Idrogeologia dell'area del Vulture (Basilicata)

The groundwaters of the Vulture volcanic area are widely known in Italy because they are bottled and commercialised as effervescent mineral waters. In this area many hydrogeological studies have been carried out, generally analysing particular aspects of the groundwater flow on a local scale only (CASORIA, 1901; MONGELLI, 1964; REINA, 1969; CIET & TAZIOLI, 1981; FIDELIBUS et alii, 1981; FUGANTI et alii, 1994). Instead systematic studies on the whole hydrogeological structure have only been recently carried out. Therefore in the hydrogeological knowledge of the Vulture there was a lack of an overall systematic scheme for groundwater flow, which could be useful for hydrogeological analysis applied to the assessment and protection of the groundwater resources. In this sense, the present paper can be considered the first contribution to a certainly complex and articulated knowledge development. Mount Vulture is a Pleistocene stratovolcano, located in the northeastern sector of the Basilicata region, along the external edge of the Apennine Chain, close to the Bradano river Miocene foredeep. Mount Vulture's volcanic structure developed during the period 730 and 130 kyr BP (BROCCHINI et alii, 1994), with a period of maximum activity from 800 kyr to 580 kyr BP (BOENZI et alii, 1987). Mount Vulture is different from the other volcanoes belonging to the Co-Magmatic Roman Province. In fact, it is the only one to be located along the eastern flank of the Apennine Chain, to have the hauyne as the dominant feldspathoid in the place of the leucite and to have lavas with a K 2 O/Na 2 O rate close to the HKS magma series. Moreover, the strontium isotopic composition is the lowest known among the potassic volcanic rocks of the continental part of Southern Italy (LA VOLPE & PRINCIPE, 1989a), besides remaining stable during the evolution of the volcano ( 8 7 Sr/ 8 6 Sr: 0,70563-626). The evolutional history of Mount Vulture can be outlined in three principal phases (BOENZI et alii, 1987). The hydrogeological data have been specifically surveyed through quantitative and qualitative monitoring carried out in a period between August and September 1999, which consisted of: a piezometric levels survey in more than 90 wells; the control of more than 40 springs; the interpretation of aquifer tests executed in 16 wells, the analysis and interpretation of stratigraphy of the same wells; the measure of stream discharge in 26 stream sections; the estimation of the mean hydrological budget (1964÷1994); the determination of the principal chemical and physical parameters in 65 water points. Results of hydrogeological surveys in the volcanic area of Mount Vulture, mainly carried out in the period August-September 1999, in combination with regional and local structural data, have allowed the deepening of the knowledge about general groundwater circulation. Two hydrogeologically independent groundwater basins have been found: Monticchio-Atella and Melfi-Barile. The Monticchio-Atella basin is confined between the most important faults of the volcano (Grigi valley-Corbo creek and Southern fault); the central part is the recharge area; the preferential outflow destinations (springs and stream channels) are located eastward in the Atella zone and westward in the Monticchio zone; the groundwater flow pattern is complicated by the presence of lakes; the dominant hydrogeochemical type is the sodium-bicarbonate; in the Monticchio area the acquifer has a relatively moderate transmissivity value (5÷10×10 - 3 m 2 /s), instead in the Atella area the highest transmissivity values have been estimated.