Interaction between shallow and deep aquifers in the Tivoli Plain (Central Italy) enhanced by groundwater extraction: A multi-isotope approach and geochemical modeling

• Published in: Applied geochemistry 2012, Vol.27 (1), p.266-280
• Main Authors: Carucci, Valentina, Petitta, Marco, Aravena, Ramon
• Format: Article
• Language: English
• Subjects: Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Geochemistry; Pollution, environment geology
• ISSN: 0883-2927; 1872-9134
• DOI: 10.1016/j.apgeochem.2011.11.007

► Groundwater mixing in travertine aquifer has been enhanced by groundwater extraction. ► Chemical and isotope tracers distinguish different sources and groundwater flowpaths. ► Geochemical modeling results confirm a conceptual model inferred from collected data. ► Previous equal contribution from different sources is changing now in a 1:2 proportion. ► Geochemical changes along flowpaths evidence that the aquifer is a dynamic system. In the Tivoli Plain (Rome, Central Italy) the interaction between shallow and deep groundwater flow systems enhanced by groundwater extraction has been investigated using isotopic and chemical tracers. A conceptual model of the groundwater flowpaths has been developed and verified by geochemical modeling. A combined hydrogeochemical and isotopic investigation using ion relationships such as DIC/Cl −, Ca/(Ca + Mg)/SO 4/(SO 4 + HCO 3), and environmental isotopes ( δ 18O, δ 2H, 87Sr/ 86Sr, δ 34S and δ 13C) was carried out in order to determine the sources of recharge of the aquifer, the origin of solutes and the mixing processes in groundwater of Tivoli Plain. Multivariate statistical methods such as principal component analysis and Cluster analyses have confirmed the existence of different geochemical facies and the role of mixing in the chemical composition of the groundwater. Results indicate that the hydrochemistry of groundwater is characterized by mixing between end-members coming directly from carbonate recharge areas and to groundwater circulating in a deeply buried Meso-Cenozoic carbonate sequence. The travertine aquifer is fed by both flow systems, but a local contribution by direct input in the Plain has also been recognized. The stable isotope data ( 18O, 2H, 13C and 34S) supports the flow system conceptual model inferred from the geochemical data and represents key data to quantify the geochemical mixing in the different groundwaters of the Plain. The results of numerical modeling (PHREEQC) are consistent with the flowpaths derived from the hydrogeochemical conceptual model. The inverse models performed generated the main geochemical processes occurring in the groundwater flow system, which also included mixing. Geochemical and isotope modeling demonstrate an increasing influence of groundwater from the deeply buried aquifer in the travertine aquifer, enhanced by lowering of the travertine aquifer water table due to quarry pumping.