Geophysical investigations for the characterization of fractured rock aquifers in Itu, SE Brazil

$Page 1: Geophysical investigations for the characterization of fractured rock aquifers in Itu, SE Brazil$
www.elsevier.com/locate/jappgeo

Journal of Applied Geophys

Geophysical investigations for the characterization of

fractured rock aquifers in Itu, SE Brazil

Jorge Luıs Porsani*, Vagner Roberto Elis, Francisco Yukio Hiodo

Departamento de Geofısica, Instituto de Astronomia, Geofısica e Ciencias Atmosfericas, Universidade de Sao Paulo, Rua do Matao,

1226, Cidade Universitaria, 05508-090, Sao Paulo, Brazil

Received 15 April 2004; received in revised form 15 April 2004; accepted 25 October 2004

Abstract

This paper presents the results of integrated geophysical investigations to characterize aquifers in fractured rocks in the

Granite complex of Itu, SE Brasil, to help locate sites for tubular wells for groundwater exploration. Ground penetrating radar

(GPR) profiles, dipole–dipole electric survey, gamma spectrometry, and radon gas emanometry were applied on a same line for

a comparative study of these methodologies. The results allowed us to characterize structural discontinuities up to 30 m in

depth, such as, dipped, or vertical fractures. The dipped fractures appear as strong GPR reflectors, probably due to the presence

of water. Besides, two anomalous regions were identified, one at 50 m and other at 75 m, both showing high attenuation of the

GPR signals, and they correspond to the vertical fracture zones. 2D modeling of the dipolar electric survey shows that the two

anomalous areas correspond to high electric conductivity zones, and that in the position of 75 m, a vertical fracture zone is

clearly identified. In the gamma rays profiles, the values of K and Th concentrations observed in the position of 50 m indicate

the presence of vertical fractures filled with clay minerals. On the other hand, in the position of 70 m of the Rn gas emanometry

profile, the peak of Rn emanation is five times higher than the regional level, indicating the presence of a vertical fracture zone,

clearly filled with fresh water in circulation. The geophysical characterization of the vertical fracture zones with fresh water

subsidized the drilling of a well for groundwater exploration in fractured aquifers, which was an important contribution for the

local community because the main sources of surface water are contaminated.

D 2004 Elsevier B.V. All rights reserved.

Keywords: Ground penetrating radar (GPR); Electric resistivity; Gamma ray spectrometry; Radon gas emanometry; Fractured aquifer; Granite

complex of Itu; SE Brazil

0926-9851/$ - see front matter D 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.jappgeo.2004.10.005

* Corresponding author. Tel.: +55 11 3091 4734; fax: +55 11

3091 5034.

E-mail address: [email protected] (J.L. Porsani).

1. Introduction and objectives

Nowadays, there are several geophysical methods

for the mapping of fractured rocks filled with some

representative mineral (Orellana, 1972; Morse, 1977;

Daniels, 1996; Lane et al., 2001). The Ground

ics 57 (2005) 119–128

J.L. Porsani et al. / Journal of Applied Geophysics 57 (2005) 119–128120

penetrating radar (GPR) and the electric resistivity

methods are the most commonly used in the world.

These methods allow the locating of fractures filled

with water, but they do not bring any information

about the subsurface circulation itself, since the

fracture can be filled with clay and have a low free

water content.

In many cases, the nuclear techniques can bring

some additional information about water circulation

in fracture zones, in spite of the low penetration of

the gamma photons of the natural radioactive decays

in hard rock. Soil created by the exposure of the

basement rock to the weather elements carries in it

almost the same minerals present in the crystalline

rock. Besides, the radon (Rn) radioactive gas of the

uranium (U) and thorium (Th) series can decay

before escaping to the atmosphere, leaving polonium

(Po) halos that can decay to 214 Bi and 208 Tl, and

then can be detected by gamma ray spectrometry.

Another nuclear technique used to detect fractures

was radon gas emanometry, as was previously

explained.

In this paper, GPR and dipole–dipole electric

surveys were performed to locate fracture zones and

to determine the top of the fresh granite rock. As these

methods do not discriminate if the fractures are filled

with clay minerals or free water, gamma ray spec-

Fig. 1. Map of the location of the study area and geologic

trometry and radon gas emanometry techniques were

also applied to locate fractures filled with fresh water.

The geophysical profiles were surveyed on a same

line, hence a comparative study between these

methodologies was executed, and the integrated

interpretation was effected to characterize the aquifer

in fractured rocks.

The study area is the Granite complex of Itu, an

area of environmental protection located in the

municipal district of Itu, State of Sao Paulo, SE

Brazil (Fig. 1). In that area, the main sources of

surface water (Tiete, Piraı and Fonte Rivers) are quite

polluted, and the provisioning of potable water for the

local community is accomplished through the explo-

ration of groundwater, by means of tubular wells in

fractured aquifers. Therefore, the application of the

geophysical methods to locate fracture zones filled

with free water becomes of great importance for the

countryside communities.

The main contribution of this project was to locate

fracture zones filled with fresh water, given that the

exploration of groundwater in fractured aquifers in

granite rocks can be efficiently carried out in this area.

Results from the geophysical surveys showed ideal

areas to drill wells for the exploration of groundwater,

and they were important for the provisioning of the

local community.

al structures of the Itu Granite complex, SE Brazil.

J.L. Porsani et al. / Journal of Applied Geophysics 57 (2005) 119–128 121

2. Local geology

The Granite complex of Itu is located approx-

imately 90 km from Sao Paulo city, SE Brazil, and it

has an area about of 400 km2 (Fig. 1). In the area, a

transition region between the Pre-Cambrian terrain of

the state of Sao Paulo and the Parana sedimentary

basin occurs (Pascholati, 1989). Due to the lack of

outcrop and the covering by more recent geological

units, exhibitions of the contacts of the Granite

complex with the host rocks are rare and can be

tectonic or intrusive. The most prominent geological

Fig. 2. Location of the ge

structures of the Granite complex of Itu are the

lineaments that correspond to the curved fault zones,

subparallel or convergent to the Jundiuvira fault

zone. Those zones coincide partially with the

orientation of the main drainages of the region, such

as, the Tiete, Piraı and Fonte Rivers. The most

important lineaments that affect the Granite complex

show preferential directions of N20–30E and N45–

50W (Fig. 2). Geologically, these lineaments repre-

sent the fault/fracture zones, which are important

structures for the exploration of groundwater in

granite rocks.

ophysical profiles.


3. Acquisition and processing of the geophysical

data

The GPR, dipolar electric resistivity, gamma ray

spectrometry, and radon gas emanometry profiles

were acquired along an 80-m line, along the N45E

direction (Fig. 2). This direction was chosen so that

the profiles crossed the most representative structural

lineaments in the study area. The profiles are on the

same line to evaluate the geophysical signatures of

fracture zones through a comparative study between

these methodologies.

A very irregular relief characterizes the study area.

Hence, the geophysical profiles were positioned on

the land based on field logistics, the topography, and

the direction of the main fractures. Profiles were

disposed following a same topographical level. There-

fore, it was not necessary to do a topographical

correction in the GPR profiles.

The GPR data were acquired after a period of 20

days of rains in the study region. This is a favorable

situation for the mapping of fracture zones in the

granite rocks, because the high contrast between the

dielectric constant of the water present in the fractures

and the host rock results in strong reflection in the

GPR profiles (Olhoeft, 1998). On the other hand, the

presence of a fracture zone filled with free water

produces an increase in the electric conductivity,

consequently, this induces a strong attenuation in the

GPR profile. Besides, an anomaly is expected in the

radon gas emanometry profile due to its leakage to the

atmosphere.

3.1. Ground penetrating radar

With the GPR method (Davis and Annan, 1989;

Daniels, 1996; Porsani, 1999), three reflection

profiles of 50, 100, and 200 MHz were acquired to

map the fracture zones and the top of the fresh

granite rock (Fig. 2). The data were acquired with

the Ramac equipment from the Geophysics Depart-

ment of the IAG/USP. The profiles were performed

on a same line to get good penetration with the 50

MHz antenna and sharp resolution with the 200

MHz antenna. The data were acquired with apertures

of 2 m for the 50 MHz antenna, 1 m for 100 MHz,

and 0.6 m for 200 MHz. The interval between the

traces was 0.5 m (for 50 and 100 MHz antennas) and

0.25 m (for 200 MHz). The total stacking times of

the traces in all the profiles was 512. All data were

acquired in the step-by-step mode, and the trans-

mitter and receiver antennas were positioned in a

transverse orientation in relation to the direction of

the profile to guarantee maximum coupling between

the transmitted and received signals (Annan and

Cosway, 1992; Versteeg, 1996).

In this paper, a representative GPR profile of 100

MHz of the studied area is presented (Fig. 2). On the

reflection profiles, four velocity soundings of the wide

angle reflection and refraction (WARR) type were

performed, using 100 MHz antenna and spacing of 0.1

m between the traces. The propagation velocity of the

electromagnetic wave in the subsurface was deter-

mined by the Semblance method (Yilmaz, 1987), and

it was used in the migration and in the conversion of

the time profiles for depth.

The GPR data were processed by the Radan

software (GSSI). A time filtering band pass was

applied to remove noise. To compensate energy losses

due to the absorption and the geometric scattering,

gains in time were applied to the data. The fk-

migration was applied to spatially reposition the

reflectors in subsurface. The time to depth conversion

was performed using a constant speed of 0.125 m/ns.

A spatial filtering of a three trace moving average

kind was applied, and it resulted in a horizontal

smoothing.

3.2. Electric resistivity

By the electric resistivity method (Orellana, 1972;

Elis, 1999), it was possible to obtain a dipolar electric

sounding with 10 m aperture to characterize the

geoelectric stratigraphy of the fracture zones in the

Granite complex of Itu (Fig. 2). The data were

acquired with an Iris resistivimeter, and five levels

were studied, allowing a theoretical investigation of

up to 30 m in depth. For comparative purposes, the

origin of that profile corresponds to the 15 m position

in the GPR profile.

To explain the true spatial positions of the geo-

electric anomalies and to identify the presence of the

fracture zones, the data were interpreted quantitatively

through 2D modeling (Ross et al., 1990), and the

many geological structures of the subsurface were

identified.


A smoothing modeling technique based on the

Resixip2di software (Interpex) was used for inter-

pretation. This type of modeling is an interpretation

process that calculates the response of a homoge-

neous semispace for the data obtained in the field.

The 2D model divides the subsurface in a series of

rectangular blocks to determine its resistivities and to

produce a pseudosection of apparent resistivity that

agrees with the field data, using an inversion process

based on a variation of the minimum square method.

The result obtained is showed in the form of

resistivity isovalues that assume the approximate

forms of the investigated structures.

3.3. Gamma spectrometry

The gamma ray spectrometry method in geo-

physical prospecting is based on the mapping of

surface anomalies induced by the decay of byprod-

ucts of the natural radioactive series of 238 U and

232 Th, and also of the natural isotope 40 K. The

anomalous values of concentration of these radio-

active elements can be useful to map mineralized

zones in auriferous deposits (Hiodo et al., 1999a)

and fractured zones with circulation of free water

due to the presence of 214 Bi, due to ascension of

the 222 Rn gas transported by water (Hiodo et al.,

1999b). In this case, the Rn gas decays to 218 Po

before escaping to the atmosphere. After some

natural radioactive decays, the radioactive element

214 Bi is produced, and its decay generates gamma

counting in the U window (Bristow, 1983).

The measurements were made with a portable

Geofyzika GS512 detector with NaI (Tl) volume

sensor of 0.33 l, coupled with a multichannel

analyzer comprising 512 channels. The calibration

constants of the detection system were obtained

from measurements done on eight cement blocks

with well-known concentrations of the radioactive

elements K, U, and Th, that belong to the Institute

of Radioprotection and Dosimetry of the National

Council of Nuclear Energy (CNEN). These param-

eters allowed for the subtraction of Compton noise

and the interference between windows (stripping)

and for the conversion of the net count of the

interest windows into radioactive element concen-

tration values. The technique used for the con-

version of the value range of the three windows (K,

U, and Th) in concentrations is described in Grasty

et al. (1991).

Measurements were made every 2 m along a line

(Fig. 2), and the energy spectra between 700 KeV and

3 MeV were accumulated in the detector memory. In

the processing of the data, the regional noise and the

stripping were eliminated.

3.4. Radon gas emanometry

The radon gas emanometry uses the 222 Rn,

with a half-life of 3.62 days, resultant of the alpha

decay of the 226 Ra, of the 238 U series. The fresh

water that percolates into the rock fractures carries

the radioactive gas that can travel several meters

before escaping through some fracture, towards the

surface, even considering the small half-life of this

gas. The escape to the atmosphere occurs through

the transport mechanism known as diffusion (Soon-

awala and Telford, 1980). Measurements were made

at 5-m intervals along a line (Fig. 2). For accumu-

lation and detection of the radioactive gas Rn, PVC

tubes of 10 cm (diameter) and 40 cm (length) were

buried in vertical position, being the upper side closed

and the lower opened for the Rn gas inlet and its

byproducts. These tubes were totally buried in the soil

for 4 h for the capture of 222 Rn gas before it escaped

to atmosphere. After the accumulation time was

completed, two holes in the upper side were made

to establish a closed circuit through an air filter, a

controlled flow diaphragm pump and a Lucas alpha

scintillator. For this purpose, a system of forced

airflow circulation, controlled by a feedback circuit,

was developed in the Laboratory of Geophysical

Instrumentation of the IAG. The air is pumped to the

Lucas cell by a flow diaphragm pump, controlled by a

feedback system, formed by a rotameter, an infrared

optoelectronic device, and a PID servocontrol circuit

(Doebelin, 1986), which controls the flow of air in a

closed circuit. Measurement of Rn decay is made

during 5 min in the Lucas cell to compare the

emanometry rate of all the holes. To remove the

effects of the fluctuation of atmospheric pressure,

measurements were performed almost at the same

time in all accumulation chambers.

The rate of alpha disintegration is measured

through a Lucas cell in the Scintrex RD-200 scin-

tillator device, with 0.10-l capacity. Alpha ionizing

Fig. 3. WARR velocity sounding of 100 MHz and velocity spectrum.


particles from radon decay interact with the internal

phosphor film of the Lucas chamber, which emits a

luminous radiation near the ultraviolet range, which

is converted into an electric pulse by a photo-

multiplier tube. A countercircuit controlled by an

adjustable timer allows for the determining of the

number of events in the adjusted interval. After each

measurement, the Lucas cell is changed because of

the byproduct elements of the Rn that become

impregnated in the chamber wall. After about an

hour, the counting level reaches the electronic noise

and the cell can be used again.

Fig. 4. GPR profile acquired

4. Interpretation and discussion of the results

4.1. Ground penetrating radar

The GPR profiles supplied information of the

subsurface until about 20 m of depth. To convert

time to depth, the velocity of the WARR surveys was

used. Fig. 3 shows the WARR survey of 100 MHz

obtained in the position of 45 m of the GPR profile,

followed by the velocity spectrum. In this figure, the

arrival of the airwave and of the groundwave are

observed; besides, two hyperbolic reflectors are

with 100 MHz antenna.


clearly observed in 140 and 240 ns, and they

presented a velocity adjustment of 0.125 and 0.150

m/ns, respectively. These hyperbolic reflectors corre-

spond to the fractures observed on the GPR reflection

profile.

Fig. 4 shows the 100 MHz GPR profile, where

strong reflectors (A and B) dipped towards the NE,

along the profile, can be observed. The reflector (A),

around 8 m of depth, is discontinuous, and it is

interrupted around the 50-m position. It is probably

related to an inclined fracture filled with water, due to

its high amplitude, which is typical of a strong

Fig. 5. 2D modeling of the dipolar electric survey with dipole of 10 m, pseu

synthetic resistivity (b), and interpreted geoelectric model (c).

contrast between the dielectric constant of the water

and of the granite (Olhoeft, 1998). The reflector (B),

around 14 m of depth, has the same inclined tendency

and amplitude of the reflector (C), suggesting it to be

only one reflector, although it is not continuous. This

reflector, is probably related with the top of the fresh

granite rock, because starting from it, no more

reflectors are observed, being an indicative of the

arrival of the GPR electromagnetic wave in the top of

the homogeneous granite rock (Orlando, 2003). In this

figure, two anomalous areas, characterized by a high

attenuation, can also be observed: one under the

dosection of the apparent field resistivity (a), section of the apparent

Fig. 6. Gamma spectrometry profile for the K channel.


position of 50 m (discontinuity of the reflector A) and

the other in the end of the profile (starting from the

75-m position). Both areas are interpreted as vertical

fracture zones filled with water or clay, due to the high

electric conductivity of these materials.

4.2. Electric resistivity

Fig. 5 shows the result of the 2D modeling of the

dipolar electric survey, where the pseudosection of

apparent electric resistivity (Fig. 5a), the section of

synthetic apparent resistivity (Fig. 5b), and the

interpreted geoelectric model (Fig. 5c) are presented.

The geoelectric model shows a tendency of dipping of

the isovalue lines of electric resistivity towards NE up

to the position of 70 m, agreeing with the tendency of

the GPR reflectors (Fig. 4). The high resistivities

found around the 20-m depth agree with the hypoth-

Fig. 7. Gamma spectrometry p

esis of the top of the fresh granite rock. In this figure,

two conductive anomalous areas can be observed: one

under the position of 50 m (with about 5 m of

thickness) and the other starting from the 70 m

position (with at least 30 m of thickness). These

conductive anomalies coincide with the high attenu-

ation anomalies observed in the GPR profile (Fig. 4).

4.3. Gamma spectrometry

Figs. 6 and 7 show the profiles of the concentration

of K and Th obtained by gamma ray spectrometry. At

the 50-m position of the gamma profile, K and Th

concentration peaks can be clearly seen, at about

twice the regional level, and they show the presence

of a fractured zone filled with clay material. Besides,

another small fracture zone in the position of 34 m can

also be observed. The micas and feldspars of the rocks

rofile for the Th channel.


are easily decomposed in potassium-enriched clay

minerals. The clay minerals have an open crystalline

structure that favors the inclusion of radioactive

elements, such as Th, by ionic exchange or adsorp-

tion. As Th is insoluble in water, after the erosion

process and the liberation of the rock, it can be carried

to the fracture by mechanical action, and K by

dissolution. In the absence of clay, a depletion of K

and a small enrichment of U occurs, due to the

ascension of the Rn gas, whose byproduct 214 Bi

provides a net count in the window used for the

detection of U. The small decrease of the concen-

tration of K on the border of the fractures can be

explained by the fact that the micas and feldspars of

the rocks are easily decomposed by the meteoric water

and transported to the inside of the fracture, provoking

the observed depletion. This anomaly corresponds to

the area of high electric conductivity observed in the

dipolar electric survey (Fig. 5) and to the area of high

attenuation of the electromagnetic waves observed in

the GPR profile (Fig. 4).

4.4. Radon gas emanometry

Fig. 8 shows the radon gas emanometry profile

performed in the same line of the gamma spectrom-

etry for the windows of K and Th. In the 50-m

position, where K and Th gamma anomalies were

detected due to the clay minerals filling the fracture,

no peak of Rn emanation was detected. Probably this

result is due to the absence of porosity in the

constituent material, which did not permit the

ascension of the Rn gas to the surface. On the other

Fig. 8. Radon gas ema

hand, in the 70-m position, an anomalous area

characterized by a peak of Rn emanation five times

higher than the regional level is clearly observed. The

radioactive gas is carried by the free water that

percolates the microfractures of the rock, and when

the gas finds a fracture, it probably ascends in a

convective movement and escapes to the atmosphere.

Before escaping to the atmosphere, the Rn gas can

travel hundreds of meters before its decay. Therefore,

the emanometry detection becomes a good indicative

of the presence of free water in the fractured aquifers.

These results are in agreement with the GPR profiles

and the dipolar electric survey that showed a very

fractured zone of high attenuation and high electric

conductivity, respectively.

5. Conclusions

The GPR investigations, electric resistivity, gamma

spectrometry, and radon gas emanometry were inter-

preted in an integrated study through the comparison

of the geophysical results. The results obtained

showed an excellent agreement among the methods,

and they allowed the characterization of a zone of

vertical fractures filled with free water in the granites

of Itu up until a depth of 30 m. These results were

used as subsidies to drill a tubular well for the

exploration of groundwater in fractured aquifers, this

being of fundamental importance for the resident

community in the municipal district of Itu, SE Brazil,

because in the study area, the sources of superficial

water are completely polluted.

nometry profile.


Acknowledgements

We thank Mr. Luiz Henrique Hacker for permis-

sion to perform fieldwork in the study area. We thank

the Geophysical Department (IAG/USP) for providing

the necessary infrastructure for the accomplishment of

this project.

References

Annan, A.P., Cosway, S.W., 1992. Ground penetrating radar

survey design. Proceedings of the Symposium on the

Application of Geophysics to Engineering and Environmental

Problems (SAGEEP’92), Oakbrook, IL, USA, Apr. 26–29,

pp. 329–352.

Bristow, Q., 1983. Airborne gamma-ray spectrometry in uranium

exploration-principles and current practice. In: Clayton, C.G.

(Ed.), Nuclear Geophysics: Selected Papers on Applications of

Nuclear Techniques in Mineral Exploration, Mining and Process

Control. Pergamon Press, pp. 199–229.

Daniels, J.J., 1996. Surface Penetrating Radar. The Institution of

Electrical Engineers, London, UK.

Davis, J.L., Annan, A.P., 1989. Ground penetrating radar for high

resolution mapping of soil and rock stratigraphy. Geophys.

Prospect. 37, 531–551.

Doebelin, E.O., 1986. Measurements Systems-Application and

Design. McGraw-Hill.

Elis, V.R., Avaliacao da aplicabilidade de metodos eletricos de

prospeccao geofısica no estudo de areas utilizadas para

disposicao de resıduos. DSc thesis, Instituto de Geociencias da

UNESP, Campus de Rio Claro-SP, Brasil.

Grasty, R.L., Holman, P.B., Blanchard, Y.B., 1991. Transportable

calibration pads for ground and airborne gamma-ray spec-

trometers. Geological Survey of Canada, Internal Report IR-

90. 23 pp.

Hiodo, F.Y., Mendonca, C.A., Moraes, C.F., Shiraiwa, S., 1999.

Deteccao de zonas mineralizadas em depositos aurıferos na

regiao de Pocone-MT usando espectrometria gama. Proceedings

of the Sixth International Congress of the Brazilian Geophysical

Society, Rio de Janeiro. SBGf, Rio de Janeiro, Brazil. Expanded

Abstract, CD-ROM.

Hiodo, F.Y., Mane, M.A., Yamabe, T.H., 1999. Uso de emanometria

do gas radioativo 222Rn da serie do 238U, para deteccao de

fraturas em rochas. Proceedings of the Sixth International

Congress of the Brazilian Geophysical Society, Rio de Janeiro.

SBGf, Rio de Janeiro, Brazil. Expanded Abstract, CD-ROM.

Lane, J.W., Williams, J.H., Johnson, C.D., Savino, S.D.M.,

Haeni, F.P., 2001. Application of a geophysical btool-boxQapproach to characterization of fractured-rock aquifers: a case

study from Norwalk, Connecticut. Proceedings of the Sym-

posium on the Application of Geophysics to Engineering and

Environmental Problems (SAGEEP ’2001), Denver, Colorado,

USA, CD-ROM.

Morse, J.G., 1977. Nuclear Methods in Mineral Exploration and

Production. Elsevier Scientific Publishing.

Olhoeft, G., 1998. Electrical, magnetic, and geometric properties

that determine ground penetrating radar performance. Proceed-

ing of 7th International Conference on Ground Penetrating

Radar (GPR’ 98), Lawrence, USA, pp. 177–182.

Orellana, E., 1972. Prospeccion geolectrica en corriente continua.

Ed. Paraninfo, Madrid.

Orlando, L., 2003. Semiquantitative evaluation of massive rock

quality using ground penetrating radar. J. Appl. Geophys. 52,

1–9.

Pascholati, E.M., 1989. Caracterizacao geofısica da suıte intrusiva

de Itu. DSC thesis, Instituto de Astronomia, Geofısica e

Ciencias Atmosfericas, Universidade de Sao Paulo, Brasil.

Porsani, J.L., 1999. Ground Penetrating Radar (GPR): Proposta

metodologica de emprego em estudos geologico-geotecnicos

nas regioes de Rio Claro e Descalvado-SP. DSc thesis,

Instituto de Geociencias da UNESP, Campus de Rio Claro-SP,

Brasil.

Ross, H.P., Mackelprang, C.E., Wright, P.M., 1990. Dipole–dipole

electrical resistivity surveys at waste disposal study sites in

Nothern Utah. In: Ward, S.H. (Ed.), Geotechnical and Environ-

mental Geophysics, Investigations in Geophysics n. 5, vol. II.

Society of Exploration Geophysicist Press, pp. 145–152.

Soonawala, N.M., Telford, W.M., 1980. Movement of radon in

overburden. Geophysics 45, 1297–1315.

Versteeg, R., 1996. Optimization of GPR acquisition and noise

elimination parameters. Proceedings of the Sixth International

Conference on Ground Penetrating Radar (GPR’96), Sendai,

Japan, pp. 289–292.

Yilmaz, O., 1987. Seismic Data Processing. Society of Exploration

Geophysics Press, Tulsa.

Geophysical investigations for the characterization of fractured rock aquifers in Itu, SE Brazil

Documents