Abstract

SANCHEZ-MURILLO, Ricardo et al. ^{_{Spatial variation of 222Rn composition within the Barva and Colima superior aquifers, Costa Rica}}. Rev. Geol. Amér. Central [online]. 2016, n.55, pp.147-165. ISSN 0256-7024.  http://dx.doi.org/10.15517/rgac.v55i0.27072.

Radon (222Rn) is a useful natural-occurring tracer to elucidate groundwater to surface water connectivity with important implications for human health. This study presents the first spatial distribution of 222Rn in groundwater, surface water, and tap water within the Barva and Colima Superior aquifers of the Central Valley of Costa Rica. Forty samples were analyzed for 222Rn, δ18O, and in situ electrical conductivity, water temperature, pH, and redox potential. High elevation springs presented a nearly-uniform 222Rn composition (21,3±17,5 Bq/L). In groundwater wells, 222Rn composition ranged from 2,0 up to 50,5 Bq/L. High 222Rn concentrations in groundwater could be attributed to natural degasification within the local faults system. Tap water 222Rn concentration ranged from 4,7 up to 30,8 Bq/L. These concentrations are greater than the maximum contaminant level (11,1 Bq/L) proposed by the Environmental Protection Agency of the United States of America for drinking water purposes. The use of intermediate water storage tanks prior to the distribution to residential areas could improve water aeration and facilitate longer residence times resulting in lower 222Rn levels. A nation-wide assessment is still required with particular interest in areas near active faults and volcanic activity.

Keywords : Costa Rica; Barva and Colima Superior aquifers; ²²²Rn; δ¹⁸O; natural-occurring radioactivity; faults.

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