Giuseppe Sappa, Sibel Ergul, and Flavia Ferranti
Abstract
The present study deals with the characterization of Mazzoccolo karst spring which feeds the most important water supply network in southern part of Latium region, in Central Italy.
During sample collections from 2006 to 2008, a series of in situ measurements were conducted for pH, electrical conductivity (EC), total dissolved solids (TDS) and temperature. The environmental isotopic and hydrochemical measurements were carried out for the vulnerability assessment and geochemical modeling with the aim of achieving (i) proper management and protection of this important resource, (ii) hydrochemical processes controlling the evolution of groundwater and (iii) identification of recharge areas. All sampled spring waters are characterized as Ca-HCO3type waters reflecting the main rock types in the area investigated, where limestones and Pliocene conglomerates are the most dominant formations. The electrical conductivity (EC) and TDS values of water samples from springs varies from with a maximum value of 341µS/cm and 268 mg/l and minimum value of 28 µS/cm and 104 mg/l, respectively. The pH values of spring samples range from 7.4 to 9 indicating alkaline nature.
The anion composition is quite stable showing HCO3−>Cl−>SO42−(in mg/l), while calcium is the dominant cation, followed by magnesium, sodium and potassium. The comparison ofδ18O and δ2H values of spring water samples with meteoric water lines shows that most of the samples fall to the Local Meteoric Water Line suggesting input to local rain-fall derives from the Mediterranean Sea. The elevation of the recharge areas range between 600 and 800 m a.s.l confirming the Aurunci karst aquifer is feeding Mazzoccolo spring.
Keywords
Karst aquifer
VulnerabilityMajor ions and stable isotopes265.1 Introduction
Due to increasing population pressure and climate change, groundwater resource need an optimization in their exploi-tation and management. Hydrochemical analysis and isotope studies are recognized as valuable hydrogeologic tools for
determining the evolution of water resources and determi-nation of recharge areas which influences the quality of water and vulnerability of the aquifer systems (Clark and Fritz1999). The application of isotope-based methods and conventional hydrogeochemical studies has become an integral part of many water quality and environmental studies (Marfia et al.2003; Long and Putnam 2004). This understanding can contribute to effective management, uti-lization and protection of these natural resources (Casa et al.
2008). In southern Latium region of Central Italy, spring and groundwater from karst aquifers play an important role for drinking and agricultural uses (Sappa et al. 2012). In this G. Sappa (&) S. Ergul F. Ferranti
DICEA, Department of Civil, Building and Environmental Engineering—Sapienza, University of Rome, Via Eudossiana 18, 00186, Rome, Italy
e-mail: [email protected]
G. Lollino et al. (eds.), Engineering Geology for Society and Territory – Volume 5,
DOI: 10.1007/978-3-319-09048-1_265,© Springer International Publishing Switzerland 2015 1387
that feeds drinking water supply networks of Formia and other communities with an average withdrawal of 900 l/s.
This study examines the relationship between water com-position, hydrochemical processes, and water vulnerability assessment of this karst spring.
265.2 Geological and Hydrogeological Setting
Mazzoccolo spring take place on the base of Pliocene con-glomerates, which is tectonically in contact with the lime-stones. This spring is located at an altitude of 11.5 m above sea level where the area fractured due to the intersection of numerous faults. Mazzoccolo spring is captured at an ele-vation of 7.50 m by a drainage tunnel, where the path is generally parallel to the slope (Fig.265.1).
The morphological setting of the study area is charac-terized by conglomeratic limestone on the hills (Mola Mountain), surrounded by clayey-arenaceous and alluvial deposits of debris. The abundance of water is due to the
karst), which stores a significant quantity of rainwater feeding perennial springs. The Pliocene conglomerates are strongly cemented, while the contacts with different forma-tions show highly fractured structures. The karstified lime-stones stored groundwater, which outcrops mostly at Mazzoccolo spring and also some smaller pools, that occur to the west part. The underground reservoir of Mazzoccolo spring was formed by high permeable limestones to the N-W and N-NW of the spring, while the bottom is composed of impermeable dolomites underlying the West part of the limestones.
265.3 Methodology
The main spring water sampling survey was carried out in Mazzoccolo spring, from 2006 to 2008. Water temperature, electrical conductivity and pH values were determined in the field using PC 300 Waterproof Hand-held meter. Bicarbonate content was measured by titration with 0.1 N HCl. Water samples werefiltered through cellulose filters (0.45 µm), and
Fig. 265.1 Simplified geological map of the study area
Metrohm 761 Compact IC ion chromatograph (replicabil-ity± 2 %). Analyses of2H/H isotopes used the method of Kendall and Coplen (1985) (reaction with Zn at 450 C), while
18O/16O analyses relied on the CO2—water equilibration technique (Kendall and Coplen1985). Mass spectrometry was performed with a Finnigan Delta Plus mass spectrometer and the results are reported in‰ units (permil deviation of the isotope ratio from the V-SMOW isotopic standard). δ is defined by the relationship:
d ¼ R R½ð SMOWÞ=RSMOW 103 ð265:1Þ where R = D/H or18O/16O. For the identification of water types, the chemical analysis data of the spring water samples have been plotted on the Piper diagram using Geochemistry Software AqQA. The vulnerability analyses were carried out by SINTACS method.
265.4 Results and Conclusions
Major ion concentrations and physico—chemical charac-teristics of the analyzed spring and well water samples are presented in Table265.1. The temperature of springs range
9 highlighting alkaline nature. The total dissolved solids (TDS) content within the range 104–269 mg/l. Calcium and bicarbonate is the dominant constituents in spring samples, followed by magnesium, chloride, sodium, sulphate and potassium. The electrical conductivity (EC) value varies from 28 to 341μS/cm.
Based on the dominance of major cationic and anionic species, Ca-HCO3 water type was identified (Fig. 265.2), suggesting that all groundwater feeding Mazzoccolo spring come from the karst limestone aquifer. The isotopic com-position (18O and 2H) and the calculated elevations for recharge areas of springs, recorded in different periods, are presented in Table265.2.
For the identification of mean recharge elevations, the altitude effect has been employed. The mean isotope gradi-ents for18O and2H were calculated using the isotope and elevation values of precipitation, obtained from the four sampling pluviometers near study area The altitude effect is found by the relation between precipitation isotope values and elevation in meters (h) highlighting a depletion of heavy stable isotopes of about–0.22 and –1.55‰ per 100 m ele-vation for δ18O andδ2H, respectively. The elevation of the recharge area range between 600 and 800 m a.s.l.
(Fig.265.3).
Table 265.1 Main physico-chemical characteristics and chemical composition of spring samples Sample
M1 11/05/06 122 8.12 15 23.539 3.230 1.702 0 2.512 1.509 85.428
M2 15/06/06 336 7.84 13 49.252 9.374 4.519 0.44 7.436 3.990 183.06
M3 13/07/06 335 7.78 15 35.221 9.499 4.580 0.445 7.435 3.816 146.448
M4 04/08/06 28 9.03 14 25.440 0.636 0.356 0.007 0.5 0.299 76.275
M5 21/09/06 155 7.91 12 20.848 8.932 4.030 0.209 6.549 2.572 100.683
M6 27/10/06 65 8.1 11 23.673 3.810 1.712 0.210 2.505 1.099 88.479
M7 28/11/06 328 7.75 10 27.492 9.592 4.372 0.474 7.048 3.709 122.04
M8 21/12/06 323 8.04 13 47.725 9.477 4.274 0.463 6.920 3.779 183.06
M9 16/01/07 324 8.08 13 47.477 9.534 4.283 0.468 7.007 3.589 183.06
M10 27/02/07 330 7.57 13 51.866 7.702 4.562 0.41 6.640 4.628 186.111
M11 24/04/07 333 7.65 11 51.522 8.648 4.520 0.414 6.859 4.423 189.162
M12 05/06/07 327 7.62 12 51.325 9.081 4.526 0.402 6.867 4.455 189.162
M13 10/07/07 327 7.42 10 50.370 9.250 4.376 0.471 6.947 4.074 189.162
M14 26/09/07 326 7.65 14 48.54 9.637 4.360 0.442 6.692 4.008 186.7212
M15 25/10/07 341 7.52 15 48.241 9.692 4.259 0.507 6.744 3.855 183.06
M16 27/11/07 328 7.94 13 46.332 9.584 4.156 0.556 7.688 3.666 176.958
M17 19/12/07 332 7.74 11 45.376 9.562 4.066 0.343 7.665 3.528 173.907
M18 31/01/08 326 7.44 10 42.670 8.805 4.012 0.406 7.696 3.68 161.703
M19 26/03/08 334 7.56 14 51.211 7.073 4.323 0.284 7.785 4.428 176.958
M20 22/04/08 325 7.62 12 49.531 7.929 4.655 0.525 7.512 3.838 178.7886
The comparison ofδ18O and δ2H values of spring water samples with meteoric water lines (Fig. 265.4) shows that most of the samples fall to the local meteoric water line suggesting the input to local rain-fall derives from weather fronts from the Mediterranean Sea.
According to SINTACS method (Civita and De Maio 2004) the karst aquifer feeding the Mazzoccolo spring has a high vulnerability, while presents very low capacity of groundwater protection (Fig. 265.5). The results of
applied methods suggest that the identified recharge areas, located in Aurunci Mts., are consistent with the highest vulnerability levels (i.e. obtained by SINTACS method).
The geochemical and isotopic characterization of spring water provides us important information for bet-ter management of the aquifer systems, which has signi fi-cant implications for contamination of flow paths, identification of recharge areas and evaluation of aquifer vulnerability.
Table 265.2 Isotope composition and calculated recharge elevations of Mazzoccolo springs
Sample codes Date
Mazzoccolo spring
Sabaudia
-64.0 -56.0 -48.0 -40.0 -32.0 -24.0 -16.0 -8.0
-8.0 -7.0 -6.0 -5.0 -4.0 -3.0 -2.0 -1.0 0.00.0
δ2H ‰ vs V-SMOW δ18O ‰ vs V-SMOW
M1 M2
M3 M4
M5 M6
M7 M8
M9
WMWL δ2H‰ = 8,13 δ18O‰ + 10,8 MMWL δ2H‰ = 8 δ18O‰ + 22 LMWL δ2H‰ = 7,53 δ18O‰ + 10,58
Fig. 265.4 Isotope values (δ2H andδ18O) of Mazzoccolo spring water samples plotted together with mediterranean meteoric water line (MMWL), the world meteoric water line (WMWL) and the local meteoric water line (LMWL)
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the karst aquifer feeding the Mazzoccolo Spring
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