Unit 08b : Advanced Hydrogeology

1. Unit 08b : Advanced Hydrogeology Groundwater Chemistry

2. Groundwater Analysis • It is not feasible (or sensible) to attempt to measure all possible constituents present in groundwaters. • A “routine” analysis involves measuring a standard set of constituents. • The “routine” analysis forms the basis for assessing the suitability of the water for human consumption or various agricultural and industrial uses.

3. Calcium Magnesium Sodium Bicarbonate Chloride Sulphate pH Alkalinity TDS Conductivity Total Hardness Silicon Carbonic Acid Major Constituents (> 5 mg/L)

4. Other Reported Results • pH is routinely recorded that measures the hydrogen ion concentration (-log[H+]). • Conductivity (electrical) is routinely measured in mS/m (TDS  0.66 Ec). • TDS is the total dissolved solids measured as the residue on evaporation. • Total alkalinity (expressed as mg/L CaCO3) measures the acid-neutralizing capacity of a water sample. It is an aggregate property, primarily due to the carbonate, bicarbonate, and hydroxide content. • Total hardness (expressed as mg/L CaCO3) is another aggregate property of a water sample. Hardness measures the concentration of multivalent cations, particularly calcium and magnesium.

5. Potassium Iron Ammonium Carbonate Fluoride Bromide Nitrate/Nitrite Carbon Dioxide Oxygen Boron Strontium Minor Constituents (0.01 to 10 mg/L)

6. Li 3 Be 4 Al 13 Sc 21 Ti 22 Cr 24 Mn 25 Co 27 Ni 28 Cu 29 Ru 44 Ag 47 Cd 48 In 49 Sn 50 Sb 51 Cs 55 Ba 56 La 57 Ce 58 Trace Constituents ( < 100 mg/L) • Zn 30 • Ga 31 • Ge 32 • As 33 • Se 34 • Rb 37 • Yt 39 • Zr 40 • Nb 41 • Mo 42 • W 74 • Pt 78 • Au 79 • Tl 81 • Pb 82 • Bi 83 • Ra 88 • Th 90 • U 92 • Iodide • Phosphate

7. Humic acid Fulvic Acid Carbohydrates Amino Acids Tannins Lignins Hydrocarbons Acetate Propionate Organic Constituents Typically concentrations are very low

8. Routine Analysis • A “routine” analysis usually includes all the major constituents (except carbonic acid). • All the minor constituents (except B and Sr that tend to be regarded as trace consituents) are also to be expected.

9. mg/L Calcium <1 Magnesium <1 Sodium 550 Potassium 3.5 Iron 8.7 Total Hardness 8 _______________________ pH 7.7 Conductivity 23 mS/m mg/L Sulphate 59 Bicarbonate 1315 Chloride 45 Fluoride 0.25 Nitrite/Nitrate <0.1 Total Alkalinity 1078 TDS 1321 Balance* 1.01 Example Routine Analysis *The balance is the ratio of anions to cations in meq/L

10. mg/L meq/L Calcium <1 <0.05 Magnesium <1 <0.08 Sodium 550 23.9 Potassium 3.5 0.09 Iron 8.7 0.31 Total 24.4 Molarity 0.0477 M mg/L meq/L Sulphate 59 1.22 Bicarbonate 1315 21.6 Chloride 45 1.27 Fluoride 0.25 0.01 Nitrite/Nitrate <0.1 >0.01 Total 24.1 Cations/Anions 1.01 Charge Balance

11. Errors in Analysis • Checking the ion balance is good practice to eliminate gross errors • Errors mainly arise as a result of: • failure to measure rapidly changing parameters in the field (pH, alkalinity, etc) • poor or no filtration (removal of suspended solids) • improper sample storage (pressure, temperature, buffering, sealing)

12. Specialized Analysis • Additional specialized measurements are sometimes required for specific projects including: • trace metals • nutrients (mainly N and P species) • organics (mainly hydrocarbons, chlorinated hc’s) • stable isotopes (14C, 18O, 2H etc) • radionuclides (226Ra, 207Pb,208Po,231Th etc) • Such analyses (listed above in order of increasing cost) can be very expensive and QA/QC is a significant concern.

13. Visualizing Chemical Data • There are a large number of plots used to visualize ion abundances: • Pie Chart • Collins Diagram (Bar Chart) • Stiff Diagram • Other plots are use to group waters and interpret their origins: • Piper Diagram • Fence Diagram

14. 1 100 1000 10000 mg/L Pie Charts

15. Collins Diagram 120 Na++K+ Mg2+ 100 Ca2+ Cl- 80 SO42- HCO3-+CO32- Concentration (meq/L) 60 40 20 0 Sample 1 Sample 3 Sample 2

16. Na++K+ Ca2+ Mg2+ Cl- HCO32- SO42- Stiff Diagram meq/L 80 70 60 50 40 30 20 10 0 10 20 30 40 50 Cations Anions

17. Piper Diagram SO4 + Cl Ca + Mg Groundwater Facies SO4 Mg Cations Anions HCO3 + CO3 Na + K Ca Na + K HCO3 + CO3 Cl

18. Plotting on a Piper Diagram Ca + Mg SO4 + Cl SO4 Mg HCO3 + CO3 Na + K Ca Na + K HCO3 + CO3 Cl

19. Calcium-Magnesium Chloride-Sulphate Chloride-Sulpahte-Bicarbonate Calcium-Sodium Sodium-Calcium Bicarbonate-Chloride-Sulphate Bicarbonate Sodium-Potassium Groundwater Facies Cations Anions

20. Ca + Mg SO4 + Cl SO4 Mg HCO3 + CO3 Na + K Ca Na + K HCO3 + CO3 Cl Classification Grouping of waters on the Piper Diagram suggests a common composition and origin. Red: Ca-Mg-SO4 Yellow: Ca-Mg-Na-Cl-SO4

21. Facies Mapping • Spatial mapping groundwater facies based on classification on the Piper Diagram can help in the visualization of progressive changes in chemistry. • A fence diagram is a convenient method of viewing a 3D region as a series of intersecting cross-sections.

22. Fence Diagram Fence diagrams can be used to show groundwater facies in the same way that lithofacies are displayed. calcium-magnesium calcium-sodium sodium-calcium sodium