1

HYDROGEOCHEMICAL PROCESSES

ASSOCIATED WITH

SEAWATER INTRUSION

I. Seawater intrusion experiments in laboratory columns

II. Determination of hydrodynamic parameters

III. Analyzing reactive proceses during seawater intrusion

Departamento de Ingeniería Química

Nuria Boluda Botella

PART 2

Seawater intrusion experiments in laboratory columnsNuria Boluda Botella (1994). “Estudio hidrogeoquímico de la intrusión marina.

Simulación experimental y desarrollo de un modelo teórico”. Tesis Doctoral. University of Alicante.

Porous medium

Equilibrium with fresh waterFresh water Fresh water

Sea water

Sea water

Sea water

Sea water Sea water

Sample

Reservoir

Filter

HPLC pump

Pressuregauge

Thermostated column

Thermostatic bath

Seawater intrusion experiments in laboratory columns

Experimental configuration for the column experiments

Seawater intrusion experiments in laboratory columnsVicente Pascual Cases López (2009). “Estudios de procesos de transporte del alquilbenceno

sulfonato lineal en la zona saturada mediante columnas de laboratorio”. DEA. University of Alicante

Seawater intrusion experiments in laboratory columns

Materials (Boluda-Botella, 1994)

Ion Fresh water Sea water

mg/L mmol/L mg/L mmol/L

Na+ 50 2.17 12000 522

K+ 3.4 0.0872 400 10.3

Ca2+ 125 3.13 450 11.3

Mg2+ 15 0.617 1500 61.7

Cl- 105 2.96 21500 606

SO42- 165 1.72 2900 30.2

HCO3- 200 3.28 130 2.13

Characteristics of the natural sediment

Composition %

Calciumcarbonate

53

Quartz 35

Clay 12

CEC 7 meq/100g

Composition of the synthetic freshwater and seawater

Seawater intrusion experiments in laboratory columns

Methods (Boluda-Botella, 1994)

Parameters analyzed:

ChlorideSulfateBicarbonatepHSodiumPotasiumCalciumMagnesium

Continuously sampling at the output of the column

The average results of analysis of pore solution and the exchange complex composition

Natural sediment Treated sediment

Pore solution

(mmol/L)

Exchange complex

(meq/100g)Pore solution

(mmol/L)

Exchange complex

(meq/100g)

CEC 7 10

Na 2.29 0.09 2.20 0.25

K 0.07 0.10 0.09 0.13

Ca 3.03 5.71 3.05 8.35

Mg 1.08 1.10 1.28 1.27

Cl 3.67 3.70

S 1.84 1.97

TIC 3.32 3.40

Study of the cation exchange in batch experiments(Boluda-Botella et al., 2008)

Seawater intrusion experiments in laboratory columns

Longitudinal dispersion of a tracer passing through a column of porous medium; a) Columnwith steady flow and continuous supply of tracer after time t0; b) Step-function-type tracerinput; c) Relative tracer concentration in outflow from column (dashed line indicates plugflow condition and solid line ilustrates effect of mechanical dispersion and moleculardiffusion; d) concentration profile in the column at various times (Freeze and Cherry, 1979).

Determination of hydrodynamic parameters

Determination of hydrodynamic parameters

0 100 200 300 400 500

Time (h)

0

100

200

300

400

500

600

700

Chl

orid

e (m

mol

/l)

Experiment I

Experiment II

C = [Cl]t = timex = distance

Numerical model applied to experimental data (Gomis et al., 1997)

u = Darcy velocitye= porosityDL = dispersion coefficient

2

2

LxCD

xCu

tC

Determination of hydrodynamic parameters

The variation of the concentration of tracer versus the time can be determined with theanalytical solution of the equation:

where C represents the concentration of the solute, x the distance, t the time, DL is thehydrodynamic dispersion and v is the interstitial velocity.

If we consider a semi-infinite column from x = 0 to x =∞, with a constant concentration at

the inlet, with the boundary condition, x = 0 , , the obtained equation is(Lapidus y Amundson, 1952):

2

2

LxCD

xCv

tC

t4Dvtxerfc

Dvxexp

t4Dvtxerfc

2)C(CCt)C(x,

LLL

i0i

)C0)t(C(0, 0

Analytical equation to calculate transport parameters

Determination of hydrodynamic parameters

The software, available in http://hdl.handle.net/10045/2691, was developed in theChemical Engineering Department of the University of Alicante. It use the analyticalsolution proposed by Lapidus and Amundson (1952).

ACUAINTRUSION TRANSPORT software

Determination of hydrodynamic parameters

The software calculate the best fit to the experimental data. From this, the program obtainthe transport parameters (Boluda-Botella et al., 2010).

ACUAINTRUSION TRANSPORT software

Experimental chloride breakthrough curve (symbol) obtained in experiment I (Q=20mg/min), experiment II (Q=35 mg/min), experiment A (Q=82 mg/min) and experiment B(Q=20 mg/min, treated sediment) versus experimental time (h).

Best fit of the experimental data (continuous line) obtained with the analytical solution ofthe convection-dispersion equation of ACUAINTRUSION TRANSPORT (T=theoretical).

0

100

200

300

400

500

600

700

0 100 200 300 400

Time (h)

Chl

orid

e (m

mol

/L)

Exp. I

T Exp. I

Exp. II

T Exp. II

Exp. A

T Exp. A

Exp. B

T Exp. B

(a)

Determination of hydrodynamic parameters

Determination of hydrodynamic parameters

Q = flow rateu = Darcy velocitytm = average time of residencePe = Péclet number

Exp. Q(mg/min)

Porousmedia

u(cm/h)

tm(h)

Pe=vL/DL e v(cm/h)

DL(cm2/h)

a(cm)

I 20 Natural 0.15 241 183 0.37 0.41 0.23 0.55

II 35 Natural 0.27 143 166 0.38 0.70 0.42 0.60

A 82 Natural 0.63 65 5.6 0.41 1.54 27.3 17.7

B 20 Treated 0.15 203 147 0.31 0.49 0.33 0.68

The following parameters were determined with ACUAINTRUSION TRANSPORT

e= effective porosityv = interstitial velocityDL = dispersion coefficienta = dispersivity

Experimental chloride breakthrough curve (symbol) for the experiments versus experimental dimensionless time (time/tm). (Boluda-Botella el al., 2008)

0

100

200

300

400

500

600

700

0 0.5 1 1.5 2 2.5 3

Dimensionless time

Chlo

ride

(mm

ol/L

)

Exp. IExp IIExp. AExp. B

(b)

Determination of hydrodynamic parameters

17

REFERENCES

Boluda-Botella, N. 1994. Estudio hidrogeoquímico de la intrusión marina. Simulación experimental ydesarrollo de un modelo teórico. Tesis de Doctoral. Universidad de Alicante.

Boluda-Botella, N., Gomis Yagües, V. and Ruiz Beviá, F. 2008. Influence of the transport parametersand chemical properties of the sediment in experiments to measure reactive transport in seawaterintrusion. J. of Hydrol. 357: 29-41.

Boluda-Botella, N., León, V.M., Cases, V., Gomis, V. and Prats, D. 2010. Fate of linear alkylbenzenesulfonate in agricultural soil columns during inflow of surfactant pulses. J. of Hydrol., 395: 141-152.

Cases López, V.P. 2009. Estudios de procesos de transporte del alquilbenceno sulfonato lineal en lazona saturada mediante columnas de laboratorio. DEA. Universidad de Alicante.

Egea Llopis, E. 2009. Estudios de transporte reactivo de contaminantes en zona saturada:experimentos de inyección de LAS en columna y modelización con PHREEQC. Proyecto Fin de Carrera.Universidad de Alicante.

Freeze, R.A. and Cherry, J.A. 1979. Groundwater. Prentice Hall, Inc.

Gomis, V., Boluda, N., Ruiz, F. 1997. Column displacement experiment to validate hydrogeochemicalmodels of seawater intrusions. J. Cont. Hydrol. 29: 81–91.

Lapidus, L., and Amundson, N.R. 1952. Mathematics of adsorption in beds. VI. The effect oflongitudinal diffusion in ion exchange and chromatographic columns. J. Phys. Chem. 56: 984-988.