16 Dissolved Mass in Groundwater Hydrochemistry. Introduction Water Chemistry: Origin of water Uses...
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Transcript of 16 Dissolved Mass in Groundwater Hydrochemistry. Introduction Water Chemistry: Origin of water Uses...
16Dissolved Mass in
Groundwater
Hydrochemistry
Introduction Introduction
Water Chemistry: Origin of water Uses of water Water quality (contamination)
Topics: 16.1 Dissolved constituents in groundwater 16.2 Types of water analyses 16.3 Water-quality standards 16.4 Examples of data collected in chemical
surveys 16.5 Working with chemical data Case studies :
Madinah Basalt aquifer, Taif Alluvium Aquifer
16.1 Dissolved constituents in groundwater
Rocks, minerals dissolve in water: ions Cations: positively charged ions
(e.g., Ca2+, K+)
Anions: negatively charged ions (HCO3-, Cl-)
Organic compounds, dissolve, form non-charged molecules
16.1 Dissolved constituents in groundwater
Examples of dissolution of minerals, liquids,
Halite dissolution: NaCl = Na+ + Cl-
Calcite dissolution: CaCO3 + H+ = Ca2+ + HCO3
-
TCE dissolution: TCE = TCEaq
Concentration Scales
1. Molar concentration: Number of moles of a species per liter of solution (mol/L)
mole: formula weight of a substance in grams
Example: one-liter solution containing 1.42 g of Na2SO4 has a molarity of (Na2SO4) of:
1.42/(2X22.99 + 32.06 + 4 x 16.00) = 0.010 M
2. Molal concentration
Number of moles per kilogram of solvent (mol/Kg)
Concentration Scales
3. Equivalent charge: number of equivalent charges of an ion per lietr of solution (units: eq/L, meq/L)
Equivalent charge = number of moles of an ion multiplied by the absolute value of the charge:
Example: 1 M Na+ equals 1 eq/L1 M Ca2+ equals 2 eq/L
4. Mass per unit massMass of a species or element per total mass of the system (ppm,
ppb, mg/kg, ug/kg)
5. Mass per unit volume (most common):Mass of a solute dissolved in a unit volume of solutionunits: mg/L, g/L)1 ppm = 1 mg/kg = 1 mg/L
Concentration Scales
Conversion between mg/L to molar concentration:
molarity = mg/L x 10-3
___________________________
formula weight Conversion between mg/L to meq/L:
Meq/L = mg/L___________________________
formula weight/ charge
Example 16.1:The concentration of SO42- in water is 85.0 mg/L. Express this
concentration as molarity and meq/L:
SOLUTION:
mol/L = 85x10-3 / (32.06 + 4 x 16.0) = 0.89 x 10-3
meq/L = 85 /(32.06 + 4 x 16.0)/2 = 1.77
16.2 Types of Water Analyses
Minerals
Organic solids
Organic liquids
Gases Oxygen carbon dioxide hydrogen sulfide, methane
Dissolve in groundwater
Dissolved Constituents in Groundwater Classified by Relative Abundance (Table 16.1)
Major ( 5
mg/L)
Minor
.01 - 10.0 mg/L
Trace (< 0.1 mg/L)
Bicarbonate Boron Aluminum Platinum Copper
Silicon Nitrate Arsenic Radium Gold
Calcium Carbonate Barium Rubidium Lead
Sodium Potassium Beryllium Silver Lithium
Chloride Fluoride Bromide Cobalt Manganese
Sulfate Strontium Cadmium Selenium Nickel
Magnesium Iron Cerium Thorium Phosphate
Carbonic Acid
Chromium Zinc Platinum
Tungsten Vanadium Uranium
Dissolved Constituents in Groundwater Classified by Relative Abundance (Table 16.1)
Organic Compounds
(shallow)
Organic Compounds (Deep)
Humic Acid Acetate
Fulvic acid Propionate
Carbohydrates
Amino acids
Tannis
Lignins
Hydrocarbons
Routine Water Analyses
Routine: measuring concentration of standard set of
most abundant constituents : Major constituents (except Silicon, Carbonic Acid)
Minor constituents (except Boron, strontium)
pH, TDS (mg/L), Conductance (microS/cm, micromhos/cm)
TDS: total quantity of solids when a water sample is
evaporated to dryness
SC: measure of sample’s ability to conduct electricity
Routine analyses: defines almost all dissolved mass, except
when water is highly contaminated
Example of a routine water analysis(Wadi Al-Arj, Taif, Summer 2002)
Parameter Mg/L Parameter Mg/L
pH (25 C) 7.3 Total Iron ND
TDS 1610 Bicarbonate 274Conductivity 2300 Chloride 340
Sodium 265 Sulfate 430Potassium 12 Nitrate 46Calcium 168 Phosphate 12Magnesium 38 Carbonate 134
Mercury ND Ammonia ND
Total Bacteria 1000 Arsenic 1
Specialized Analyses
Trace metals ( Mn, Cr, Cd, Pb, Zn)
Radioisotopes
Organic compounds
Nitrogen-containing species (NO3-, NH4+)
Environmental isotopes
Gases
Specialized analyses done for:
groundwater contamination problems
Water-quality assessment
Research
Regulatory issues
16.3 Water Quality Standards
Designed to protect public health by requiring that
contaminants or naturally occurring constituents in water
be less than certain limits
Microorganisms
Disinfection and disinfection byproducts
Inorganic chemicals
Organic chemicals
radionuclides
16.3 water Quality Standards
Primary drinking water standards:
Secondary drinking water standards:
MCL: maximum contaminant level: highest level of a
contaminant that is allowed in drinking water
(enforceable standards)
MCLG: maximum contaminant level goal: the level of a
contaminant in drinking water below which there is no
known or expected health risk (targets)
Non-enforceable standardEPA Web page
16.5 working with chemical data
Presenting results of chemical analyses:
Abundance or relative abundance
1. Collins Bar diagram
2. Stiff pattern diagram
3. Pie diagram
4. Piper diagram
Abundance and patterns of change
Graphical/illustrative type diagrams
Statistics
Wadi Al-Arj Samples
Well samples
Runoff samples
Average Average
TDS 2148 810
Conductivity (μS/cm 2843 1244
pH 6.5 6.48
T (oC) 24.2 24.3
Sodium 363.1 182
Potassium 18.9 14.4
Calcium 126.2 67.0
Magnesium 74.5 31.2
Sulfate 451.9 191.4
Chloride 584 177
Nitrate 85.9 60.6
Bicarbonate 251.1 266.5
Pb 0.3 0.02
Iron 1.6 0.3
Zn 0.5 0.3
Mercury (ppb) 12 ND
Co (ppb) 0.01 0.01
As (ppb) 1.1 0.2 Coliform Bacteria (per 100 ml) 33 46
BOD 2.8 5
Piper diagram
Procedure for plotting piper (trilinear)
1. Convert concentrations from mg/L (ppm) to equivalents
2. Normalize, cations an anions each separately add to 100
(combining Na + K)
3. Plot proportions on triangles
4. Transfer data from triangles to quadrilateral by drawing
straight lines In cation triangle, line is parallel to Mg axis
In anion triangle, line is parallel to SO4 axis
5. Intersection of the two lines is the location of point on diamond
plot
Piper diagram, EXAMPLE
Ca 40 HCO3 2.8 meq/l
Mg 15 SO4 234
Na 120 Cl 45
K 20Ca 1.996 HCO3 2.8
Mg 1.234 SO4 4.87
Na 5.22 Cl 1.27
K 0.511
equivalents
Ca HCO3
Mg SO4
Na + K Cl
proportions
100 100
Runoff
Groundwater
Madinah Basaltic Aquifer
80 60 40 20 20 40 60 80
20
40
60
80 80
60
40
20
20
40
60
80
20
40
60
80
Ca Na+K HCO3 Cl
Mg SO4
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A A
A
A A
A
AA
A
A A
A
A
A
A
AA
A
AA
A
A
A
A
A
A
A
A
A
A
A
A
A
A A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
AA
A
A
A
A
AA
A
80 60 40 20 20 40 60 80
20
40
60
80 80
60
40
20
20
40
60
80
20
40
60
80
Ca Na+K HCO 3 C l
M g SO 4
I I
I
II
I
II
I
II
I
CC
C
CC
C
C C
C
CC
C
CC
C
CC
C
CC
C
HH
H
HH
H
H H
H
HH
H
LegendLegend
I U pstream -2003C U pstream -1978H D ow nstream -1978
20
40
60
80 80
60
40
20
20
40
60
80
20
40
60
80
Ca Na+K HCO3 Cl
Mg SO4
Piper Plot
H
H
H
HH
H
H H
H
H
H
H
L
L
L
LL
L
L
L
L
LL
L
LL
L
LL
L
LL
L
LL
L
LL
L
LL
L
L L
L
L
L
L
II
I
II
I
I I
I
II
I
KK
K
B B
B
JJ
J
JJ
J
K K
K
BB
B
JJ
J
JJ
J
J J
J
J J
J
J
J
J
J J
J
J J
J
J J
J
JJ
J
JJ
J
KK
K
J J
J
JJ
J
JJ
J
J
J
J
J J
J
JJ
J
J J
J
JJ
J
JJ
J
J
J
J
J J
J
J
J
J
JJ
J
JJ
J
EE
E
CC
C
CC
C
CC
C
CC
C
CC
C
CC
C
LegendLegend
E DefaultJ Dry season-groundwaterK Dry season-RunoffL Wet season-groundwaterB Wet season-RunoffI Upstream-2003C Upstream-1978H Downstream-1978
Pie chart
Stiff diagram
1 1 2 2 3 3 4 4 5 (meq/l) 5
Na Cl
Ca HCO3
Mg SO4
wet-ro-001
LegendLegend
2.2 2.2 4.4 4.4 6.6 6.6 8.8 8.8 11 (meq/l) 11
Na Cl
Ca HCO3
Mg SO4
dry-gw-020
LegendLegend
Stiff diagram
Stiff diagramexample
Bar diagram(frequency)
Na+k
Mg
HCO3
0
1
1.5
2
3
SO4
Cl
Ca
cation anion
Meq/l