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

Neuchatel CHYN (hydrogeology and geothermy)

Kriging is a way of estimating spatial data where there is none. Easy said but it deals with high mathematics, probabilities, statistics and random variables. Do you have only a few points of data on a map but you want to create a reasonable contour area and even extrapolating values? Kriging is for that. Uses of kriging  are many: in environmental remediation, mineral and fossil fuels exploration, biology…to name a few.

Kriging maths

Another fundamental tool is FEFLOW of course: flow and mass simulation on a PC (actually I do it on my laptop). The learning curve is rather steep but little by little I am getting used here at teh University of Neuchatel (CHYN) where I am doing my master in hydrogeology and geothermy. We are using the old interface by the way…here it is:

feflow hydrogeology simulation numerical

 

 

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Hydrogeology hands-on week-end

A good general course into applied hydrogeology

 

I recently partecipated in an applied hydrogeology course for NGOs dealing with water wells in Africa and Developing countries.

We drilled a 15m deep borehole in a sand aquifer, carried out a quick geological log, introduced the casing with screen and geotextile, then had an example of pumping test (lasted only 20 minutes instead of the usual 12+ hours), we saw another drilling method in practice, had a good on equipment and the geology of the area.

Then we moved inside for another two days of intensive Groundwater undertstanding. While much of the teaching was known, it was very interstinng to hear professional hydrogeologists exxpress in few words their understanding of groundwater hydraulics.

Personally I found very enriching the moment of water exploration where we localised the siting of water well drilling location by using real information from the ground and Google Earth.

Here some pictures of the event:

chalk hills, uk, silsoewater well drilling direct circulation water tankPumping test for aquifer properties

 

 

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Water Springs Monitoring

A hole in the mountain, any problem?

When a tunnel is cut through a mountain, it might be that the internal water circulation inside the mounatin is affected and changed with a result to dry water springs present on the surface.

Here I followed a hydrogeologist friend and we measured the following parameters:

  • air temperature
  • water temperature
  • water flow rate (Q)
  • water conductivity
  • water PH
  • water REDOX
  • water Oxigen

The water flow rate, water temperatue and water conductivity are the three more important parameters to assess if somethings goes wrong in this case. The others parameters are more related to the quality of water (geochemistry)

The water flow (Q) is simply measured with a bucket(s) of different capacity (e.g. 2 liters, 7 liters, 10 liters)

Hydrogeology

English: Groundwater is found beneath the soli...
English: Groundwater is found beneath the solid surface. Notice that the water table roughly mirrors the slope of the land’s surface. A well penetrates the water table. (Photo credit: Wikipedia)

 

I am helping UNIWATER EDUCATION ltd in their fundraising effort. Here is SWitzerland many raw material, mining and oil companies have their headquarter….

Discussing with Laurra Olmsted, I could confirm a strange pattern fo hydrogeologist (and geologist dealing with water): there is no job for them despite the desperate need for water in many rural areas in Africa. LAurra pointed out also another alarming fact: the lack of knowledge about Groundwater in general. here is what she says:

“I find incredible is the lack of knowledge or information on groundwater.  As a groundwater specialist it is frustrating to see the potential if gw were to be developed, but for some reason, even those people who should be informed about the potential (vs surface water) continue to only talk about surface water.  As a profession, this is a challenge, and one that needs to be talked up in general, at every opportunity that arises.”

Next to dealing with the Internet and marketing, I am Msc geologist myself and so I decided to step in and take action for what I can..

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