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Natural Resources and the Environment > Hydro-geology and aquifer properties > Flashcards

Hydro-geology and aquifer properties Flashcards

1
Q

The emergence of groundwater is determined by?

A
  • Lithology
  • Regional geological structures
  • Geomorphology of landforms
  • Availability of recharge sources
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2
Q

How much of earths water is groundwater?

A
  • 97.25 of earths water is in the sea
  • 74.9 of fresh water is locked up in ice
  • most of water left is ground water
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3
Q

Lithological factors are related to:

A

Physical properties of the material:

  • Porosity
  • Permeability
  • Transmissivity
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4
Q

What do the physical properties of a rock affect? And what are they referred as?

A

The ability, and ease at which groundwater can pass through the subsurface.
- Aquifer properties

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5
Q

Define porosity:

A

The fraction of a given volume of material occupied by void space.

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6
Q

What is the equation for porosity?

A

n = 1 - known bulk mass density / particle mass density

void ratio (e) = Volume of void / Volume of solid

n = e / (1 - e)

n = Sy + Sr

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7
Q

What is primary porosity?

A

Determined by the inherent character of a soil/rock matrix, formed during rock formation

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8
Q

What is secondary porosity?

A

Develops from physical and chemical weathering along cleavage planes and in surface weathering.

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9
Q

Name the factors affecting porosity in sedimentary rock and sediments

A
  • Packing (Cubic,0.48 and Rhombic, 0.26)
  • Grain sorting
  • Grain shape/orientation
  • Diagenesis (compaction, removal/addition of material, mineral replacement/phase changes)
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10
Q

What is specific yield (Sy)?

A

ratio of water that drains from a saturated rock owing to the attraction of gravity to the total volume of rock - like water out of a sponge due to gravity.

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11
Q

What is specific retention (Sr)?

A

ratio of the volume of water in a rock can retain against gravity drainage to the total volume of the rock.

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12
Q

Sr increases with:

A

decreasing grain size

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13
Q

Coarse grain rocks have large pores therefore:

A

capillary films occupy very small proportion of n such that Sy is almost = n

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14
Q

n =

A

Sy + Sr

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15
Q

Fine grain rocks have small pores therefore:

A

capillary forces dominate such that Sr will almost = n

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16
Q

Particularly in fine grained aquifers:

A

Not all water contained in pores is viewed as available to groundwater.

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17
Q

Total porosity relates to:

A

the storage capability of the material

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18
Q

Effective porosity relates to:

A

the transmissive capability of the material (drainable)

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19
Q

Darcy studied the flow of water through porous material contained in a column and found:

A

the total flow, Q, is proportional to the difference in water level and the cross sectional area of flow; and inversely proportional to column length.

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20
Q

What is transmisivity?

A

the degree to which a medium allows something to pass through it.

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21
Q

Darcy’s law equation:

A

Q = -KA(dh/dl)

Q = Flow rate
A = cross sectional area
K = hydraulic conductivity
dh/dl = hydraulic gradient
dh = change in head between two points separated by small distance dl
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22
Q

What is the hydraulic conductivity (K or coefficient of permeability)?

A

Measure of the ease of movement of water through a porous medium. (Length/Time)

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23
Q

Whats the hydraulic conductivity (K) equation?

A 
K = -Q / [A(dh/dl)]
[L^3/T[L^2(L/L)] = L/T]
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24
Q

Whats specific discharge

A

A.K.A. Darcian velocity.

V = Q/A = -K(dh/dl)

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25
Q

Define an aquifer:

A

A layer of rock or soil sufficiently porous to store water and permeable enough to allow water to flow through them in economic quantities.

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26
Q

Aquitard:

A

An aquifer with low permeability strata that transmit water very slowly.

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27
Q

Aquiclude:

A

Impermeable strata that transmit negligible quantities of water

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28
Q

What are major/principle aquifers:

A

These are layers of rock or drift that have high intergranular and/or fracture permeability.
- high level water storage

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29
Q

What are minor/secondary aquifers:

A

Formations of variable permeability which support locally important abstractions

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30
Q

Define a non-aquifer/unproductive strata:

A

Have negligible permeability and support only very minor groundwater abstractions.

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31
Q

Give some examples of potential aquifers

A
  • London clay (H Po, L Pe - non aquifer)
  • Mercia mudstone (M Po, L Pe)
  • Sherwood sandstone (L-M primary Po+Pe, H sec Pe - major aquifer)
  • river terrace deposits (H Po+Pe - very small deposits)
  • coal measures (tainted water from coal, variable primary, H secondaey Pe fractures)
  • lower chalk (H Po, L primary Pe, H sec Pe - major aquifer)
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32
Q

Name the types of aquifer:

A
  • Unconfined
  • Perched
  • Confined - completely saturated
  • Leaky
  • Artesian conditions - spring
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33
Q

Changes in what cause groundwater flow?

A

Head

34
Q

What is affected by change in Head?

A
  • Topography
  • Aquifer properties
  • Recharge (injection/rainfall)
  • Discharge (surface water features/groundwater abstractions)
35
Q

What can groundwater contour maps be used for?

A
  • Determine groundwater flow direction & hydraulic gradient
  • Examining recharge and discharge features
  • Assessing groundwater - surface interactions
36
Q

How do you plot groundwater?

A
  1. Select data (water table elevation or piezometric head)
  2. Draw the groundwater contours (lines of equipotential) between the points
  3. Construct a flow net (lines drawn perpendicular to contours show flow direction)
37
Q

Define hydraulic gradient:

A

difference in head / distance between the two points

38
Q

Difference in head =

A

difference in water table depth

39
Q

What is the equation for hydraulic conductivity using head values

A 
Q = -KA [ha-hb) / L]
K = -Q / [A(dh / dl)]
Q = the discharge rate in cm^3/sec and is negative
K = Hydraulic conductivity cm/sec
L = Sample length (cm)
A = Sample cross sectional area
h = Hydraulic head (cm)
dh/dl = hydraulic gradient
40
Q

What is the equation for Transmissivity?

A

T = bK

T = transmissivity (m^2/d)
b = saturated thickness of aquifer (m)
K = Hydraulic conductivity (m/day)
41
Q

Chemical and biochemical interactions between ground water and geological materials provide:

A

a wide variety of dissolved inorganic and organic constituents in natural ground waters.

42
Q

What factors affect the chemical composition of ground water?

A
  • Chemical and biochemical provide (in)organic constituents.
  • Rainfall composition
  • uptake by biological processes
  • mixing with sea water
43
Q

Name the 6 major constituents of groundwater:

A 
Cations: 
- Ca^2+
- Mg^2+
- Na+
Anions:
- Bicarbonate (HCO3^-)
- Cl^-
- Sulphate (SO4^2-)
44
Q

What is the concentration of major ions?

A

> 5mgL^-1

45
Q

What is the concentration for minor constituents? But what can increase it?

A
  1. 01-10mgL^-1

- Contamination from human activity

46
Q

What are trace constituents?

A

They are the rest of the periodic table

- <0.1mgL^-1

47
Q

What concentration are organic compounds and why?

A

<0.1mgL^-1

- due to oxidation of organic matter to CO2, CO2 acidifies the water dissolving carbonate

48
Q

How do ions get into groundwater?

A

Water percolation through rocks, limestones aren’t soluble in water but in acids
CO2 + H2O = H2CO3
Evaporite minerals are soluble in water
NaCl(s) Na+(aq) + Cl-(aq)

49
Q

What does TDS stand for and why does the calculated TDS not always = measured TDS?

A

Total Dissolved solids.
Bicarbonate (HCO3-) breaks down to CO3^2-, CO2(g) and H2O and this results in a weight loss
- CO2 and H2O escape

50
Q

How can salinity of groundwater be measured?

A
  • measure dry weight of solids after evaporation (mgL^-1)

- Electrical conductivity as groundwater is an electrolyte solution.

51
Q

Salinity of groundwater classification using TDS:

A

Freshwater 0-1000
Brackish water 1000-10,000
Sea water 10,000-100,000 (35,000)
Brine water >100,000

  • TDS > 2000 - 3000 is too salty to drink
52
Q

What is water hardness?

A

Presence of Ca^2+ and Mg^2+ ions in water produce a scummy residue and scale. Expressed as mgL^-1 of CaCO3

53
Q

What is used as a sensible method of ground water analysis?

A

A “routine” analysis includes all major constituents (excluding carbonic acid) + all minor ones (except B and Sr - as they are trace elements)

54
Q

mgL^-1 is related to what other unit and how?

A

ppm or mgkg^-1. related through the density of the solution

55
Q

Molar equivalents (meq), use the molecular weights of the ions and their valencies:

A

meqL^-1 = mg^L-1 x (valence / atomic weight)

23mgL^-1 of Ca^2+:
= 23 x (2/40.08) = 1.15meqL^-1

56
Q

Aqueous solutions must be:

A

Electrically neutral

57
Q

What is CBE and what is its equation?

A

Charge balance error.

CBE(%) = [(∑cations - ∑anions) / (∑cations + ∑anions)] x 100

58
Q

What are the reasons for CBE

A
  • An important anion or cation was not included in the analysis
  • Sometimes this can point out the presence of a high concentration of a unusual anion or cation
  • Human error
  • Systematic error
59
Q

What is a hydro chemical facies?

A

A distinct zone of groundwater that can be described as having cation and anion concentrations with definite limits, or “water type”.

60
Q

Describe the Hanshaw and Black model:

A
  • Carbonates emerge from marine and are flushed of seawater by freshwater
  • Decreasing salinity + hydrochemical facies is Ca-HCO3 dominant
  • Carbonates dissolve, recrystalised, cemented dolomitized to form an aquifer
  • As recharge moves downgradient temp increases dissolving gypsum, dolomite and calcite
  • Increasing ions of SO4^2-, Ca^2+, Mg2+
  • Whilst mixing with saline water gypsum and dolomite dissolves and calcite precipitates out reducing ∑CO2
61
Q

Describe the classic evolution of groundwater:

A
  • Rainwater - dilute solution (NaCl of marine origin, dissolved CO2
  • Into soil - addition of soil CO2 and fertilizer NO3, PO4, Cl, Na, K
  • Unsaturated zone - solution of Ca and Mg carbonates Ca-Mg-HCO3 water
  • Saturated zone - Bacterial reduction of O2, NO3, SO4
  • FOLLOW INCREASING CONFINEMENT OF GROUNDWATER
  • Leaching of iron oxides; precipitation of metal sulphides
  • Ion exchange Na-HCO3 water (clays)
  • Saline water Na-Cl water
  • Static water; aquifer diagenesis
62
Q

A range of CBE values for various samples may produce certain anomalies, if this is due to missing anions why might this be the case?

A

The presence of phosphates/nitrates in the sample

  • If cations missing then possibly due to presence of silica/iron
63
Q

Which to ions are often grouped together when calculating cation and anion percentages and plotting them on piper diagrams?

A

Na+ and K+

64
Q

Define sustainable development:

A

A pattern of resource use that aims to meet human needs while preserving the environment so these needs can be met in the present and indefinite future.
- Meeting the needs of the present without compromising future generations ability to meet their needs.

65
Q

Whats the size of Greenland?

A

2,166,086km^2

66
Q

What percentage of Greenland is covered in ice?

A

81%

67
Q

Whats the population of Greenland?

A

~60000

68
Q

Facts about Greenland:

A
  • Worlds largest island (2,166,086km^2)
  • Self-governing protectorate of Denmark
  • Dependant on fishing, many Inuit still subsistence hunters and fishermen
  • Tourism becoming important, mining may follow.
69
Q

What makes up 80% of Greenland’s economy?

A

Fishing/hunting

- Climate change is opening up land (increased natural resources and farming)

70
Q

How many tourists do Greenland get per year

A

30,000 by cruise, 35,000 by air

71
Q

Why is Greenland’s tourism market so small?

A
  • seasons are short
  • accomodations are limited
  • Travel is expensive
72
Q

Denmark subsidies Greenland how much per year?

A

$620M

73
Q

How long has mining been ongoing in Greenland?

A

~150yrs

74
Q

What challenges prohibit mineral exploration in Greenland?

A
  • Weather
  • Short seasons
  • Transport
  • Infrastructure
  • no roads
  • Shipping only in summer/ light aircraft normally
75
Q

Name a currently productive mine in Greenland:

A

Seqi Olivine Mine

76
Q

Exploration in Greenland is mainly done by which companies

A
  • Greenland minerals and energy (REE)

- Platina (precious metals)

77
Q

Give some BMP rules and regulations:

A
  • Restrictions on flying over narwhal breeding areas and seabird nesting colonies
  • All companies must undertake “environmental baseline studies” ascertain the levels of flora and fauna so they can restore the mine after closure.
78
Q

What does BMP stand for?

A

Bureau of Minerals and Petroleum.

79
Q

What benefits come from mining exploration in Greenland?

A
  • Jobs and labourers, cooks, drivers etc.
  • Opened up mining school to produce mining engineers and geologists for further work
  • Sanaartornermik Ilinniarfik
80
Q

In Greenland in 2007:

A

The goverment invited Oil and Gas companies to explore for hydrocarbons offshore - Cairn energy

81
Q

Name the responsibilities Cairn Energy have to Greenland:

A
  • A program of social and environmental responsibility
  • Monitoring marine life in operational areas
  • Utilising local Greenlandic contractors for transport ect.
  • Greenpeace protested in 2010 on one of the rigs and stopped production for a few days
82
Q

What is the future for Greenland?

A
  • They need a stronger economy
  • They are the ones most effected by climate change but need money from oil
  • Declining income from their fisheries
  • No other potential profitable resources

Natural Resources and the Environment (3 decks)

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