The Montagnola Senese aquifer (known as “Luco”) is an important and strategic water reserve in Southern Tuscany. With this study we have furthered our knowledge for the geometrical/structural, hydrodynamic and hydrochemical aquifer characterization and for the development of a conceptual model of it. In addition, this model provides the results of a work that aims to create a conceptual model and a first approach to the numerical model of flow in permanent regime for the evaluation and management of groundwater resources, while also assessing its vulnerability to pollution. New aquifer geometry data, represented by carbonate formation of Calcare Cavernoso and Breccia di Grotti, were acquired through geoelectrical surveys, geophysical tomography, borehole stratigraphy, a new deep borehole and compared with the geological mapping of Regione Toscana Continuum Map. This allowed to estimate the outcropping and non-outcropping aquifer extension (166,3 Km2), in respect of a feeding area of about 91,6 Km2. The entire permeable hydrogeological complex is found to have an average thickness of about 178 m. With regard to the hydrodynamic characterisation of the aquifer, which is necessary to describe the spatial and temporal trend of the piezometric surface, it can be stated that, despite the uneven spatial distribution of the measurement points, two main directions of underground water flow have been identified: southward (Piano di Rosia) and northwestward (Abbadia a Isola and Strove). This characterization of flows and hydrodynamic parameters needs further investigation in the future. The assessment of aquifer recharge was approached with two methodologies: - First one, evaluating the total infiltration in relation to the calculated water surplus infiltration, once the recharge area has been defined. This assessment (average data from 1967-2006) leads to estimate an average aquifer recharge of over 21·106 m3/year. - Second one, based on the excursion of the measured groundwater piezometric levels (March 2009-January 2010); it identifies a dynamic resource that, using an effective porosity (ne) of 8%, can be estimated at about 8,1·106 m3/year, to which should be added 12·106 m3/year of water that is currently withdrawn from the aquifer for a total amount of the annual hydric resource of about 20·106 m3. Even with all the limitations associated with this type of evaluation, the results obtained, with the two criteria, are in complete agreement with each other. As far as the water reserve is concerned, it is evaluated at around 1.5 billion m3, that is to say about 100 times greater than the dynamic resource. Comparing the renewable resource evaluations with current drinking water demand, we note that in the face of an average aquifer recharge of about 21·106 m3, water consumption is about 11,7·106 m3. Further utilisation of the aquifer hosted in the Montagnola Senese aquifer is therefore theoretically possible. Based on the knowledge gained, the conceptual model of the aquifer was created. The aquifer system has been represented using a three-dimensional finite element numerical model (FEM), by using FEFLOW (Finite Element subsurface FLOW system) numerical code, operating in permanent regime. Input data have been entered into the system by assigning boundary conditions at the hydraulic loading, at the water outflows and to the material properties such as permeability, porosity and infiltration. Final results made possible to estimate water quantities present in the aquifer, highlighting the importance and role played by meteoric infiltration in balancing the water outflows and keeping the system in balance. Given its strategic importance, to complete the hydrogeological study of Montagnola Senese aquifer, an assessment of its intrinsic vulnerability to pollution was also carried out using a simiparametric method called SIPS. This original methodology, which can be ascribable to a simplified SINTACS, made it possible, through the estimation of four basic parameters, to assess the intrinsic vulnerability of the groundwater aquifer, which is for 75% high to medium-high.
L’acquifero della Montagnola Senese (conosciuto come “Luco”) codice regionale CIS 99MM030, è considerato un importante serbatoio idrico strategico della Toscana Meridionale. Questo studio ha consentito l’approfondimento delle conoscenze per una migliore caratterizzazione geometrico-strutturale, idrodinamica e idrochimica dell’acquifero e restituisce i risultati di un lavoro che ha l’obiettivo di realizzare un modello concettuale e un primo approccio al modello numerico di flusso in regime permanente ai fini della valutazione e gestione delle risorse idriche sotterranee valutando anche la sua vulnerabilità all’inquinamento. I nuovi dati relativi alla geometria dell’acquifero, costituito dalle formazioni carbonatiche del Calcare Cavernoso e della Breccia di Grotti, sono stati acquisiti attraverso sondaggi geoelettrici, tomografie geofisiche, stratigrafie di pozzi, una nuova perforazione profonda e confrontati con la cartografia geologica del continuum regionale. Ciò ha permesso di valutare la sua estensione, affiorante e non, pari a circa 166,3 Km2 a fronte di un’area di alimentazione pari a circa 91,6 Km2. L’intero complesso idrogeologico permeabile risulta avere uno spessore medio di circa 178 m. Per quanto riguarda la caratterizzazione idrodinamica dell’acquifero, necessaria alla descrizione dell’andamento spaziale e temporale della superficie piezometrica, si può affermare che, nonostante la disomogenea distribuzione spaziale dei punti di misura, sono state individuate due principali direzioni di flusso della falda idrica sotterranea: verso Sud (Piano di Rosia) e verso Nord-Ovest (Abbadia a Isola e Strove). Tale caratterizzazione sia dei flussi, sia dei parametrici idrodinamici, necessita di futuri approfondimenti con esecuzione di nuove indagini. La valutazione della ricarica dell’acquifero è stata affrontata con due metodologie: - La prima, una volta definita la superficie dell’aree di ricarica per infiltrazione, valutando indirettamente l’infiltrazione totale in relazione all’eccedenza idrica calcolata. Tale valutazione (dati medi del periodo 1967-2006) porta a stimare la ricarica media in oltre 21·106 m3/anno. - La seconda, basata sulle escursioni dei livelli piezometrici di falda misurati (Marzo 2009-Gennaio 2010), individua una risorsa dinamica che, in virtù di una porosità efficace ne del 8% (da letteratura tale complesso è caratterizzato da ne tra 5-10%), può essere valutata in circa 8,1·106 m3/anno a cui andrebbero sommati i circa 12·106 m3/anno di acqua che attualmente vengono prelevati dall’acquifero per un ammontare complessivo della risorsa annua pari a circa 20·106 m3. Pur con tutti i limiti connessi a tale tipo di valutazione, i risultati ottenuti, con i due criteri, sono in pieno accordo tra loro. Per quanto concerne la riserva idrica la sua valutazione è dell’ordine di 1,5·109 m3, vale a dire circa 100 volte superiore alla risorsa dinamica. Infine, se confrontiamo le valutazioni della risorsa rinnovabile con l’attuale domanda d’acqua ad uso idropotabile si nota che a fronte di una ricarica media pari circa 21·106 m3, i consumi ammontano a circa 11,7·106 m3, risulta quindi teoricamente possibile un ulteriore utilizzo della falda ospitata nell’acquifero della Montagnola Senese. Sulla base delle conoscenze acquisite è stato realizzato il modello concettuale dell’acquifero, base fondamentale della modellazione numerica. Il sistema acquifero è stato quindi rappresentato, per mezzo di un modello numerico tridimensionale ad elementi finiti (FEM), con l’utilizzo del codice numerico FEFLOW (Finite Element subsurface FLOW system), operando in regime permanente. I dati di input sono stati inseriti nel sistema attraverso l’assegnazione di condizioni ai limiti (Boundary Condition) di carico idraulico, di trasferimento di flussi, di emungimenti e delle proprietà dei materiali (Material Properties) come la permeabilità, la porosità e l’infiltrazione. I risultati finali hanno permesso di stimare i quantitativi d’acqua presenti all’interno dell’acquifero in studio mettendo in risalto l’importanza e il ruolo che ricopre l’infiltrazione meteorica che riesce a bilanciare gli emungimenti e a mantenere in equilibrio tutto il sistema. Data l’importanza strategica dell’acquifero, a completamento dello studio idrogeologico della Montagnola Senese, è stata effettuata anche la valutazione della sua vulnerabilità intrinseca all’inquinamento attraverso un metodo simiparametrico denominato SIPS. Questa metodologia originale, riconducibile ad un SINTACS semplificato, ha consentito, attraverso la stima di quattro parametri base, di valutare la vulnerabilità intrinseca del corpo idrico sotterraneo che per il 75% risulta essere compresa tra elevata e medio alta.
Capacci, F. (2022). LA GESTIONE DELLE RISORSE IDRICHE E DEL TERRITORIO NELL’AMBITO DELLA PIANIFICAZIONE DI AREA VASTA: L’ESEMPIO DELL’ACQUIFERO DELLA MONTAGNOLA SENESE [10.25434/capacci-fausto_phd2022].
LA GESTIONE DELLE RISORSE IDRICHE E DEL TERRITORIO NELL’AMBITO DELLA PIANIFICAZIONE DI AREA VASTA: L’ESEMPIO DELL’ACQUIFERO DELLA MONTAGNOLA SENESE
Capacci, Fausto
2022-01-01
Abstract
The Montagnola Senese aquifer (known as “Luco”) is an important and strategic water reserve in Southern Tuscany. With this study we have furthered our knowledge for the geometrical/structural, hydrodynamic and hydrochemical aquifer characterization and for the development of a conceptual model of it. In addition, this model provides the results of a work that aims to create a conceptual model and a first approach to the numerical model of flow in permanent regime for the evaluation and management of groundwater resources, while also assessing its vulnerability to pollution. New aquifer geometry data, represented by carbonate formation of Calcare Cavernoso and Breccia di Grotti, were acquired through geoelectrical surveys, geophysical tomography, borehole stratigraphy, a new deep borehole and compared with the geological mapping of Regione Toscana Continuum Map. This allowed to estimate the outcropping and non-outcropping aquifer extension (166,3 Km2), in respect of a feeding area of about 91,6 Km2. The entire permeable hydrogeological complex is found to have an average thickness of about 178 m. With regard to the hydrodynamic characterisation of the aquifer, which is necessary to describe the spatial and temporal trend of the piezometric surface, it can be stated that, despite the uneven spatial distribution of the measurement points, two main directions of underground water flow have been identified: southward (Piano di Rosia) and northwestward (Abbadia a Isola and Strove). This characterization of flows and hydrodynamic parameters needs further investigation in the future. The assessment of aquifer recharge was approached with two methodologies: - First one, evaluating the total infiltration in relation to the calculated water surplus infiltration, once the recharge area has been defined. This assessment (average data from 1967-2006) leads to estimate an average aquifer recharge of over 21·106 m3/year. - Second one, based on the excursion of the measured groundwater piezometric levels (March 2009-January 2010); it identifies a dynamic resource that, using an effective porosity (ne) of 8%, can be estimated at about 8,1·106 m3/year, to which should be added 12·106 m3/year of water that is currently withdrawn from the aquifer for a total amount of the annual hydric resource of about 20·106 m3. Even with all the limitations associated with this type of evaluation, the results obtained, with the two criteria, are in complete agreement with each other. As far as the water reserve is concerned, it is evaluated at around 1.5 billion m3, that is to say about 100 times greater than the dynamic resource. Comparing the renewable resource evaluations with current drinking water demand, we note that in the face of an average aquifer recharge of about 21·106 m3, water consumption is about 11,7·106 m3. Further utilisation of the aquifer hosted in the Montagnola Senese aquifer is therefore theoretically possible. Based on the knowledge gained, the conceptual model of the aquifer was created. The aquifer system has been represented using a three-dimensional finite element numerical model (FEM), by using FEFLOW (Finite Element subsurface FLOW system) numerical code, operating in permanent regime. Input data have been entered into the system by assigning boundary conditions at the hydraulic loading, at the water outflows and to the material properties such as permeability, porosity and infiltration. Final results made possible to estimate water quantities present in the aquifer, highlighting the importance and role played by meteoric infiltration in balancing the water outflows and keeping the system in balance. Given its strategic importance, to complete the hydrogeological study of Montagnola Senese aquifer, an assessment of its intrinsic vulnerability to pollution was also carried out using a simiparametric method called SIPS. This original methodology, which can be ascribable to a simplified SINTACS, made it possible, through the estimation of four basic parameters, to assess the intrinsic vulnerability of the groundwater aquifer, which is for 75% high to medium-high.File | Dimensione | Formato | |
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https://hdl.handle.net/11365/1217666