Unusual behaviour of epikarst in the Acqua dei Faggi carbonate aquifer (Southern Italy) Emma Petrella, Paolo Capuano and Fulvio Celico Dipartimento di Scienze e Tecnologie per l’Ambiente e il Territorio, Universita ` degli Studi del Molise, Contrada Fonte Lappone, 86090 Pesche (IS), Italy Introduction The epikarst is the uppermost zone of carbonate rocks in which the per- meability due to fissuring and diffuse karstification is substantially greater, when compared with the underlying main vadose zone (Klimchouk, 1997). The increase in fracture density and diffuse karstification are mainly due to rock decompression and biochemical processes such as dissolution and widening of fractures caused by plant roots. The epikarst was defined and characterized through different approaches. From the hydrogeologi- cal point of view, Mangin (1975, 1994) developed a functional model by ana- lysing time series of spring discharge, while Drogue (1992) and Kiraly (1975) developed a structural model based on thorough knowledge of the aquifer geometry and hydraulic pro- perties. In some cases, the description of the epikarst was also based on morphological observations (Klim- chouk, 2000). The epikarstic zone was schematized by several authors (e.g. Mangin, 1975, 1994; Gunn, 1981; Williams, 1983, 1985; Klimchouk, 2000; Perrin et al., 2003; Perrin, 2003). Some hydraulic characteristics are in common with their models: • hydraulic conductivity is high and quasi-uniform at the surface and within the top of the epikarst but rapidly diminishes with depth; • diffuse infiltration which dominates in the top of the epikarstic zone is much easier than drainage out of it due to fissure density and diffuse karstification decrease with depth; • consequently, percolation retention and water storage in a perched aquifer temporary occurs in the epikarst; • this perched aquifer has an import- ant lateral flow component because it flows towards the nearest vertical fissure; this ÔfunnellingÕ effect can explain nervous hydraulic responses at karst springs. In Southern Italy, the existence of a thin near-surface high conductivity layer in carbonate aquifers was hypothesized based on Lugeon test results (Celico et al., 1986), but no studies were carried out in order to analyse its hydrogeological beha- viour. The main purpose of this study was to characterize the epikarst in a car- bonate test site in Southern Italy in order to compare its hydrogeological behaviour with those described in European karst aquifers. The test site is an interesting aquifer, in the South- ern Apennines, where it is possible to analyse groundwater level fluctuations in the near-surface carbonate rocks. The research was carried out through hydrogeological and geophysical surveys. Description of the field site The Acqua dei Faggi carbonate aquifer (Matese, Longano, Southern Italy) consists mainly of limestone (Creta- ceous-Oligocene; De Corso et al., 1998). The rocks have very low primary permeability but they are extensively fractured and subordinately karstified (Celico et al., 2004). The saturated aquifer comprises more than 100 m of limestone, while the unsaturated med- ium is made up of limestone and soil. In the test area (1014 m a.s.l.) a Pachi- Vitric Andosols crops out (Soil Refer- ence Base; FAO, 1988) up to 5 m thick. The unconfined aquifer (Fig. 1) is bordered by low-permeability marls and clays and/or normal faults which have produced significant cataclastic zones. The groundwater flows west- wards to spring ÔAÕ (980 m a.s.l.) which has an average annual dis- charge of about 0.04 m 3 s )1 during the research period. Within the aqui- fer, the lower permeability of some fault cores causes a discontinuous heterogeneity although a significant groundwater flowthrough and a good interdependence of piezometric heads upgradient and downgradient of the faults were observed. On the whole, the aquifer looks like a basin-in-series system (Celico et al., 2006). Data and methodology A large borehole (LB in Fig. 1 and Table 1) was continuously cored in order to detect fractures of wide ABSTRACT Hydrogeological and geophysical investigations demonstrated the existence of an epikarstic zone in a carbonate aquifer of Southern Italy, about 10 m thick. Nevertheless, the hydro- geological behaviour of the epikarst is different from that schematized by several authors. In the test site, the contrast in permeability at the bottom of the epikarst does not cause retention of percolation and storage of water in a perched temporary aquifer within the uppermost portion of the carbonate medium. Because of the high fracture density and good interconnection of openings within the underlying lime- stone, the percolation is diffuse also below the epikarstic zone, as well as the groundwater flow. The ‘funnelling’ effect into larger shafts does not play an important role on the hydro- geological behaviour of the aquifer. Terra Nova, 19, 82–88, 2007 Correspondence: Emma Petrella, Diparti- mento di Scienze e Tecnologie per l’Ambi- ente e il Territorio, Universita` degli Studi del Molise, Contrada Fonte Lappone, 86090 Pesche (IS), Italy. Tel.: +39 0874 404121; fax: +39 0874 404123; e-mail: emma.petrella@unimol.it 82 Ó 2007 Blackwell Publishing Ltd doi: 10.1111/j.1365-3121.2006.00720.x