Abstract
The thermal waters of the Island of Ischia, an active volcano located in Southern Italy, are widely used for supplying numerous spas. Groundwater withdrawals occur mainly through wells in the coastal strip. This study explores the impact of withdrawals on the quality of the waters used in thermal facilities, which is required to be constant in terms of composition and temperature by law. For this purpose, specific investigations were conducted including 155 pumping tests, 124 water temperature measurements during pumping tests, 31 temperature and electrical conductivity logs and periodic chemical analysis of the waters of 21 selected wells. By comparing the response to pumping of the aquifer and the quality of the water extracted from the wells, it turned out that the quality of groundwater supplying spas depends not only on natural phenomena (meteoric recharge, seawater intrusion, and rising of deep hydrothermal fluids) but also relies on the island sector where groundwater is pumped and on the pumping method. The distance of the wells from the coast, the type of aquifer formation intersected by the wells, and the field of groundwater temperature of the hydrothermal system strongly affect the aquifer pumping response, determining the quality of water extracted from wells and its variation over time. In Ischia, techniques and regimes of groundwater withdrawals should adapt to the local aquifer pumping response, more than in another hydrogeological context. The concomitant analysis of drawdown, water temperature, and salinity during pumping turned out to be a valuable tool to define the sustainable yield of the single well.
Highlights
The Island of Ischia, an active volcano located in the Gulf of Naples, has a long tradition in the use of its groundwaters as a resource for health, wellness, and recreational tourism
Specific capacity spans over 4 order of magnitude (10−5 –10−1 m2 /s) and shows a log-normal frequency distribution (Figure S2)
The transmissivity values obtained from the recovery test (Tr) were compared with specific capacity (SC)
Summary
The Island of Ischia, an active volcano located in the Gulf of Naples (southern Italy, Figure 1), has a long tradition in the use of its groundwaters as a resource for health, wellness, and recreational tourism. Water 2020, 12, 2576 centers, available on a surface area of 46 km. Water 2020, 12, 2576 centers, available on a surface area of 46 km2 Such activities sustain directly or indirectly the economy of the island [1]. The groundwater withdrawals for the supply of the thermal and recreational centers are mainly distributed in the coastal strip of the island (Figure S1) and occur through 244 wells and from 20 springs [2]
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