Assessment of aquifer age and replenishment rate by utilizing 36 Cl-pulse

Abstract EN

The present study aims at estimating the residence-time of groundwater based on bomb-produced 36Cl.

Water samples were collected from some selected wells located around Al-Zulfi province, Riyadh central region, Saudi Arabia.36 The Cl/Cl ratios in the water samples were determined by Inductively Coupled Plasma Mass Spectrometry (ICPMS) and Liquid Scintillation Counting(LSC).36 The Cl/Cl ratios in the groundwater were estimated to be 1.0–2.0×10−10.

The shallow unconfined aquifer of the area is mainly replenished by the water infiltration from the seasonal rains.

Estimates of residence time were obtained by comparing the measured bomb-derived36 Cl concentrations in groundwater with the background reference.

Dating based on a 36Cl bomb pulse may be more reliable and sensitive for groundwater recharged before 1975, back as far as the mid-1950s.The above 36Cl-background concentration was deduced by determining accurately the background corrected Dye-3 ice core data from the frozen Arctic Data, according to the estimated total36Cl resources, including bomb-produced36 Cl fallout.

An estimated residence time of 7.81×104 y was obtained from extrapolated flow velocity.

It was noticed that 36Cl concentration in groundwater does not reflect the input of bomb pulse36 Cl, it belongs to the era before 1950.