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Hydrogeology > Properties of aquifers > Flashcards

Properties of aquifers Flashcards

1
Q

it is the capacity to do work

A

energy (J)

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2
Q

is equal to the product of net force and the distance through which the force moves

A

work (J)
work = force x distance

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3
Q

is equal to the product of mass and acceleration

A

Force
F=ma

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4
Q

is equal to the mass multiplied to the gravitational force

A

weight

weight = mass x gravity

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5
Q

it is the mass per unit volume

A

density

p = mass/volume

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6
Q

weight per unit volume

A

specific weight

y = gravity x density
y = weight / volume

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7
Q

is the force applied to a unit area perpendicular to a force

A

Pressure

P= F/Area

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8
Q

In hydrogeology pressure is measured relative to ____

A

atmospheric pressure

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9
Q

standard atm

A

1.013x10^5 Pa

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10
Q

What is a newtonian fluid

A

it’s resistance to relative motion is directly proportional to its dynamic viscosity

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11
Q

standard unit for dynamic viscosity

A

n.s/m^2

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12
Q

poise unit

A

g/s.cm

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13
Q

t or f: water is not a compressible fuid

A

F

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14
Q

the change in density is directly proportional to ____

A

change in pressure

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15
Q

proportionality constant for compressibility

A

bulk modulus n/m^2

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16
Q

unit for specific weight

A

N/m^3

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17
Q

unit for pressure

A

N/m^2

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18
Q

assemblages of individual grains that were deposited by water, wind, ice, and gravity

A

sediments

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19
Q

openings between individual grains

A

pore spaces

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20
Q

____, ____, and ____ in earth materials are important in the study of hydrogeology

A

cracks, voids, and pore spaces

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21
Q

it is the percentage of rock or soil that is void of material

A

porosity

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22
Q

porosity is defined mathematically by the equation:

A

n = 100Vv / V

where; Vv is the volume of void per unit volume of earth material

and V is the unit volume of earth material including voids and solids

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23
Q

explain immersion lab method

A
  1. known volume of sample is taken
  2. the sample will be dried under 105 degrees celsius until it reaches a constant weight
  3. sample is submerged into a known volume of water
  4. the volume of the porosity is equal to the difference in the initial volume of water and final volume
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24
Q

porosity that excludes pores that are too small and not interconnected

A

effective porosity

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25
Q

according to peyton et. al (1986), effective porosity is a function of ____ and ____

A

the size of the molecule ; the size of the passageways that connect the pores

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26
Q

it is the term that refers to the passageways that connect the pores

A

pore throats

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27
Q

t or f: pore throats are typically smaller than the pores

A

T

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28
Q

if the molecule being transported is greater than the pore throats this would

A

limit the effective porosity with respect to that molecule

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29
Q

the formula for total porosity is :

A

n = 100 [1-(Pb/Pd)]

pb - bulk density of aquifer
pd - particle density of aquifer

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30
Q

porosity for cubic packing and rhombohedral packing

A

47.65
25.95

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31
Q

the diameter of the sphere ___ influence the porosity

A

DOES NOT

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32
Q

porosity of well rounded sediments is _______ to the particle size and ______ to the packing

A

independent ; dependent

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33
Q

range of porosity for well rounded sediments

A

26-48%

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34
Q

if a sediment contains a mixture of grains of different sizes, the porosity will be ___

A

lowered

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35
Q

porosity is also affected by the ___ and ____

A

shape of grains
fabric/orientation of the praticles

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36
Q

classification for roundness

A

very angular
angular
sub angular
sub rounded
rounded
well rounded

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37
Q

classification for sphericity

A

prismoidal
sub prismoidal
spherical
sub discoidal
discoidal

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38
Q

sediments are classified based on the basis of ___

A

grain size

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39
Q

t or f: the larger the phi scale, the smaller the grain size

A

t

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40
Q

phi scale for gravel sediments

A

< -1.00

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41
Q

phi scale for sand sized sediments

A

4 - -1.00

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42
Q

phi scale for silt sediments

A

8-4

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43
Q

phi scale for clay sediments

A

14-8

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44
Q

other term for gravel, sand, and mud sediments

A

rudite, arenite, lutite

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45
Q

sediment diameter for clay particles

A

< 1/256

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46
Q

sediment diameter for silt particles

A

1/256 - 1/16

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47
Q

sediment diameter for sand particles

A

1/16 - 2

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48
Q

sediment diameter for gravel size

A

2 - >256

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49
Q

two types of grain size scale

A

used by soil scientists
used by engineers

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50
Q

us standard sieve series by soil scientists

A

gravel - 75mm
very coarse sand - no. 10
coarse sand - no. 18
medium sand - no 35
fine sand - 60
very fine sand - no 140
silt - no. 270
clay - N/A

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51
Q

separates sand from fines

A

200-mesh screen with 0.075 mm openings

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52
Q

sediments <0.075 mm in size are classified by ____ or the rate at which sediments settle in water

A

hydrometer test

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53
Q

a measure of how poorly or well sorted sediments are

A

uniformity coefficient

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54
Q

formula for uniformity coefficient

A

Cu = d60/d10

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55
Q

what is an effective grain size?

A

d10, size corresponding to the 10% line on the grain size curve

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56
Q

a sample with a Cu of less than 4 is

A

well sorted

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57
Q

a sample with a Cu of more than 6 is

A

poorly sorted

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58
Q

size corresponding to the 10% line on the grain size curve

A

d10, effective grain size

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59
Q

porosity ranges for sediments (davis)

A

well sorted sand or gravel - 25-50%
SAG mixed - 20-35%
glacial till - 10-20%
silt - 35-50%
clay - 33-60%

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60
Q

porosity of claystone (morris and johnson)

A

41-45%

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61
Q

porosity of sandstone (morris and johnson)

A

14-49%

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62
Q

porosity of shale (morris &johnson)

A

1-10%

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63
Q

porosity of crystalline rocks by morris and johnson

A

basalt - 3-35%
weathered granite - 34-57%
weathered gabbro - 42-45%

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64
Q

t or f: unconsolidated materials have higher porosity

A

T

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65
Q

cementing materials

A

silica, dolomite, calcite

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66
Q

compaction reduces pores by ____ and ____

A

rearranging mineral grains
reshaping them

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67
Q

t or f: dissolution of materials decreases porosity

A

F (increases)

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68
Q

t or f: the primary structures of the sediment may be preserved in the sedimentary rock

A

T

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69
Q

two main types of porosity

A

primary and secondary

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70
Q

four categories of porosity

A

primary
secondary
fracture
vuggy

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71
Q

the main or original porosity system in a rock or unconfined alluvial deposit

A

primary porosity

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72
Q

secondary porosity occurs either by _____ or ______

A

fracturing ; chemical leaching of mineral grains

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73
Q

subsequent or separate porosity system in a rock, either by fracturing or chemical leaching of minerals

A

secondary porosity

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74
Q

t or f: secondary porosity can replace or co-exist with primary porosity

A

T

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75
Q

porosity associated with fracture system or faulting

A

fracture porosity

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76
Q

t or f: hydrocarbons becomes a reservoir once it exhibits secondary porosity

A

T

77
Q

this porosity was generated by dissolution of large features (macrofossils) leaving large holes, caves, or vugs

A

vuggy porosity

78
Q

two well-known examples os sedimentary rocks of chemical/biochemical origin

A

limestone
dolomite

79
Q

the materials that formed limestone and dolomites were originally part of an:

A

aqueous solution

80
Q

example of a cavern that exemplify large openings

A

Carlsbad cavern in new mexico

81
Q

may also be cavernous

A

gypsum and salt

82
Q

as more water moves through the bedding plane, they are preferentially ____ and ____, causing rocks to become very porous

A

dissolved and enlarged

83
Q

t or f: percent porosity of sedimentary rocks is highly variable

A

T

84
Q

percent porosity of clastic sedimentary rocks

A

3-30%

85
Q

porosity for limestones and dolomites

A

<1-30%

86
Q

t or f: high ground resistivity means high porosity

A

F (low porosity)

87
Q

_______ cools and solidify quickly because they are formed in a surface environment; this gives them radically _________

A

extrusive rocks ; different porosity characteristics

88
Q

lava cooling rapidly at the surface will __________, resulting in holes in the rock or ______

A

trap degassing products ; vesicular texture

89
Q

porosity of basalt

A

1-12%

90
Q

porosity of tuff

A

14-40%

91
Q

porosity of volcanic ash

A

50%

92
Q

deep granite test hole in Northern Illinois, what percentage of porosity without, and with fractures

A

1.42 %
2.15 %

93
Q

_______ and _____ increases overall rock porosity

A

weathering and fracturing

94
Q

weathered plutonic and metamorphic rocks porosity

A

30-60%

95
Q

porosity of pumice

A

less than or equal to 87%

96
Q

weathered volcanic deposits porosity

A

> 60%

97
Q

dumoy aquifer is composed of what deposit

A

volcanic deposit

98
Q

t or f: as depth increases, fractures decreases

A

T

99
Q

it is the volume of water that gets drained from a saturated rock owing to gravitational attraction to the total volume of the rock

A

specific yield (sy)

100
Q

water molecules cling to the surface because of

A

surface tension

101
Q

what would happen if gravity exerts a force on a film of water surrounding a mineral grain?

A

water will pull away and drip downward, causing the film to thin, and increase in surface tension in order to balance gravity

102
Q

material with highest specific yield

A

coarse sand (35-20)

103
Q

material with lowest specific yield

A

clay (5-0)

104
Q

moisture clinging to soil because of surface tension

A

pendular water

105
Q

what materials generally have high specific yield?

A

sand and gravel

106
Q

grain size distribution of sediments can be conveniently plotted in a

A

semilogarithmic paper

107
Q

is the ratio of the water that is retained against the gravity to the total volume of the rock

A

specific retention (Sr)

108
Q

formula for porosity as a function of specific yield and retention

A

n = Sy + Sr

109
Q

the ability of rock to transmit water

A

hydraulic conductivity

110
Q

constitute the most significant hyfrologic properties

A

ability to hold and transmit water

111
Q

t or f: some rocks exhibit porosity but lack interconnectedness

A

T

112
Q

example of a rock that exhibit porosity but lack interconnectedness

A

vesicular basalt

113
Q

what percentage of vesicles does vesicular basalt have?

A

<50%

114
Q

examples of sediments that have porosity but isn’t large enough to allow transmit of water

A

clay and shales

115
Q

french engineer who made the first systematic study of the movement of water through a porous medium

A

henry darcy

116
Q

what did darcy study?

A

systematic study of the movement of water through a porous medium

117
Q

darcy found that

A

the rate of water flow is directly proportional to the difference in water height in both ends of the filter beds and inversely proportional to the flow path

118
Q

darcy determined that the quantity of flow is ____ to a coefficient, K, which is a function of ____

A

proportional
function of the nature of the porous medium

119
Q

a thin vertical pipe used to measure pressure

A

piezometer

120
Q

what is discharge according to darcy

A

discharge is directly proportional to the difference in the height of water, h (hydraulic head) and inversely proportional to the flow length (L)

121
Q

t or f: flow is proportional to the cross-sectional area of the pipe

A

T

122
Q

discharge formula

A

Q= -KA [(ha-hb)/L]

or

Q = -KA (dh/dl)

123
Q

it is known as the hydraulic gradient

A

dh/dl

dh - change in head between two points
dl - distance between these points

124
Q

the negative sign of a discharge indicates:

A

the flow is going in the direction of decreasing hydraulic head

125
Q

specific discharge is also known as___

A

darcinian velocity (L/T)

126
Q

formula for specific discharge

A

q = Q/A

127
Q

why is darcinian velocity not considered as a true velocity

A

because the discharge is blocked by soil or rock material

128
Q

measure of quantity of any fluid flow over time

A

discharge

129
Q

dimensions of discharge

A

volume/time (L^3/T)
area (L^2)
gradient (L/L)

130
Q

formula for K

A

K = -(L^3/T)/L^2 (L/L) = L/T

131
Q

Hubbert (1956) pointed out that Darcy’s K is a function of

A

the nature of the porous medium and the fluid passing through it (specific weight and viscosity)

132
Q

t or f: discharge is directly proportional to specific weight

A

T

133
Q

is the force exerted by gravity over a unit volume, basically a downward flow

A

specific weight

134
Q

t or f: discharge is directly proportional to the dynamic viscosity of the fluid

A

F (inversely)

135
Q

measure of the resistance of fluid to shearing

A

dynamic viscosity

136
Q

it is the function of the size of the openings through which fluid pass through

A

intrinsic permeability

137
Q

unit for intrinsic permeability

A

darcy

138
Q

darcy can be described as

A

1 darcy = 1cp (1cm^3/s) / 1cm^2 / (1atm/ 1cm)

passing of one cubic meter of fluid (with a viscosity of 1 centipoise) per second through a one square centimeter cross sectional area under a pressure of 1 atm per cm thickness

139
Q

represent some of the most profilic producers of groundwater

A

unconsolidated coarse-grained sediments

140
Q

t or f: the smaller the size of the sediment grains, the larger the surface area the water contacts

A

T

141
Q

for well sorted sediments, the intrinsic permeability is directly proportional to the

A

grain size

142
Q

1 darcy is equal to

A

10^-8 cm^2

143
Q

for sand sized alluvial deposits, what are the factors relating to intrinsic permeability

A
  1. large median grain size = high intrinsic permeability
  2. high SD = low intrinsic permeability
  3. dako ang effect sa decrease sa permeability sa pagtaas sa SD sa coarse than fine
  4. unimodal (one dominant size) has higher intrinsic permeability than bimodal
144
Q

clastic sedimentary rocks have primary porosity similar to

A

unconsolidated sediments

145
Q

____ can reduce the size of the pore throats through compaction and _____

A

diagenesis ; cementation

146
Q

t or f : crystalline rocks have typically low permeability

A

T

147
Q

secondary permeability can develop through

A

fracturing, dissolution, and weathering

148
Q

hydraulic conductivity of earth materials can be measure through a

A

permeameter

149
Q

undulating surface, top most portion of aquifer

A

water table

150
Q

in the water table the atmospheric pressure is equal to the ____

A

pore water pressure

151
Q

in the absence of groundwater flow, water table will be

A

flat

152
Q

a sloping water table indicates

A

presence of groundwater flow

153
Q

groundwater discharge zones are in

A

topographical low spots

154
Q

the position of the water table follows the ____

A

general shape of the topography

155
Q

groundwater flows from

A

topographic highs to lows

156
Q

a geologic unit that can hold and transmit water at rates fast enough to supply wells

A

aquifer

157
Q

intrinsic permeability of an aquifer

A

10^-2 darcy upwards

158
Q

examples of aquifers

A

unconsolidated sand and gravel, sandstone, limestone, dolomite, basalt flow, and fractured metamorphic and igneous rocks

159
Q

geologic unit having little to no intrinsic permeability

A

confining layer

160
Q

classification of confining layers

A

aquitard
aquiclude
aquifuge

161
Q

an absolutely impermeable unit that will not transmit any water

A

aquifuge

162
Q

also known as the leaky confining layer, can hold and transmit water but at very slow rates

A

aquitard

163
Q

inappreciable amount of water moves or is transmitted

A

aquiclude

164
Q

an aquifer close to land surface with high intrinsic permeability extending from land surface to the base of the aquifer

A

unconfined aquifer or water table aquifer

165
Q

aquifers overlain by confining layers

A

confined aquifers or artesian aquifer

166
Q

surface representative of the level at which groundwater will rise in a well cased to an aquifer

A

potentiometric surface

167
Q

if the potentiometric surface is above the land, ____ may occur

A

flowing artesian well

168
Q

is a saturated soil directly above the main water table

A

perched aquifer

169
Q

where can we find perched aquifer in mindanao

A

bislig, surigao del sur

near former usep bislig campus

170
Q

three ways in which confined aquifers can be formed

A
  1. deposition of alternating layers of permeable sand and gravel and impermeable clay and silts deposited in intermontane basins
  2. alternating layers of aquifers and confining units deposited on a regional dip
  3. upwarping of beds by intrusion
171
Q

maps showing construction of water table maps in areas with surface-water bodies

A

water table and potentiometric surface maps

172
Q

characteristics of aquifer

A

transmissivity
storage coefficient
elasticity
specific storage
compressibility and effective stress
homogeneity and isotropy

173
Q

the measure of the amount of water that can transmitted horizontally over a unit width by the saturated thickness of the aquifer under the hydraulic gradient of 1

A

transmissivity

174
Q

formula for transmissivity

A

T = bK

b= thickness of aquifer
K= hydraulic conductivity

175
Q

it is the volume of water that a permeable unit will absorb or expel from storage per unit surface area per unit change in head

A

storage coefficient (storativity)

176
Q

in the saturated zone, the head creates pressure affecting the ___ and ___-

A

arrangement of mineral grains and density of the fluid

177
Q

if the pressure in the head is high, mineral skeleton will ____

A

expand

178
Q

the amount of water than can be absorbed or expelled owing to the compressibility of the mineral skeleton and the pore water per unit change in head

A

specific storage (elastic storage coefficient)

179
Q

a downward stress placed on the aquifer skeleton by the weight of the overlying rock layer and water

A

total stress

180
Q

the upward stress on the plane caused by the fluid pressure that counteracts the total stress

A

effective stress

181
Q

t or f : effective stress is less than the total stress

A

t

182
Q

formula for total stress

A

oT = oE + P

total = effective plus pressure

183
Q

t or f : overextraction of groundwater decreases effective stress, causing subsidence

A

T

184
Q

a unit that has the same properties in all locations

A

homogenous unit

185
Q

a unit whose hydraulic property spatially change

A

heterogenous unit

186
Q

units that have the same intrinsic permeability in all directions

A

isotropic

187
Q

units that have non-uniform intrinsic permeability, geometry of the voids is not uniform

A

anisotropic

188
Q

graphical method to see groundwater flow using three or four well situations

A

gradient of the potentiometric surface

Hydrogeology (13 decks)

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