Groundwater Geochemistry (Hydrogeochemistry)

Wan Zuhairi Wan Yaacob (PhD, Assoc. Prof) Program Geologi, UKM

2/12/2010 drwzwy Geochemistry • / rock interactions in unsaturated/saturated zones

• Geochemistry is important to groundwater studies:- – Characterizing the natural system (or groundwater composition) – Understanding contaminant migration – Designing remediation programs

2/12/2010 drwzwy Simple geochemical model

• Aqueous geochemistry – Water/rock interactions – To control the groundwater composition and the movement of dissolved constituents

Deutch WJ. 1997. Groundwater Chemistry. CRC Press

2/12/2010 drwzwy Fresh water without any Reactions that dissolve dissolved constituents gases and minerals and (disequilibrium) changes the solution composition

Dynamic geochemical system consisting (i) Solid phase (ii) Gas phase (iii) Aqueous solution phase

disequilibrium

2/12/2010 drwzwy Groundwater solution • Definitions and concentration units

2/12/2010 drwzwy • Concentration of solute in solution • Milligram per liter (mg/L) • Part per million (ppm) mg/L  ppm mg/L ppm mg/L ------= solution density (g/cc) – TDS (g/cc) ppm

Solution density = 1.008 g/cc TDS = 10,000 mg/L (0.01 g/cc)

Then, 1 ppm = 0.998 mg/L (0.2 % difference!)

2/12/2010 drwzwy 2/12/2010 drwzwy • Groundwater solutes – Major (concentration > 1 mg/L) – Minor ions (concentration < 1 mg/L)

2/12/2010 drwzwy • Converting measured concentration (mg/L or ppm) to electrical equivalent unit (meq)

= 4.6 meq / L

(1000 miliequivalents = 1 equivalent)

2/12/2010 drwzwy • Conversion to meq • Electrical balance

Electrical balance:

Electrical balance for Table 1-2 = +0.5% + (excess cations; insufficient anions) - (excess anions; insufficient cations) Reasonable2/12/2010 balance for routine analysis < 5% drwzwy Several possible reasons that create an electrical imbalance in the data

1. The design of the sampling program neglected a major dissolved species 2. Laboratory error 3. Using unfiltered water samples 4. Precipitation of a mineral in the sample 5. In certain cases, the dissolved species may not correspond to the typical species used in the making the balance calculation

2/12/2010 drwzwy Groundwater types • Classify groundwater based on dominant cations and anions

• Ca-HCO3 type (dominant with Ca and HCO3) • Displayed graphically by several methods – Bar graph – Circular diagram – Stiff diagram – Trilinear or Piper diagram – Durov diagrams

2/12/2010 drwzwy Bar Diagram Circular Diagram

2/12/2010 drwzwy Stiff Diagram Piper Diagram

Durov Diagram

2/12/2010 drwzwy STIFF DIAGRAM

1. Ion concentrations in meq L-1 are plotted on the horizontal axis. 2. Cations are plotted to the left, anions to the right, of a vertical axis. 3. The data are plotted in four rows and the points are connected to form a polygon. 4. Advantage: each water type produces a distinct shape. 5. Disadvantage: each analysis requires its own plot; only a limited number of data can be shown on a single plot.

2/12/2010 drwzwy Pine Creek, CDA Valley, Idaho An example of a Stiff diagram drawn for M ine Wat er s mine from the Pine Creek district, Cat ions m e q / l Anion s Coeur d’Alene Valley, ID. The anions are 15 10 5 5 10 15 mostly dominated by , with lesser N a + K Cl bicarbonate, whereas the cations are

Ca AD0 0 2 H C O 3 + C O 3 dominated by and .

Mg S O 4 N a + K Cl

Ca AD0H 0 C 4 O 3 + C O 3

Mg S O 4 N a + K Cl

Ca AD0 0H 5 C O 3 + C O 3

Mg S O 4 N a + K Cl

Ca AD0 0 7H C O 3 + C O 3

Mg S O 4 N a + K Cl

Ca S97 - 3 H C O 3 + C O 3

Mg S O 4 N a + K Cl

CaSP0 0 2 H C O 3 + C O 3

Mg S O 4 N a + K Cl

CaSPNEWH C O 3 + C O 3 2/12/2010 drwzwy Mg S O 4 Stiff pattern

Stiff pattern are centered over locations of wells

Isocon of TDS

2/12/2010 drwzwy PIPER DIAGRAMS 1. Consists of two triangles (one for cations and one for anions), and a central diamond-shaped figure. 2. Cations are plotted on the Ca-Mg-(Na + K) triangle as percentages. - 2- - 3. Anions are plotted on the HCO3 -SO4 -Cl triangle as percentages. 4. Concentrations are in meq L-1. 5. Points on the anion and cation diagrams are projected upward to where they intersect on the diamond. 6. Many water analyses can be plotted on the same diagram and can be used to classify waters.

2/12/2010 drwzwy Percentage of cations and anions as percentage of the total (Step 2 and 3)

Cations meq/L % of Anions meq/L % of total total Ca2+ 1.15 36 Cl - 0.27 9 2+ 2- Mg 0.39 12 SO4 0.02 1 + + 2- Na + K 1.64 52 CO3 + 2.80 90 - HCO3 Total 3.18 Total 3.09

2/12/2010 drwzwy Figure 1-6 from Kehew (2001). Water analyses plotted on a Piper diagram. Cation percentages in meq L-1 plotted on the left triangle, and anion percentages in meq L-1 plotted on the right triangle.

Ca = 22.3 % Mg = 13.7 % Na+K = 64 %

HCO3 = 31.3 % SO4 = 54.5 % Cl = 14.2 %

2/12/2010 drwzwy Figure 1-7 from Kehew (2001). Classification of hydrochemical facies using the Piper plot.

2/12/2010 drwzwy 2/12/2010 drwzwy Pine Cr eek, CDA Valley, I daho An example of a Piper M ine W aters diagram drawn for mine waters from the Pine 80 AD002 ) g M ( m u i s e n g a M + ) a C ( m u i c l a C 80 AD004 Creek district, Coeur

60 AD005 d’Alene Valley, ID. These 60 AD007 may be characterized as 40 S97- 3 Ca-Mg sulfate- 40 SP002 bicarbonate-type S ulfate(S O 4)+C hloride(C l) 20 SPNEW waters. 20

Mg 20 SO 4

20

20 80 ) K ( m u i s s a t o P + ) a N ( m u i d o S 40

80 20

40

40 ) 4 O S 60 ( e t a f l u S 60

60 40 60

60 40 80 M agnesium (M g) 60 40

80

80 20

C arbonate(C O 3)+Bicarbonate(H C O 3) 20 80

Ca 80 60 40 20 N a +H K C O 3 + C3 O20 40 60 80 Cl Calcium ( Ca) Chlo r id e ( Cl) % m e q / l 2/12/2010C A T I O N S drwzwyA N I O N S Ke he w ( 2 0 0 1) An example of a Piper diagram with

80 ) g M ( m u i s e n g a M + ) a C ( m u i c l a C TDS circles.

80

60 5 3 60

40

0 1 , 0 02 0 , 0 03 0 , 0 04 0 , 0 05 0 , 0 0 0

40 Tot al Diss olv ed Solids 8

( Par t s Per M illion) S ulfate(S O 4)+C hloride(C l) 20 Plot the radius of TDS 120 4 2 using suitable scale (5000 ppm) 7

Mg 20 SO 4 TDS – represents

20 overall salt content of

20 80 the water ) K ( m u i s s a t o P + ) a N ( m u i d o S 40

80 20 7 40

40 ) 4 O 60 S ( e t a f l u S 60 3 60 40 5 4 60 60 40 80 M5 agnesium (M g) 60 40 2 80 6 8 80 20

3 C arbonate(CO 3)+Bicarbonate(H CO 3) 20 8 80 1 7 4 1 2 6 6 Ca 80 60 40 20 N a +H K C O 3 + C3 O20 40 60 80 Cl Calcium ( Ca) Chlor ide ( Cl) % m e q / l 2/12/2010C A T I O N S Adrwzwy N I O N S Can you guess the type of karst rivers systems aquifer of this groundwater ?

2/12/2010 drwzwy 2/12/2010 drwzwy Thank you

2/12/2010 drwzwy