Groundwater flow in E and NE part of Bohemian Cretaceous Basin (3H, 14C and SF6 tracers, nitrate content): mean residence time and question of effective contamination monitoring

 

Zdenka Churáčková, Jiří Bruthans, Vladimír Lachman, Vojtěch Musil, Renáta Kadlecová

Geoscience Research Reports 43, 2010 (GRR for 2009), pages 283–287

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Abstract

Tritium activity, nitrate content and in 17 cases SF6 was measured in samples of 22 springs and 46 wells in limy sandstones and spiculitic marlstone aquifers in E and NE part of Bohemian Cretaceous Basin. Based on the study, aquifer could be split into two parts: A) Flow zones with mean residence time in decades, having high nitrate content and sometimes carrying trace amounts of organic pollutants. Water from these zones was sampled in springs and intensively pumped wells. B) Stagnant zones with negligible flow rates, residence time in centuries or millennia, have nitrate content often below detection limit due to denitrification. Most of the monitoring wells are situated at the B type of the environment. Previously published water residence times based on radiocarbon dating (up to 11.5 kyr BP) are concerning the B type of the environment and are possibly biased too old (real mean residence time of water may be much lower than apparent radiocarbon age).