T103 Ground Water Age Dating: Current Issues and Applications

Monday, 23 October 2006
1:30 PM - 5:30 PM

ENVIRONMENTAL TRACER APPLICATIONS IN AQUIFERS IN AQUIFERS WITH ELEVATED AS CONCENTRATIONS IN BANGLADESH

Paper number: T103-7
Program: Technical Sessions
Time: 3:00 PM – 3:15 PM

Authors

Abstract

Distributions of 3H/3He, atmospheric noble gases, CFCs, and SF6 were determined in aquifers in Bangladesh with elevated dissolved Arsenic concentrations. Tracer distributions provide evidence for degassing during recharge and rapid recharge caused by flooding. Comparison of groundwater 3H+3He data with 3H concentrations in precipitation suggests that some samples are affected by mixing with pre-bomb groundwater. CFC 11 and 12 concentrations in this reducing environment decline rapidly as a function of 3H/3He age at rates of ~0.4 to ~6 yr-1 and from ~0.25 to ~5 yr-1, respectively. SF6 ages were generally higher than 3H/3He ages, most likely due to interactions with subsurface gas phases. SF6 was found in 3H-free deeper groundwater indicating the occurrence of natural SF6 in Bangladesh aquifers. 3H/3He-derived recharge rates are consistent with hydraulic estimates. A tight relationship between arsenic and groundwater age implies that hydrogeology plays an important role in determining the variability of Arsenic concentrations in Bangladesh.