Natural and anthropogenic factors affecting groundwater quality of an active volcano (Mt. Etna, Italy) A. Aiuppa a , S. Bellomo a , L. Brusca b , W. D’Alessandro b, *, C. Federico b a Dipartimento CFTA, Universita ` di Palermo, via Archirafi 36, 90123 Palermo, Italy b Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, via La Malfa 153, 90146 Palermo, Italy Received 11 March 2002; accepted 28 July 2002 Editorial handling by H. A ´ rmannsson Abstract New geochemical data on dissolved major and minor constituents in 276 groundwater samples from Etna aquifers reveal the main processes responsible for their geochemical evolution and mineralisation. This topic is of particular interest in the light of the progressive depletion of water resources and groundwater quality in the area. Multivariate statistical analysis reveal 3 sources of solutes: (a) the leaching of the host basalt, driven by the dissolution of magma- derived CO 2 ; (b) mixing processes with saline brines rising from the sedimentary basement below Etna; (c) con- tamination from agricultural and urban wastewaters. The last process, highlighted by increased concentrations of SO 4 , NO 3 , Ca, F and PO 4 , is more pronounced on the lower slopes of the volcanic edifice, associated with areas of high population and intensive agriculture. However, this study demonstrates that natural processes (a) and (b) are also very effective in producing highly mineralised waters, which in turn results in many constituents (B, V, Mg) exceeding maximum admissible concentrations for drinking water. # 2002 Elsevier Science Ltd. All rights reserved. 1. Introduction Permeable volcanic rocks of the Mount Etna edifice cover an area of about 1200 km 2 that hosts one of the largest groundwater reserves of Sicily (Ogniben, 1966). The availability of reliable and substantial water resources and the fertility of volcanic soils, have brought about since ancient times the intense settlement and agricultural exploitation of the lower flanks of the vol- cano, especially along the Ionian coast. In the same areas during the last 30 a, building activity, both for primary and recreational needs, has rapidly increased, often without adequate planning. The enhanced anthro- pogenic pressure together with improved standards of living has substantially increased the demand for water. The consequence has been a greater exploitation of groundwater resources, which are the only available source, in this area, for drinking, agricultural and industrial purposes. Ferrara (1991) highlighted a pro- gressive lowering of the piezometric surface and the increase of the mineral content, particularly on the eastern flank of the volcano. The importance of the Etna groundwaters should not be understated because they are the only water resource for drinking and agri- cultural purposes not only for the people living in this area (700,000) but also for those who live in the sur- rounding areas, up to 50 km away (300,000). Mt. Etna’s groundwater quality is, in addition to anthropogenic activities, also influenced by volcanic activity. Due to the huge quantity of volcanic CO 2 , which partially dissolves in the aquifers enhancing rock weathering, many solutes exceed maximum admissible concentrations for drinking water (Giammanco et al., 1996, 1998). Sincethelate1980smanyhydrogeochemicalstudieson theEtnagroundwatershavebeenpublished (Anza` etal., 0883-2927/03/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0883-2927(02)00182-8 Applied Geochemistry 18 (2003) 863–882 www.elsevier.com/locate/apgeochem * Corresponding author. Fax: +39-091-6809449. E-mail address: walter@pa.ingv.it (W. D’Alessandro).