The gravelly horizon of the Pisa plain multilayered system, located at a depth between 50 and 100 m under the sea level and about 10-20 m thick, is a confined aquifer tapped by a large number of wells. It contains a very important water resource for drinking, industrial and irrigable uses, although in some cases the groundwater is of poor quality. In order to evaluate if in the coastal area between Arno River and Scolmatore Canal this aquifer is interested by seawater intrusion and to know the mixing mechanisms with fresh water, a multidisciplinary study was carried out by means hydrostratigraphic correlations, water level collection and chemical and isotopic analysis. In particular, three on-site surveys were carried out in June and August 2008 and April 2009. In each point measured, piezometric values below the sea level were collected; particularly depressed levels were registered in August 2008 in the southern part of the study area. Water-wells sampled along the coast, less than 1.5 km far from the coastline, show chemical composition and 18O/16O ratios indicative of seawater-fresh water mixing. This phenomenon, in agreement with piezometric conditions, is more evident in the southern zone, toward the Scolmatore Canal, where the fraction of salt water, calculated using the mass balance model of Cl, Br and 18O/16O ratio, is about 7-8%. The most part of the other samples, collected up to 5 km from the coastline, was not interested by seawater; in these cases, groundwater shows the same characteristics found toward the internal part of the Pisa plain, with relatively low TDS and 18O/16O ratios indicative of recharge average altitudes higher than local altitudes. Only two samples, collected near the Arno River, showed chemical and isotopic characteristics indicative of a seawater presence. In these cases 18O/16O ratios values show clearly that the seawater intrusion does not directly happen in the gravelly aquifer but trough the shallow sandy aquifer which in this zone is in contact with the gravel
Hydrogeologic-hydrogeochemical multidisciplinary study of the gravel confined aquifer in the coastal Pisan Plain (Tuscany) between the Arno River and Scolmatore Canal (Tuscany)
Doveri M.;GIANNECCHINI, ROBERTO;
2009-01-01
Abstract
The gravelly horizon of the Pisa plain multilayered system, located at a depth between 50 and 100 m under the sea level and about 10-20 m thick, is a confined aquifer tapped by a large number of wells. It contains a very important water resource for drinking, industrial and irrigable uses, although in some cases the groundwater is of poor quality. In order to evaluate if in the coastal area between Arno River and Scolmatore Canal this aquifer is interested by seawater intrusion and to know the mixing mechanisms with fresh water, a multidisciplinary study was carried out by means hydrostratigraphic correlations, water level collection and chemical and isotopic analysis. In particular, three on-site surveys were carried out in June and August 2008 and April 2009. In each point measured, piezometric values below the sea level were collected; particularly depressed levels were registered in August 2008 in the southern part of the study area. Water-wells sampled along the coast, less than 1.5 km far from the coastline, show chemical composition and 18O/16O ratios indicative of seawater-fresh water mixing. This phenomenon, in agreement with piezometric conditions, is more evident in the southern zone, toward the Scolmatore Canal, where the fraction of salt water, calculated using the mass balance model of Cl, Br and 18O/16O ratio, is about 7-8%. The most part of the other samples, collected up to 5 km from the coastline, was not interested by seawater; in these cases, groundwater shows the same characteristics found toward the internal part of the Pisa plain, with relatively low TDS and 18O/16O ratios indicative of recharge average altitudes higher than local altitudes. Only two samples, collected near the Arno River, showed chemical and isotopic characteristics indicative of a seawater presence. In these cases 18O/16O ratios values show clearly that the seawater intrusion does not directly happen in the gravelly aquifer but trough the shallow sandy aquifer which in this zone is in contact with the gravelI documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
