Groundwater mixing following the flow paths and topography iscomplicated by the lithologic complexity. An uncommon,highly depleted stable isotope and zero-3H groundwater, observed in a nearly east – west stretch through the central sector ofthe catchment, is coincident with the Filwoha Fault zone. Here, deep circulating meteoric water has lost its isotopic contentthrough exchange reactions with CO2originating at deeper sources or it has been recharged with precipitation from a differentrainfall regime with a depleted isotopic content. Copyright2006 John Wiley & Sons, Lt