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Hydrogeology of the western Po plain (Piedmont, NW Italy)

Domenico Antonio De Luca, Manuela Lasagna & Laura Debernardi

To cite this article: Domenico Antonio De Luca, Manuela Lasagna & Laura Debernardi (2020) Hydrogeology of the western Po plain (Piedmont, NW Italy), Journal of Maps, 16:2, 265-273, DOI: 10.1080/17445647.2020.1738280 To link to this article: https://doi.org/10.1080/17445647.2020.1738280

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Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=tjom20 JOURNAL OF MAPS 2020, VOL. 16, NO. 2, 265–273 https://doi.org/10.1080/17445647.2020.1738280

Science Hydrogeology of the western Po plain (Piedmont, NW Italy) Domenico Antonio De Luca, Manuela Lasagna and Laura Debernardi Earth Sciences Department, Turin University, Turin, Italy

ABSTRACT ARTICLE HISTORY This paper describes the hydrogeological map of the western Po Plain, located in Piedmont Received 30 July 2019 (north-western Italy). Po plain represents a hydrogeological system of European relevance, Revised 18 November 2019 and the Piedmont Plain is the most important groundwater reservoir of the Region. The Accepted 2 March 2020 1:300,000 scale map was realised using previous and new data to update the knowledge of KEYWORDS this area. The map provides information about the hydrogeological complexes and their type fl Groundwater; Quaternary and degree of permeability, water table levels and depth, piezometric level uctuation, alluvial aquifer; lithostratigraphic cross-sections, thickness, and percentage of the permeable deposits hydrogeological map; Po between 0 and 50 m from the ground surface. All this information is essential to public plain; Italy administrations, stakeholders, researchers, and professionals for defining possible tools for groundwater protection and management and for planning new groundwater exploitation (i.e. municipal drinking water supplies).

1. Introduction table, water table level fluctuation, thickness, and per- centage of the permeable deposits between 0 and 50 m The hydrogeological map of the Piedmont plain (NW from the ground surface and lithostratigraphic cross- Italy) is presented in this paper. The Piedmont plain sections. is located in the westernmost part of the Po Plain, The hydrogeological map was produced in English representing a hydrogeological system of European rel- and Italian because this study is addressed not only evance (WHYMAP, 2008). to an international audience of researchers, but also The study starts from previous researches, especially to public administrations, stakeholders, and local pro- PR.I.S.M.A.S. (acronym of PRogetto Interregionale fessionals working on groundwater management. More Sorveglianza e Monitoraggio delle Acque Sotterranee specifically, this map represents a basic step for future ‘Interregional Groundwater Monitoring Project’), investigations (aquifer vulnerability, recharge areas, PR.I.S.M.A.S. II and VALLE TANARO projects, con- wellhead protection areas …) or studies aimed at sol- ducted from 1996 and 2000. These projects aimed to ving current problems of groundwater resources in reconstruct the hydrogeological model of the Piedmont Piedmont, such as groundwater contamination Region and to realize a groundwater monitoring net- (Lasagna et al., 2013, 2015, 2016b, 2018; Lasagna & work under a quantitative and qualitative point of De Luca, 2016, 2019; Martinelli et al., 2018), overex- view. These data were used for a publication on Pied- ploitation (De Luca et al., 2018; Lasagna et al., 2014, mont Region hydrogeology (Bove et al., 2005), charac- 2019a), piezometric level variations as response to cli- terized by a limited number of printed copies and mate change (Lasagna et al., 2019b, 2020). distribution on a local level. In the present work, preliminary hydrogeological information has been improved using new and updated 2. Study area data, especially regarding the piezometric reconstruc- tion. Moreover, a collection of recently published Piedmont is a region in north-western Italy, extended papers and unpublished technical reports concerning for approximately 25,400 square kilometers. Piedmont the different aspects of Piedmont plain hydrogeology plain covers 27% of the regional territory, and is sur- was compiled and used for updating. rounded by the alpine chain on the north and east sec- The hydrogeological map of the Piedmont plain at tors, and by the Apennines Mountains on the south. a scale 1:300,000 shows some of these findings. More Consequently, about 43% of its territory is constituted specifically, it provides information about the hydro- by mountains and 30% by hills. Piedmont plain, that logical complexes and their type and degree of per- represents the westernmost part of the Po Plain (Figure meability, water table levels and depth of water 1), is the most important groundwater reservoir of the

CONTACT Manuela Lasagna [email protected] Earth Sciences Department, Turin University, Via Valperga Caluso 35, Turin, Italy This article has been republished with minor changes. These changes do not impact the academic content of the article. © 2020 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of Journal of Maps This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 266 D. A. DE LUCA ET AL

Figure 1. Location of the study area.

Region because of its size, the features of its deposits, and Marine complex (Pliocene) (Barbero et al., 2007; and its possibility to recharge (Debernardi et al., 2008). Bortolami et al., 1976; Bortolami et al., 1990; Bove The hydrogeological conceptual model of Piedmont et al., 2005; Cavalli & Vigna, 1992; Civita et al., 2005; plain (Figure 2) consists of superimposed complexes rep- Comazzi et al., 1988; Debernardi et al., 2008; Forno resented, from top to bottom, by Alluvial deposits com- et al., 2018; Lucchesi, 2001; Vigna et al., 2010). plex (lower Pleistocene-Holocene), ‘Villafranchiano’ The shallow unconfined aquifer is hosted in the transitional complex (late Pliocene–early Pleistocene) Alluvial deposits complex, consisting of coarse gravel

Figure 2. Sketch of the hydrogeological complexes of the alluvial Po plain. The cross-section has a W-E orientation, passing through Turin city. The black arrows represent groundwater flow direction in the different aquifers. JOURNAL OF MAPS 267 and sand of fluvial or fluvioglacial origin, with subordi- hydrogeological complexes hosting deep aquifers out- nate silty-clayey intercalations. This complex has a crop or the low permeable intercalations have limited thickness generally ranging between 20 and 50 m and spatial continuity and thickness (De Luca et al., 2019a). − − high permeability (k = 5*10 3 ÷ 5*10 4 m/s). Groundwater flow is therefore conditioned by Deeper aquifers are present in the underlying different factors: (i) the presence of the Alps that drives fluvial-lacustrine ‘Villafranchiano’ complex and the groundwater flow direction from the high to the low pliocenic marine sediments. They generally serve as plain; (ii) GW-SW interactions, where main water- key sources of drinking water in the Piedmont plain, courses are generally losing rivers close to the Alps because of their productivity and the better ground- and gaining river in the low plain; (iii) grain size of water quality compared to the shallow aquifer (De shallow aquifer, that normally decreases from moun- Luca et al., 2019d). tains to low plain, along Po River. When a sharp Highly consolidated sediments, especially marls, decrease in slope of the topographic surface is present clays, silts, clayey limestone, conglomerates, sandstone, in the middle plain or when shallow groundwater, and gypsum, generally represent the Tertiary Piedmont flowing in the coarse-grained sediments in the high Basin deposits (Eocene-Miocene). These sediments plain, meets the fine-grained sediments, groundwater have low permeability and permit only a limited rises to ground level and provides the origin of the fon- groundwater circulation along fractured zones with tanili, typical springs of the Po plain areas (De Luca the presence of springs with low and very low discharge et al., 2009, 2014; Minelli et al., 2002). (smaller than 1 L/s or few L/s). Crystalline rocks of the Alps border the plain on the 3. Materials and methods northern and western sides. They are mostly imperme- able or slightly permeable by fissuration. In the moun- The plain area of Alessandria, Asti, Biella, Cuneo, tain area, water resources are mainly located in the Novara, Turin, and Vercelli provinces were investi- valley-floor aquifers, in sedimentary non-cohesive gated, and the new insights were mapped in a hydro- bodies (e.g. debris, landslide, and glacial deposits), or geological map at a scale 1:300,000. A in intensely fractured rocks. Springs with low discharge hydrogeological map represents a complex system of (smaller than 1 L/s or few L/s) are generally connected water and rocks and describes their properties and to thin and discontinuous Quaternary deposits. Springs interrelations (Struckmeier & Margat, 1995). The ana- with higher discharge are, instead, linked to significant lyses were conducted starting from a collection of avail- aquifers corresponding to large and thick landslide able published and unpublished papers, maps, and bodies or very fractured bedrocks affected by deep- technical reports, concerning different hydrogeological seated gravitational slope deformations (DSGSDs) aspects. (De Luca et al., 2015, 2019c). Moreover, in alpine The hydrogeological map of the western Po plain areas, locally karstic circuits can exist in calcareous resumes different elements such as hydrogeological rocks. complexes, piezometric lines, depth of the shallow Glacial deposits are at last present in amphitheaters aquifer, phreatic level fluctuation, lithostratigraphic of Rivoli-Avigliana, Serra d’Ivrea and Upper Novarese. cross-sections, permeable deposits distribution They are composed by glacigenic successions with between 0 and 50 m from the ground surface interglacial paleosols and deposits, ranging in age (described as thickness and percentage). from terminal Early Pleistocene to Late Pleistocene (Gianotti et al., 2015). The permeability of these depos- 3.1. Hydrogeological complexes its vary depending on the grain size, weathering, and argillization of its sediments; glacial and fluvioglacial Starting from the lithologies of the geological map at a deposits may host a shallow aquifer and some perched scale 1:100,000 of the study area, the hydrogeological aquifers. complexes were defined based on the prevalent type Recharge areas of the shallow aquifer are located in and degree of permeability. Then, hydrogeological the entire plain, due to infiltration of rainfall and sec- complexes were digitalized in a vector format and ondly by surface water in the high plain sectors. The implemented in a Geographical Information System low plain sectors are generally discharge areas, and (GIS), georeferenced in the UTM projection WGS84/ the Po River represents the main regional discharge zone 32N. axis for the groundwater flow (Lasagna et al., 2016a). Along the main watercourses of Piedmont plain more 3.2. Water table level map and water table than 200 quarry lakes are present (Castagna et al., depth map 2015a, 2015b; De Luca et al., 2007) connected to quar- ries for extraction of sand and gravel. A field campaign was conducted in Piedmont plain in The recharge areas of the deep aquifers occur in the summer 2016 for the measure of water table depths. high plain sectors, close to the Alps, where the Phreatic groundwater levels were measured in 268 D. A. DE LUCA ET AL correspondence of 588 points (wells and piezometers) sistemapiemonte.it/cms/privati/agricoltura/servizi/378- homogenously distributed in the plain. These piezo- ram-banca-dati-agrometeorologica-consultazione-dati- metric data were then integrated using monitoring giornalieri-dati-storici-statistiche). wells 92 belonging to of the Piedmont Region monitor- Then the average monthly water table level was cal- ing network (www.regione.piemonte.it/monitgis/ culated for the subsequent analyses. public/welcome.do) and 41 belonging to of the Città The average monthly water table levels for the Metropolitana di Torino monitoring network period 2002–2017 were plotted with the average (https://webgis.arpa.piemonte.it/geoportale/index.php/). monthly rainfall of the same period. In the hydrogeolo- The reason for the integration was dual: (i) control and gical map of the western Po plain, seven bi-plot are pre- validation of piezometric data previously collected; (ii) sented, showing some characteristic behavior of the integration in areas where groundwater information study area. was insufficient. Water stages from the gauge stations on the water- 3.4. Lithostratigraphic sections courses were also used (www.regione.piemonte.it/ monitgis/public/welcome.do). All data were at last col- Nine lithostratigraphic cross-sections were identified lected in a database to produce the piezometric map of using the lithological data from 124 boreholes. Bore- the shallow aquifer at a scale 1:300,000. hole data were collected from the database of the Starting from piezometric data, the isopiezometric Earth Science Department (Hydrogeology Research lines were interpolated with the triangulation method Group) of Turin University. All boreholes are charac- using the Surfer 11 software (Golden Software, Golden, terized by spatial coordinates (UTM projection CO, USA). Then, the piezometric map was manually WGS84/zone 32N). Profiles were chosen to describe edited because many features of the study area, such all different lithostratigraphic situations of Piedmont as the presence of high terraces, large towns, fontanili plain. Particularly 2 profiles are located in Cuneo springs, and rivers, made the triangulation interp- Plain, 2 in Turin Plain, 2 in Vercelli Plain, 1 in Novara olation inaccurate. Plain, 2 in Alessandria Plain. Longitudinal and trans- Control factors were also considered. A topographic verse profiles are shown on the hydrogeological map control has been obtained using a Digital Elevation of the western Po plain. Model (DEM) with a resolution of 50 m, avoiding a water table above the topographic surface. The congru- 3.5. Map the permeable deposits between 0 and ence of the water table with geological and geomorpho- 50 m from the ground surface logic data has been verified. Moreover, the relations between groundwater and surficial water bodies have Lithologic data related to 0–50 m depth from ground been taken into account. Piezometric lines (equidis- level are derived from 2000 stratigraphic logs from tance 10 m) were plotted in a map with the hydrogeo- the database of the Earth Science Department (Hydro- logical complexes. The data interpretation was made at geology Team) of Turin University. These logs describe a scale 1:50,000 and then simplified and reported on a the sediment for depth greater than or equal to 50 m. scale 1:300,000. Different subsoil layers have been classified in litho- Main groundwater flow directions were indicated logic classes, and the thickness of the various deposits using flow lines. Successively, GIS application has has been calculated. At last, the sum of the layers thick- allowed subtracting the groundwater levels grid from ness of permeable deposits (gravel and sand) were a DEM to obtain the values of depth to the ground- calculated. water table. These values were classified into 5 groups A map (scale 1:600,000) representing the thickness (0–5m; 5–10 m; 10–20 m; 20–50 m; higher than and relative percentage of permeable deposits in the 50 m) and mapped (1:600,000 scale). Piedmont plain has been realized by using a kriging statistical interpolating method. 3.3. Water table level fluctuation 4. Results and discussion Phreatic groundwater levels, registered in 37 Piedmont Region monitoring wells, were collected for the period Ten hydrogeological complexes were recognized and 2002–2017. Moreover, rainfall data from 30 rain gauges mapped in the Piedmont plain based on their geologi- managed by the Regional Agency for Environmental cal media and permeability (degree and type). More Protection Piedmont (ARPA Piemonte) and located specifically, the following hydrogeological complexes in the Piedmont Plain were collected for the same were identified (in order from youngest to oldest): period. Piezometric and rainfall data were validated by ARPA Piemonte and made available online to (1) Recent fluvial deposits (FS1) (Upper Pleistocene- local authorities and professionals (www.regione. Holocene): incoherent and heterometric sedi- piemonte.it/monitgis/public/welcome.do; http://www. ments of fluvial (Holocene) and fluvioglacial JOURNAL OF MAPS 269

(Upper Pleistocene) origin, mainly gravelly- They contain a shallow unconfined aquifer, sandy and secondly silty-clayey; the general where they are undifferentiated or in coarse grain-size decreases from the mountains towards facies; they constitute the main multi-aquifer sys- the axis of the plain at the Po River. These sedi- tem (confined and semi-confined aquifers) of the ments are located in the bottom of the valleys Piedmont plain, where represented by an alter- and in the Piedmont Plain; they have a prevalent nating facies. permeability for porosity from high to medium (5) Marine sands (MS) (Pliocene): very or little stra- and contain a shallow unconfined aquifer, locally tified yellow sands, with fossiliferous banks with confined, in connection with surface rivers. faunas of the shallow sea, sometimes strongly (2) Medium and ancient fluvial deposits (FS2) cemented; sandstones, sands and pelites of a mar- (Middle – Lower Pleistocene): incoherent and ine environment. At times, they have gravel levels heterometric sediments, locally cemented, grav- (Asti, Alessandria and Biella areas) and marly or elly-sandy, and silty-clay, sometimes in alterna- sandstone intercalations (Asti and Alessandria tion; the fine fraction may be prevalent. These areas). The prevalent permeability for porosity deposits, which border the Apennine-Alps chains has a medium degree. The coarser terms of this from Tanaro River to Maggiore Lake, are in con- complex represent confined aquifers of good pro- tact with the morainic arches to which they are ductivity, sometimes artesian (Villafranca d’Asti genetically connected. These deposits are some- and Val Maggiore area). Marine sands can host times characterized by the presence of a loessic shallow unconfined aquifer if the sediments are covering and, in the most ancient terms, by a red- in outcropping. dish-colored cover, with a thickness of few (6) Marine clayey silt (MC) (Pliocene, Piacenzian): meters. A prevalent permeability of medium- Blue clay and silt, clayey and sandy marl with grade, due to porosity, characterizes these depos- abundant marine fossils and with microfaunas; its, but a lower degree of permeability is frequent, upwards, intercalation of yellow sands. These especially in the oldest and altered terms. They are sediments with permeability generally from contain a shallow unconfined aquifer, locally low to very low, which constitute aquitards or confined, in continuity with the aquifer hosted aquicludes. They can represent local confined in the FS1 Complex; perched aquifers can be and poorly productive aquifers in correspon- located in correspondence with the terraced dence to the coarsest deposits. areas. (7) Sedimentary rocks of the Tertiary Piedmont (3) Slope glacial and morainic hills deposits (GS) Basin Auct. (MT) (Lower Pliocene – Oligocene): (Pleistocene): slope glacial deposits and deposits sedimentary rocks of the Tertiary Piedmont of the morainic amphitheaters of Rivoli-Avigli- Basin Auct. (including the Formation of Cassano ana, Serra d’Ivrea and Upper Novarese; they con- Spinola, Messinian-Pliocene Inf). Complex sist of sediments with variable grain-size from silt characterized by extreme lithological variability and clay with pebble to sand and boulder. This (conglomerate, sandy-arenaceous, marly-clayey complex may include various types of deposits formations, with a prevalent calcareous com- such as ablation, bottom, fluvioglacial, and lacus- ponent, evaporitic (gypsum) and alternations of trine deposits. The prevalent permeability for deposits with different permeability). The preva- porosity varies from medium to low, locally lent permeability is low and very low, even if high. The slope glacial deposits on the mountain- very variable depending on the grain-size, the sides host a shallow unconfined aquifer while the degree of cementation and fracturing. Aquifers moraine of the plains can constitute a multi-aqui- productivity is generally low. In chalk, there is fer system. frequent groundwater circulation for karst. The (4) Lacustrine, swamp and fluvial sediments (Villa- natural quality of the water is generally accepta- franchian series) (V) (Upper Pliocene-Lower ble, except in chalky terms. Pleistocene): predominantly lacustrine, swamp (8) Calcareous and dolomitic rocks (CR) (Triassic – and fluvial sediments outcropping near the Paleogene): limestone-dolomitic rocks and Alpine arc (Stura di Lanzo fan, Serra d’Ivrea strongly tettonized evaporitic-carbonatic levels and Maggiore Lake), in the Alessandria plain (carbonates breccias) of the Alpine and Apennine and in the Poirino Plateau. They form a litostrati- substratum. They are characterized by a remark- graphic complex consisting of both permeable able water circulation due to the development of deposits (pebble, gravel, sand) and low-per- superficial and deep karst phenomena. In the meability deposits (silt and clay). The prevalent most calcareous deposits, the prevalent per- permeability for porosity is of medium degree, meability (for fracturing and karst) results from even if they are characterized by high heterogen- high to medium; in the dolomitic rocks, the per- eity, depending on the depositional environment. meability and karst phenomena are smaller. This 270 D. A. DE LUCA ET AL

complex often feeds springs with high flow rates In high plain, the hydraulic gradients show the (Le Vene, Dragonera and Bossea) very often maximum values (e.g. 7–8% near Biella). Lowest values above 100 L/s (average annual flow). The natural are located in the low plain (about 0.01%). quality of the water is generally good except in the The water table depth map in the Piedmont plain presence of evaporitic terms (carbonates breccia, shows a high variability of this parameter moving anhydrite, gypsum and related cataclasite). from the high to the low plains. In the low plain, the (9) Alpine and Apennine Flyschoid rocks (FR) (Late most frequent range is inferior to 5 m, especially Cretaceous-Early Eocene): alternations of argil- along the Po River and near the main rivers of the laceous schists with clay or sandstone limestones, plain. The highest values (more than 50 m) are distrib- or with sandstones, brown argilloschists, slate uted in Cuneo plain and in the northern part of Turin schists and subordinately limestone and con- plain due to the presence of a high morphological glomerates (Alpine flyschoid rocks); alternations terrace. of calcareous, calcareous-marly, arenaceous Average monthly water table levels in the period layers and blackish clayey banks and gray-black- 2002–2017 highlight different situations. Starting ish argillites (Apennine flyschoid rocks). In both from the north of Piedmont plain, monitoring well cases, the prevalent permeability is low or very PII27, located in Novara plain, shows a quite constant low. The extent of water circulation, generally water table level during the year. A little variation of the limited and of local importance, is related to the phreatic level is due to the precipitation regime. In Ver- lithology and the degree of fracturing. celli plain, monitoring well PII1 displays a high seaso- (10) Metamorphic, volcanic and plutonic rocks nal change, with a water table level fluctuation higher (MVP) (Paleozoic – Neozoic): magmatic (pluto- than 4 m. A maximum phreatic level is registered in nic and volcanic) and metamorphic rocks of the August and a minimum in March. The fluctuations Alpine and Apennine substratum. They are are not exclusively connected to rainfall but also irriga- gneisses, mica schists, quartzites, green stones tion practices (flooding of paddy fields). The maximum (serpentinites, amphibolites and prasinites), water table level and rainfall, indeed, are not always granites, porphyries and their metamorphic contemporary. P26 in Turin area does not show a derivatives. Groundwater circulation is absent notable variation of phreatic level and scarce corre- or limited to surface fracture systems and signifi- lation with rainfall. Monitoring well P17 in the cant faults. The prevalent permeability is variable southern Turin plain reveals a close relation between from low to very low. The degree of permeability phreatic level and rainfall, with a maximum in May can also be medium along with the most frac- and a minimum in August. In Cuneo and Asti plain, tured bands. Springs are characterized by modest two analysed monitoring wells (T2 and T30) shows a flow rates (few L/s) and by good natural quality little variation of phreatic level during the year, lower (mineral waters). than 1 m. T12 located in Alessandria plain displays a maximum phreatic level in March and a minimum in The water table level map in the western Po plain September. normally follows the topography of the land surface. Lithostratigraphic cross-sections were useful to Due to the morphological assessment, piezometric highlight the different lithologies in the study area lines are generally parallel to the Alps reliefs. Po and their geometric relationship. River represents the base level and the main gaining Section 1 is characterized by a high sequence of stream of the plain. The main watercourses are usually coarse deposits of the Cuneo plain. The Alpine crystal- gaining in the middle and low plain. line substrate is crossed on the eastern part, under allu- Groundwater generally flows from the Alps to the vial deposits. low plain; high terraces, consisting of medium and Section 2 shows the different lithology correspond- ancient fluvial deposits, modify the morphology of ing to recent fluvial deposits (mainly gravel and sand piezometric lines. In the Novara plain and the northern with subordinate fine-grained intercalations) and med- Vercelli plain, the groundwater flow direction is from ium and ancient fluvial deposits (silt and clay). A high N to S. In the southern Vercelli plain and Biella plain thickness of fine deposits alternated with coarse- groundwater flows from W-NW to E-SE. Flow direc- grained deposits is present on the western portion of tion in the northern Turin plain is NNW- SSE, while the section. in the southern plain it is directed from W to E with Section 3 is located in Turin plain and highlights the some exceptions. In Cuneo plain the shallow ground- presence of Pliocene and pre-Pliocene marine deposits water flows from SW to NE in the central and southern under the fluvial deposits. Fluvial deposits consist of portions of the plain, and from S to N in the northern coarse-grained sediments with local conglomerate in sector. Alessandria plain is characterized by ground- the shallow subsoil and alternating fine and grained- water flow from SE to NW. sediments at a depth superior to 40 m. JOURNAL OF MAPS 271

Section 4 crosses the plain from NW to SE, close to circulation, to obtain a more complete overview of the Turin Hill. It highlights a thick sequence of fluvial this essential resource. deposits, more coarse in the shallow subsoil and fine in-depth, and the presence of Pliocene marine sedi- ment on the eastern portion. Software Section 5 is located in Biella plain. It crosses the Data processing and statistical analysis were performed crystalline substrate in the northern part of the section, by Surfer 11 software. The elaboration of the individual fl close to the Alps, and a thick sequence of uvial depos- maps was produced using QGIS 2.18. The assembly of its in the plain. individual maps in the final map was achieved by Sur- Section 6 has N-S development in Novara plain. It fer 11. crosses the crystalline substrate at a high depth from ground level (about 150 m). Fluvial deposits are gener- ally coarse, and fine levels appear at a depth higher than Acknowledgments – 100 120 m from ground level. The authors thank PhD Mancini Susanna for her help in the The cross-section in Vercelli plain (section 7) has E- collection and analysis of phreatic levels fluctuation. W development. Alternating fine and grained-sedi- ments are present in the plain, with a predominance of gravel and sand in the first tens of meters of Disclosure statement depth. On the western portion of the section, silt and No potential conflict of interest was reported by the author(s). clay layers are predominant. Sections 8 and 9 are positioned in Alessandria plain and show quite different situations with respect to the ORCID previous ones. Section 8 highlights the presence of a Manuela Lasagna http://orcid.org/0000-0003-3464-2370 sedimentary basin filled by a succession of generally coarse deposits. Pre-Pliocene deposits are present on both ends of the sections. References Section 9 does not intercept the Pre-Pliocene depos- Barbero, T., De Luca, D. A., Forno, M. G., Masciocco, L., & its, located at a greater depth. Sediments are prevalently Massazza, G. (2007). Stratigraphic revision of the subsoil fine-grained, with a thickness higher than 120 m on the of the southern turin plain for hydrogeologic purposes. NE end of the section. In the other portions, fine Memorie Descrittive della Carta Geologica d’Italia, – deposits are located at a depth inferior to 50, and coarse LXXVI,9 16. Bortolami, G. C., De Luca, D. A., & Filippini, G. (1990). Le sediments are present in the shallow subsoil. acque sotterranee della pianura di Torino. Aspetti e pro- The map of the permeable deposits between 0 and blemi. Litografia Massaza & Sinchetto. p. 67. 50 m from the ground surface highlights better the Bortolami, G. C., Maffeo, B., Maradei, V., Ricci, B., & situation described by the cross-sections and the areal Sorzana, F. (1976). 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