sieve analysis?
60 0.25mm |
100 0.15 mm | SAND
200 0.075 mm |
pan <0.075 mm | silt and clay
sieve analysis -> % finer and % retained
% retained = mass sieve / total mass x 100
% finer = 100 - sum of % retained on all sieves on and above
what is the purpose of D60 in well design
used as sizing criteria for holes in a well’s screen: >D60 into well during development
how to classify soil by sieve analysis (4 steps)
- sieve sample
- weigh each sieve
- put in chart and calculate % finer
- plot on particle size distribution curve
how does a hydrometer work?
based on the idea that particles will settle out of a fluid medium at different rates (based on particle size, weight, and shape)
how to do a hydrometer analysis (5 steps)
- 50 g oven-dried sample
- place in sediment cylinder
- create soil suspension
- insert hydrometer
- measure soil still in suspension
cohesiveness
describes the ability of a soil to be reshaped in the presence of some moisture without crumbling
classification of fine grained soils is based on (2)
- grain size (hydrometer)
2. plasticity (atterberg method)
what is cohesive behaviour in soils attributed to? (2)
the presence of clays in soil and their ability to adsorb water
differences between cohesive and consolidated
cohesive: fine sediment, degree depends on water content
consolidated: clastic rocks, created by chemical bonding that cements grains together
when is the atterberg method used?
to describe the consistency and plasticity of fine grained soils
how to do the atterberg method (4 steps)
- determine plastic limit (PL)
- determine liquid limit (LL)
- determine plasticity index
PI = LL - PL - plot on plasticity chart (x: PI, y: LL)
what is the plastic limit (PL)
moisture content of a soil at which it will crumble when its rolled into threads
what is the liquid limit (LL)
moisture content of a soil required to close a distance at bottom of groove after 25 blows
when and when not to use three point method to calculate hydraulic gradient
when: few wells, but at least 3
when not: many wells on a contour map
steps to the 3 point method to calculate hydraulic gradient (5)
- draw a line from well with highest to lowest head
- find out where on that line well with intermediate head would be place
distance from lowest = (int - low)(line)/ (high - low) - draw a line from int head well to place on first line where it should be
- on new line draw a line from highest head well that intersects this line @ 90 degree
- i=h/l calculation on this final line
flow nets
a geographical way to represent 2D groundwater flow
flow net assumptions (2)
- unit is homogeneous and isotropic
2. in a steady state (Qin = Qout)
what are equipotential lines?
They are like contour lines, joint points of equal head together in a single aquifer
what are flow lines
Flow lines intersect equipotential lines at 90 degrees and they show the path of groundwater flow through an aquifer.
what is a hubert section
a vertical flow net map
what is a regional system of groundwater flow
there is a single recharge and discharge area
localized groundwater flow systems
multiple localized flow systems surrounded by an intermediate flow system surrounded by a regional flow system
why create squares when constructing flow nets?
so each flow tube has about equal volumetric discharge (Q)
what is a flow net called for a confined and an unconfined aquifer?
confined: potentiometic map
unconfined: water table map
what are the types of boundaries? (3)
- impermeable
- water table
- constant head
what creates an impermeable boundary (2)
- geology, impermeable beds like granite or shale
2. planes of symmetry -> water flows away from drainage dividers
why is a constant head boundary created?
aquifer meets up with an area with constant head like a lake or a river -> flow lines intersect the constant head boundary at 90 degrees
drilling terms: make footage
drill as fast as possible
drilling terms: cavings
pieces of sides of borehole will cave in
drilling terms: lost circulation
drilling fluids/muds leave leachate -> lost in subsurface (due to the hydraulic conductivity of the formation)
drilling terms: mud cake
“filter cake,” build up of solids on leachate wall
drilling terms: cuttings
“chips,” very small pieces of rock created by drill bits during drilling
drilling terms: lag time
time between chips down hole to when they appear on the surface
drilling terms: tripping in / out
time to pull drill bit out of hole
drilling terms: fishing
drill-less, loggers lost drill and they are trying to find (very expensive)
how to choose which drilling method to use (6)
- cost
- site accessibility
- depth
- geology
- program purpose
- equipment availability
which drilling method to use based by cost
hand auger, cable tool
which drilling method to use based by site accessibility
site accessibility - hand auger
which drilling method to use based by depth
depth - deep: conventional rotary; shallow: driven, direct push, hand auger
which drilling method to use based by geology
geology: unconsolidated: driven, direct push, rotary bucket, hand auger BUT NEVER AIR; bedrock: air rotary and air hammer.
which drilling method to use for water supply well
cable tool, rotary (any), air
which drilling method to use for representative samples
direct push
which drilling method to use for gravel
becker hammer
what is a driven well
‘drive point, sand point;’ installed by hand using a sledge hammer, percussion, or a driver head.
what is a direct push well
hydraulic unit mounted on a truck -> pushes a steel core barrel into the ground
what are the types of auger well (4)
- rotary bucket
- solid stem
- hollow stem
- hand auger
what to install a monitoring well into unconsolidated sediments?
put well assembly into hollow stem before removing auger from borehole
cable tool wells
‘percussion drilling, spudder rigs;” earliest develop drilling method. simple -> life, drop, and then rotate a heavy drill bit thats on the end of a cable
what do drilled well require
use of drilling fluids
two types of drilled wells
conventional and reverse rotary - depends on the direct of mud flow
types of drilling fluid (4)
- water
- air
- chemical foams
- mud
how does rotary drilling work? (3)
- rotation of a drill bit on end of drill pipe at high speeds
- drilling fluids pumped down drill pipe and out drill bit
- fluid picks up cutting from bottom of well and they go to surface through the annulus
disadvantages of drilling with mud (2)
- mudcake build up (can seal off a low yield aquifer)
2. Pmud»_space; P formation (can break into or contaminate formation)
purpose of drilling fluids (4)
- lubricate drill bit
- coat drill bit
- bring chips to surface
- mudcake over permeable zone
why bring chips to surface? (2)
- save money by not stopping drilling
2. bit doesn’t get stuck
why want mudcake over permeable zones? (2)
- stops lost circulation
2. stop further formation contamination
how to choose what drill bit to use
based primarily on geology
common drill bits (3)
- drag |____|
- roller cone \/
- diamond core -——*
disadvantage of rotary mud drilling
not good for representative samples
advantages of rotary mud drilling (2)
- fast
2. very food for high pressure aquifers that are deep
why do you want P mud»_space; P formation?
prevents blowouts -> happen when formation fluids reach surface quickly
what is a becker hammer?
special type of reverse rotary drilling method -> can deal with gravels (very important in alberta)
can a well be straight but not plumb?
yes
plumb well
borehole will track an imaginary line to the surface of the earth
straight well
perfect alignment of casing sections, more important than a well being plumb
drilling safety (3)
- PPE
- line locates
- drugs/alcohol
potential water system clients (5)
- residential households
- agricultural farms
- livestock operations
- municipalities
- industrial users
a water well producing _____ gpm is minimum for household use
0.5
water well producing ___ to ___ gpm do not require additional storage capacity
5, 10
how to choose a drilling contractor (2)
- on alberta list of approved drillers
2. local experience (knowledge of formations, depths, and any problems
how to choose a well location (3)
- maximize well yield
- minimize contamination potential
- maximize safe well operation
well information sources (4)
- door to door
- ab geologic survey
- ab groundwater database (free, yikes)
- local hydrogeologic reports and maps
considerations in choosing well location (4)
- geology of area (thickest aquifer = greatest yield)
- contaminant location (always build upgradient)
- accessibility (cleaning, testing, monitoring)
- ground sloping away from well (or able to artificially mound)
types of water wells - based by way drilled (4)
- dug (hand)
- driven/setted (hydraulically)
- bored (auger)
- drilled (rotary)
general components of water well design (4)
- casing
- intake design
- annulus fill
- surface considerations
casing is usually made of
plastic (never recycled)
minimum inside diameter of casing
10.16 cm
minimum casing extension above ground level
> 60cm historic flood record
intake design considerations
want to allow water, but not sediment, to enter well during production (D60). intake only across saturated aquifer
types of intake screen and formation material best suited for (2)
screens - unconsolidated sediment (regular hole pattern)
slotted casing - consolidated sediment (irregular hole pattern)
types of annulus fill (2)
- annular seal
2. filter/gravel pack
purpose of annular seal (2)
- prevent surface contaminants from entering well
2. prevent fluids from uphole zones from entering aquifer
annular seal materials (3)
- clay
- bentonite
- grout (mix of clay and bentonite)
purpose of filter pack
paced in annulus of fine grained aquifers to increase well yield
surface considerations (law) (3) and how to solve each
- ensure surface water cannot enter well (mounding)
- water well covered to stop things (animals/people/etc) from falling into well (capped and locked)
- prevent contamination (pump house contains only well and pump)
after well installed, driller must do following before well can be used (3)
- development
- disinfection
- yield test
well development purpose (2)
- increase yields
2. clean up well
what happens during well development
removal of fine sediments and muds from intakes as well as introduced water
well development methods (3)
- overpumping: pump h2o out until clear
- surging: high pressure air or water through
- jetting: high pressure air or water in and out
what is a naturally developed well
non cohesive sediments (coarser components) left around intake after well development
what is a gravel packed well
sand/gravel filter place in annulus - used if well drilled in bedrock or cohesive sediments
how to disinfect a well
200 mg/L Cl for at least 12 hours
yield test purpose (2)
- rate to pump well
2. depth to place pump
safe pumping rate
rate at which a well can supply water for an extended period without lowering level below pump intake
pump must not lower water level below (3); also, why is this?
Water level not below: 1. aquifer 2. perforation 3. pump intake don't want to introduce bacteria or air into aquifer
what do you have to submit to AEP to get a well license? (2)
- general stratigraphic log
2. well construction and design details
in order for geophysical methods to work….
differing physical or chemical properties must be present in earth material and water
geophysical survey are an ______ method of subsurface assessment
indirect
how to interpret data from geophysical survey
correlate data to core, cuttings, or stratigraphic logs
geophysical survey general steps (4)
- generate energy waves at or near surface
- waves pass into subsurface
- wave returns to subsurface -> recorded on receiver
- recordings are then processed and interpreted
noise
disturbances that obscure or reduce clarity of signal that you want to interpret
geophysical survey provides information on subsurface: (4)
- stratigraphy (thickness and rock types)
- structural features (orientation, folding, faulting)
- groundwater (delineate contaminant plumes, depth to water table)
- man made inclusions (like a buried drum)
types of geophysical surveys (2)
- seismic
2. EC/resistivity
seismic survey energy types (3)
- p -waves : primary/compressional waves that are interpretation target
- s-waves
- surface waves
Seismic survey types (4)
- hammering on a metal plate
- drop a heavy ball
- dynamite in a borehole
- vibroesis trucks
EC/resistivity surveys measure
ability of a subsurface formation to either transmit (conduct) or impede (resist) movement of an electrical current through it
ability of a formation to conduct electrical current is dependant on (3)
- porosity
- pore water volume
- type of pore fluid
types of conductivity surveys (2)
- ground penetrating radar (GPR)
2. em survey
use EC/resistivity surveys to see (2 examples)
- water table (conductivity zone saturation > conductivity zone aeration)
- contaminant spills (conductivity water > oil)
compare conductivity surveys (2)
- GPR: transducer on wagon/sled, measure time taken for wave to move above ground, time = depth
- EM survey: transmitter coil, measure strength of electric field to see areas of high and low conductivity
GPR uses (3)
- locate shallow waste sites
- water table
- depths
always confirm geophysical readings by
taking soil and groundwater samples of the area
EM survey tools (3)
- EM 31 - single person long boi medium depth
- EM 34 - double person split transmitter and receiver deepest depth
- EM 38 - run alongside EM 31 kinda like a metal detector as it is very shallow
EM survey advantages (4)
- very mobile
- non invasive
- quick turn around time
- lower cost
types of resistivity surveys (2)
- ERI (imaging)
2. ERT (tomography)
what type of current does a resistivity survey use?
direct and low frequency
is resistivity survey invasive?
yes, current is generated between two spikes drilled in ground
what does resisitivity survey measure
record voltage drop when it encounters resisitivity
resistivity survey electrode arrays (3)
- wentworth: receiver inside source
- schlumberger: source inside receiver
- dipole-diple: source beside receiver
two different ways to perform resistivity survey
- electrical sounding: depth, change space of electrodes to record different depths (wentworth and schlumberger)
- horizontal profiling: lateral, move along grid at the same depth
resistivity survey uses (3)
- locate faults and vertical fractures
- locate buried stream channels
- outline areas of saline groundwater
examples of saline groundwater would want to monitor (2)
- oil and gas - contamination from brine or flare pit
2. natural - saltwater intrusion of coastal aquifers
Increase transmissivity = _______ in aquifer quality
Increase
Transmissivity Ranges (low, medium, and high yield)
Low Yield: <100 gpd/ft (good for domestic waste water well)
Medium Yield: About 10 000 gpd/ft (good for industrial, municipal, irrigation)
High Yield: 1 million gpd/ft
Specific Yield
Volume of water absorbed or expelled from storage per unit surface per unit change in water table elevation
Drawdown (symbol/def/eqn)
”s,” distance between static water level (SWL, H) and pumping water level in well (PWL, h). Also, seen as the distance between cone of depression and static water level.
“s” = PWL - SWL
“s” = h - H
Static Water Level (other names/def/measured in)
SWL, Static Water Table, h
Level of water in a well that is not being affected by groundwater removal (natural level based on natural pressures)
Measured as mbgs, mbTOC
Pumping Water Level (other names/def/general rule)
Dynamic Water Level, PWL, H
Level of water in a well during pumping. General rule is that this should never be lower than pump location.
Cone of Depression (names/def)
COD, Area of Influence
Depression in water table (unconfined) or in potentiometric surface (confined), looks like an inverted cone, and forms around a pumping well.
Where PWL meets SWL.
Cone of Depression size dependant on (3)
- Pumping rate of well
- Aquifer properties (T, S) Example - if you decrease transmissivity then the COD will increase because cone will deepen and widen.
- Pumping duration. Example - if you increase pumping duration it will increase the time taken which increases the COD.
Residual drawdown
After pumping stopped - water level will gradually return to static, during this time distance between PWL and SWL.
Radius of Influence (def/couple facts)
Radial distance from centre of a pumping well to point where water table or potentiometric surface no longer lowered.
Can be estimated from a distance drawdown graph.
Good to know for high capacity water wells.
COD continues to expand until (4) (reaches equilibrium state, so water in = water out.)
- Captures enough groundwater flow in aquifer
- Intersects surface (river, lake) water
- Vertical recharge (precipitation in unconfined.)
- Vertical leakage from overlying aquitards.
Aquitard
Retarding water flow (slowing it down) - still some flow, just not useful for us to withdraw
Well Yield (symbol/units/def)
y
m^3/sec, gpm
Volume of water per unit time discharged from a well either by pumping or free flow
Specific Well Capacity (symbol/def/eqn/units)
sc
Rate of discharge of a water well per unit of drawdown
sc = (pumping rate/ ‘s’) = (Q/’s’) = (well yield/drawdown)
m^2/day, gpm/ft
Specific well capacity generalization for unconfined and confined aquifers
Unconfined: will decrease as drawdown increases because water will no longer be through entire thickness of saturated aquifer - decreases yield
Confined: may not remain constant as pumping time increases in a confined aquifer if well dewatered (2 x well yield = 2 x drawdown)
Well efficiency (2 rules, symbol, equation)
Only for confined aquifers and efficiency typically 70 to 80 %
E
E = (drawdown aquifer/drawdown well) x 100 = (drawdown outside casing/drawdown in pumping) x 100
Loss of well efficiency can be result of (3)
- Clogging of screens by fine material
- Inadequate well development during construction
- Insufficient screen length (doesn’t cover entire length of aquifer)
Infinite Areal Extent
Under ideal conditions an aquifer is assumed to have no boundaries
Types of aquifer boundaries (2)
- No flow, impermeable, negative: impermeable. Ex., a rock unit laterally like shale
- Recharge, positive: infinite permeability. Ex., like a surface body of water like a lake
How do aquifer boundaries affect drawdown (2)
- No flow: no additional water can be added to aquifer - must increase drawdown significantly to supply well
- Recharge: drawdown eventually stabilizes
Vertical leakage
water leaks from saturated rock layers above an aquifer
Pump tests can be used to (9)
Estimate:
- transmissivity (T)
- storativity (S)
- hydraulic conductivity (K)
- radius of influence
- specific capacity
- well efficiency
And:
- Determine presence of non-ideal conditions like boundaries
- Collect representative groundwater samples for analysis
- Meet permit requirements
Constant Rate Pumping Test Procedure (7)
- Install pumping test equipment
- Check pump operation (pump 30 seconds) to see if everything is working properly
- Aquifer recovery - check return to static coniditions
- Perform a step drawdown test - determine most appropriate rate during this test
- Aquifer recovery
- Perform long term constant rate test ($$$ and several days)
- Aquifer recovery
What is pumping test equipment (5)
- pumping and monitoring wells
- submersible pump and power supply
- flow meter, flow control, and flow check (must have constant flow rate)
- discharge line and storage facilities
- measuring tape
Consideration for discharge line used in pumping test
Can discharge to surface, but must be far away from pumping well because you don’t want to recharge aquifer in immediate vicinity. Must be >30m.
Why do a step drawdown test (3)
- Estimate drawdown for a long term pumping test
- Select pumping rate for pump test and final well production
- Gain preliminary information on T, S, and E
Step drawdown test process (3)
- Choose a pumping rate, pump @ that rate for 1/2 to 1 hour, record drawdown vs. time
- Choose a new, higher pumping rate and repeat step 1
- Repeat step 2 four to six times with increasing higher pumping rates
Theis assumptions used to model groundwater flow
Aquifer is: 1. homogeneous and isotropic 2. infinite areal extent and thickness 3. perfectly confined above and below by impermeable layers Pumping well is: 4. penetrates and receives water from full saturated aquifer thickness 5. 100 % efficient And... 6. pumping occurs at a constant rate 7. no other pumping wells in area
Simplified version of theis equation
cooper-jacob line method of analysis
cooper-jacob line method of analysis can be used without signifcant error if… (2)
- pump test is sufficiently long
2. distance between pumping and observation well is sufficiently small
why are pump tests expensive
must have 1 pumping well and 1 to 3 observation wells
only well test that works in unconfined aquifers
single well response test
single well response test
performed on small diameter monitoring wells - water level is suddenly raised (slug test)/lowered (bail test) and then well response is measured by monitoring water returning to original level
can only use hvorslev equation if
L/R > 4
compare pump tests to single well response tests by
- cost
- well types
- length of test
- major requirement
- aquifer properties - certainty
- aquifer properties (T, S, E)
- cost
pump test- 10’s thousands
single well- inexpensive - well types
pump test- 1 pump + 1 to 3 monitoring
single well- 1 monitoring - length of test
pump test- several days
single well- seconds to hours - major requirement
pump test- constant pumping rate, confined only
single well- instantaneous h2o levels change - aquifer properties - certainty
pump test- more accurate due to test length
single well- low - aquifer properties (T, S, E)
pump test- T/S/E
single well- Tr
chemicals dissolve in groundwater can be transported through the subsurface by (3)
- molecular diffusion
- advection
- mechanical disperrsion
if groundwater is not moving can ionic and molecular species migrate?
yes, through the process of diffusion
solute movement is driven by
concentration gradients (molecules move from areas of high to low concentration)
What law describes diffusion?
Fick’s law
what is D*
effective diffusion coefficient
D*=wxDm
w (what it is/eqn)
tortuosity coefficient
w = (straight line distance between ends of flow path)/ (actual length of flow path)
w depends on
sediment/rock type and packing arrangement of the grains (unconsolidated grains (0.5 -> 0.01)
diffusion main mechanism of contaminant transport where?
low ‘K’ zones like clay or aquitards
advection
process by which moving groundwater carries dissolved solutes along with it
if a contaminant moving solely by advection it is at the same rate as groundwater
mechanical dispersion
as contaminated water moves through an aquifer it mixes with the uncontaminated groundwater - results in dilution of contaminant with time
dispersion can occur in all three dimensions, like howwww
Longitudinal
1. along the flow path - x/horizontal
Lateral/transverse
- transverse horizontal (TH) - y
- transverse vertical (TV) - z
pore scale dispersion rules (3)
- pore size in aquifer (ex., if pore size smaller, than dpt is smaller, so there will be slower flow)
- longer flow paths slow down solute
- friction - if closer to grains, solute slows down
dispersion varies on ____ and ____ scales
macro, micro
what does ‘dispersivity is scale dependent” mean?
longer the transport distance, the greater the dispersivity
contaminant plume vs. slug
plume - formed from continuous contaminant loading, moves outward from a source over a long period of time
slug - formed from pulse loading, one time release of contaminants into the subsurface
hydrodynamic dispersion (HD)
combined effects of molecular and mechanical dispersion (contaminant concentration changes over time)
examples of seeing hydrodynamic dispersion (HD) on a breakthrough curve (2)
- spreads contaminant out over a larger area
2. concentration of contaminant is less at any time or location than what it was originally
how to measure breakthrough curve
- fill a column with porous media like sand
- have water flow through column at a constant rate
- at t=0s add tracer to water flow
- concentration of tracer at column outlet (C/Co) is then measured at different times
breakthrough curve
demonstrate the effects of hydrodynamic dispersion and advection on the flow of contaminants through the subsurface
plot of concentration (C/Co) vs. time (t) at the column outlet
retardation
describes any physical or chemical process which causes solutes to flow at a slower rate than would be predicted by advection alone
what are the two main groups solutes can be grouped into?
conservative and reactive species
conservative species
will only show a decrease in concentration in groundwater because of the effects of dispersion and/or diffusion
reactive species - process that will change concentration of solute over time (3)
- reacting with groundwater or aquifer matrix
- biodegradation
- radioactive decay
adsorption (def/example)
usually occurs due to charge imbalances on surface of a mineral matrix
example - clays typically negatively charged and therefore attract/adsorb cations
Kd (what/def)
distribution coefficient
represents the partitioning of a compound between and liquid phase (groundwater) and a solid phase (aquifer matrix)
Kd used to
calculate the retardation of a solute as it moves through soil
increase kd = increase adsorption and therefore there is slower movement through aquifer
general rules of retardation (3)
- if a solute is not adsorbed kd=0
- if kd=0, then R=1 and it is a conservative species
- if R=2, solute travels 1/2 velocity of groundwater
what type of tracer to use for
- clay
- soils with heavy metals adsorbed
- clay - Cl-, negative won’t get trapped in clay
- soils with heavy metals adsorbed - don’t want these metals to move into groundwater, so don’t acidify because H+ is small and can knock metals out of lattice
why can clays greatly retard the movement of some inorganic solutes by adsorption? (2)
- large surface area
2. charge imbalances
how are synthetic organic chemicals retarded in the subsurface?
adsorption onto organic matter in the soil
Koc (def/rule)
partitioning soil-water coefficient of a compound
low Koc = low adsorption = high solubility = less retardation = more mobile
estimate Koc by (2)
- solubility in water
2. octanol-water partitioning coefficient (octanol is organic C)
ADE (what/def)
advection-dispersion equation (ADE)
describes the movement of solutes through sediments
ADE dependant on (2)
- centre of mass of solute is moving at the same rate as the groundwater velocity (advection)
- hydrodynamic dispersion causes the solute to spread out both ahead and behind the centre of mass in a pattern that follows statistical normal distribution
ADE equation
longitudinal flow (dispersion) + dispersion @ 90 to main flow direction but in horizontal phase + dispersion in vertical direction + advection (main flow direction)
geochemical reactions and resulting groundwater composition are the result of (3)
- initial groundwater composition
- sediment/rock type of the aquifer
- chemical reaction rates and controls
why is most groundwater alkaline/basic?
in uncontaminated groundwater much more dissolution of carbonate and silicate minerals occurs than ionization of strong acids
6 major ions in groundwater (90% of TDS)
- bicarbonate
- chloride
- sulphite
- sodium
- calcium
- magnesium
There is usually < ___ mg/L organic matter in groundwater because of ….
<0.1mg/L
due to oxidation (aerobic respiration) of organic matter as it moves through soil
Reccommended limits and why for these drinking water components
- iron and magnesium
- zinc
- nitrates
- iron and magnesium
Fe <0.3 mg/L, mg <0.05 mg/L
aesthetics because at higher concentrations these will precipitate out of groundwater and stain sinks and tubs - zinc
<5.0 mg/L
bad taste at higher concentrations - nitrates
<45 mg/L
cause methemoglobinaemia (blue baby syndrome) and gastric/stomach cancer
TDS (what, units)
total mass of all dissolved chemicals per unit litre of water
units: mg/L, ppm
Water category + where typically found
- fresh
- brackish
- saline
- brine
- fresh
- brackish - coastal marshes and estuaries
- saline - sea water
- brine - very deep and old groundwater, oil and gas production
TDS can be measured by (3)
- directly - dry water sample, weigh solids
- indirectly - lab analysis, sum concentrations of major ions
- approximately - multiply water conductivity by a constant
EC values are usually normalized to a ______ ______ as EC ______ with temperature
certain temperature, increases
what affect chemical composition of groundwater (4)
- lithology
- temperature
- porosity
- rate of water flow
what is the TDS of sea water?
approximately 35000 mg/L
what is the chebetov sequence?
the chart in equations book that shows water categories and TDS associated. this was developed by analyzing 10 000 groundwater samples
chebetov discovered that groundwater tends to
evolve with time towards (and past) a composition similar to sea water
over time, the _____ _______ changes in groundwater. this change is seen as three stages (list)
dominant anion
change in stages
- young - HCO3
- middle aged - SO4
- old - Cl-
Changes in groundwater over time can be explained by (2)
- mineral availability - what minerals groundwater comes into contact with
- mineral solubility - as solubility increases so does the influence on groundwater chemistry
HCO3 is the dominant anion in almost all ________ areas. It originates from … (2)
recharge areas
- Soil Zone - CO2 in soil water from atmosphere, respiration of animals, and decomposition of organic matter
- the minerals dolomite and calcite that dissolve rapidly when in contact with CO2 water
groundwater usually travels __ ______ distance before SO42- is the dominant anion, this is because SO4 is ___ ________ than HCO3 but it is in _____ ________. Minerals that contribute to this are _____ and _____
a long distance
more soluble than HCO3, but in smaller concentrations
minerals that contribute are gypsum and anhydrite
old groundwater is associated with Cl- which is from the minerals _____ and _____ which together form _____
halite, potash, sylvinite
least soluble minerals have the ______ effect on young groundwater due to _____ concentrations
greatest, high
why do some groundwater system never evolve beyond the HCO3 or SO4 composition?
because there are no Cl- containing minerals present in the basin
groundwater from precipitation to depths of basin (2 steps)
- precipitation arrives with DO at near saturation levels
- water travels down to water table, in this area bacteria remove DO as they oxidize organic matter. DO will be present but lower than in overlying sediments.
Once all of the DO is consumed, other microbes can biodegrade remaining organic matter by using e- acceptors other than O2.
Oxidizing agent is used in preferential sequence (4)
1. NO3 -> N2 denitrification 2. Fe 3+ -> Fe 2+ iron reduction 3. SO42- -> HS- -> H2S sulfate reduction 4. CO2 -> CH4 methane fermentation
the main formats used to display major ion chemistry are (4)
- collins diagrams
- pie diagrams
- stiff diagrams
- piper plots
what does a collins diagram look like
its a bar graph with a bar for cations followed by a bar for anions
how to plot a pie diagram for displaying major ion chemistry (3 steps)
- meq/L
- meq/L % (out of total)
- pie chart degrees (360 x meq/L % as decimal)
what are stiff diagrams good for and what do they show (2)?
a quick visual comparison to see if different water samples are from the same source. shows both water source and relative ion concentration
what does a stiff diagram look like
polygonal shape
what units do ion concentration need to be in to create a stiff diagram?
meq/L
what does a piper plot look like
grid triangles
piper plot procedure (5 steps)
- convert all ion [] to meq/L
- normalize cations
- normalize anions
- plot normalized on respective triangle
- transfer triangle points up to diamond
uses of a piper diagram (3)
- see relative proportions of major ions in water
- to compare numerous water samples to see if from same source or hydrochemical facies (seen as a cluster of points)
- to determine if changes in water chemistry are a result of waters mixing from different sources (seen as points in a straight line)
facies
identifiable parts of different nature (house: roof, floor, walls) belonging to a genetically related body of system (house)
hydrochemical facies
bodies of groundwater in an aquifer that have different chemical compositions
how to check routine lab ion analysis
use cation to anion ratio method - water should always end up being neutral so the acceptable range is within 1 +/- 0.05
ratio = sum cations/sum anions
what is the primary goal in designing a groundwater sampling program
delineate and monitor the extent of the contamination as cost effectively as possible
well locations need to be
placed both within and outside the contaminant plume
what are the three basic well types?
- sampling
- monitoring
- background
sampling wells placed ____ contaminant plume and tell you about the _____ and _____ of the plume, and the ______ and ______ of contaminants
placed within contaminant plume
tell you size and volume of plume as well as type and concentration of contaminants
monitiring wells are placed ______ contaminant plume
outside
background wells are placed _______ contaminant plume
upgradient
if a sampling well screen only covers a short vertical section of the aquifer it is called a ______ sample. Used primarily to detect _______ ________ of contaminants
Point sample
representative concentrations
If a sampling well screen covers a significant vertical section of an aquifer it is called a _______ sample. The concentration of contaminants is ______ but it is good for _____________
Non-point sample
concentration detected not representative as it will be diluted
good for detecting presence/absence
sampling well types (3)
- conventional water wells and piezometers
- nestled piezometers
- multilevel samplers
Conventional water wells and piezometers - ______ are installed to measure _______________ and are ______ samples
piezometers
measure water levels in an aquifer
non point samples
Nested piezometers - ______ are installed in ______________, and the screens are all at _________ ______
piezometers are installed in individual boreholes located in close proximity to each other and the screens are all at diferent depths
multilevel samplers - several _______ are placed in a single borehole with _________
piezometers
with intakes at various lengths
every sample taken in the field is sent to the lab but
quite often not all are analyzed
