ORIGINAL ARTICLE

A geophysical and geochemical approach for seawater intrusionassessment in the Acquedolci coastal aquifer (Northern Sicily)

A. Cimino Æ C. Cosentino Æ A. Oieni ÆL. Tranchina

Received: 24 April 2007 / Accepted: 22 October 2007 / Published online: 13 November 2007

� Springer-Verlag 2007

Abstract Vertical electrical sounding (VES’) surveys

and chemical analyses of groundwater have been executed

in the coastal plain of Acquedolci (Northern Sicily), with

the aim to circumscribe seawater intrusion phenomena.

This urbanized area is representative of a more general

problem interesting most of Mediterranean littoral areas,

where intensive overdraft favors a heavy seawater intrusion

through the coastline. Aquifer resistivity seems decisively

to be conditioned by the chlorine and magnesium content

in the main aquifer of the region. Schlumberger VES’,

together with piezometric and chemical–physical

information of groundwater, allowed us to perform hy-

drogeological and geophysical elaborations, to propose the

occurrence of a relatively narrow belt marked by fresh–salt

water mixing. In the considered plain, pollution risk studies

have been already realized by authors with the proposal to

identify—by parametric and synthetic zoning of significant

hydrogeological elements—the most vulnerable sectors. In

detail, an intrinsic vulnerability mapping has been already

performed, applying the well-known SINTACS system.

This paper intends to give—in this sector of Sicily—an

example of integration of different methodologies, showing

the role of geophysics to describe the degradation of

aquifers on the whole as well as to assess their pollution

risk better.

Keywords Sicily � Acquedolci plain � Groundwater �Apparent resistivity � Seawater intrusion

Introduction

Recently, interdisciplinary research programs have per-

mitted the collection and organization of a great number of

territorial information, including geophysical and geo-

chemical data in Sicily. The aim was mainly to perform a

cartography of pollution vulnerability in this sector of

Sicily. In fact, various methodologies of vulnerability

assessment have been carefully applied and compared in

many countries of the world (Gemitzi et al. 2006; Gogu

et al. 2003). At this proposal, the notable role played by

vulnerability in the general ambit of pollution risk assess-

ment is well known (Civita and De Maio 1997).

This is particularly true in similar contexts as the

Acquedolci case, in which this very crowded sector of

Sicily is locally subjected to heavy groundwater overdraft:

this area has been opportunely interested by the SINTACS

method application (Cimino et al. 2006). This point-count

system model (PCSM) (Civita 1994; Civita and De Maio

2000) considers seven parameters strictly related with

intrinsic hydrogeological features of aquifers, permitting

their elaboration in GIS environment. SINTACS has been

diffusely applied in other Italian areas (Civita et al. 1995).

In the purposely considered area of Acquedolci (Fig. 1),

the most vulnerable sectors lie in the alluvial fan of the

A. Cimino (&) � C. Cosentino � A. Oieni � L. Tranchina

Dipartimento di Fisica e Tecnologie Relative,

University of Palermo, Viale delle Scienze, Edificio 18,

90128 Palermo, Italy

e-mail: cimino@unipa.it

A. Oieni

e-mail: a.oieni@unipa.it

L. Tranchina

e-mail: tranchina@difter.unipa.it

C. Cosentino � A. Oieni

Dipartimento di Geologia e Geodesia,

University of Palermo, Via Archirafi 20, 90123 Palermo, Italy

e-mail: cosentino@difter.unipa.it

123

Environ Geol (2008) 55:1473–1482

DOI 10.1007/s00254-007-1097-8

Furiano torrent, where the grain size features cause a

notable increase of permeability of saturated and non-sat-

urated strata. Here, as in other Sicily sectors, authors have

created georeferenced archives of directly collected and

analyzed data, also including available records from public

bodies, field notes and GIS features. Records were gener-

ally organized at different spatial scales: so, georeferenced

database structures have met additional difficulties, wholly

overcome by the efforts of various researchers involved in

this program. Considering the noticeable help offered by

geophysical prospecting to delineate groundwater flows

and pollution phenomena (Orellana 1982), in this note,

authors also explain interpretations of electrical resistivity

data.

In the last decades, the progressive increase of water

requirements and the consequent depauperation of its

availability, together with the qualitative deterioration must

certainly be included among the most serious environ-

mental problems of Sicily and other world countries. In

fact, the wild exploitation causes a notable lowering of

water table, in spite of the natural recharge by rainfall and

carbonate relieves.

In anthropized areas—as the considered one—many

sources of potential contamination points of groundwater

occur; among these, authors remember sanitary landfills,

municipal wastewater, cemeteries, agricultural fertilizers

and accidental gasoline spills. In a certain area, these

sources can be classified assigning to them particular

danger contamination indexes (DCI) (Cimino and Andolina

2002).

An important cause of increasing groundwater contam-

ination in coastal plains as Acquedolci is commonly

represented by salt waters. Heavy pumping, if associated

with geological factors as grain size, can originate a

landward migration of fresh–salt groundwater interface.

Human action resulting in marine water entering an aquifer

is generally called seawater intrusion. It occurs as ‘‘a result

of the diversion of fresh water that previously had

discharged from a coastal aquifer’’ (Fetter 1973, 2001).

As a result, intense anthropic activity influences coastal

hydrologic systems, leading to groundwater pollution by

seawater intrusion. Incidence of this problem is noticeably

increased in many littoral, urbanized regions of the world

(Chachadi et al. 2003). Here the continuous exploitation of

aquifers can be frequently observed, justifying a growing

attention by the scientific community, as testified by

numerous recent experiences (Demirel 2004; Liu and

Cheng 1997; Melloul and Goldenberg 1997; Polemio et al.

2006).

The evaluation of seawater intrusion has been dealt

through different approaches. Some authors used radioac-

tive isotopes in order to explain the increase of salinity, due

to seawater intrusion, in the coastal aquifer of Israel

(Yechieli et al. 2006). Other authors (i.e. Polemio et al.

2006; Pulido-Leboeuf 2004) employed only geochemical

methods based on variations of salinity and, cation and

anion concentrations, while others have introduced both

geophysical and geochemical approaches to obtain a more

comprehensive picture of this phenomenon (Di Sipio et al.

2006; Melloul and Goldenberg 1997; Sodde and Barrocu

2006).

The aim of this paper is to display how different

approaches (by geophysics and geochemistry) have been

integrated and successfully used to identify and circum-

scribe seawater intrusion near the coastline in the

Acquedolci area (Fig. 1). The definition of this aspect is

very important for its close relation with the vulnerability

assessment of a definite area and, consequently, with the

whole hydrogeological risk pollution (Cimino et al. 2006).

Indeed, it has to be considered in the studied plain,

occurrence of intensive agricultural practices, with a rela-

tively great diffusion of greenhouses and related spreading

of chemical fertilizers. A contemporary inhomogeneous

lowering of water table, estimated in [5 m during the last

10 years, is also observed. This imposes a correct definition

of the hydrogeological problem, suggesting the possible

Fig. 1 a Hydro-structural sketch and b AA’ section of the Acquedolci

area. 1 Sandy–gravely–arenaceous complex; 2 sandy–arenaceous

quaternary complex; 3 clayey–marly–arenaceous complex; 4 meso-

zoic calcareous–dolomitic complex; 5 piezometric level and 6 contour

lines of piezometric levels (meters above sea level)

1474 Environ Geol (2008) 55:1473–1482

123

ways to monitor and recover, for agricultural and urban

needs, the partially compromised aquifer.

Geological and hydrogeological setting

The coastal plain of Acquedolci is located in the Northern

coast of Sicily (Fig. 1); this plain is bounded by Tyrrhenian

Sea on the North, by a group of steep relieves (Pizzo

Castellaro and San Fratello Mt.) on the South, by Inganno

and Furiano torrents on the East and West, respectively. It

is mainly constituted by quaternary alluvial deposits, often

terraced, characterized by different permeability degrees,

in accordance with the grain size, and a generally medium–

high pollution vulnerability. In particular, it is possible to

distinguish four principal geostructural complexes, char-

acterized by hydrogeological homogeneity (Abbate et al.

2003; Cimino et al. 2002):

(1) A sandy–gravelly-arenaceous complex, grouping the

quaternary alluvions of the torrent fans and the thin

coastal belt deposits, with medium to high perme-

ability for porosity.

(2) A sandy–arenaceous quaternary complex, covering

most of the plain, with medium permeability grade for

porosity and in close hydrogeological continuity with

the first one; this complex, together with the first one,

hosts an unconfined aquifer, intensely exploited by

farms and greenhouses. Figure 1 shows contour lines

of piezometric levels.

(3) A clayey–marly-arenaceous complex, mostly includ-

ing all the deposits belonging to metamorphic

fragments as well as to tertiary flysch units; these

ones usually exhibit low or very low permeability

values, locally performing a tamponage function with

regard to the groundwater circulation; in detail,

numidian flysch unit represents the impervious bed

to the upper quaternary aquifers (see section AA0 in

Fig. 1).

(4) A Mesozoic calcareous-dolomitic complex, with

medium–high secondary permeability for fractures

and karst (Pizzo Castellaro and San Fratello Mt.); it

forms a conspicuous aquifer (up to 200 m deep)

below the plain, supplying it along the detrital

foothills. This carbonate aquifer can be reached in

certain wells of the southern sectors of Acquedolci.

Karst relieves of Pizzo Castellaro and San Fratello Mt. are

comprised in the Nebrodi East–West chain, mostly consti-

tuted by rocks belonging to Mesozoic complex and,

subordinately, by metamorphic and flysch units (Cimino

et al. 1998). Furthermore, the great permeability of these

inland units evidences high vulnerability too, influencing

the protection areas of certain springs supplied by karst

groundwater (i.e. the Favara of Acquedolci source, indi-

cated in Fig. 1). Since 10 years, periodical inventories of

main hydrogeological and geophysical features have

begun, with the aim to elaborate a wide-ranging vulnera-

bility cartography of Acquedolci plain (Cimino et al.

1997).

Seawater intrusion in coastal aquifers

The seawater intrusion phenomenon is well known in

coastal aquifers. It occurs when the sea, interesting per-

meable rocks (for porosity or fractures), creates an

interface below freshwaters, according to density contrast

and to aquifer geometry. In fact, density of saline water

(qw) is greater than density of fresh water (q). The interface

salt water–fresh water depends very little on marine level,

except for low sea fluctuations due to tidal and long-term

climatic changes (Fetter 2001). So, the boundary can be

considered in a quasi-equilibrium state, any movement

caused by seasonal fresh–water discharge as well as by

groundwater exploitation. As a matter of fact, this phe-

nomenon can be considered—in a first approximation—

essentially stationary, and the equilibrium between the two

fluids subjected to the common hydrostatic laws. Accord-

ing to the hydrostatic equilibrium between sea water and

fresh water:

Hi þ Hð Þq ¼ Hi qw ð1Þ

the Ghyben-Herzberg principle states that:

Hi ¼ H q= qw � qð Þ ð2Þ

where qw saline water density, q fresh water density, Hi

depth to the interface below sea level and H elevation of

the piezometric surface above sea level.

The Ghyben–Herzberg principle states that interface

depth depends on the density of liquids—considered as

immiscible—and on the distance between piezometric

surface and sea level. Its application is possible only if the

equilibrium is permanent and the interface is regular; but

this equilibrium is difficult to be reached, because the

mixing zone is strictly dependent on tidal cycles; while the

fresh water zone is also regulated by seasonal conditions

(above all rainfall) and human actions, as overdrafts by

pumping systems. In fact, Hubbert (1940) verified that the

equilibrium is never established because fresh water causes

a dynamic balance of interface; so, it must be considered as

a surface that can advance landward owing to the above-

mentioned factors.

Besides, due to the different density, fresh groundwater

generally grades into saline water with a steady increase in

the content of dissolved solids. In some cases, the contact

Environ Geol (2008) 55:1473–1482 1475

123

may be quite sharp, producing a very thin mixing zone. In

aquifers with tidal hydraulic fluctuations, this layer will be

thicker. Where this zone is only few meters thick,

the Ghyben–Herzberg principle can be fairly applied. For

the purposes of this note, it is essential to express that the

mixing layer can likely involve wells and degrade water

quality.

According to Ghassemi et al. (1993), the intrusion fea-

tures depend, besides depth, exploitation and recharge rates

and well distance from the coast, also on aquifer geometry,

porosity, hydraulic conductivity and dispersivity, taking

into account local or general anisotropy of these hydro-

geological characteristics. So, complex models are needed

to quantify these factors. In fact, over the years, different

mathematical and numerical models, more or less complex,

have been developed with the aim to understand seawater

intrusion and to establish the position and thickness of

transition zone between fresh and salt water in coastal

zones (Bear 1979; Reilly and Goodman 1985; Oude Essink

2001; Narayan et al. 2007). Moreover, in different recent

works (Cheng and Ouazar 1999; Cheng et al. 2000; Barlow

2003; Mantoglou 2003; Mantoglou et al. 2004), as well as

in this paper, freshwater and saltwater zones are considered

to be separated by a sharp boundary, with the approxima-

tion based on the Ghyben–Herzberg law and on unconfined

aquifers and steadystate flow.

To determine groundwater deterioration, seawater

intrusion can be detected both directly (in wells by elec-

trical probes or samplings) and indirectly by geophysical

methods (Melloul and Goldenberg 1997). This study takes

into account direct groundwater samplings and analyses as

well as indirect geophysical approaches in order to suggest

the fresh–salt water interface geometry.

Materials and methods

Hydrochemical and geophysical surveys have been carried

out in the study area. Inventories, arrays and geochemical

analyses have been executed in different times, interesting

a total of 41 wells and 41 VES’. Wells involved generally

more aquifers. In detail, quaternary complexes are

hydraulically connected, both being supplied by the karst

aquifer. As quoted above, essential data relevant to water

wells have been organized in a georeferenced database. In

particular, information on geometry of wells, including

piezometric levels and depths, were opportunely recorded.

Most of the drilled boreholes present 0.20–0.40 m diame-

ters, while older wells are up to 3 m larger. Sampling

method is strictly dependent on well diameter: for small

diameter wells (mainly involving the karst aquifer) a pri-

vate pump was utilized, while for the large ones a direct

sampling has been executed. Samplings for chemical

analyses as well as piezometric measurements have been

executed in the late-fall season, after a rainy period. This

high recharge phase of aquifers constitutes the best con-

ditions to opportunely evaluate the depth to water

parameter, utilized in the pollution vulnerability assess-

ment of Acquedolci region (Cimino et al. 2006). In

particular, wells of Acquedolci plain show piezometric

levels up to at least 120 m, with higher values in corre-

spondence with the deep karst aquifer (wells AO-7 and

AO-8 in Fig. 2). Wells generally reach in depth the salt-

water–freshwater interface, depending on the overdraft

intensity as well as on the distance from the coast. Inte-

grated tools represented by hydrochemistry and geophysics

define the seawater intrusion entity. The role of tidal

effects, generally affecting the already mentioned salt–

fresh transition zone, is here retained wholly negligible in

all the zones of the plain, in the alluvial fans as well as in

the central sectors.

Groundwater chemical analyses

All chemical analyses of groundwater samples were carried

out in the laboratory of the Azienda Municipalizzata Ac-

quedotti of Palermo, according to the following national

reference methods: complexometric method by IRSA 2040

for HCO3- measurement; ion chromatographic method

UNICHIM and UNICHIM 800 for Ca2+, Mg2+, Na+, K+

and Cl-, SO42- measurements, respectively. Conductivity

was estimated on field using a common portable instru-

ment. These values have been automatically compensated

to a temperature of 20�C by the instrument during mea-

surements. Figure 2 illustrates the location of wells; in each

point, the circle size is proportional to chloride concen-

tration. Table 1 reports the results of geochemical

prospecting relevant to the mostly characterizing ions; it

Fig. 2 Map of the investigated area, exhibiting well locations and

distribution of electrical conductivity of groundwater. Size of circles

is proportional to chloride concentration

1476 Environ Geol (2008) 55:1473–1482

123

must be underlined that other groundwater measurements

have been performed, interesting bacteriological analyses

(Cimino et al. 2006) and trace elements as well. In this

paper, only ions which may characterize the seawater

intrusion phenomenon are summarized. Table 1 also shows

data on well temperatures, which are characterized by great

Table 1 Chemical–physical data, involved in the encroachment phenomena, relevant to part of groundwater samples

Well ID UTM T (�C) Conductivity

(20 lS cm-1)

Piezometric

level (m)

Cations (mg L-1) Anions (mg L-1)

X Y Ca2+ Mg2+ Na+ K+ HCO3- Cl- SO4

2-

AO-7 462540 4210590 19.8 611 181.35 57.17 12.26 51.40 9.83 125.66 73.98 108.76

AO-8 462725 4210725 18.5 852 177.53 84.39 8.65 56.45 12.37 311.1 115.80 68.84

FC-10 462840 4211265 16.2 622 165.4 109.00 3.20 35.00 12.00 527.04 45.93 34.93

FC-7 466050 4212450 17.1 779 113 106.64 22.76 41.61 9.11 484.95 43.29 99.48

FC-8 465775 4213190 19.5 1,767 10.8 198.42 58.08 95.30 3.72 506.3 265.60 172.60

FC-9 465650 4212260 18.7 1,322 95 72.92 76.64 72.23 3.66 509.96 178.97 177.66

LD-1 461740 4212545 17.7 1,070 1.68 112.56 38.86 70.86 10.14 184.22 156.70 97.24

LD-2 461510 4212460 18.8 961 9.14 119.31 27.11 62.78 10.50 289.14 75.80 159.75

LD-3 461490 4212200 18.0 946 8.24 86.66 24.14 51.25 3.60 267.18 59.15 159.65

LD-4 461660 4212310 18.4 1,076 15.15 134.00 28.52 76.38 6.70 337.94 107.97 186.77

LD-6 465050 4212960 19.2 670 8 71.15 14.70 30.60 5.93 351.36 40.24 74.70

LD-7 464440 4212885 19.3 5,820 0.8 288.30 157.02 768.90 24.33 412.97 1241.00 470.16

LD-8 465300 4213210 19.9 760 10.8 109.20 20.20 42.76 5.72 358.68 42.50 108.35

LD-9 465550 4213240 18.8 1,587 14.2 178.30 57.97 106.40 6.40 290.36 360.00 176.62

OT-2 463475 4211360 16.5 1,057 131.59 193.44 18.70 42.70 34.24 440.42 161.04 89.64

OT-3 463250 4211210 17.6 714 109.7 94.91 21.09 39.22 3.06 342.82 79.45 48.32

OT-4 464000 4212000 17.9 1,125 78.8 151.60 40.85 73.24 3.60 497.76 132.50 77.90

OT-5 461320 4211080 19.9 1,015 34.7 145.70 30.17 59.62 9.00 315.98 59.31 210.02

OT-6 460580 4212200 19.1 1,254 7.6 170.51 32.80 71.88 5.23 357.46 78.30 219.06

OT-7 460430 4212000 21.0 1,512 5.97 230.55 42.83 82.67 5.70 351.36 98.80 274.05

OT-8 461075 4212470 19.0 945 8.46 145.61 26.77 51.74 8.84 323.3 51.92 162.16

OT-9 461570 4211275 21.4 894 35.09 116.52 28.72 58.43 4.32 287.92 55.25 163.24

PM-1 462050 4212160 13.9 2,800 7.98 192.11 75.37 386.64 7.55 500.2 709 244.80

PM-10 465450 4212775 18.6 1,501 23.53 160.40 44.64 138.90 4.62 335.5 204.35 207.55

PM-11 463525 4211960 19.0 2,960 53.23 138.50 70.62 507.44 5.40 524.6 417.52 511.70

PM-12 463450 4212450 17.3 910 10.25 97.42 34.06 80.38 3.20 323.3 96.5 101.27

PM-13 462575 4212610 18.0 1,240 4.33 111.30 33.45 132.00 9.34 341.6 158.65 138.85

PM-2 462440 4211425 18.8 2,080 50.5 173.50 73.36 216.20 6.23 518.5 532 186.95

PM-3 462110 4210925 16.8 893 123.03 108.30 28.60 67.22 7.90 213.5 68.9 165.00

PM-4 462100 4212460 19.0 1,295 8.31 148.00 40.09 83.58 3.06 256.2 360 156.00

PM-5 464050 4211950 15.0 1,637 67.45 165.20 60.70 176.00 1.50 457.5 249 233.50

PM-6 463715 4211605 17.2 900 115.88 151.43 18.30 46.45 2.03 433.1 85.58 54.80

PM-7 463150 4212060 17.9 738 45.08 106.26 15.07 55.98 7.15 341.6 50.48 75.96

PM-8 464710 4212125 15.5 1,426 44.8 175.50 55.86 111.37 4.08 512.4 180.5 165.20

PM-9 464225 4212410 18.2 1,014 23.3 126.50 39.80 53.58 3.01 408.7 97.92 95.42

RM-10 464700 4211650 12.0 552 91 65.26 32.86 27.00 1.60 311.1 50.66 24.82

AO-6 466590 4213645 19.1 963 2.37 138.90 28.62 56.43 11.55 418.46 102.55 139.69

FC-1 466300 4213790 19.0 1,332 3.6 155.04 29.53 117.40 6.06 573.4 159.8 154.36

FC-5 466275 4213180 18.3 1,039 17.16 134.71 20.44 85.08 10.25 459.33 116.3 163.90

FC-6 466560 4213290 18.8 2,150 6 139.06 61.03 211.82 5.03 539.24 300.6 341.70

PF-1 466575 4212450 12.1 2,130 83.22 97.80 114.40 274.80 10.74 628.3 532 159.00

Environ Geol (2008) 55:1473–1482 1477

123

variability. In fact, in the studied area at least two different

water springs occur (Favara of Acquedolci and Mascarino

sources in the North and South of calcareous relieves,

respectively) with different temperatures. Their waters

belong to different hydrological pathways that contribute to

feed the arenaceous aquifer; waters of the northern spring

are characterized by temperatures higher than the southern

one: this can explain the differences of temperature in

certain sampled wells. Since the aquifers—as above quo-

ted—are hydraulically connected, well waters show a

gradient of temperature due to the mixing of ground waters

relevant to different sources.

More in detail, total and fecal coliforms (Entero bacte-

riacee and E. coli) as well as bacteria belonging to the genus

of Streptococcus have been detected near the Inganno tor-

rent course, reaching values up to respectively 55,000 and

63,000 UFC/100 mL. This occurrence in groundwater

suggests a well-localized bacteriological risk due to nitrate

fertilizers in agriculture or to non-treated urban discharges.

Statistical principal component analysis (PCA) of

chemical–physical groundwater features was also per-

formed, in order to assess possible correlations among

variables, also evaluating possible matching between well

locations and measured ion concentrations.

Geophysical survey

As universally recognized and described (Kunetz 1966),

geoelectric prospecting is the most suitable geophysical

method for hydrogeological studies. It differentiates pervi-

ous and impervious formations, easily depicting geometry of

hydrostructures as well as groundwater contaminations

through seawater intrusion. In most of the cases, VES’

(vertical electrical soundings) surveys by Schlumberger

arrays are normally executed, using four probes put into the

ground. Briefly, a vertical electrical sounding is represented

by a discrete sequence of apparent resistivity measures of

underground, carried out with a growing spacing between a

couple of current electrodes, so interesting deeper and deeper

formations. Centre and orientation of VES’ array are main-

tained fixed. Quantitative interpretation processes permit to

investigate geometric and hydrogeological features of

aquifers: among these, VES’ allow us to find out salt con-

taminations of groundwater and to perform a zoning of a

considered area on the basis of aquifer resistivity, taking into

account a preliminary hydrogeological model (stratigraphic

and geochemical information). Among the very numerous

application of Schlumberger VES’ to identify seawater

intrusion in coastal aquifers, the authors consider the expe-

riences in Mediterranean areas of Shaaban (2001) and Khalil

(2006). In both the cases, resistivity relevant to intruded

aquifers is\5–10 X m.

In the Acquedolci area, the geophysical survey has been

principally carried out in the coastal deposits; in particular,

a small group of soundings has been opportunely located in

the sandy–gravelly alluvial fan of Furiano torrent, in the

western sector of the plain (Fig. 3). The entire studied area

has been densely interested by a set of 41 VES’. As it is

well known, the applied geophysical method portrays the

distribution of ground electric resistivity (Kunetz 1966;

Orellana 1982). In this paper, the specific experience car-

ried out in the structurally complex Acquedolci area shows

the good integration among hydrogeological, hydrochem-

ical and geophysical methodologies, thanks to the fair

correlation between resistivity of aquifer and salinity of

groundwater for seawater intrusion. Authors refer to simi-

lar VES’ surveys in Egypt (Shaaban 2001; Al-Sayed and

El-Qadi 2007), also mentioning the application of other

geophysical methods, as TDEM (time domain electro-

magnetic method). These electromagnetic surveys have

been carried out to investigate sea-intrusion in coastal

aquifers of Israel (Melloul and Goldenberg 1997). The

application of TDEM is recommended in presence of very

low resistivity values of the conductive layers as well as of

notable shallow lateral heterogeneity, where interpretation

of DC measures can be characterized by uncertainty and

ambiguity. Easy interpretations of VES’ curves in Ac-

quedolci area, corroborated by the stratigraphic knowledge,

widely justified the use of this inexpensive method. This is

confirmed by the survey carried out by the Azienda

Nazionale Autonoma Strade, during the preliminary geo-

logical study of the Furiano torrent delta construction of a

new bridge, where electro-stratigraphic cross section of the

alluvial fan was derived (Abbate et al. 1994).

Geoelectrical prospecting has been accurately planned

in order to depict the trend of sea pollution, which follows

Fig. 3 Location of vertical electrical soundings (VES’), with relevant

number, in the surveyed area. Topographic contour lines are also

exhibited

1478 Environ Geol (2008) 55:1473–1482

123

the above quoted Ghyben–Hertzberg law taking into close

account the irregular permeability features of aquifers and

their seasonal exploitation for different uses. For the pur-

pose of this work, authors here present and discuss only

VES’ numbers 1, 2 and 3, close to coastline, and VES

number 4, far from the shore (Fig. 3).

The shown VES’ (Fig. 4) have been executed by means

of Schlumberger arrays; resistivity values have been mea-

sured using a PASI digital georesistivimeter, model 16 GL.

The maximum VES’ spacing was 600 m. The investigation

depths were suitable to the aquifer geometry (see piezo-

metric levels in Table 1), reaching the saturated zone and

also revealing the eventual occurrence of impervious in-

terbeddings (clays). According to the depths of saturated

zone and/or clay top, the depiction of aquifer geometry

needed an investigation depth of at least 150 m, assuring

the reaching of the polluted sectors. Furthermore, strati-

graphic controls aided the inversion of geophysical data.

Examples are easily found in the Furiano torrent fan, where

well-drillings together with close VES’ occurred, crossing

completely the delta sector, as described in the relevant

reference (Abbate et al. 1994).

Very low resistivity of the saturated zone of aquifer was

clearly depicted in certain VES’ and compared with

stratigraphic and geochemical outlines. As a matter of fact,

values \10 X m were interpreted in the alluvial western

fan of Furiano torrent and in the eastern narrow belt of the

area, in which high chlorine contents in groundwater were

detected ([500 mg L-1).

VES’ interpretation allowed us to easily and quickly

solve the geoelectrical inverse problem, applying relatively

simple geological model based on horizontally layered

stratification. In fact, acquired curves exhibited a reliable

assessment of the curve asymptotes relevant to the main

hydrostructures also involved in the marine encroachment

process as well.

As a final result, the distribution knowledge of apparent

resistivity parameter, running in GIS environment, per-

mitted to explain local problems, with a comprehensive

and up-datable view of the hydrogeological patterns.

Results and discussion

Figure 2 shows that—as expected—groundwater electrical

conductivity, in the investigated area, agrees with the chlo-

ride distribution, as shown in Table 1. This is confirmed by

the significant value of their correlation factor, as illustrated

in Table 2. Observing this table, it is possible also to evi-

dence a very high correlation value between Na+ and

conductivity. This result has to be carefully taken into

account, because sodium rate can also be affected by ionic

exchange processes between groundwater and clay minerals:

Na+ concentration can locally increase in relation to the clay

interbeddings in layered sectors of aquifer. In this case,

further procedures could be useful to better assess the geo-

statistical trends of the quoted elements. Furthermore, the

concentration of HCO3-, in spite of the apparent absence of

any appreciable statistical correlation with almost the

remaining variables (Table 2), allows us to recognize

the eastern zones of plain where aquifers are supplied by the

karst and fracture network of inland relieves (Pizzo

Castellaro and San Fratello Mt., see Fig. 1), also through the

Inganno torrent. These considerations appear decisive to

draw the groundwater pathways in the whole Acquedolci

region, including the calcareous-dolomitic southern out-

crops, distinguishing sectors with different chemical

behaviours, as shown in PCA diagram (Fig. 5).

Fig. 4 VES’ curves with

relative interpretation

Environ Geol (2008) 55:1473–1482 1479

123

VES’ curves generally exhibit highest values of resis-

tivity along torrent deposits and, primarily, at the foothills

of the limestone relieves (debris), where resistivity values

overcome 2,000 X m (VES number 4, Fig. 4).

Resistivity increases in the inland part of the alluvial

deposits of Furiano torrent, sharply decreasing towards

Western and Eastern coastal belts. Lower resistivity values,

relevant to clayey layers, have been found in central sectors

of the investigated area. Geoelectrical interpretation has

evaluated the true resistivity of the quaternary aquifer,

which ranges between 50 and 200 X m, with higher values

up to 500 X m, as tested by shallow measures.

The understanding of the geophysical results has evi-

denced the clear influence of sea water intrusion on

apparent resistivity. This confirms, in the investigated

plain, the fair relationship among the investigated param-

eters relevant to geochemical and geophysical prospecting,

in spite of the possible occurrence of shallow clayey in-

terbeddings into the sandy–arenaceous overburden. At this

proposal, eventual interpretation ambiguities can be easily

solved by available stratigraphic information and resistivity

gradient.

It has to be noted that geoelectrical interpretation of

intrusion phenomena—with the consequent salt–fresh

water mixing—does not appear anywhere coherent with

the shore–well distance. Indeed, referring to the quoted

figures, VES 2, relatively far from the coastline, exhibits an

asymptotic resistivity value lower than VES 3, closer to the

sea. This indicates an inland advance of brackish belt in the

Furiano torrent delta: in this sector, high permeability of

Table 2 Correlation matrix among chemical–physical parameters measured on the 41 selected well-waters, see also Table 1

Conductivity Ca2+ Mg2+ Na+ K+ HCO3- Cl- SO4

2-

Conductivity 1 0.687 0.893 0.966 0.305 0.354 0.949 0.813

Ca2+ 1 0.533 0.552 0.319 0.296 0.616 0.573

Mg2+ 1 0.841 0.137 0.421 0.849 0.680

Na+ 1 0.280 0.346 0.917 0.813

K+ 1 0.029 0.320 0.110

HCO3- 1 0.332 0.239

Cl- 1 0.653

SO42- 1

Significant values (except diagonal) at the level of significance a = 0.050 (two-tailed test) are given in bold numbers

Fig. 5 Principal component

analysis (PCA), relevant to the

measured parameters (see

Tables 1, 2). In the delimited

region of the graph, the most

HCO3- enriched waters are

evidenced

1480 Environ Geol (2008) 55:1473–1482

123

the sandy–gravely formation and a local groundwater

overdraft determine an anomalous trend of the seawater

intrusion phenomenon, recognized thanks to resistivity data

acquired in the alluvial fan. In detail, bore–hole data and

indirect permeability evidences, based on well productivity

estimations, confirm the noticeable occurrence of gravels

and conglomerates in well-localized portions of this allu-

vial aquifer (Abbate et al. 1994). As a matter of fact, this

area—in which an alluvial fan is present—is characterized

by higher values of permeability owing to the presence of

coarser materials with respect to the central coastal sector

of the plain. These considerations permit to hypothesize

diverse distances of the saltwater–freshwater interface

from the coastline, owing to difference grain sizes among

the formations of the plain, as evidenced by the resistivity

survey outcomes in Western and Eastern sectors of the

plain. In fact, Eastern sectors of Acquedolci plain are

characterized by a narrow salty belt, very close to the lit-

toral line, see VES 1 in Fig. 4. Here, aquifer is

characterized by more homogeneous grain size, with a

thinner or almost missing mixing layer and a sharp salinity

gradient towards the sea. Finally, higher resistivity values

generally evidence the absence of salt–brackish ground-

water or clayey interbeddings.

Conclusions

This article highlights the notable importance of integrated

methodologies to delineate groundwater flows and seawa-

ter pollution in a coastal area. The considered Sicily sector

is a good test-site to study the aquifer contamination

problem, very common to urbanized Mediterranean litto-

rals, where severe groundwater exploitations cause

seawater intrusion. The simultaneous interpretation of

geophysical and hydrogeochemical outcomes, in the frame

of interdisciplinary projects, constitutes the first attempt

towards the exhaustive pollution risk assessment in Sicily.

Relevant mapping will be available to local government as

a necessary new tool of territorial planning.

The survey validates the expected contamination risk for

sea intrusion from the North, especially in the circumscribed

sectors of the torrent fans. The shown investigations and

outcomes are relevant to a particular zone of Northern Sicily

characterized by elevate hydrogeological risk mainly due to

seawater intrusion, as vulnerability and quality evidences

have testified. This sector of Sicily represents a significant

example of serious and uncontrolled exploitation of ground-

water: this paper intends to update the contributions and the

improvements carried out by researchers in the ambit of

interdisciplinary projects, addressed towards a better man-

agement of water resources on the whole. A decisive role in

this research has also been played by GIS elaboration of

georeferenceddata, inorder to typify theaquifersaccording to

chemical–physical features of groundwater. Considering that

groundwater could constitute, in future, the main quality

resourcesofthewholeNebrodiregion,authors,bymonitoring

their quoted chemical and physical features, consider essen-

tial a protection and a recovery strategy are essential.

Further water samplings and geoelectrical measure-

ments, periodically executed, can be inserted in a control

program of the pollution trend in the Acquedolci area. By

now, the continuous demand of waters for the different

needs, also considering the growing demand for tourism, is

only partially satisfied by local aqueducts, mainly supplied

by the mentioned Favara spring. So, the plain is subjected

to a whole hydrogeological risk not only for seawater

intrusion and groundwater overexploitation, but also for the

intense spreading of fertilizers.

The shown updateable representations, pertaining to

vulnerability and risk concepts, are essential to consider the

problem of the aquifer protection in this crowded sector of

Sicily.

Acknowledgments Authors would like to thank the staff of the

chemical laboratory of the Azienda Municipalizzata Acquedotti di

Palermo for the help during the collection and analyses of wellwaters,

the Azienda Nazionale Autonoma Strade for the availability of VES’

and boreholes data, and anonymous referee for his critical revision of

the manuscript.

References

Abbate R, Cimino A, Emma S, Martorana Tusa A, Orecchio S (1994)

Lineamenti geomorfologici e idrogeologici dell’acquifero

carbonatico del territorio di Acquedolci, Messina (Geomorpho-

logical and hydrogeological outlines of the karst aquifer of

Acquedolci area). Boll Acc Gioenia Sci Nat 27:579–597

Abbate R, Cappadona Ignazzitto S, Cimino A, Di Patti C, Orecchio S

(2003) Indagini integrate per la valorizzazione delle risorse

ambientali nell’area carbonatica di Monte San Fratello—Zona b

del Parco dei Nebrodi (integrated surveys for the valorisation of

the environmental resources in the karst area of Monte

San Fratello—B zone of Nebrodi Park). Thalassia Salentina

26(supp):65–76

Al-Sayed EA, El-Qady G (2007) Evaluation of seawater intrusion

using the electrical resistivity and transient electromagnetic

survey: case study at fan of Wadi Feiran, Sinai, Egypt. EGM

2007 International Workshop innovation in EM, grav. and mag.

methods: a new perspective for exploration, Capri, Italy

Barlow PM (2003) Ground water in freshwater–saltwater environ-

ments of the Atlantic coast. US geological survey, information

services, Denver federal center, Denver, US, Circular 1262,

121 p

Bear J (1979) Hydraulics of groundwater. McGraw Hill, New York.

569 pp

Chachadi AG, Lobo Ferreira JP, Noronha L, Choudri BS (2003)

Assessing the impact of sea-level rise on salt water intrusion in

coastal aquifers using GALDIT model. APRH/CEAS, Seminario

Sobre Aguas Subterraneas, Lisbon, 13 p

Cheng AH-D, Ouazar D (1999) Analytical solutions. In: Bear J,

Cheng AHD, Sorek S, Ouazar D, Herrera I (eds) Seawater

Environ Geol (2008) 55:1473–1482 1481

123

intrusion in coastal aquifers—concepts, methods and practices.

Kluwer, Dordrecht. pp 163–187

Cimino A, Andolina F (2002) The territorial danger in the cartog-

raphy of groundwater contamination risk in Palermo Plain. Mem

Soc Geol It 57:561–568

Cheng AH-D, Halhal D, Naji A, Ouazar D (2000) Pumping

optimization in saltwater-intruded coastal aquifers. Water Re-

sour Res 36:2155–2165

Cimino A, Abbate R, Macaluso M, Orecchio S (1997) Karst hydrog-

eology and vulnerability in a coastal sector of Nebrodi Mts. region

(Northern Sicily). Sci Tech Envir, Mem H S 12:205–208

Cimino A, Abbate R, Martorana Tusa A (1998) The Regional Park of

Nebrodi Mts. (Sicily): a contribution to an integrated manage-

ment of groundwater. Environ Geol 34:320–328

Cimino A, Abbate R, Cappadona Ignazzitto S, Orecchio S, Sambataro

S (2002) Protection and monitoring of water resources in North–

West Sicily (with particular regard to the S. Fratello-Acquedolci

karst area). Speleologia Iblea 10:107–115

Cimino A, Artino C, Oieni A (2006) Rischi idrogeologici e sanitari in

aree urbane della Sicilia soggette a contaminazione degli

acquiferi: recenti risultati e rappresentazioni cartografiche in

ambiente GIS (hydrogeological and sanitary risks in urban area

of Sicily subjected to aquifer contamination: recent results and

cartographic representation in GIS environment). 24th environ-

ment day meeting ‘‘climate and health’’. Accademia Nazionale

dei Lincei, Rome, pp47–50

Civita M (1994) Le carte della vulnerabilita degli acquiferi

all’inquinamento: Teoria e pratica (Vulnerability pollution maps

of aquifers: theory and practice). Pitagora Ed, Bologna. 325pp

Civita M, De Maio M (1997) Assessing groundwater contamination

risk using ARC/INFO via GRID function. ESRI International

USER Conference, San Diego

Civita M, De Maio M (2000) Valutazione e cartografia automatica

della vulnerabilita degli acquiferi all’inquinamento con il

sistema parametrico SINTACS R5 (evaluation and automatic

pollution vulnerability of aquifer using SINTACS R5 parametric

system). Pitagora Ed, Bologna. 226pp

Civita M, Gargini A, Manzone L, Pranzini G (1995) Applicazione del

sistema parametrico SINTACS alla valutazione della vulnerab-

ilita intrinseca degli acquiferi nel bacino intrappenninico del

Valdarno Medio. Quaderni di Geologia Applicata 3:37–40

Demirel Z (2004) The history and evaluation of saltwater intrusion

into a coastal aquifer in Mersin, Turkey. J Environ Manage

70:275–282

Di Sipio E, Galgaro A, Zuppi GM (2006) Salt water contamination on

Venice lagoon mainland: new evaluation of origin, extension and

dynamics. Proceedings of 1st SWIM-SWICA (19th salt water

intrusion meeting-3rd salt water intrusion in coastal aquifers),

Cagliari

Fetter CW (1973) Water resources management in coastal plain

aquifers. Proceedings of the international water resources

association, first world congress on water resources. pp322–331

Fetter CW (2001) Applied Hydrogeology. Prentice-Hall. Upper

Saddle River. 598 pp

Gemitzi A, Petalas C, Tsihrintzis VA, Pisinaras V (2006) Assessment

of groundwater vulnerability to pollution: a combination of GIS,

fuzzy logic and decision making techniques. Environ Geol

49:653–673

Ghassemi F, Chen TH, Jakeman AJ, Jacobson G (1993) Two- and

three-dimensional simulation of seawater intrusion: perfor-

mances of the ‘‘SUTRA’’ and ‘‘HST3D’’ models. AGSO J

Aust Geol Geophys 14:219–226

Gogu RC, Hallet V, Dassargues A (2003) Comparison of aquifer

vulnerability assessment techniques. Application to the Neblon

river basin (Belgium). Environ Geol 44:881–892

Hubbert MK (1940) The theory of ground-water motion. J Geol

48:785–944

Khalil MH (2006) Geoelectric resistivity sounding for delineating salt

water intrusion in the Abu Zenima area, West Sinai, Egypt.

J Geophys Eng 3:243–251

Kunetz G (1966) Principles of direct current resistivity prospecting.

Geoexploration monographs, Gebruder-Borntraeger, Berlin. 103 pp

Liu CW, Cheng LH (1997) Hydrogeological investigation of a

groundwater contamination site in southern Taiwan. Environ

Geol 29:238–245

Mantoglou A (2003) Pumping management of coastal aquifers using

analytical models of saltwater intrusion. Water Resour Res

39:1335

Mantoglou A, Papantoniou M, Giannoulopoulos P (2004) Manage-

ment of coastal aquifers based on nonlinear optimization and

evolutionary algorithms. J Hydrol 297:209–228

Melloul AJ, Goldenberg LC (1997) Monitoring of seawater intrusion

in coastal aquifers: basic and local concerns. J Environ Manage

51:73–86

Narayan KA, Schleeberger K, Bristow KL (2007) Modelling seawater

intrusion in the Burdekin Delta irrigation area, North Queens-

land, Australia. Agr Water Manage 89:217–228

Orellana E (1982) Prospeccion geoelectrica en corriente continua.

Paraninfo, Madrid. 578 pp

Oude Essink GHP (2001) Salt water intrusion in a three dimensional

groundwater system in the Netherlands: a numerical study. Trans

Porous Media 43:137–158

Polemio M, Dragone V, Limoni PP (2006) Salt contamination in

Apulian aquifer: spatial and time trend. Proceedings of 1st

SWIM-SWICA (19th salt water intrusion meeting-3rd salt water

intrusion in coastal aquifers), Cagliari

Pulido-Leboeuf P (2004) Seawater intrusion and associated processes

in a small coastal complex aquifer (Castell de Ferro, Spain).

Appl Geochem 19:1517–1527

Reilly TE, Goodman AS (1985) Quantitative analysis of saltwater

freshwater relationships in groundwater systems: a historical

perspective. J Hydrol 80:125–160

Shaaban FF (2001) Vertical electrical soundings for groundwater

investigation in northwestern Egypt: a case study in a coastal

area. African Earth Sci 33:673–686

Sodde M, Barrocu G (2006) Seawater intrusion and arsenic contam-

ination in the alluvial plain of the rivers Quirra and FluminiPisale, south–eastern Sardinia. Proceedings of first SWIM-

SWICA (19th salt water intrusion meeting-third salt water

intrusion in coastal aquifers), Cagliari

Yechieli Y, Kafri U, Sivan O (2006) The interrelation between the sea

and the coastal aquifer, deduced from analyses of radioactive

isotopes. Proceedings of first SWIM-SWICA (19th salt water

intrusion meeting-third salt water intrusion in coastal aquifers),

Cagliari

1482 Environ Geol (2008) 55:1473–1482

123