ORIGINAL ARTICLE

Stable isotopes, carbon-14 and hydrochemical composition
from a basaltic aquifer in São Paulo State, Brazil

Didier Gastmans1 • Amauri Antônio Menegário1 • Ian Hutcheon2

Received: 3 February 2016 / Accepted: 6 February 2017 / Published online: 13 February 2017

� Springer-Verlag Berlin Heidelberg 2017

Abstract The Cretaceous Serra Geral Aquifer (SGA) is

contained within one of the largest continental flood basalts

in the world, reaching a thickness up to 1700 m in the

center of the Paraná Basin. The SGA is one of the most

important groundwater reservoirs in northeastern São Paulo

State (Brazil), responsible for water supply to cities and

agriculture. In order to evaluate the geochemical and iso-

topic evolution of SGA, as well as to determine the mean

residence time, a groundwater sampling campaign was

carried out over the SGA in São Paulo State (Brazil) from

January to April 2013. Two main hydrochemical facies

were recognized: Ca–Mg–HCO3 related to water–rock

interaction reactions in basaltic outcrop, such as mineral

dissolution due to atmospheric CO2 uptake, and alkaline

Na–HCO3 groundwater, evolved from mixing with

groundwater from the underlying Guarani Aquifer System.

Stable isotope (d18O and d2H) ratios range from -8.87 to

-5.32% VSMOW and -61.31 to -31.64% VSMOW,

respectively, closely following the GMWL. Spatial and

temporal variations in isotope ratios are associated with the

South Atlantic convergence zone activities and the type of

rain responsible for recharge. Values for d13C vary from

-21.53 to -7.11% VPDB, while 14C activities vary from

1.2 pcm to more than 100 pcm, presenting a trend to

enrichment and decrease in 14C activities westward, con-

cordant with the regional groundwater flow direction. Most

recent groundwaters have d13C ratio contents mostly con-

sistent with C3 plants.

Keywords Serra Geral Aquifer � Hydrochemistry �
Stable isotopes � Groundwater age � Brazil

Introduction

Basaltic rock aquifers represent an important groundwater

resource, constituting excellent aquifer units, hosting water

supply in several parts of the world, mainly due to the

excellent quality of the stored water, generally character-

ized by low salinity. Basaltic lava flows present geologic

structures that provide discontinuities responsible for

groundwater storage and flow in these units (Deutsch et al.

1982; Domenico and Schwartz 1998; Dafny et al. 2006).

Due to heterogeneities associated with groundwater flow in

basaltic aquifers, mainly related to discontinuities in the

lava flows, different approaches have to be used as auxil-

iary tools to deduce groundwater flow within basaltic

aquifers (Léonardi et al. 1996; Rosenthal et al. 1998;

Locsey and Cox 2003; Dafny et al. 2006; Bretzler et al.

2011; Alemayehu et al. 2011; Gastmans et al. 2016).

Evaluation of groundwater residence times based on 14C

measurements, combined with stable isotope data and the

hydrochemical evolution, is being increasingly used,

especially in studies focused on understanding the flow

condition and origin of groundwater in fractured and

heterogeneous aquifers. Hydrochemical studies enable the

& Didier Gastmans

gastmans@rc.unesp.br

Amauri Antônio Menegário

amenega@rc.unesp.br

Ian Hutcheon

ian@earth.geo.ucalgary.ca

1 Environmental Studies Center, São Paulo State University

(UNESP), Av. 24A, 1515 – Bela Vista, Rio Claro,

SP CEP 13506-900, Brazil

2 Applied Geochemistry Group, Department of Geoscience,

University of Calgary, 2500 University Drive NW, Calgary,

AB, Canada

123

Environ Earth Sci (2017) 76:150

DOI 10.1007/s12665-017-6468-1

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definition of chemical reactions, due to processes of water–

rock interaction that are responsible for the chemical

characteristics, while stable isotope ratios provide infor-

mation about the origin of the groundwater and past cli-

matic conditions during recharge. 14C activities determine

the residence time of the water in the aquifer. These

methods can also be used to identify quality changes in

groundwater associated with anthropogenic sources of

contamination (Plummer et al. 1990; Rosenthal et al. 1998;

Glynn and Plummer 2005; Betheke and Johnson 2008;

Coetsiers and Walraevens 2009; Blaser et al. 2010; Bretzler

et al. 2011; Abid et al. 2014; Scheiber et al. 2015; among

others).

In the southeastern portion of South America, basalts from

the Serra Geral Formation cover an area of over

1,200,000 km2, representing one of the largest observed

continental basaltic floods. Lava flows, mostly basalts and

andesites (Milani et al. 1994), are up to 1700 m thick toward

the center of theParaná SedimentaryBasin.This stratigraphic

unit represents an important aquifer, responsible for public

water supply, irrigation and industrial uses, largely in the

states of Paraná, Santa Catarina, Rio Grande do Sul andMato

Grosso do Sul, Brazil, where most part of hydrochemical

studies of groundwater in the SGA have been carried out.

These studies allowed groundwater chemical characteriza-

tion and the establishment of the hydraulic relationship with

the underlying unit, the Guarani Aquifer (Bittencourt et al.

2003; Lastoria et al. 2006; Boff et al. 2006; among others).

Due to the importance of Mesozoic sedimentary aquifers

for water supply in the western portion of São Paulo State

(Bauru and Guarani Aquifer), the hydrodynamics and

hydrochemistry have been studied since the 1970s (Gallo

and Sinelli 1980; Sracek and Hirata 2002; Gastmans et al.

2010a, b; among others), and several conceptual models for

groundwater flow and hydrochemical evolution have been

formulated. However, geochemical evolution and deter-

mination of residence times of the SGA in São Paulo State,

based on chemistry, stable isotopes and radiogenic 14C,

have not been yet studied extensively.

The main purpose of this paper is to address questions

regarding the regional functioning of the Serra Geral Aquifer

in São Paulo State. This paper: (1) evaluates the geochemical

characteristics of groundwater from SGA, (2) establishes

recharge conditions based on the stable isotope composition

of groundwater, (3) provides constrains on the mean resi-

dence time of groundwater using radiocarbon age dates.

Geological and hydrogeological settings

Basalts of the Serra Geral Formation are present in the

Paraná Magmatic Province (PMP), which constitutes one

of the largest volcanic igneous manifestations of basic

rocks in a continental area, inserted in Paraná Sedimentary

Basin (Fig. 1). This magmatic province includes lava flows

and intrusive basic rocks (sills and dykes) representing an

important contribution to generation of continental crust

during the Mesozoic related to the Atlantic breakout (Mi-

lani et al. 1994). Some important structures from this

intracratonic basin are associated with the breakout, such as

the Ponta Grossa Arch located in Paraná State, whose axis

strikes N45 W. Parallel to the arch important distension

faults are recognized, up to the border between São Paulo

and Paraná states, represented by the Paranapanema River.

The radiometric ages indicate that volcanic activity

began between 133 and 132 Ma, starting in the south and

moving toward the north in a relatively short time interval

of approximately 3 Ma (Renne et al. 1992, 1996; Ernesto

et al. 1999). This vast volume of basaltic lavas reaches

thicknesses up to 1700 m toward the center of the Paraná

Sedimentary Basin and was deposited over the eolian

sandstones of the Botucatu Formation. Breaks in magmatic

events are marked by the occurrence of beds of sandstones

interfingered with the basalt (‘‘intertrap sandstones’’) that

originated by the movement of desert dunes over the

basaltic substrate (Zalán et al. 1986; Scherer 2000).

Three major lithotypes associated with the Serra Geral

Formation are recognized based on petrographic and geo-

chemical differences. The greatest part of the magmatic

volume (up to 97%) is represented by basalts and andesites,

while in the southern region of Brazil rhyodacites and

rhyolites [Palmas (ATP) and rhyodacites and quartz latites

Chapecó (ATC)] are recognized, representing, respec-

tively, 2.5 and 0.5% of magmatic volume (Bellieni et al.

1986; Nardy et al. 2002). In São Paulo State there are

mainly basalts of mafic to intermediate composition, con-

sisting of plagioclase (mainly labradorite), pyroxene

(augite and pigeonite) and olivine, mainly as pseudo-

morphs, with modal percentages ranging from 25 to 50, 20

to 40 and 4%, respectively. Vesicular zones of variable

thickness are recognized at the boundary between basaltic

lava flow events. Secondary minerals forming amygdales

fill these vesicles, including quartz, calcite, zeolites, fluo-

rite and commonly greenish clays, probably of the cela-

donite group (Machado et al. 2007). The weathering of

basaltic rocks produces very deep soils in the southern

portion of Brazil. Three main weathering pathways for

plagioclase phenocrystals from basaltic rocks have been

recognized: plagioclase to gibbsite; plagioclase to gels

(amorphous silica) and gibbsite; and plagioclase to gels

(amorphous silica), gibbsite and kaolinite. Pyroxenes

weather to smectite and goethite or to goethite and gibbsite

(Clemente and Azevedo 2007).

The generic hydrogeological model for groundwater

flow in the basalts of the Serra Geral Formation encom-

passes permeable and impermeable zones for each lava

150 Page 2 of 16 Environ Earth Sci (2017) 76:150

123



flow event. At the top and bottom of each sequence a

highly permeable zone is observed, associated with basalt

weathering, and groundwater flow is associated with the

occurrence of a vesicular basaltic layer that has extensive

horizontal fractures. The central portion of each sequence

represents an aquitard, where minor vertical movement of

water is associated with vertical discontinuities (joints and

fractures) (Rebouças and Fraga 1988). In the northeastern

portion of the aquifer in São Paulo State, recharge toward

the underlying unit, the Guarani Aquifer, was proposed

(Wahnfried 2010; Fernandes et al. 2010). Based on

chemical and isotopic tracers, groundwater flow was

inferred to be predominantly along horizontal discontinu-

ities in the basaltic rocks, and a lack of vertical flow

through the geological lineaments identified by aerial sur-

veys that limits recharge of the Guarani Aquifer by water

from the Serra Geral basalts.

Groundwater from the SGA has low electrical conduc-

tivities, due to low total dissolved solids, and a wide range

of pH values, from acid to alkaline. The chemical com-

position shows the groundwater to be mainly Ca–HCO3

and Ca–Mg–HCO3 type (DAEE 1974, 1976; Campos

1993). In the northwestern region of São Paulo State

hydrochemical anomalies have been recognized, charac-

terized by TDS values up to 200 mg L-1, and associated

with fractures or faults filled by hydrothermal mineraliza-

tion. These may be due to contamination by more saline

waters originating from underlying aquifers (DAEE 1976).

In the northeastern portion of São Paulo State, ground-

water flow in Serra Geral aquifer is driven by the topog-

raphy, and the main rivers crossing the area represent local

discharge of the aquifer. The existence of higher pressure

head in wells drilled in the Guarani Aquifer System indi-

cates the possibility of groundwater flow into the overlying

basalts, and potentially, mixing of groundwater. SGA

groundwater composition is directly related to the influence

of water–rock interactions, mainly due to the dissolution of

plagioclase and pyroxene, in the presence of atmospheric

CO2, leading to secondary formation of kaolinite and

releasing calcium, sodium, magnesium, silica and bicar-

bonate to solution. Modifications in chemical composition

of groundwater due to upward flow from Guarani Aquifer

Fig. 1 Left map location map of the Serra Geral Aquifer, showing in

detail the study area and the artesian zone of Guarani Aquifer System

located along the Paraná River and in red the strike of the Ponta

Grossa Arch (regional geological base map modified from OAS

2009). Right map location map of sampled wells showing the

simplified groundwater potentiometric map for SGA in the study area,

based on water level information from wells’ reports archived in

DAEE (Dep. Águas e Energia Elétrica do Estado de São Paulo)

(Local geological base map modified from DAEE/UNESP 1980)

Environ Earth Sci (2017) 76:150 Page 3 of 16 150

123



along Rio Grande, state border between São Paulo and

Minas Gerais states, were confirmed using NETPATH

modeling (Gastmans et al. 2016).

Methods

Twenty-one groundwater samples were collected directly

from water supply wells between January 2013 and April

2013. The location of sampled wells, drilled in basalts of

the SGA, is presented in Fig. 1, and information about

depth of the wells and elevation is presented in Table 1.

The pH, electrical conductivity and temperature of each

water sample were measured in situ. Each sample was

filtered (0.45 lm), and part was acidified using HNO3 to

pH\ 2 for cation analysis and part preserved refrigerated

(*4 �C) for anion analysis. Samples collected for the

determination of water isotopic ratios (d18O and d2H) were
stored in 200-mL polyethylene bottles, avoiding the pres-

ence of headspace inside to prevent evaporation. Samples

collected for d13C and for 14C activity were stored in

500-mL amber glass bottles, also avoiding the presence of

headspace to prevent CO2 isotopic exchange. Samples for

cation and anion determination were delivered within a

week to the laboratory, and samples for isotopic determi-

nation were delivered at the end of the sampling campaign.

Stable isotope ratios (d18O, d2H and d13C) and 14C

activities (pmc) were analyzed in the Environmental Iso-

tope Laboratory at the Department of Earth and Environ-

mental Sciences at the University of Waterloo, Canada.

d18O and d2H ratios were determined using laser absorp-

tion spectroscopy, and the results reported as % relative to

Vienna Standard Mean Ocean Water (VSMOW). 14C

activities and d13C ratios were determined using accelera-

tor mass spectrometry (AMS), with a precision of 0.4 pmc

and 0.15%, respectively.

The cation and anion concentrations in groundwater

samples were determined in the Hydrogeology and

Hydrogeochemistry Laboratory of the Department of

Applied Geology IGCE/UNESP Rio Claro. Alkalinity was

determined by titration, anions (F, Cl, NO3 and SO4) were

measured by ion chromatography, and cations (Na, K, Ca,

Mg and Si) were measured by ICP-AES. The quality of

water analyses was checked by charge balance

(Dmeq = 100•(
P

meq
? -

P
meq
- )/(

P
meq
? ?

P
meq
- )\ 10%).

All samples were less than 10%, with samples ASG-SP-47

and ASG-SP-101 showing a difference of about 12%,

acceptable for the purpose of this work. Results of field

measured data, chemical and isotopic data are presented in

Tables 1 and 2, respectively.

The geochemical computer program PHREEQC (Par-

khurst and Appelo 1999) was used to calculate the PCO2
in

the groundwater, as well as saturation index for some

mineral species (Table 2) at the temperature measured in

the field. If the temperature was not measured, calculations

were performed at 25 �C, which is considered to be the

average temperature in the aquifer. To calculate individual

groundwater residence times based on 14C activity, the

modeling code NETPATH XL (Plummer et al. 1994;

Parkhurst and Charlton 2008) was used.

Results and discussion

Groundwater flow in the study area for the SGA is driven

by the topography, with flow from elevated areas located to

the east, where basalts outcrop between 700 and 600 masl,

and westward toward the main rivers that cross São Paulo

State SW–NE (Grande, Tietê and Paranapanema rivers),

about 300–350 masl. Two groundwater divides were rec-

ognized, where sediments of the Bauru Group cover the

SGA, accompanying the watershed division between these

main rivers (Fig. 1). This behavior indicates that SGA in

the study area represents an unconfined aquifer, at least in

the outcrop zone, and the main rivers represent discharge

zones for the aquifer. Along the major rivers in the western

portion of São Paulo State, an important regional hydro-

geological feature is observed, the artesian zone of the

GAS, which indicates the possibility of upward ground-

water flow from the underlying Guarani toward basaltic

discontinuities (Fig. 1).

Groundwater chemical and isotopic composition

The amount of dissolved solids of SGA groundwater varies

from 1.35 to 8.28 mmol L-1 (arithmetic mean of

4.61 mmol L-1), and electric conductivity (EC) varies

from 48.3 to 413 lS cm-1 (arithmetic mean of 215.1

lS cm-1), reflecting the low content of solutes. Values of

pH vary from 6.4 to 10.2 (arithmetic mean of 8.3), indi-

cating the existence of acid and alkaline water in the

aquifer. Table 3 summarizes the correlation between

measured physicochemical parameters. EC and pH have a

strong correlation (r = 0.86), mainly related to the control

exerted over pH by CO3 and total alkalinity (r = 0.90 and

0.63, respectively), which represents the most abundant

anion in SGA groundwater (Fig. 2) and explains the cor-

relation between total alkalinity, EC and TDS (r = 0.90

and 0.92, respectively).

Chloride and NO3 concentrations show a wide range of

values (from 0.002 to 0.255 lmol L-1 Cl and from 0.001

to 0.463 lmol L-1 NO3) and have a good correlation

(r = 0.82), which could indicate an anthropogenic origin

for these compounds due to leakage of sanitation systems

as observed in some cities of São Paulo State (Bertolo et al.

2006). This origin is corroborated by the low correlation

150 Page 4 of 16 Environ Earth Sci (2017) 76:150

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Table 1 Hydrochemical data

set (concentrations in

mmol L-1)

Sample Locality Date Alt. Well depth EC pH Temp

m ls cm-1 (�C)

ASG-SP-02 Jaú 14/01/13 497 150 237.0 7.2 24.3

ASG-SP-04 Jaú 14/01/13 550 150 102.2 7.2 24.2

ASG-SP-11 Jaboticabal 16/01/13 596 150 157.1 7.8 24.0

ASG-SP-16 Matão 18/01/13 531 180 370.0 9.9 26.7

ASG-SP-19 Novo Horizonte 18/01/13 422 300 215.0 9.0 27.0

ASG-SP-23 Reginópolis 19/01/13 452 250 254.0 9.9 27.5

ASG-SP-33 Zacarias 21/01/13 390 115 374.0 10.0 25.8

ASG-SP-37 José Bonifácio 22/01/13 405 125 326.0 10.0 27.9

ASG-SP-40 Avaré 05/03/13 616 110 48.3 6.4 23.3

ASG-SP-47 Marı́lia 06/03/13 468 300 413.0 10.2 26.5

ASG-SP-51 Ibirarema 07/03/13 481 120 104.0 7.8 24.4

ASG-SP-64 Orlândia 19/03/13 693 125 109.2 7.2 24.2

ASG-SP-66 Guará 20/03/13 644 145 96.4 7.2 28.0

ASG-SP-72 Colômbia 21/03/13 485 145 194.9 7.3 26.8

ASG-SP-77 Olı́mpia 22/03/13 476 161 247.0 8.0 25.2

ASG-SP-81 Cravinhos 22/03/13 690 115 115.7 7.6 23.9

ASG-SP-85 Icém 01/04/13 431 151 301.0 9.7 27.3

ASG-SP-88 Pontes Gestal 02/04/13 462 100 149.5 7.8 26.6

ASG-SP-99 Sant. Ponte Pensa 03/04/13 414 220 314.0 8.2 25.5

ASG-SP-101 Sta. Clara do Oeste 03/04/13 355 250 196.4 7.6 28.5

ASG-SP-106 Araraquara 05/04/13 661 135 192.0 7.9 nm

HCO3 CO3 Total

Alk.

Cl NO3 SO4 F Na K Ca Mg Si Mass

balance

(mmol L-1) %

1.868 nd 1.868 0.255 0.229 0.026 0.007 0.423 0.031 0.644 0.444 1.065 4.37

0.829 nd 0.829 0.051 0.121 0.001 0.004 0.144 0.038 0.274 0.189 0.780 4.89

1.596 nd 1.596 0.002 0.001 0.000 0.004 0.207 0.182 0.462 0.190 0.997 2.70

1.573 1.015 2.588 0.014 0.001 0.031 0.024 4.006 0.009 0.021 0.005 0.605 4.69

1.655 0.126 1.781 0.076 0.040 0.098 0.012 2.375 0.003 0.039 0.003 0.566 4.89

0.919 0.810 1.729 0.032 0.001 0.012 0.007 2.597 0.016 0.064 0.037 0.680 3.90

1.408 1.155 2.563 0.009 0.001 0.022 0.011 4.480 0.008 0.013 0.000 0.602 8.84

1.096 1.030 2.126 0.014 0.001 0.047 0.010 3.558 0.005 0.013 0.001 0.602 4.63

0.542 nd 0.542 0.008 0.004 0.001 0.003 0.072 0.086 0.164 0.058 0.409 3.67

0.819 1.533 2.353 0.026 0.001 0.052 0.022 5.176 0.001 0.012 0.001 0.634 12.60

1.000 nd 1.000 0.019 0.038 0.000 0.002 0.144 0.025 0.319 0.188 0.691 5.52

1.029 nd 1.029 0.018 0.097 0.001 0.004 0.274 0.043 0.339 0.139 0.634 5.08

0.724 nd 0.724 0.060 0.181 0.001 0.003 0.592 0.017 0.145 0.062 0.360 2.60

1.254 nd 1.254 0.252 0.463 0.002 0.004 0.439 0.031 0.569 0.289 1.054 5.02

2.032 nd 2.032 0.235 0.369 0.008 0.003 0.887 0.056 0.753 0.176 0.584 2.69

1.060 nd 1.060 0.048 0.120 0.001 0.004 0.151 0.048 0.372 0.205 0.726 4.62

0.808 0.675 1.483 0.162 0.010 0.362 0.107 3.223 0.018 0.053 0.016 0.694 3.35

1.639 nd 1.639 0.013 0.032 0.000 0.001 0.866 0.035 0.334 0.101 0.488 2.50

3.343 nd 3.343 0.109 0.146 0.003 0.020 0.792 0.036 0.776 0.992 0.883 9.27

1.950 nd 1.950 0.085 0.091 0.001 0.008 0.280 0.095 0.604 0.551 1.150 11.35

1.375 nd 1.375 0.072 0.166 0.022 0.021 0.375 0.070 0.536 0.221 0.741 7.71

nm not measured, nd not detected

Environ Earth Sci (2017) 76:150 Page 5 of 16 150

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observed between Cl and Na (r = -0.22), excluding the

possibility of groundwater recharge by precipitation

affected by salt dissolution or evaporative enrichment of

rainwater. Therefore, chloride cannot be used as a con-

servative tracer to interpret residence times of groundwater

using 14C. Concentrations of Cl ? NO3 are greater than the

concentration of SO4 (usually\0.01 lmol L-1), and only

one sample (ASG-SP-85) has high SO4 concentration.

Dissolved cations are dominated by calcium and magne-

sium, which do not have a good correlation with TDS or

total alkalinity, but have a good correlation with each other

(r = 0.80) and with HCO3 (r = 0.65 for Ca and r = 0.78

for Mg). Sodium concentration increase is observed,

strongly correlated with EC, TDS, pH and CO3 (respec-

tively, r = 0.86, r = 0.83, 0.94 and r = 0.96).

The concentration of cations and anions in SGA

groundwater allows the identification of two main hydro-

chemical facies: Ca–Mg–HCO3 and Na–HCO3 waters, as

presented in the Piper diagram (Fig. 2). Ca–Mg–HCO3

groundwater has Ca as the most abundant cation, followed

by Mg, in variable relative concentrations, reaching ratios

between Ca and Mg values close to 1. Relative concen-

trations of Na and K in these samples are very low, but an

increase in the contribution of Cl ? NO3 is observed.

These samples show pH varying from acid to neutral val-

ues. Na–HCO3 waters are characterized by the occurrence

of Na as the most abundant cation, with relative concen-

trations of Ca, Mg and K that are much smaller. An

increase in SO4 is observed in two samples, and pH values

indicate alkaline waters.

The relationship between the isotopic ratios of oxygen

and hydrogen of samples from SGA groundwater is pre-

sented in Fig. 3, with the Global Meteoric Water Line

(GMWL) and the Brazilian Tropical Meteoric Water Line

(BTMWL) [d2H = 7.7 d18O ? 10.1 (r2 = 0.95)]. This

latter line is based on isotopic data from stations located in

the tropical region of Brazil (Cuiabá, Brasilia, Campo

Grande, Rio de Janeiro and Porto Alegre) available in the

GNIP database (IAEA/WMO 2006, available at http://iso

his.iaea.org). SGA groundwater exhibits isotopic ratios

from -59.6 to -34.5% VSMOW for d2H, and -8.8 to

-5.4% VSMOW for d18O. Comparing the groundwater

data to rainwater from GNIP stations shows that most

groundwater has an isotopic signature similar to rainwater,

and plots along the two meteoric lines, indicating a mete-

oric origin for the recharge of this groundwater (Fig. 3).

Spatial distribution of d18O (Fig. 4a) shows more enri-

ched values for isotopic ratios in the southern zone of the

Table 2 Isotopic data set and thermodynamic calculations

Sample Locality d18O d2H d13C 14C SI_Calcite LogPCO2
SI_SiO2(a) SI_Chalcedony SI_Quartz

% VSMOW % VPDB pmc

ASG-SP-02 Jaú -6.31 -41.3 -15.34 105.73 -0.73 -2.15 -0.26 0.59 1.02

ASG-SP-04 Jaú -6.55 -40.17 -15.71 108.85 -1.41 -2.50 -0.39 0.45 0.88

ASG-SP-11 Jaboticabal -7.31 -45.13 -20.61 79.32 -0.33 -2.82 -0.29 0.56 0.99

ASG-SP-16 Matão -8.79 -59.55 -7.98 3.67 0.10 -5.08 -0.89 -0.05 0.37

ASG-SP-19 Novo Horizonte -7.34 -48.14 -12.72 22.39 -0.22 -4.02 -0.62 0.21 0.64

ASG-SP-23 Reginópolis -8.28 -52.97 -11.68 17.63 0.43 -5.31 -0.85 -0.02 0.41

ASG-SP-33 Zacarias -7.56 -50.58 -8.01 13.46 -0.10 -5.25 -0.93 -0.1 0.33

ASG-SP-37 José Bonifácio -7.61 -50.72 -8.64 12.48 -0.15 -5.35 -0.97 -0.14 0.28

ASG-SP-40 Avaré -6.48 -39.01 -19.87 80.37 -2.60 -1.88 -0.66 0.18 0.62

ASG-SP-47 Marı́lia -8.28 -55.83 -7.11 1.22 -0.14 -5.66 -1.06 -0.23 0.20

ASG-SP-51 Ibirarema -5.43 -34.49 -21.53 97.35 -0.67 -3.02 -0.45 0.39 0.82

ASG-SP-64 Orlândia -7.03 -46.21 -16.26 97.58 -1.22 -2.40 -0.48 0.36 0.79

ASG-SP-66 Guará -6.13 -41.34 -16.53 83.73 -1.68 -2.53 -0.76 0.07 0.49

ASG-SP-72 Colômbia -6.56 -41.44 -17.73 102.52 -0.81 -2.41 -0.28 0.55 0.98

ASG-SP-77 Olı́mpia -7.33 -45.14 -16.05 72.24 0.17 -2.92 -0.53 0.31 0.74

ASG-SP-81 Cravinhos -6.99 -43.11 -17.85 97.03 -0.78 -2.80 -0.42 0.42 0.86

ASG-SP-85 Icém -7.43 -50.51 -15.12 38.94 0.19 -5.08 -0.73 0.1 0.52

ASG-SP-88 Pontes Gestal -6.70 -43.94 -17.59 71.34 -0.42 -2.79 -0.62 0.22 0.64

ASG-SP-99 Sant. Ponte Pensa -6.41 -42.67 -18.41 67.53 0.55 -2.92 -0.36 0.48 0.91

ASG-SP-101 Sta. Clara do Oeste -6.77 -43.75 -12.63 36.24 -0.29 -2.51 -0.26 0.57 0.99

ASG-SP-106 Araraquara -7.28 -44.84 -14.16 97.4 -0.22 -2.98 -0.42 0.42 0.85

150 Page 6 of 16 Environ Earth Sci (2017) 76:150

123

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http://isohis.iaea.org


SGA (sample ASG-SP-51), while in the northern and

central basaltic outcrop zones the isotopic ratios are

slightly depleted.

The d13C ratios vary from -21.53 to -7.11% VPDB,

with a trend to enrichment westward, concordant with the

main groundwater flow direction. In the basalt outcrop,

d13C presents variable values. In the northern portion d13C
ratios are about -16.5% VPDB, while in the central zone

these values are about -15.5% VPDB, and in the southern

portion more depleted values are observed, about -21.5%
VPDB (Fig. 4b).

Considering the existence of equilibrium between the

carbonate system in groundwater and the atmospheric CO2

in outcrop zones, as previously discussed, it is possible to

calculate the values of d13C of CO2 using the following

expression:

d13Cg�eq ¼ dT � aea�g þ beb�g þ cec�g

mHCO3

� �

ð1Þ

Table 3 Correlation matrix
EC pH d13C 14C HCO3 CO3 Tot.Alk Cl NO3

EC 1.00 – – – – – – – –

pH 0.86 1.00 – – – – – – –

d13C 0.78 0.79 1.00 – – – – – –
14C 20.77 20.89 20.81 1.00 – – – – –

HCO3 0.31 20.02 20.07 20.02 1.00 – – – –

CO3 0.81 0.90 0.84 20.84 20.24 1.00 – – –

Tot.Alk 0.86 0.63 0.54 20.62 0.72 0.50 1.00 – –

Cl 0.10 20.22 20.17 0.31 0.33 20.30 0.08 1.00 –

NO3 20.18 20.48 20.30 0.55 0.26 20.49 20.12 0.82 1.00

SO4 0.33 0.44 0.17 20.32 20.19 0.31 0.05 0.22 20.23

F 0.41 0.44 0.18 20.30 20.09 0.33 0.16 0.20 20.23

Na 0.86 0.94 0.85 20.89 20.13 0.96 0.57 20.22 20.46

K 20.44 20.50 20.53 0.38 0.15 20.50 20.22 20.08 0.02

Ca 20.25 20.60 20.54 0.62 0.65 20.69 0.09 0.58 0.69

Mg 20.03 20.38 20.36 0.35 0.78 20.47 0.36 0.38 0.38

Si 0.07 20.19 20.14 0.24 0.43 20.25 0.21 0.46 0.34

TDS 0.99 0.83 0.74 20.77 0.39 0.77 0.90 0.12 20.17

SO4 F Na K Ca Mg Si TDS

EC – – – – – – – –

pH – – – – – – – –

d13C – – – – – – – –
14C – – – – – – – –

HCO3 – – – – – – – –

CO3 – – – – – – – –

Tot.Alk – – – – – – – –

Cl – – – – – – – –

NO3 – – – – – – – –

SO4 1.00 – – – – – – –

F 0.95 1.00 – – – – – –

Na 0.42 0.41 1.00 – – – – –

K 20.26 20.21 20.57 1.00 – – – –

Ca 20.36 20.26 20.70 0.48 1.00 – – –

Mg 20.26 20.11 20.47 0.26 0.80 1.00 – –

Si 20.08 20.01 20.30 0.41 0.61 0.64 1.00 –

TDS 0.32 0.39 0.83 20.41 20.20 0.05 0.13 1.00

Correlation values in bold showing significance level q\ 0.001

Environ Earth Sci (2017) 76:150 Page 7 of 16 150

123



where dT is the measured d13C in groundwater; a, b and c

stand for molarities of H2CO3, HCO3, and CO3
2-,

respectively; ea–g, eb–g, ec–g are the fractionation factors

between the carbon species at equilibrium; and mHCO3 is

the total dissolved inorganic carbon content (mol L-1).

Based on the range of values for calculated d13C of CO2

in soils, HCO3 concentrations and d13C of groundwater,

three groups of samples can be distinguished. Group 01 is

characterized by a large range of d13C values (from -21.53

to -14.16% VPDB), which do not have a strong correla-

tion with HCO3 concentrations, probably due to calcite

precipitation in samples that are oversaturated in calcite

(ASG-SP-77 and 99) or related to the uptake of atmo-

spheric CO2, that is responsible for decrease in the isotopic

ratios in samples ASG-SP-11 and 51 (Fig. 5a). These

groundwaters are Ca–Mg–HCO3 type.

The gradual increase in alkalinity and pH corresponds to

values of d13C more enriched, characteristic of the Group 02,

which have d13C ranging from -15.11 to -11.68% VPDB.

Group 03 is characterized bymore enriched groundwater, with

d13C ranging from -8.64 to -7.11% VPDB (Fig. 5a).

Groundwater fromGroups 02and03 ismostlyNa–HCO3 type.

Fig. 2 Piper diagram. Samples from Groups 02 and 03 are marked with cross and black cross, respectively

Fig. 3 d18O versus d2H cross-plot for SAGS groundwater from the

study area. Brazilian Tropical Meteoric Water Line (BTMWL dashed

line) and Global Meteoric Water Line (GMWL solid line) are shown

150 Page 8 of 16 Environ Earth Sci (2017) 76:150

123



For Group 01, the calculated values for d13C from CO2

present in the soil must be between -29.2 and -21.85%
VPDB (Table 4), characteristic of plants with a C3 pho-

tosynthetic cycle (Clark and Fritz 1997). The calculated

value d13C of CO2 for samples from Group 03 is about

-15% VPDB, while samples from Group 02 present

intermediate values, about -20% VPDB (Table 4).
14C activities measured in SGA groundwater samples

range from 108.8 to 1.22 percent modern carbon (pmc),

and the relationship between 14C activities and d13C

Fig. 4 Spatial distribution along the study area of d18O (a), d13C (b) and 14C activities (c)

Fig. 5 a d13C versus total alkalinity, showing the increase in

alkalinity accompanied for an increase in d13C. For samples from

Group 01 no correlation is observed between the two variables;

possible explanation is given in text. b d13C versus 14C activity

showing the decrease in activity followed by the decrease in d13C

Environ Earth Sci (2017) 76:150 Page 9 of 16 150

123



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150 Page 10 of 16 Environ Earth Sci (2017) 76:150

123



content (r = -0.81) indicates the tendency of decreasing

in 14C activity followed by an increase in d13C ratios. The

relationship between TDS and 14C activities (r = -0.77)

indicates a progressive increase in TDS associated with the

decrease in 14C activities, indicating that longer ground-

water residence time correlates with greater content of

dissolved solids in groundwater. Spatial distribution of 14C

activities indicates higher values in outcrop areas, repre-

sented by samples from Group 01, decreasing toward the

west, where samples from Groups 02 and 03 are present

(Fig. 4c).

Discussion

Groundwater geochemical evolution for samples inGroup 01

ismostly related to the incongruent dissolution of plagioclase

and pyroxene from basaltic rocks in the presence of atmo-

spheric CO2, leading to secondary formation of kaolinite,

releasing major cations (calcium, sodium and magnesium),

silica and bicarbonate to solution, according to Eqs. 2 to 4, as

previously discussed in Gastmans et al. (2016). As bicar-

bonate represents the main anion dissolved in SGA ground-

water, produced during mineral dissolution reactions by the

uptake of atmospheric CO2, a proportional increase in alka-

linity with respect to the sumof Na, Ca andMg concentration

is expected, as shown in Fig. 6a, up to the point that

groundwater reaches saturation with respect to calcite.

Besides the release of cations and alkalinity, mineral

weathering is responsible for the introduction of silica into

groundwater.

CaAl2Si2O8
anorthite

þ2CO2 þ 3H2O ! Al2Si2O5 OHð Þ4
kaolinite

þCa2þ

þ 2HCO�
3

ð2Þ

2NaAlSi3O8
albite

þ2CO2 þ 11H2O

! Al2Si2O5 OHð Þ4
kaolinite

þ2Naþ þ 2HCO�
3 þ 4Si OHð Þ4 ð3Þ

Ca; Mg; Feð Þ2
augite

Si2O6 þ 2CO2 þ 5H2O

! 2 Caþ2; Mgþ2; Feþ2
� �

þ 2HCO�
3

þ 2Si OHð Þ4þ1=2O2 ð4Þ

Silica concentrations range from 0.36 to 1.15 mmol L-1,

presenting a good relationship with Ca and Mg concentra-

tions (r = 0.61 and r = 0.64, respectively). All samples are

oversaturated with respect to quartz (solubility of

0.18 mmol L-1 H4SiO4 at 25 �C; Rimstidt 1997) and sat-

urated with respect to chalcedony (solubility of

1.35 mmol L-1 H4SiO4 at 25 �C; Fournier 1977), but are
undersaturated with respect to amorphous silica (solubility

of 1.9 mmol L-1 H4SiO4 at 25 �C; Rimstidt and Barnes

1980) (Table 2). Gastmans et al. (2016) have shown that if

the source of silica is directly associated with basaltic

mineral dissolution due to uptake of atmospheric CO2, a

stoichiometric relationship between concentrations of SiO2

and HCO3, especially for samples in Group 01 should be

expected; however, many samples fall below the 1:1 stoi-

chiometric ratio (Fig. 6b). Two geochemical processes in

outcrop areas may explain the observed relationship. As

groundwater becomes saturated with respect to quartz or

chalcedony; removal of SiO2 from the solution by sec-

ondary silica precipitation associated with precipitation of

silica polymorphs or aluminous silicates (e.g., clay miner-

als) could be responsible for the decrease in silica concen-

tration compared to alkalinity. The second process could be

associated with preferential dissolution of anorthite, causing

alkalinity to increase faster than silica content.

For samples in Groups 02 and 03 that have silica values

lower than samples from Group 01, the increase in total

Fig. 6 a Relationship between cations (sodium, calcium and mag-

nesium) concentrations and the total alkalinity (expressed as bicar-

bonate concentration) from SGA groundwater. The dashed line

represents the ratio 1:1, representing the sum of stoichiometric

relations observed in Eqs. 2, 3 and 4. b Relationship between silica

and total alkalinity (expressed as bicarbonate concentration). The

dashed line (1:1) represents the sum of stoichiometric relations

observed in Eqs. 2, 3 and 4

Environ Earth Sci (2017) 76:150 Page 11 of 16 150

123



alkalinity is not associated with an increase of silica con-

centrations. Most samples are saturated or oversaturated

with respect to calcite and quartz, but the saturation index

of chalcedony and amorphous silica is lower than samples

from Group 01. Gastmans et al. (2010a, b) have shown that

dissolved silica in the GAS groundwaters shows a tendency

to decrease as a function of increasing aquifer confinement,

and that the chalcedony saturation index in confined con-

ditions indicates groundwater undersaturated with respect

to this silica phase.

Ion exchange processes seem to be the most important

factor related to the increase in Na concentrations for

samples from Groups 02 and 03 that is associated with a

decrease in Ca concentrations. It should be observed that

this process is not related to reactions presented above

(Eqs. 2 to 4), so there are two possible explanations. If the

increase is related exclusively to groundwater evolution

within the basaltic aquifer, calcite precipitation and ion

exchange on smectite are possibly an important process

controlling Na/Ca ratios in the SGA, as observed by

Gastmans et al. (2016) in the northern portion of the

aquifer, where it is outcropping. On other hand, this cannot

explain the observed high values of pH (up to 9.0) for

samples from Groups 02 and 03. Under closed conditions

rapid consumption of CO2 is expected during silicates

dissolution; however, there is no important carbon sink in

the aquifer framework to explain the observed increase in

pH values.

Higher values of d13C in samples from Groups 02 and

03 is an indication that heavier carbon was introduced to

the system. Although measured values for d13C for car-

bonate minerals filing vesicles in basaltic rocks range from

-15 to -3.72% VPDB (Kimmelmann et al. 1994), and

dissolution of these carbonate minerals can lead to the

values measured in dissolved carbon present in ground-

water under closed conditions, it should be observed that

groundwater is saturated or oversaturated with respect to

calcite, as previously discussed, and dissolution of these

minerals could not occur.

Several authors have described high pH alkaline Na–

HCO3 groundwater in the confined zone of GAS associated

with ionic exchange (Silva 1983; Meng and Maynard 2001;

Sracek and Hirata 2002; Gastmans et al. 2010a, b; Hirata

et al. 2011, among others). Geochemical evolution of GAS

groundwater along flow paths leads to an increase in d13C
values toward the center of the Paraná Basin, reaching

values about -6% along the Tietê River (Gastmans et al.

2010a, b), values similar to those observed in groundwater

from Groups 02 and 03. The artesian zone of the GAS

provides hydraulic evidence of groundwater mixing along

the Tietê River (Fig. 1), as previously discussed by Gast-

mans et al. (2016), using geochemical modeling, along

River Grande in the northern portion of the São Paulo

State. Based on these findings, upward groundwater flow

from Guarani Aquifer could be responsible for the presence

of Na-high pH and d13C-enriched water in SGA.

Groundwater residence time and climatic recharge

conditions

The use of 14C to determine groundwater residence times

in aquifers is based on evaluating the radioactive content of

dissolved carbonate species in groundwater, which

decreases with time since recharge. The method is limited

to dating groundwater recharged over the past

30,000–40,000 years, due to the half-life of the isotope

(Kulogoski et al. 2008). Other complications for the use of
14C to determine residence time of groundwater are related

to the determination of the initial 14C activity (A0) and the

evolution of d13C, which may be influenced by reactions

and exchange with external sources of inorganic carbon.

Plummer and Glynn (2013) provided an extensive review

of radiocarbon dating in groundwater.
14C activities and d13C content are presented in Fig. 5b,

showing the tendency of decreasing 14C activity, followed

by an increase in d13C ratios. Particularly for Group 01,

wide ranges of values for d13C are not directly related to a

decrease in the 14C activity, which is consistent with the

observed relationship between d13C and total alkalinity.

Due to the introduction of carbon from atmospheric

sources and the lack of carbonate minerals in basaltic

rocks, calculation of groundwater ages for Group 01

requires only the application of the radioactive decay

constant, while for Groups 02 and 03 specific corrections of

the initial 14C activity (A0) are necessary before the resi-

dence time based on radioactive decay is calculated. The

residence time of groundwater samples can be determined

using the following equation (Clark and Fritz 1997):

t ¼ �8267 � ln A0
14C

A14C

� �

ð5Þ

where A14C refers the measured radiocarbon content in the

analyzed sample and Ao
14C is the radiocarbon activity in the

soil CO2 in the recharge areas. Due to the dominance of

silicates in basaltic rocks isotopic exchange is not supposed

to take part in recharge area, value for Ao
14C could be

assumed to be equal 100 pmc, and uncorrected ages were

calculated on this basis. However, d13C values were found

to vary about 10% in groundwater from Group 01 to Group

03, and these variations may reflect different geochemical

evolution process, as previously discussed involving silica

and total alkalinity variations, as well as the factors related

to increase in sodium concentrations. These processes seem

to involve mixing of groundwater from GAS, which have

very low 14C activity in the confined zone, with ground-

water ages measured using 81Kr reaching almost 1000 ky

150 Page 12 of 16 Environ Earth Sci (2017) 76:150

123



(Aggarwal et al. 2015), and chemical characteristics similar

to those observed in SGA groundwater.

According to Plummer and Glynn (2013), several geo-

chemical processes along the flow path can affect the iso-

topic evolution of groundwater, and the selection of an

adjustment model to correct groundwater ages has to take

into account these processes. For this work three models,

implemented in NETPATH XL codes, were selected to

estimate groundwater residence times: (1) Fontes and

Garnier (1979), the most geochemical complete of tradi-

tional adjustment models, (2) the revised Fontes and Gar-

nier models by Han and Plummer (2013) and (3) the Mook

model (Mook 1980), determined to be the most applicable

to silicate terrains, because it assumes that cations and

alkalinity do not necessarily come from dead carbonate.

For both corrections, the calculated value of d13Cg soil was

used (Table 4). The value of d13C for the carbonate min-

erals is assumed to be -3% VPDB. The dating of these

groundwaters considering natural decay and using both

corrections is presented in Table 4.

Groundwater residence times for samples from Group

01 are concordant for all the correction methods selected

and indicate that most of the samples have recent ages,

reaching a maximum of 3000 years (Table 4). However,

groundwater ages corrected based on Mook and revised

F&G models are similar, mainly due to the equilibrium

with atmospheric CO2. Higher groundwater residence

times are observed in samples presenting lower PCO2
. Due

to the absence of isotopic exchange with calcite, ground-

water ages calculated according to the revised F&G solid

exchange model tend to be underestimated.

Different geochemical evolution associated with mixing

with older groundwaters leads to significant differences in

calculated residence times for samples from Groups 02 and

03. As expected, the adjusted 14C residence times were in

most of the cases younger than unadjusted 14C, due to the

reactions that occur during geochemical and isotopic

evolution of groundwater. It should be noted that the

groundwater ages are in agreement with the proposed

division of groups, and greater values are obtained for

groundwater from Group 03, up to 10 Ky, than 5 to 10 Ky

as observed for Group 02.

Urban and agricultural soil processes in the study area

can exert pressure on the quality of groundwater, especially

on waters that are recently recharged. In the western por-

tion of the state of São Paulo, cases of groundwater con-

tamination by nitrate are reported in several cities

(CETESB 2013) related to the management of wastewater

and the absence of basic sanitation in these places. Nitrate

concentrations above 0.15 mmol L-1 are observed in

several groundwater samples, which indicates groundwater

contamination, especially in the samples belonging to

Group 01 (Fig. 7a). Samples of Groups 02 and 03 seem to

be more protected from the leakage of wastewater, prob-

ably due to their greater residence times and depth, which

provides more protection for this type of contamination.

The concentration about 0.1 mmol L-1 observed for these

groups is probably associated with construction aspects of

the wells.

Variations in d2H and d18O in groundwater are currently

interpreted to be the result of climatic variations occurring

during recharge (Clark and Fritz 1997). Groundwater from

SGA with low 14C activities has the most negative isotope

ratios (d18O\-8% VSMOW), but mostly shows modern

ages with respect to their 14C activities, meaning that the

isotopic composition of these groundwater represents the

average composition of present day precipitation. It should

be noticed that values of d-excess (d-excess = d2H -

8d18O, Dansgaard 1964) are very similar for the bulk of

samples, and for samples presenting low values for 14C

activities (14C\ 40 pcm) values of d-excess are about

10% VSMOW (Fig. 7b). The most depleted values

(d18O & -8.0% VSMOW) are observed to be similar to

those recognized in Guarani Aquifer groundwater collected

Fig. 7 a 14C activity versus NO3 concentration. Samples from Group 01 present high nitrate concentration. b d18O versus 14C activity, more

depleted samples (Groups 02 and 03) present low 14C activity

Environ Earth Sci (2017) 76:150 Page 13 of 16 150

123



from wells located in the study area by several authors

(e.g., Gallo and Sinelli 1980; Kimmelmann et al. 1986;

Chang et al. 2013, among others).

Two processes could be associated with the observed

variations observed in isotopic composition. One could be

a regional feature, the South Atlantic convergence zone

(SACZ), a meteorological system of predominant precipi-

tation zone extending from the Amazon basin in southwest

Atlantic Ocean, responsible for more than 75% of the

precipitation over this area. According to Chang et al.

(2015) the influence of the SACZ over shallow ground-

water leads to more depleted values along this meteoro-

logical feature. This corresponds to the northern and central

basalt outcrop, while toward the south groundwater is more

enriched, reaching d18O isotopic ratios about -5%
VSMOW. The large variation observed in isotopic com-

position for modern groundwater also could be associated

with the type of rain related to the SACZ. Aggarwal et al.

(2016) have found that tropical and midlatitude precipita-

tion can be divided in two types, spatially limited and high-

intensity convective rains, and frontal and lower-intensity

stratiform precipitation. The processes associated with

these rain types lead to variations in isotopic composition

of precipitation and consequently in groundwater recharge.

More depleted precipitation is directly related to stratiform

rains, for which values can vary approximately from -30

to -10% VSMOW for d18O.

Conclusions

The evaluation of hydrochemical and stable isotopic data

from the Serra Geral Aquifer in São Paulo State (Brazil) has

contributed to the recognition of the main geochemical

processes and controls related to groundwater evolution and

groundwater residence times within the basaltic reservoir.

Groundwater flow is driven by the topography, and the main

rivers crossing the area represent local discharge.

In outcrop areas, groundwater composition is directly

related to water–rock interactions, mainly the dissolution of

plagioclase and pyroxene, in the presence of atmospheric

CO2, leading to an increase in Ca–Mg–HCO3 concentra-

tions. The d13C ratios show a large range of values, asso-

ciated with calcite precipitation and continuous uptake of

atmospheric CO2. Variable values for d
13C in groundwater

samples in outcrop areas lead to different values for d13C
of CO2 that are characteristic of plants with a C3 photo-

synthetic cycle. This groundwater has been recharged

recently, as observed in residence times calculated based

on 14C and spatial variations in d2H and d18O composition.

The recharge is associated with the most important climatic

feature acting over the region, the SACZ, and also with the

influence of stratiform fraction of precipitation, which

leads to more depleted rain and consequently depleted

groundwater recharge.

The wide range of groundwater residence times in the

outcrop area indicates a hydrogeological system that is

very active, where young waters could be affected by

anthropogenic sources of nitrate, while downgradient older

groundwater is not affected by nitrate contamination.

When the SGA is under closed conditions, decrease in
14C activities and more depleted values for d13C suggest

higher residence times, as do an increase in pH and Na

concentrations. This is correlated with a gradual increase in

the alkalinity that cannot be exclusively explained by dis-

solution of carbonate minerals present in basaltic rocks.

Higher pressure head in wells drilled in the Guarani

Aquifer System, which has groundwater with enriched

values of d13C, and a geochemical evolution, which leads

to Na–HCO3 groundwater types, are factors that can

explain the geochemical evolution in the basaltic aquifer

under closed conditions and incorporating groundwater

mixing between the SGA and GAS.

Acknowledgements This project was funded by a grant from the

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

under the process 2012/00241-5. Authors wish to acknowledge Dr.

James W. LaMoreaux, editor in chief of Environmental Earth Sci-

ences, and two anonymous reviewers for suggesting significant

improvements to this manuscript.

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http://dx.doi.org/10.14295/ras.v20i1.9727
http://dx.doi.org/10.1029/2001JD002038

	Stable isotopes, carbon-14 and hydrochemical composition from a basaltic aquifer in São Paulo State, Brazil
	Abstract
	Introduction
	Geological and hydrogeological settings
	Methods
	Results and discussion
	Groundwater chemical and isotopic composition

	Discussion
	Groundwater residence time and climatic recharge conditions

	Conclusions
	Acknowledgements
	References