The issue of sustainable yield of some wells drilled in hard rocks of the Mediterranean Region was examined. The objective of the study was to verify which information may be obtained from the results of pumping tests in order to define the long-term well functioning. These aquifers might play a strategic role in drinking and irrigation water supplies for the Mediterranean Region in a near future.
Data analyzed concern results of pumping tests performed in three areas with similar climate conditions, which differ in hard-rock type (intrusive, effusive and metamorphic rocks). The pumping data were interpreted with analytical techniques and commercial software. This allowed to recognize three main drawdown trends, coherent with three hydrogeological settings: i) delayed response coherent with the presence of double porosity; ii) rapid increase of drawdown coherent with the presence of a barrier boundary, iii) stabilization of the water level over time coherent with the presence of a recharge boundary. On the basis of the identified trends and hydraulic parameters, different pumping scenarios were simulated through available analytical solutions and finite difference flow model.
The transmissivity values derived from the pumping tests cover two orders of magnitude and permit to categorize the hard rocks in the classes III and IV according to Krásný’s classification. The storativity is included in a wider range of values. The previous hydraulic properties, together with the simultaneous response to pumping of the drawdown for the piezometer (or piezometers) and the pumped well, may permit to treat the aquifer as a porous equivalent medium at the volume scale of the pumping test. All these properties, associated with an appreciable aquifer recharge, make these aquifers of interest for the local water supply. In this regard, some suggestions to define the sustainable yield of a single well may be derived from the comparison of results of pumping tests with the performed simulations. The results show that the long-term trend in the drawdown and the initial thickness of the aquifer constrain the sustainable yield of a well. In the worst cases examined, the sustainable well yield is from 1 to 2 L/s. These well discharge values are significant if compared with those found in other regions of the world.