Studio idrogeologico sull’acquifero di Chiasso

Blick gegen Chiasso_16473088301_l Sto preparando la mia tesi al Master di idrogeologia e geotermia dell’Università di Neuchatel (CHYN) che avrà come oggetto di studio la piana di Chiasso ed il suo acquifero superficiale. Sarà uno studio sui suoi processi geochimici, in particolare attorno al pozzo di Pra Tiro (quello vicino allo stadio comunale). Una prima ricerca é già stata fatta ed esiste già un programma di monitoraggio preso in carica dall’Istituto di scienze della Terra di Trevano (IST).

L’acqua potabile di Chiasso é estratta unicamente dal sottosuolo. Si sono osservati dei valori di nitrati al di sopra della normativa svizzera di 25mg/l e si vuole capire l’origine e la fenomelogia di questi nitrati nell’acqua di falda.

Lavorero’ con il prof. Daniel Hunkeler (CHYN) ed il Dr. Pera (IST).

Aggiungo una presentazione piu’ dettagliata in inglese.

Situation

 

Chiasso, Switzerland Evening_6160275141_lChiasso is a town of about 8000 inhabitants prevalently occupied in the service and industrial business whereby the agricultural activities are limited. About half of the surface of the study area is occupied by the Swiss Federal Railways hub as part of the national second most important logistical center as it gradually developed[1],[2] from the opening of the Gotthard Tunnel (1882) until the contemporary dismantling.

The area is also the location of a 4x1km unconfined, pre-alpine, cross-border aquifer set in a quaternary sedimental plane which shows sequences of glacial, fluvial, marsh and lacustrine soft deposits (fig.1 from Gasperini, 2013). Highly organic deposits were also observed in several boreholes in the area, and the presence of hystorical gas seepage has been recognized (Greber et al., 1997)[3].

Chiasso and its railways

The plain is crossed by three rivers from West to East (fig.2): the tributaries Roncaglia, Faloppia and the main stream Breggia, which in turn flows into the 3 km distant Como Lake,in Italy. The rivers’ bed were completely cemented under the 1970-80s environmental policy and in theory do not play an important role for the recharge of the aquifer which is happening by snow and rainfall almost uniquely. We assume normal climatic values (i.d. 30% ) for evapotranspiration.

fiumi e pozzo e sorgente
Fig. 2 fiumi, pozzo e sorgente sulla piano di Chiasso

 

Since 2013, IST operates a groundwater observation network monthly measuring piezometric levels. Data are analyzed, interpolated to create a continuous surface and then published through web gis services for public administration use. According with those surveys, Pra Tiro well pumping strongly influences piezometric levels in the whole acquifer crating a large depression cone. In some observation points some artesian piezometric levels were also recorded in the west portion of the aquifer.

 

On the basis of this piezometric observation network, IST proposed a groundwater quality monitoring network currently operated by Sezione per la protezione dell’aria dell’acqua e del suolo (SPAAS) from Cantone Ticino.

 

On the Northern border of the plain a karstic source (“Rovagina”) in the calcalreous rocks of the Mount Generoso massif feeds substantially the 1914 firstly built aqueduct while in the middle of the plain is a well (“Pra Tiro”) which is in use since 1942 [4] and which was an extension to the original aqueduct (fig.2). Thus, the city of Chiasso (and the nearby city of Balerna) depends exclusively from groundwater from these two sources for its water supply. In order to fulfill quantitatively drinking water requirements the Rovagina Spring is now exploited by pumping.

 

Following the observation of NO3 values above the quality limits of 25 mg/ml fixed by the water protection ordinance[5] in certain abandoned industrial wells, public authorities performed in 2012 – 2013 an aquifer extensive groundwater quality survey. Collected data were successively used to conduct a hydrogeochemical study that was carried out in collaboration with IST – SUPSI and Pisa University[6]. The aim of the study was to do a description of the chemical characteristics of groundwater and the analysis of presence and spatial distribution of nitrogen related compounds.

situation - from gasperini et al

It has been concluded that the Nitrogen (and Potassium) comes from natural origin from interaction

of organic Quaternary lenses present in the alluvial plane[7] but other sources are envisaged (sewage discharge, fertilizers, wastewaters treatment facilities). Ion exchange processes ( Na – K) and calcite precipitation seems to play the major role and occur along paths. Thus the groundwater geochemical evolution is being controlled by oxidation of organic matter along the flow direction and water-rock interaction mechanisms6.

 

Study Objective

 

The fact that groundwater represents the only water source for the town of Chiasso explains the interest in studying and monitoring the hydrogeology of this densely populated area (up to >80 inhabitants/hectare[8]).

 

We aim at understanding more in detail the origin, behavior along flow paths, mechanisms of the oxidation process of the Nitrogen compounds around the well “Pra Tiro” by using environmental isotopes, in particular the N and O isotopes of the NO3 molecule and those of the water molecule (D,O). The role of artesian groundwater which is characterized by negative redox potential in releasing N related compounds will be also studied.

 

 

Chiasso_7885936504_l

 

Preliminary Bibliograhy

 

 

  1. Gasperini Greta, Geochemical Carachterization of the Chiasso Aquifer, Bachelor Thesis, University of Pisa, 2013. https://etd.adm.unipi.it/t/etd-06172013-161931/
  2. Istituto Geologico Cantonale (data). Idrogeologia del bacino di Chiasso. Rapporto interno
  3. Appelo C.A.J, Postma D., Geochemistry, Groundwater and pollution, 2nd Edition, 2010,CRC Press
  4. Glynn P.D, Plummer L.Niel, Geochemistry and the Understanding of Groundwater Systems, Hydrogeol J (2005) 13:263-287

 

  1. Greber E., Leu W., Bernoulli D., Schumacher M.E., Wyss R., 1997. Hydrocarbon Provinces in the Swiss Southern Alps – a gas geochemistry and basin modelling study. Marine and petroleum geology vol 14 no 1 pp. 3 -25.
  2. Krauskopf K.B, Bird, D.K, Introduction to Geochemistry, 3rd Edition, 1995, McGraw-Hill
  3. Sigg L, Stumm W., Aquatische Chemie, Einführung in die Chemie natürlicher Gewässer, 2011, VDF Verlag
  4. Geochemistry notes of the Master of Hydrogeology and Geothermy, CHYN, Université de Neuchâtel, 2013-2014
  5. Kendall C., Mc Donnell (Eds.), Isotope Tracers in Catchment Hydrology, 1998, Elsevier Science B.V.
  6. Clark I.D, Fritz P., Environmental isotopes in hydrogeology, 1997, CRC Press
  7. Churchod B., Gonthier J., Miéville P., Risse J., Introduction à la Chimie, 2011 Edition LEP

[1] SCUOLA CANTONALE DI COMMERCIO, I cento anni della ferrovia del San Gottardo, 1882-1982, Edizioni Casagrande SA, Bellinzona

[2] MARIO GILARDI, Saluti da Chiasso, Edizioni Tipo-Print, Mendrisio, 1971

[3] Greber E., Leu W., Bernoulli D., Schumacher M.E., Wyss R., 1997. Hydrocarbon Provinces in the Swiss Southern Alps – a gas geochemistry and basin modelling study. Marine and petroleum geology vol 14 no 1 pp. 3 -25.

[4] http://www.age-sa.ch/cenni-storici
[5] http://www.bafu.admin.ch/gewaesserschutz/10428/index.html?lang=en
[6] Gasperini Greta, Geochemical Carachterization of the Chiasso Aquifer, Bachelor Thesis, University of Pisa, 2013. https://etd.adm.unipi.it/t/etd-06172013-161931/

 

6 Gasperini Greta, Geochemical Carachterization of the Chiasso Aquifer, Bachelor Thesis, University of Pisa, 2013. https://etd.adm.unipi.it/t/etd-06172013-161931/
[7] Istituto Geologico Cantonale (data). Idrogeologia del bacino di Chiasso. Rapporto interno

[8] Population density map on the Swiss Geological Survey, https://map.geo.admin.ch

Author: sandro

Geologo, Idrogeologo.

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