The gravelly horizon of the Pisa plain multilayered system is a confined aquifer tapped by a large number of wells. It hosts a very important water resource for drinking, industrial and irrigable uses, but may be affected by seawater intrusion coming from the coastal area; most wells is distributed inland, anyway a significant exploitation along the coastal area is also present to supply farms and tourist services. Previous hydrogeological and geochemical investigations carried out in coastal area stated maximum percentage of seawater in gravelly aquifer of about 7-9% and suggested the presence of two different mechanisms (Doveri et alii, 2010): i) a direct seawater intrusion from the zone where the gravelly aquifer is in contact with the sea floor; ii) a mixing process between freshwater and seawater, the latter deriving from the Arno river-shallow sandy aquifer system. Basing on these results, since January 2012 a new two-year project was financed by the MSRM Regional Park. Major aims are a better definition of such phenomena and their distribution on the territory, and an assessing of the seawater intrusion trend in relation to groundwater exploitation. Eleven piezometers were realised during first semester of 2012, thus improving the measurement network, which is now made up by 40 wells/piezometers distributed on about 60 km^2. Comparing new and previous borehole data a general confinement of the gravelly aquifer is confirmed, excepting in the northern part where the aquifer is in contact with the superficial sandy one. Preliminary field measurement was performed in June 2012, during which water level (WL) and electrical conductivity (EC) data were collected. WLs below the sea-level were observed on most of the studied area, with a minimum value of about -5 m a.s.l. in the inner part of the northern zone, where major exploitation is present. Moreover, a relative minimum of WL (about -2 m a.s.l.) is present near the shoreline in the southern zone. In the latter EC is diffusely high from shoreline up to 5 km apart and reaches a maximum value of about 7,000 μS/cm. Toward North a general EC decreasing is observed and values below 2,000 μS/cm are measured in most of water-wells. On a limited area close to the Arno River, values higher than 3,000 μS/cm are nevertheless present. Hydraulic conductivity values between E-03 and E-05 m/s were achieved by means of some slug and pumping tests performed on new piezometers. During this month other hydraulic tests will be performed, and monitoring of EC, T and WL will be started using automatic probes; at the same time, the pumping rates of major farms wells will be monitored. Furthermore, a water sampling field will be carried out in the next month, and the collected samples will be analysed in chemical elements and water isotopes. Thus, a first picture of the seawater intrusion and its causes will be available. References Doveri M., Giannecchini R. & Butteri M., 2010. Seawater intrusion in the Versiliese-Pisan coastal aquifer system (North-western Tuscany): results from a hydrogeologic-hydrogeochemical study. Salt Water Intrusion Meeting, Azores 2010. Proceedings SWIM21, 150-153.

Seawater intrusion in the gravelly confined aquifer of the coastal Pisan Plain (Tuscany): hydrogeological and geochemical investigation to assess causes and consequences

GIANNECCHINI, ROBERTO;
2012

Abstract

The gravelly horizon of the Pisa plain multilayered system is a confined aquifer tapped by a large number of wells. It hosts a very important water resource for drinking, industrial and irrigable uses, but may be affected by seawater intrusion coming from the coastal area; most wells is distributed inland, anyway a significant exploitation along the coastal area is also present to supply farms and tourist services. Previous hydrogeological and geochemical investigations carried out in coastal area stated maximum percentage of seawater in gravelly aquifer of about 7-9% and suggested the presence of two different mechanisms (Doveri et alii, 2010): i) a direct seawater intrusion from the zone where the gravelly aquifer is in contact with the sea floor; ii) a mixing process between freshwater and seawater, the latter deriving from the Arno river-shallow sandy aquifer system. Basing on these results, since January 2012 a new two-year project was financed by the MSRM Regional Park. Major aims are a better definition of such phenomena and their distribution on the territory, and an assessing of the seawater intrusion trend in relation to groundwater exploitation. Eleven piezometers were realised during first semester of 2012, thus improving the measurement network, which is now made up by 40 wells/piezometers distributed on about 60 km^2. Comparing new and previous borehole data a general confinement of the gravelly aquifer is confirmed, excepting in the northern part where the aquifer is in contact with the superficial sandy one. Preliminary field measurement was performed in June 2012, during which water level (WL) and electrical conductivity (EC) data were collected. WLs below the sea-level were observed on most of the studied area, with a minimum value of about -5 m a.s.l. in the inner part of the northern zone, where major exploitation is present. Moreover, a relative minimum of WL (about -2 m a.s.l.) is present near the shoreline in the southern zone. In the latter EC is diffusely high from shoreline up to 5 km apart and reaches a maximum value of about 7,000 μS/cm. Toward North a general EC decreasing is observed and values below 2,000 μS/cm are measured in most of water-wells. On a limited area close to the Arno River, values higher than 3,000 μS/cm are nevertheless present. Hydraulic conductivity values between E-03 and E-05 m/s were achieved by means of some slug and pumping tests performed on new piezometers. During this month other hydraulic tests will be performed, and monitoring of EC, T and WL will be started using automatic probes; at the same time, the pumping rates of major farms wells will be monitored. Furthermore, a water sampling field will be carried out in the next month, and the collected samples will be analysed in chemical elements and water isotopes. Thus, a first picture of the seawater intrusion and its causes will be available. References Doveri M., Giannecchini R. & Butteri M., 2010. Seawater intrusion in the Versiliese-Pisan coastal aquifer system (North-western Tuscany): results from a hydrogeologic-hydrogeochemical study. Salt Water Intrusion Meeting, Azores 2010. Proceedings SWIM21, 150-153.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/246165
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