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Contributions of boron isotopes to understanding the hydrogeochemistry of coastal detritic aquifer of Castellón Plain, Spain. Hydrogeology Journal 16, 547-557. 2008

Contributions of boron isotopes to understanding the

hydrogeochemistry of the coastal detritic aquifer of Castellón

Plain, Spain

Elena Giménez Forcada . Ignacio Morell Evangelista

E. Giménez Forcada Technological Departmental Area Catholic University of Avila, 05005 Avila, Spain e-mail: egimenezforcada@hotmail.com Phone: +34920251020 Fax: +34920251030 I. Morell Evangelista School of Technology and Experimental Sciences

Jaume I University, 12071 Castellon, Spain e-mail: morell@camn.uji.es

ABSTRACT

The Castellon Plain alluvial aquifer, Spain, is intensively exploited to meet the demand

for agricultural irrigation and industrial water supply. The geochemistry of its

groundwater shows complex salinization in the northern and southern parts of the

aquifer, with significant pollution from human origin in the central portion. Boron

content and B isotope geochemistry are useful for distinguishing between various

sources of pollution and their relative importance in different parts of this aquifer.

Boron concentrations in the groundwater vary between 0.01 mgL-1 and 0.85 mgL-1. In

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the more saline groundwaters, found at the northern and southern ends of the study

area, the presence of B is linked to inputs from seawater and water with a calcium-

magnesium sulphate facies, which feed the aquifer and clearly influence the chemistry

of its waters. Evidence of B adsorption processes in some samples is shown by the low

B/Cl ratios and the high values of 11B. In the central portion of the aquifer, the high

B/Cl ratios and the strongly-negative 11B are related to pollution of human origin.

Keywords: Spain, Hydrochemistry, coastal aquifers, salinization, B isotopes.

INTRODUCTION

The overlap between groundwater polluting processes can frequently mask the

contribution of any one of these to the degradation of the aquifer, especially when

pollutants from the various sources coincide. Probably, the best example of this

situation is the salinization of several Mediterranean coastal aquifers, where seawater

intrusion, mobilization of connate water, discharge of regional flows, presence of

evaporite deposits, urban and industrial wastewater discharges all converge. The

aquifer of the Castellon Plain, on the Spanish Mediterranean coast, is a unique

example that exhibits all of the above-mentioned processes.

A conventional hydrogeochemical study of the chemical reactions affecting the

major ions is effective to make an initial identification of the polluting processes

involved in these situations but the inclusion of both minor ions and isotope

hydrogeochemistry is needed when the knowledge of the precise contribution of each

of them is required. Strontium, Li, iI, Br and B are the most commonly-used minor ions

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to differentiate salinization sources (Fidelibus et al., 1993; Giménez and Morell, 1991,

1992; Giménez, 1994; Morell et al., 1996).

Boron is normally found in groundwaters at low concentrations, so it can be

considered as a minor element. In certain environments, its concentration can be

abnormally elevated. In many Mediterranean regions, B in groundwater can have a

geogenic origin and be linked to salinization processes, such as seawater intrusion,

saline thermal or evaporitic environments. Its origin can also be anthropogenic

because it is found in many commonly-used products, such as ceramics, glass,

fertilizers and detergents, and so is present in domestic wastewater discharges and

industrial effluents that release high concentrations of B to the environment (Pennisi

et al., 2006).

The study of ion ratios between B and other ions, such as the B/Cl ratio, offers

the possibility of identifying and distinguishing between different types of pollution

and/or salinization. Moreover, in recent years the B isotopes have been found to be

excellent tracers of various sources of pollution, which has led to its becoming one of

the most useful, modern hydrogeochemical tools. It is also relevant that the use of B

isotope geochemistry has increased due to the improvement of associated analytical

techniques.

A growing number of studies have demonstrated the potential use of B-isotope

geochemistry as a tracer of geochemical processes in various geological environments

(Kakihana et al., 1977; Kakihana and Kotaka, 1977; Kakihana et al., 1987; Musashi et

al., 1988; Xiao et al., 1992; Vengosh et al., 1994, 2005; Eisenhut and Heumann, 1997;

Vengosh, 1998; Barth, 1997, 2000; Rose et al., 2000; Pennisi et al., 2006a, 2006b,

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amongst others), and these studies have commented specifically on the usefulness of

the behaviour of B isotopes for the characterization of groundwater pollution.

The main aim of the present report is to demonstrate the usefulness of B and its

isotopes in identifying the processes taking place in the coastal aquifer of Castellon

Plain, which is affected by seawater intrusion and other pollution processes, and to

demonstrate how B isotope geochemistry can be applied as a useful tool for

discriminating between different polluting sources within the same aquifer.

GEOLOGICAL AND HYDROGEOLOGICAL SETTING

The Castellon Plain, located in the Castellon Province (Community of Valencia, Spain)

extends over 460 km2 (Figure 1). It is limited to the west by Mesozoic reliefs, and to

the east by the Mediterranean Sea.

It is a well-delimited aquifer subsystem, which has been overexploited for urban

and industrial supply. A significant proportion of the agricultural water demand is

satisfied from groundwater pumped from more than 500 existing wells. The central

zone is an exception, where agricultural demand is satisfied with water taken from the

River Mijares.

The limits of the coastal plain coincide with fault lines of significant throw. These

fractures establish the contact between the Plioquaternary sediments of the Plain and

the surrounding Mesozoic relief (Figure 1). The most important outcrops in the Sierra

of Espadán (to the south) are the Triassic deposits. These are characterized by

Germanic facies that can be subdivided into the continental siliciclastic Buntsandstein,

Muschelkalk carbonates and the continental Keuper evaporites and redbeds. To the

north, Jurassic and Cretaceous carbonate rocks predominate. In the western-most

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corner the Plioquaternary formation is limited by the Tertiary deposits of the

Ribesalbes-Onda basin (“Cubeta of Ribesalbes-Onda”). Borehole logs indicate that this

fault continues beneath the Plioquaternary fill, so that the basement of the southern

lip corresponds to Triassic and Jurassic deposits, whereas to the north, Cretaceous

deposits are recognized.

The Castellon Plain is filled mostly by Plioquaternary deposits of various origins.

Since its origin in the Miocene, the plain represents a depositional environment fringed

by pediment deposits. Almost all the deposits infilling the plain are of continental

origin, although mixed and even marine deposits also exist.

Hydrogeologically, the Plioquaternary deposits of the Castellon Plain comprise an

important unconfined, detritic aquifer with inter-granular porosity. The aquifer

consists of intercalated layers and lenticular beds of conglomerates, sands and gravels,

embedded in a silt-clay matrix, making up a single aquifer-unit.

The wide heterogeneity of deposits that make up the Castellon Plain aquifer

means that lithological continuity is not easily established, though hydraulic

connection between the different layers allows the system to be considered as a

single, high-permeability aquifer unit.

Several technical reports on the aquifer agree that the hydrodynamics of the

aquifer are extraordinarily variable (IGME, 1984; IGME, 1986; IGME, 1988; ITGE, 1989-

90). The transmissivity values of the Plioquaternary aquifer range from less than 500 to

more than 6000 m2/day. The distribution of the storage coefficient is between 5 and

15 %, which is characteristic of an unconfined, detritic aquifer. The highest values are

recorded from the region of the River Mijares (Giménez, 1994).

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Piezometric levels drop progressively from the west towards the

Mediterranean Sea in the east (see Figure 1). Near the coastline, piezometric levels

tend to fluctuate between 10 and 0 m a.s.l. (meters above sea level), whereas inland,

they are significantly higher (normally up to 60 m a.s.l.). Annual fluctuations in

piezometric level are between 5 and 10 m in the western part of the plain and about 1

m along the coastline. Accordingly, the main flow direction of groundwater in the

Castellon Plain is from west to east.

Aquifer recharge comes from rainwater infiltration (85 x 106 m3/year), irrigation

return water (45 x 106 m3/year) and transfers from neighbouring units (90 x 106

m3/year), making a total of 220 x 106 m3/year. Outflows consist of pumped

abstractions (165 x 106 m3/year), coastal springs and wetlands (16 x 106 m3/year), as

well as submarine discharges (39 x 106 m3/year). The equilibrium of the system is

based on surpluses in the central sector. The absence of surface water has led to

intensive exploitation of the aquifer, particularly during the increasing-frequent dry

years, and this has led to overexploitation in the northern and southern sectors. The

result is a decline in piezometric levels of down to 4 metres below sea level, and this

favours the advance inland of the fresh water-saltwater interface. This process is

especially severe in the southern sector (Vall d’Uixó – Moncófar). Figure 2 gives a

general hydrogeological cross section of the aquifer, as well as a general water

balance.

Whilst the Castellon Plain aquifer used to be in surplus, nowadays its shows an

equilibrium in terms of water flow in and out of the aquifer. Despite this general

equilibrium, some sectors, Vall d’Uixó - Moncófar (in the south) and Benicasim (to the

north), show a deficit reflected by the salinization of the groundwater.

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SAMPLING AND ANALYSIS

Hydrogeochemical information was obtained from a sampling survey carried out in July

2003. Most samples were taken from the wells that supply most of the agricultural

water used on the Castellon Plain.

For this study, a representative set of groundwater samples was obtained from

33 active wells selected on the basis of salinity distribution. Most of the wells are used

for irrigation purposes and are about 20–100 m deep. One well was used to

characterise the fresh water (FW in Table 2). Samples were taken at the sites shown in

figure 1. As this figure shows, more samples were taken in the southern part of the

plain (around Moncófar) where high salinity is already known to exist. In addition,

samples of surface water were taken from the River Mijares (RM) and from the

reservoirs of María Cristina and Sichar (MC: Maria Cristina reservoir; Si: Sichar

reservoir).

Electrical conductivity, pH and temperature were recorded in the field. The

chemical composition of the water samples was analyzed in the laboratory. The

analytical techniques used to determine the chemical and physical parameters were

taken from Standard Methods for the Examination of Water and Wastewater (APHA,

AWWA, 1989). Chloride, sulphate and nitrate ions were determined with an

Autoanalyzer ALKEMP 501. The bicarbonate ion was analysed volumetrically using a

methyl orange indicator. Sodium, potassium, magnesium, calcium, strontium and

lithium were analysed using atomic absorption spectrometry; iodide and bromide ions,

by mass-ICP. Finally, total B was determined by colorimetry using the Azomethine-H

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method (Bencini, 1985; López et al., 1993). Table 1 summarises the analytical

techniques employed and their precision. Table 2 displays the results of the analyses.

Boron isotope ratios were determined by mass spectrometry using an ICP-MS

(Inductively Coupled Plasma Mass Spectrometry) HP 4500 instrument. The samples

(which had different and generally very high salinities) were treated using Amberlite

IRA 743. The instrument parameters were optimised to give the greatest signal for B

and the best precision in the measurement of the 10B/11B ratio. The resolution of the

quadrupole was set to 0.5 amu (atomic mass unit (10% of the peak height) in order to

eliminate the overlap of the tail of the 12C isotope. Instrumental mass discrimination

was corrected using a NIST SRM 951 B standard certified for isotopic ratio. To

eliminate the mass discrimination produced by the excess HCl used during treatment

of the resin, the standard was also prepared in this medium. All samples with

concentrations greater than that of the standard were diluted. Isotope measurements

were made on quintuplicate samples, with an integration time of 8 seconds for 10B and

5 for 11B, with the aim of equalizing the count-rate precision. The precision obtained

was in the order of 0.2 % of the RSD (Relative Standard Deviation).

GENERAL GROUNDWATER CHEMISTRY

Groundwater salinization in the Castellon Plain has been documented since the early

1960s. The first hydrogeochemical studies were aimed at finding out and

differentiating the possible sources of salinization.

Results of these studies revealed that salinization in this aquifer is very complex:

as a general rule, regional groundwater flow, rich in sulphate, calcium and magnesium

competes with marine intrusion for salinization of the groundwaters.

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Hydrogeochemical studies have been aimed at determining and differentiating these

potential sources of salinization. Research by Giménez (1994), who made a

hydrogeochemical characterization of salinization in the Castellon Plain aquifer based

on the behaviour of major and minor ions (Sr, Br, I, Li and B), and revealed that the

hydrochemistry of this aquifer is the result of interplay between various natural and

anthropogenic processes. The application of multivariate statistics (Morell et al., 1996)

confirmed the proposed model. Morell and Tuñón (2002) demonstrated the influence

of tectonics of the basement rocks on the local geochemistry. They determined that

aquifer recharge is strongly controlled by tectonic and structural features.

The physico-chemical characteristics of the groundwater of the Castellon Plain

generally reflect a situation of salinization that is associated principally with marine

intrusion. This can be appreciated from the Piper diagram in figure 3; nevertheless,

some deviations from this simple scheme occur. These deviations can be significant

and reveal some interesting hydrogeochemical and hydrodynamic aspects.

In an initial approximation, three sectors can be distinguished in the aquifer: the

northern sector (Benicasim), which has a predominance of Na-Cl facies, chloride

concentrations of between 10 and 20 meq/L and electrical conductivity of around 2000

S/cm; the central sector, which shows Ca-SO4,Cl facies, with chloride concentrations

of less than 10 meq/L and electrical conductivity of between 700 and 1300 S/cm; and

the southern sector (Moncófar), which shows electrical conductivity ranges of between

1400 and 3400 S/cm, chloride concentrations of between 10 and 30 meq/L, and very

varied facies, ranging from Ca,Na-Cl and Ca-Cl,SO4 to Ca,Mg-Cl,SO4 facies.

The chloride and sulphate ions are clearly the dominant anions and so there are

practically no bicarbonate waters, as might be expected from the chemistry of the

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lateral groundwater recharge, at least in the northern half of the aquifer. In the

southern sector, the Triassic aquifers laterally feed the Plain, exerting a decisive

influence on its hydrochemistry. The Muschelkalk aquifer merits special importance in

this context because it determines the chemistry of the Plioquaternary aquifer in a

particular way. In general, the water of this aquifer is of calcium-magnesium

bicarbonate type, though the influence of evaporite deposits (Keuper or the

intermediate Muschelkalk beds) can substantially increase the saline content and the

percentage of sulphate in the water. When this occurs, the calcium bicarbonate facies

gives way to a calcium-magnesium sulphate facies.

Given the influence of these feed waters in the aquifer, the groundwater

generally gives a SO4/Cl (in meq/L) ratio that is higher than that corresponding to

seawater (0.10 in seawater and an average of 0.71 in the sampled waters). This

reveals that only a part of the sulphate content can be attributed to seawater and that

a significant proportion must come from other saline contributions that differentially

enrich the water with the sulphate ion. This sulphate enrichment is accompanied by

increases in calcium and magnesium, and this suggests a common, non-marine origin

for these ions.

Since this is a coastal detritic aquifer subject to marine intrusion, the ion

exchange process assumes great significance in the salinized zones and is a very

important factor regulating ion concentrations in the groundwater (Appelo and

Postma, 2006).

The classic bibliography on ion exchange processes in coastal aquifers (Howard

and Lloyd, 1983; Tellam and Lloyd, 1986; Lloyd and Tellam, 1988; Ikeda, 1989; Appelo

and Postma, 2006) all state that the appearance of Ca-Cl facies in a coastal aquifer

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reflects the operation of inverse ion exchange, whereas the Na-HCO3 facies can

indicate direct exchange, and the predominance of Ca-Cl or Ca-Cl,SO4 facies over much

of the aquifer clearly indicates the existence of inverse ion exchange.

In the aquifer under study, the most saline waters (Cl- > 10 meq/L) show close

negative correlation between (Mg2++Ca2+)/Cl- and (Na+ + K+)/Cl- (r2 = 0.8234), and this

corroborates the hypothesis of ion exchange, according to the basic reaction:

2Na+ + X-Ca Ca2+ + X-Na

The scale of the exchange reactions in the most saline water can be judged by

comparing the difference between the measured concentration with that expected

from mixing with seawater, which is calculated by taking the concentration of the

chloride ion in the sample and assuming the conservative behaviour of this ion (Appelo

and Postma, 2006; Giménez Forcada et al., 2001; Vengosh et al., 2002; Pennisi et al.,

2006b).

Loss or gain can be expressed in terms of -ion, where -ion is the meq of all

ions involved in the reaction as a result of the freshwater-salt water mixing (Tellam and

Lloyd, 1986 [1 ]; Appelo and Postma, 2006 [2]):

-ion = [ion]R – [ion]T [1]

m i,react = m i,sample – m i,mix [2]

where -ion or m i,react represent any change in the ion concentration due to reactions,

[ion]R or m i,sample are the measured concentration in the sample and [ion]T or m i,mix

indicate the concentration of a conservative seawater-freshwater mixture, given the

chloride concentration in the sample.

Using this method, the -ions (or m i,react) of the samples were calculated for the

three hydrochemically-differentiated sectors of the aquifer. Table 2 summarizes the

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analytical data in mg/L of the water samples, as well as that of seawater and the fresh

water sample (FW) taken to be representative of the freshwater in the aquifer (see

location in figure 1).

Figure 4 shows the evolution of the -ions values. The samples have been ranked

by increasing chloride concentrations for each sector. The figure shows that ion

exchange becomes more evident and more intense as salinity increases. This is

expressed in the figure by chloride concentration, giving rise to clearly Ca-Cl waters in

the southern sector of the aquifer.

In the less saline waters in the central portion of the aquifer, these processes are

not significant and may even be absent, since it is unaffected by marine intrusion.

On the basis of this approximation of the major ions, the B isotope ratio was then

employed to confirm hypotheses concerning the processes involved in salinization of

this coastal aquifer and improve the description of the various types of pollution it

suffers.

APPLICATION OF GEOCHEMISTRY AND ISOTOPES OF BORON

Boron concentrations in the environment vary over a wide range. Uncontaminated

rainwater usually gives concentrations of a few ppb, while certain hydrothermal fluids

contain several gL-1 (Dotsika et al., 2006).

In general, the presence of B in groundwaters depends on its salinity and the B

content of the aquifer rocks (Harder, 1970). Arad and Bein (1986) and Arad (1988)

studied groundwaters in Israel and established that the B content is usually related to

the salinity of the solution, such that it generally increases as salinity increases.

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In coastal aquifers, direct marine intrusion can supply B to water, leading to an

estimated mean concentration of B of 4.6 mg/l. The relatively high concentration in

seawater, compared to the low content of the majority of fresh groundwaters,

suggests it could be of use as an indicator of marine intrusion in coastal aquifers where

no other inputs exist. In general, a good correlation is found between the content of B

and Cl (Schmassmann and Kullin, 1990; Travi and Faye, 1990), and from this comes the

interest to use B as an indicator of marine intrusion. In terms of applying B isotopes in

coastal aquifers, a few studies have used variations in the B isotope ratio to investigate

marine intrusion (Negret et al., 2002; Morell et al., 2005; Tonarini et al., 2004; Aiuppa

et al., 2006; Leeman et al., 2005) In such environments, the B/Cl ion ratio could prove

to be of great use, and its variation with respect to the seawater ratio could be

significant (Giménez, 1994, 2005).

The excess compared to seawater can be explained by the influence of other

kinds of salinization such as deep circulating flows (Giménez and Morell 1991, 1992;

Giménez, 1994; Vengosh et al., 1994; Ravenscroft and McArthur, 2004) and

anthropogenic pollution (Mirecki and Parks 1994; Vengosh et al., 1994; Sánchez-

Martos and Pulido-Bosch, 1999), while values below seawater may indicate the

influence of water-rock interactions.

However, in high-transmissivity aquifers B can be considered as a conservative

tracer (Davidson and Basset, 1993). Boron exhibits hydrogeochemical retardation in

groundwater environments containing a high clay fraction. The hydraulic conductivity

of the groundwater is not the only factor that determines B mobility in the

groundwater system; there are other crucial factors, such as salinity, type of clay, pH,

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temperature, ionic strength of the solution, etc. (Keren and Mezuman, 1981; Vengosh

et al., 1991).

In fact, depletion could be related to adsorption, since B can be adsorbed into

the clay minerals and incorporated in secondary minerals (Dotsika et al., 2006). In

general, processes of adsorption and desorption of B play an important role in

determining the B content of the water in contact with clayey sediments (Spivack et

al., 1987; Macpherson and Land, 1989; Goldberg, 1993; Goldberg et al., 1993). They

can be linked to the ion exchange reactions that usually accompany salinization of

coastal detritic aquifers (Faye et al., 2005; Ravenscroft and McArthur, 2004 ). In any

event, the effect of these processes on the B/Cl ion ratio can be significant.

Beneath the Castellon Plain, potential sources of B in the aquifer are varied.

They range from seawater or saline waters derived from regional flows, to domestic

and industrial sewage. Earlier hydrochemical studies in the area indicate that B in

groundwater is principally geogenic and appears to derive mainly from seawater

and/or the saline sulphate waters (Giménez, 1994). As a general rule, the values of

B/Cl ratio close to that of seawater are found in the Benicasim and Vall d’Uixó-

Moncófar sectors (in northern and southern sectors), where the most saline waters

occur (Figure 5).

In the northern sector marine intrusion is evident because Ca-Cl and Na-Cl facies

are dominant. Samples give B concentrations close to or slightly below the value

corresponding to mixing. In the Vall d‘Uixó-Moncófar sector (Southern sector), the B/Cl

ratio is of the same order as seawater (without dismissing the influence of the sulphate

waters and adsorption processes). This reflects the fact that the contribution of B in

this sector comes mainly from salinization: seawater and sulphate water are linked to

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Triassic aquifers. Most saline waters suggest a clear correspondence exists between

the excess sulphate and B compared to the theoretical contribution from seawater

(Giménez, 1994). The participation of adsorption/desorption in the clay fraction cannot

be rejected; this would compete with inputs of B from the sulphate waters, but it is

difficult to prove this since the processes give rise to reciprocal effects.

The maximum values encountered in the aquifer came from samples in the

central sector of the aquifer, where electrical conductivity is less than 1300 S/cm. It is

concluded that in the more saline parts of the aquifer, the B is geogenic and the

principal contribution is from seawater, with lesser contributions from regional flows

(Ca,Mg-SO4 water). In the less salinized sector (central sector) the high B

concentrations encountered can not be associated with the salinity, and so must be

primarily associated with other sources of pollution, possibly anthropogenic).

Recent hydrogeological research has successfully used the B isotope ratio for

discriminating between natural and anthropogenic sources of pollution. Research by

Davidson and Bassett (1993), Vengosh et al. (1994), Bassett et al. (1995), Eisenhut et

al., (1996), Eisenhut and Heumann (1997), Barth (2000), Hogan and Blum (2003) and

Gonfiantini (2006a, 2006b) are examples of its application.

Bearing these studies in mind, the application that has been made of the B

isotopes as tracers of pollution derive from a number of general considerations about

the two stable B isotopes found in nature, namely 11B and 10B. , whose approximate

abundances are 20 and 80% respectively in natural B. The isotopic variations of B are

expressed in parts per thousand relative to a standard, as 11B (Barth, 1997, 1998;

Vengosh, 1998):

11B = {[(11B/10B) sample / (11B/10B) standard] -1} 1000

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Because of the relatively large difference in mass between the two isotopes and

the high geochemical reactivity of B, significant isotopic fractionation produces large

variations in the 11B/10B ratio in natural waters from different geological environments.

The most extreme values recorded are +59 ‰ in the brines of salt lakes of Australia

and the Dead Sea (Israel) (Barth, 1993), and –14 ‰ in some geothermal fluids (in

Bassett et al., 1995).

Speciation of dissolved B and, thus, the fractionation of B isotopes in an

aqueous-solid system are, in turn, dependent on the pH of the aqueous phase. The

isotope-exchange reaction between the two dominant B species is given by the

chemical equation:

10B(OH)3 + 11B(OH)4- 11B(OH)3 + 10B(OH)4

-

Isotopic fractionation of B results from the differential uptake of the two species

during interaction of the dissolved B with the solid phase. This consists basically of B

adsorption by clay minerals. The borate anion, B(OH)4- is preferentially adsorbed by

clay minerals. Consequently, the aqueous phase is depleted in B(OH)4- and, since 10B is

preferentially incorporated as B(OH)4-, the aqueous phase is depleted in 10B as well. In

such cases, a higher 11B value for water might be expected. Large B isotope variations

(~90‰) have been recognized in natural reservoirs and this variability makes the B

isotope ratio a candidate for tracing the origin of dissolved salts in groundwaters.

In general, the conservative behaviour of the two B isotopes (11B and 10B) can be

used to differentiate mixing processes between groundwater, wastewater and

agricultural return flow, although the preferential adsorption of 10B by clays has also to

be considered (Barth, 1998; Leenhouts et al., 1998; Vengosh, 1998).

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In addition, the B isotope composition of contaminated groundwater can reveal

the sources of pollution, since different sources are characterized by distinct isotope

ratios.

The B isotope composition 11B of synthetic B compounds (anthropogenic B)

seems to be determined by the 11B values of their parent raw materials and the

isotope composition of anthropogenic B contained in wastewaters is normally

different from natural B in groundwater, particularly in coastal aquifers. The low B-

isotope ratio ( 11B) of urban wastewaters relative to groundwater has led to B being

used as a tracer of both direct urban pollution (Vengosh et al., 1994, 1998, 1999;

Bassett et al., 1995) and leaching from solid urban waste (Hoehn, 1999; Barth, 1998,

2000).

In open sea environments in the present-day, the 11B value is notoriously

constant at +40‰ (relative to average continental material). The considerable

enrichment of 11B in seawater is mainly attributed to B-isotope fractionation linked to

B adsorption onto the clay minerals present in the oceans.

In salinized aquifers, B isotope variations have also been used to identify the

origin of salinity. In terms of the application of B and its isotopes to coastal aquifers,

few studies have used B isotope variations to investigate marine intrusion processes.

Vengosh et al., (1992, 1994, 1998) undertook systematic studies in different

environments and found a link between ancient saline waters and salinization due to

marine intrusion in diverse coastal aquifers.

In Figure 6 it is possible to observe differences between samples collected from

different sectors of the study area. Water from the central part of the aquifer

yielded B/Cl ratios of between 1.3 x 10-3 and 4.6 x 10-3 (0.63 x 10-3 in seawater and

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0.48 x 10-3 in freshwater), and values of 11B of between +13 and -9‰, with a clear

trend towards the values measured in the waters of the River Mijares, which is used

for irrigation abstractions in this area. Water from the River Mijares is clearly affected

by point discharges into the Maria Cristina reservoir (B = 4.8 mg/L; 11B = -12 ‰) and,

to a lesser extent, into the Sichar reservoir. The water of the River Mijares (B = 0.23

mg/L; 11B = -8.9 ‰) has to be the principal source of B in this sector, though point

discharges can not be dismissed (since these must have isotope ratios in the same

range). Such point discharges could affect sectors that are not irrigated with water

from the River Mijares, which come from areas around an important industrial

nucleus.

In this central sector the existence of heavy metals (Hg and Cr from discharges

from tanning factories), pesticides and nitrate residues (derived from agricultural

activity), and other pollutants (such as B from ceramic industry effluents) suggest that

the anthropogenic input is significant (Morell and Hernández, 2001).

In terms of the most saline waters, one can observe that samples from the

northern and southern sectors tend to have the highest values of 11B, in the range

+10 and +20 ‰, with a B/Cl ratio more or less similar to seawater, though some

samples yielded lower values, perhaps due to adsorption of B in the sediments.

Under this general scheme, however, some samples from the southern sector

give very high B/Cl ratios (samples 16 and 26). These samples register relatively low

and negative values for 11B (+7.74 ‰ in sample 16 and -0.86 ‰ in the sample 26). The

ceramics industry is not present in this area, nor is there any influence of sulphate

waters that could explain the elevated B/Cl ratio in some of the samples; therefore,

other anthropogenic contributions of B must exist, that are non-marine in origin. This

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pollution is independent of salinity of the water and may be linked to infiltration of

water containing high B concentrations, with especially intense and localized inputs

coming from industrial wastewater introduced directly into the aquifer. The water

samples were taken from between the towns of Vall d’Uixó and Moncófar, in the

vicinity of the River Belcaire. With the exception of certain days in the year following

strong rains, the flow of this river is almost exclusively derived from wastewater from

Vall d’Uixó (30,000 inhabitants) and disperse discharges from tanning factories. Thus,

highly saline waters are recorded that, in many cases, have an elevated heavy metal

(Hg, Cr, Zn, Cd) and B content. In the area between the towns of Vall d‘Uixó and

Moncófar, where these wells are found, part of the river flow infiltrates the aquifer,

giving rise to intense local pollution (Morell, 1999).

The average B concentration of water in the River Belcaire is 1 to 1.5 mg/L and

the 11B is -3.1 ‰, though it can change depending on the season and type of the

discharge. Judging by the hydrogeochemistry, it is possible to conclude that some parts

of the southern sector of the aquifer are affected by wastewater infiltration from the

River Belcaire, which has a low B isotope ratio that is far below that corresponding to

salinization due to marine intrusion or sulphate water recharge.

Samples 1 and 3 correspond to saline waters from the northern part of the

aquifer and give a 11B of +29 ‰. This is clearly due to the influence of seawater,

though the lower B/Cl ratio suggests the possibility that B adsorption does occur and

that it tends to increase the 11B/10B ratio.

In this context, there may also be participation from adsorption-desorption of B

accompanying the ion exchange linked to the dynamics of the marine intrusion and

other processes of salinization. Nevertheless, the hydrochemical analysis reveals,

20

above all, the importance of the geogenic and anthropogenic pollution and their

relative influence in different parts of the aquifer.

CONCLUSIONS

The general hydrogeochemical study of the aquifer provides good support to

enable the application of the behaviour of some of the minor ions, especially B and its

isotopes, and so helps to discriminate between the different sources of pollution and

the relative importance in each of the three sectors of the aquifer under study.

The B seems to arise from multiple origins, and the study of the behaviour of the

B isotopes has enabled a reliable diagnosis of various types of pollution. In other

words, this element and its isotopes can be considered to be good tracers of the

polluting processes. The B/Cl ion ratio is very useful, as is the 11B/10B isotope ratio,

whose usefulness basically derives from the large differences encountered between

the different water types contributing to the aquifer pollution. The anthropogenic B

content of wastewaters is isotopically very different to naturally-arising B, particularly

in coastal aquifers.

The study undertaken has allowed corroboration of earlier hypotheses based on

the behaviour of major ions, and confirmed the efficacy of using B isotopes to diagnose

complex pollution problems. It has also been confirmed that the three sectors of the

aquifer correspond to areas with different pollution problems. The southern sector

contains the most saline water as a result of saline intrusion and sulphate waters, but

significant pollution also comes from infiltration of water from the River Belcaire, as

identified by a low 11B/10B ion ratio that corresponds to industrial discharges directly

into the watercourse. In the northernmost sector of the aquifer, the groundwater

21

chemistry could be principally associated with marine intrusion, as indicated by the

11B values. Moreover, the participation of B adsorption cannot be dismissed, as is

deduced from the increase in the 11B/10B ratio.

In the central sector – the least-salinized sector of the aquifer – the influence of

the River Mijares is decisive. The river is used for irrigating citrus crops and this is the

cause of high B/Cl ion ratios in borehole water from this sector. The anomaly is also

related to the discharge of untreated industrial wastewater into the watercourse. In

addition, some sampling points, situated away from the area irrigated using river

water, also exhibit elevated B concentrations. In these cases, it seems that the

proximity of the sampling points to significant industrial centres needs to be taken into

account.

In conclusion then, the usefulness of B and its isotopes has been demonstrated

by means of the 11B/10B ratio, in identifying the various pollution sources implicated in

the pollution of this aquifer. It is also concluded that this phenomenon can be

extrapolated to similar situations, where B could be used as a tracer of sources of

pollution.

Acknowledgements. This article was financed by the CICYT (Comisión Interministerial

de Ciencia y Tecnología, Interministerial Commission of Science and Technology)

within the framework of project HID1999-0597-C01-02. The authors are also grateful

to Eduard Hoehn and an anonymous reviewer, for their comments and suggestions on

the manuscript.

REFERENCES

22

AIUPPA A, AVINO R, BRUSCA L, CHIODINI G, D'ALESSANDRO W, FAVARA R, FEDERICO C,

GINEBRA W, INGUAGGIATO S, LONGO N, PECORAINO G, VALENZA M (2006) Mineral

control of arsenic content in thermal waters from volcano-hosted hydrothermal

systems: Insight from island of Ischia and Phlegrean Fields (Campanian Volcanic

Province, Italy) Chemical Geology 229:313-330.

APHA (American Public Health Association), AWWA (American Water Works

Association), WPCF (Water Pollution Control Federation ) (1989) Standard methods

for the examination of Water and Wastewater. American Public Health Association.

Washington.

APPELO CAJ, POSTMA D (2006) Geochemistry, Groundwater and Pollution. AA

Balkema, Rotterdam. 2nd edition.

ARAD A (1988) B, F and Sr as tracers in carbonate aquifers and in karstic geothermal

systems in Israel. IAH (International Association of Hydrogeologists) 21st Congress.

Karst Hydrogeology and Karst Environment Protection. Guilin (China), 1988.

ARAD A, BEIN A (1986) Saline-versus freshwater contribution to the thermal waters of

the northern Jordan Rift Valley, Israel. Journal of Hydrology 83: 49-66.

BARTH S (1993) Boron isotope variations in nature: a synthesis. Int. J. Earth. Sci. 82 (4):

640-651

BARTH S (1997) Boron isotopic analysis of natural fresh and saline waters by negative

thermal ionization mass spectrometry. Chem. Geol. (Isot. Geosci. Sect.) 143: 255-

261.

BARTH S (1998) Application of boron isotopes for tracing sources of anthropogenic

contamination in groundwater. Wat. Res. 32(3): 685-690.

23

BARTH S (2000) Boron isotopic composition of near-surface fluids: a tracer for

identification of natural and anthropogenic contaminant sources. Water, Air and

Soil Pollution 124: 49-60.

BASSETT RL, BUSZKA PM, DAVIDSON GR, CHONGDIAZ D (1995) Identification of

Groundwater Solute Sources Using Boron Isotopic Composition. Environ. Sci.

Technol. 29 (12): 2915-2922.

BENCINI A (1985) Applicabilità del metodo dell’Azometina-H alla determinazione del

boro nelle acque naturali (Application of Azomethine-H method to the

determination of boron in natural waters). Rend. Soc. It. Min. Petr. 40: 311–316.

DAVIDSON GR, BASSET RL (1993) Application of boron isotopes for identifying

contaminants such as fly ash leachate in groundwater. Environ. Sci. Technol. 29(12):

2915-2922.

DOTSIKA E, POUTOUKIS D, MICHELOT JL, KLOPPMANN W (2006) Stable isotope and

chloride, boron study for tracing sources of boron contamination in groundwater:

boron contents in fresh and thermal water in different areas in Greece. Water, air,

and soil pollution 174: 19–32

EISENHUT S, HEUMANN KG (1997) Identification of ground water contamination by

landfills using precise boron isotope ratio measurements with negative thermal

ionization mass spectrometry. Fres. J. Anal. Chem. 359: 375–377.

EISENHUT S, HEUMANN KG, VENGOSH A (1996) Determination of boron isotopic

variations in aquatic systems with negative thermal ionization mass spectrometry as

a tracer of anthropogenic influences. Fres. J. Anal. Chem. 354: 903–909.

24

FAYE S, MALOSZEWSKI P, STICHLER W, TRIMBORN P, FAYE SC, GAYE CB (2005)

Groundwater salinization in the Saloum (Senegal) delta aquifer: minor elements and

isotopic indicators. Science of the Total Environment 343 (2005) 243– 259.

FIDELIBUS MD, GIMÉNEZ E, MORELL I, TULIPANO L (1993) Salinization processes in the

Castellon plain aquifer. In: Custodio, E.; Galofré, A. (Eds.). Study and Modelling of

Salt Water Intrusion into Aquifers. Proc. 12th Saltwater Intrusion Meeting.

Barcelona, 1992: 267-283.

GIMÉNEZ E (1994) Caracterización hidrogeoquímica de los procesos salinización en el

acuífero detrítico costero de la Plana de Castellón. “Hydrogeochemical

characterization of the salinization processes in coastal aquifer of Castellón Plain”.

PhD, University of Granada.

GIMÉNEZ E (2005) Consideraciones sobre la utilidad del boro como trazador

hidrogeoquímico en procesos de salinización (Considerations on the utility of boron

like hydrogeochemical tracer in salinization proceses). Abula 7: 7-20. Universidad

Católica de Ávila.

GIMÉNEZ E, MORELL I (1991) Consideraciones sobre la utilización de iones

minoritarios en la caracterización de la intrusión marina. “Reflections about

utilization of minor ions in the characterization of marine intrusion”. El Agua en

Andalucía, I. Córdoba, 1991: 401-412.

GIMENEZ E, BENCINI A, PRANZINI G (2001) Salinization in coastal plain of Grosseto:

hydrochemical study. Water-Rock Interaction (WRI-2001): 517-520. Balkema,

Rotterdam.

25

GIMÉNEZ E, MORELL I (1992) El boro como indicador de contaminación en la Plana de

Castellón. “Boron as tracer of contamination in Castellón Plain aquifer”.

Hidrogeología y Recursos Hidráulicos XVI: 285-292.

GOLDBERG S (1993) Chemistry and Mineralogy of Boron in Soils. In: Gupta, U.C. (Ed.),

Boron and its Role in Crop Production. CRC Press, Boca Raton, FL: 3–44.

GOLDBERG S, FORSTER HS, HEICK EL (1993) Boron adsorption mechanisms on metal

oxides, clay-minerals, and soils inferred from ionic-strength effects. Soil Sci. Soc.

Am. 57: 704–708.

GONFIANTINI R, PENNISI M (2006) The behaviour of boron isotopes in natural waters

and in water–rock interaction. J. Geochem. Explor. 88: 114–117.

HARDER H (1970) Boron. In: Wedepol K.H. (eds). Handbook of Geochemistry. Chap. 5.

Springer-Verlag.

HOEHN E (1999) Preliminary analysis of boron isotope ratios in leachate-contaminated

groundwater. Integrated Methods in Catchment Hydrology- Tracer, Remote Sensing

and New Hydrometric Techniques. IAHS Publ. Nº 258.

HOGAN JF, BLUM JD (2003) Boron and lithium isotopes as groundwater tracers: a study

at the Fresh Kills Landfill, Staten Island, New York, USA. Appl. Geochem. 18: 615–

627.

HOWARD KWF, LLOYD JW (1983) Major ions characterization of coastal saline ground

waters. Ground Water 21(4): 429-437.

IGME (1984). Actualización de los recursos hidráulicos subterráneos existentes en la

comarca de Sagunto. Comunidad Valenciana. I-II. IGME (Instituto Geológico y

Minero de España, Spanish Geological Survey).

26

IGME (1986). Las aguas en la Comunidad Valenciana. Uso calidad y perspectivas de

utilización (The waters in the Valencian Community. Use, quality and perspectives

of utilization). IGME (Instituto Geológico y Minero de España, Spanish Geological

Survey). Mº Industria y Energía. Colección Informe.

IKEDA K (1989) Chemical evolution of groundwater quality in the southern foot of

Mount Fuji. Bulletin of Geological Survey Japan 40 (7): 331-404.

ITGE (1989-90). Planas de Castellón y Sagunto. Serie Manuales de Utilización de

acuíferos. Dirección de Aguas Subterráneas. ITGE (Instituto Tecnológico y

Geominero de España, Spanish Geological Survey).

KAKIHANA H, KOTAKA M (1977) Equilibrium constants for boron isotope-exchange

reactions. Bull. Res. Laborat. Nucl. React. 2: 1–12.

KAKIHANA H, KOTAKA M, SATOH S, NOMURA M, OKAMOTO M (1977) Fundamental

studies on the ion-exchange separation of boron isotopes. Bull. Chem. Soc. Japan

50: 158–163.

KAKIHANA H, OSSAKA T, OI T, MUSASHI M, OKAMOTO M, NOMURA M, (1987) Boron

isotopic ratios of some hot spring waters in the Kusatsu-Shirane area, Japan.

Geochem. J. 21: 133–137.

KEREN R, MEZUMAN U (1981) Boron adsorption by clay minerals using a

phenomenological equation. Clays and Clay Minerals 29 (3): 198-204.

LEEMAN WP, TONARINI S, PENNISI M, FERRARA G (2005) Boron isotopic variations in

fumarolic condensates and thermal waters from Vulcano Island, Italy: Implications

for evolution of volcanic fluids. Geoch. et Cosmoch. Acta 69(1): 143-163.

27

LEENHOUTS JM, BASSETT RL, MADDOCK T (1998) Utilization of intrinsic boron

Isotopes as Co-Migrating Tracers for Identifying Potential Nitrate Contamination.

Ground Water 36 (2): 240-250.

LLOYD JW, TELLAM JH (1988) Caracterización hidroquímica de las aguas subterráneas

en áreas costeras. “Hydrochemical characterization of groundwater in coastal

areas”. Tecn. Int. Sal. en Acuif. Cost. (TIAC) 1:1-18. Almuñecar (España).

LÓPEZ FJ, GIMÉNEZ E, HERNÁNDEZ F (1993) Analytical study on the determination of

boron in environmental water samples. Fresenius J. Anal. Chem., 346: 984-987

MACPHERSON GL, LAND LS (1989) Boron in saline brines, Gulf of Mexico sedimentary

basin, USA. In: Miles (Ed.). Water-Rock Interaction (WRI-86): 457-460 Balkema,

Rotterdam.

MIRECKI JE, PARKS WS (1994) Leachate Geochemistry at a Municipal Landfill,

Memphis, Tennessee Ground Water 32 (3): 390-398.

MORELL I, PULIDO-BOSCH A, VIRGILIO J, DANIELE L (2005). Geoquímica isotópica del

boro en áreas termales asociadas a vulcanismo activo. Casos de las islas de Ischia

(Italia) y San Miguel (Portugal) (Isotopic geochemistry of boron in thermal areas

associated with the active vulcanism. Cases of Ischia Island (Italy) and San Miguel

(Azores, Portugal). In: Agua, minería y medio ambiente. Ed. IGME (Instituto

Geológico y Minero de España, Spanish Geological Survey). pp:319-341

MORELL I, GIMENEZ E, ESTELLER, MV (1996) Application of the Principal Components

Analysis to the study of salinization n of the Castellón Plain (Spain). The Science of the

Total Environment 177: 161-171.

MORELL I, HERNÁNDEZ F (2001) El agua en Castellón. Un reto para el siglo XXI. “The

water in Castellón. A challenge for the XXIst century”. Jaume I University.

28

MORELL I, TUÑÓN J (2002) Contribución de las actividades agrícolas a la presencia de

sulfatos en los acuíferos costeros. El caso de la Plana de Castellón. En: Los acuíferos

costeros y las desaladoras. “Contribution of the agricultural activities to the

presence of sulfates in the coastal aquifers. The case of Castellón Plain. In: The

coastal aquifers and desalination plants”. Pulido-Bosch, Vallejos & Pulido-Leboeuf

(eds).

MORELL I. (1999). Presencia de metales en el sector meridional del acuífero de la Plana

de Castellón. “Metal presence in the southern sector of Castellón Plain aquifer”.

Technical report. Jaume I University.

MUSASHI M, NOMURA M, OKAMOTO M, OSSAKA T, OI T, KAKIHANA H (1988) Regional

variation in the boron isotopic composition of hot spring waters from central Japan.

Geochem. J. 22: 205–214.

NEGREL P, PETELET-GIRAUD E, KLOPPMANN W, CASANOVA J (2002) Boron isotope

signatures in the coastal groundwaters of French Guiana. Water Resour. Res. 38

(11): 1262

PENNISI M, LEEMAN WP, TONARINI S, PENNISI, A, NABELEK P (2000) Boron, Sr, O, and

H isotope geochemistry of groundwaters from Mt. Etna (Sicily) - Hydrologic

implications. Geoch. Cosmoch. Acta 64 (6): 961–974.

PENNISI M, BIANCHINI G, MUTI A, KLOPPMANN W, GONFIANTINI R (2006). Behaviour

of boron and strontium isotopes in groundwater–aquifer interactions in the Cornia

Plain (Tuscany, Italy). Applied Geochemistry 21:1169–1183.

PENNISI M, GONFIANTINI R, GRASSI S, SQUARCI P (2006a). The utilization of boron and

strontium isotopes for the assessment of boron contamination of the Cecina River

alluvial aquifer (central-western Tuscany, Italy). Applied Geochemistry 21: 643–655

29

RAVENSCROFT P, MCARTHUR JM (2004) Mechanism of regional enrichment of

groundwater by boron: the examples of Bangladesh and Michigan, USA. Applied

Geochemistry 19: 1413–1430.

RAYMOND K, BUTTERWICK L (1992) Perborate. In: de Oude NT (ed.) The Handbook of

Environmental Chemistry, vol 3, part F. Anthropogenic compounds. Springer, Berlin

Heidelberg New York: 288-318

ROSE EP, CHAUSSIDON M, FRANCE-LANORD C (2000) Fractionation of boron isotopes

during erosion processes: The example of Himalayan rivers. Geochim. Cosmochim.

Acta 64: 397–408.

SÁNCHEZ-MARTOS F, PULIDO-BOSCH A (1999) Boron and the origin of salinization in an

aquifer in southeast Spain. C.R. Acad.Sci. Paris. Earth and Planetary Sci. 328: 751-

757.

SCHMASSMANN H, KULLIN M (1990) Halide/Chloride and Boron/Chloride ratios in

deep groundwaters of Northern Switzerland. Memor. of 22nd Congress of IAH, XXII,

Lausanne, 1990: 296-303.

SPIVACK AJ, PALMER MR, EDMONDS JM (1987) The sedimentary cycle of boron

isotopes. Geochim. Cosmochim. Acta 51: 1939-1949.

TELLAM JH, LLOYD JW (1986) Problems in the recognition of seawater intrusion by

chemical means: An example of apparent chemical equivalence. Quarterly Journal

of Engineering Geology 19: 389-398.

TONARINI S, LEEMAN WP, CIVETTA L, D’ANTONIO M, FERRARA G, NECCO A (2004)

B/Nb and 11B systematics in the Phlegrean Volcanic District, Italy. J. of Volcanology

and Geothermal Res. 133: 123-129.

30

TRAVI Y, FAYE A (1990) Concentrations en bore de la "nappe maestrichtienne" du

Sénegal: leur influence sur l'aptitude des eaux a l'irrigation (Concentrations of boron

in the Maestrichtian aquifer of Senegal: its influence in the quality of irrigation

waters). Journal of African Earth Science 11 (3/4): 253-259.

UHLMANN K (1991) The geochemistry of boron in a landfill monitoring program.

Groundwat. Monitoring and Remediation, fall, p.139.

VENGOSH A (1998) The isotopic composition of anthropogenic boron and its potential

impact on the environment: Biological Trace Element Research 66: 145-151.

VENGOSH A, DE LANGE GJ, STARINSHY A (1998) Boron isotope and geochemical

evidence of Urania and Bannock brines in the eastern Mediterranean: effect of

water-rock interactions. Geoch. Cosmoch. Acta 62: 3221-3228.

VENGOSH A, GILL J, DAVIDSON ML, HUDSON GB (2002) A multi-isotope (B, Sr, O, H,

and C) and age dating (3H-3He and 14C) study of groundwater from Salinas Valley,

California: hydrochemistry, dynamics, and contamination processes. Water Resour.

Res. 38: 1–17.

VENGOSH A, KLOPPMANN W, MAREI A, LIVSHITZ Y, GUTIERREZ A, BANNA M, GUERROT

C, PANKRATOV I, RAANAN H (2005) Sources of salinity and boron in the Gaza strip:

natural contamination flow in the southern Mediterranean coastal aquifer. Water

Resour. Res. 41, W01013.

VENGOSH A, SPIVACK AJ, ARTZI Y, AYALON A (1999) Geochemical and boron,

strontium, and oxygen isotopic constraints on the origin of the salinity in

groundwater from the Mediterranean coast of Israel. Water Resour. Res. 35(6):

1877-1894VENGOSH A, STARINSKY A, KOLODNY Y, CHIVAS AR, RAAB M (1992)

31

Boron Isotope Variations During Fractional Evaporation of Sea-Water - New

Constraints on the Marine vs Nonmarine Debate. Geology, 20 (9): 799-802.

VENGOSH A, STARINSKY A, CHIVAS AR (1994) Boron isotopes in Heletz-Kokhav oilfield

brines, the Coastal Plain, Israel. Isr. J. Earth Sci., 43: 231-237.

VENGOSH A, KOLODNY Y, STARINSKY A, CHIVAS AR, McCULLOCH MT (1991).

Coprecipitation and isotopic fractionation of boron in modern biogenic carbonates.

Geochimica et Cosmochimica Acta 55: 2901-2910.

WAGGOTT A (1969) An investigation of the potential problem of increasing boron

concentrations in rivers and water courses. Water Research, 3: 749-765.

XIAO YK, ZHANG CG (1992) High precision isotopic measurement of chlorine by

thermal ionization mass spectrometry of the Cs2Cl+ ion. Int. J. Mass Spectrom. Ion

Process. 116: 183-192.

32

FIGURE CAPTIONS/TITLES

Figure 1. Location of the study area and geological map of the Castellón Plain and its

surroundings (Morell et al., 1998). Legend: 1: Plioquaternary; 2: Tertiary; 3:

Cretaceous; 4: Jurassic; 5: Triassic:. One can see the spatial distribution of

samples taken from the aquifer (Northern, Central and Southern sectors). RB:

River Belcaire; RM: River Mijares; MC: Maria Cristina reservoir; Si: Sichar

reservoir. The piezometric surface for 1998 is also shown, along with the main

flow paths (white arrows).

Figure 2. General hydrogeological cross section. Tb - Triassic Buntsandstein Facies; Tm

– Triassic Muschelkalk Facies; PQ – Plioquaternary; M - Miocene. The water

balance components are also represented: rainwater infiltration (85x 106

m3/year ), irrigation return water (45 x 106 m3/year), transfers from neighbouring

units (90 x 106 m3/year), pumped abstractions (165 x 106 m3/year), coastal

springs and wetlands (16 x 106 m3/year) and submarine discharges (39 x 106

m3/year).

Figure 3. Piper diagram showing fractional ion concentrations of the groundwater

sampled in different areas.

Figure 4. Trends of Na+ K deficits and Ca excesses related to the groundwaters of

the Castellón Plain. For each sector, data are ranked according to increasing

chloride concentrations. -ions in meq/L.

Figure 5. Relationship between electrical conductivity ( S.cm-1) and B/Cl ratio (in

mmolL-1) . The dashed line represent sea water-fresh water mixing.

33

Figure 6. Relationship between 11B (‰) and B/Cl ratio (in mmolL-1). RB: River

Belcaire; RM: River Mijares; MC: Maria Cristina reservoir; Si: Sichar reservoir.

34

Table 1. Analytical techniques used for determining the physico-chemical parameters and precision of the methods.

Ion Analytical Technique Method precision

Chloride (Cl-) Spectrophotometry (480 nm) 0.65% RSD

Alkalinity (HCO3- + CO32-

) Volumetry

Sulphate (SO42-

) Spectrophotometry (460 nm) 0.75% RSD

Nitrate (NO3-) Spectrophotometry (540 nm) 0.3% RSD

Ca2+

, Mg2+

, Na+, Sr

2+ Atomic Absorption Spectrometry < 1% RSD

K+ Flame Photometry (Emission) < 1% RSD

B3+

Spectrophotometry (410 nm) - Azomethine H < 2% RSD

Electrical Conductivity Conductimetry

pH Potentiometry

RSD: Relative Standard Deviation

35

Table 2. Analyses data

Sample location

Electrical Conductivity

Cl-

SO42-

NO3-

HCO3-

Na+ K

+ Ca

2+ Mg

2+ B

3+

11B

(n) S.cm-1

mgL-1

mgL-1

mgL-1

mgL-1

mgL-1

mgL-1

mgL-1

mgL-1

mgL-1

(‰)

SW 53000 21333.02 2921.76 0.00 132.37 11754.61 454.74 447.80 1736.37 4.60 40.00

FW 662 68.64 127.20 0.44 81.55 23.23 3.51 51.40 25.01 0.01 12.00

MC 1023 128.46 255.96 87.52 121.01 196.00 12.70 77.00 47.33 4.78 -11.99

Si 510 60.63 276.52 80.23 108.71 21.00 2.40 101.79 54.16 0.30 -2.43

RM 790 30.30 230.32 96.16 114.01 30.00 1.90 106.54 51.93 0.23 -8.90

1 2190 661.72 201.71 27.05 199.01 268.08 6.38 176.91 74.75 0.08 29.59

3 1890 508.36 97.05 13.77 148.82 239.29 5.54 86.51 61.28 0.01 29.78

5 1122 224.41 206.87 10.93 130.00 94.56 3.83 86.87 50.74 0.10 21.99

6 1412 353.85 197.71 8.74 186.46 160.13 5.06 121.77 51.77 0.09 20.64

7 1828 452.98 420.09 1.39 199.01 281.94 10.46 122.71 62.39 0.28 18.79

8 1008 122.35 152.20 30.55 307.49 58.48 6.88 123.50 39.82 0.12 7.35

9 937 95.48 177.00 2.03 233.63 36.22 2.30 104.66 36.90 0.08 -0.43

11 1284 170.33 289.03 31.09 267.79 60.76 3.30 150.69 71.14 0.09 9.08

12 776 80.00 114.96 5.15 225.94 34.94 2.52 83.84 33.72 0.06 13.46

13 870 116.93 179.41 2.21 240.11 48.50 7.57 109.62 35.73 0.20 0.86

14 760 73.90 163.43 0.64 175.75 36.19 2.57 91.74 31.41 0.04 -5.12

15 733 108.14 172.43 0.42 175.75 44.89 2.53 91.22 34.52 0.04 3.86

16 1412 312.43 222.67 3.99 217.83 156.14 8.18 120.30 49.08 0.85 7.74

30 1388 152.38 348.44 24.72 232.21 44.75 2.23 157.79 78.22 0.12 10.01

31 1363 174.77 302.18 29.89 242.78 40.67 4.04 155.31 85.65 0.11 1.28

32 720 78.68 152.32 1.02 167.75 31.50 2.49 86.34 24.81 0.07 -9.29

17 1765 362.75 433.68 30.89 205.28 85.84 5.49 185.71 136.90 0.10 12.60

18 2310 632.45 586.58 30.98 186.46 114.46 2.90 318.14 164.35 0.13 12.60

19 1990 552.95 419.52 30.64 236.65 109.77 6.98 276.65 116.96 0.15 7.28

20 1827 490.92 298.09 30.51 155.10 115.72 4.26 173.43 116.74 0.18 20.40

21 2400 697.93 438.90 30.70 142.55 140.55 9.59 298.02 125.81 0.21 20.46

22 3120 929.39 796.90 29.57 224.10 273.12 13.44 416.65 147.68 0.35 15.60

23 1707 436.68 244.06 29.71 155.10 75.63 4.48 181.99 104.28 0.13 16.44

24 1399 325.42 223.17 29.99 148.82 72.00 2.76 147.86 89.29 0.12 18.65

25 2090 631.07 283.80 30.44 161.37 176.35 5.22 223.83 110.95 0.17 19.64

26 1598 380.92 125.07 19.90 136.28 191.12 20.96 54.43 47.06 0.79 -0.86

27 3060 1012.82 377.95 30.58 98.64 266.40 7.34 318.14 187.28 0.18 6.04

28 2710 813.66 252.04 20.16 142.55 104.48 3.25 366.77 159.01 0.11 12.59

29 2420 757.60 303.54 30.71 167.64 89.46 2.60 304.94 164.80 0.13 15.38

33 2450 690.81 211.20 244.90 257.20 140.31 5.43 314.52 119.13 0.12 12.40

34 2500 635.05 291.99 303.04 318.20 122.26 5.09 340.10 134.13 0.13 4.90

35 3350 1064.00 574.13 257.70 355.84 311.99 6.60 398.41 207.72 0.15 6.20

SW: seawater; FW: freshwater; MC: Maria Cristina reservoir; Si: Sichar reservoir; RM: River Mijares; n: sample number.

No

rth

ern

S

ecto

r C

en

tra

l

Se

cto

r S

ou

the

rn

Se

cto

r

7

MEDITERRANEAN SEA

3

8

11

12

13

14 28

35 27

23

BENICASIM

VALL D'UIXÒ

River Belcaire (RB)

50

10

20

32 31

17

30 16

22

26

24

VALL D’UIXÓ

ESPADÁN RANGE

RIBESALBES-ONDA BASIN

DESERT OF LAS PALMAS

1

3 4

5

2

Fault

MEDITERRANEAN

SEA

Castellón

Plain

SPAIN

FRANCE

PO

RTU

GA

L

Madrid

9

29

15

21 20

33 -2

MONCÓFAR 25

River Mijares (RM)

MC

RB

4 km 2 0

19

Central Sector

Northern Sector

Southern Sector

Maria Cristina reservoir (MC)

Si

Sichar reservoir

(Si)

Groundwater samples Northern Area

Groundwater samples Central Area

Groundwater samples Southern Area

Surface water samples

1BENICASIM

34

18

5

6

RM

6 2

4(FW)

CASTELLÓN

MEDITERRANEAN

SEA 0 5 km

Tb

Tm

M

0

100

200 m

Seawater

intrusion

90 x106 m3/year

85 x106 m3/year 165 x106 m3/year

16 x106 m3/year

39 x106 m3/year Aquitard

PQ

45 x106 m3/year

Sea level

Piezometric surface of water table

←

Ca 2+ Cl - + NO 3 - →

Northern Sector

Central Sector

Southern Sector

- 20

- 10

0

10

20

30

Cen

tral

Sec

tor

Sout

hern

Sec

tor

(c)

(a)

(a)

(a)

(c)

(c)

(b) (b)

(b)

(a) Cl - (in meq/L)

(b) ∆∆∆∆ Ca 2+ (in meq/L)

(c) ∆∆∆∆ Na + + ∆∆∆∆ K + (in meq/L)

Nor

ther

n Se

ctor

[Cl] [Cl] [Cl]

0 2000 4000 6000

0

2.10-3

4.10-3

6.10-3

8.10-3

10-2

16

26

Electrical Conductivity µµµµ S cm-1

B/C

l

Northern Sector

Central Sector

Southern Sector

seawater

13

SALINE

WATERS

CENTRAL

SECTOR

- 20

10-4 10-3 10-2 10-1 1

0

20

40

60

δ δ δ δ 11

B (

‰)

9

MC RM

Si

RB

B/Cl

Northern Sector Central Sector Southern Sector

26

16 13

B/C

l in

seaw

ate

r

1 3

Boron

SALINE WATERS

SECTOR CENTRAL

Pollution

Surface water samples

Adsorption