×

Warning

JUser: :_load: Unable to load user with ID: 291
July 27, 2016

« All News

Geosyntec's Ivan Mihajlov Published in Water Resources Research

Ivan Mihajlov (California) published a research article entitled "Recharge of low-arsenic aquifers tapped by community wells in Araihazar, Bangladesh, inferred from environmental isotopes" in Water Resources Research an AGU Journal, Volume 52, Issue 5, pages 3324-3349, May 2016.

This article is an outgrowth of Ivan's Ph.D. research at Columbia University and is a significant step forward in the evaluation of groundwater conditions in Bangladesh, where a large rural population is exposed to potentially harmful levels of arsenic in groundwater.

In the article, he and his colleagues applied a broad spectrum of isotopic and chemical data in an assessment of both the quality and age of various portions of the aquifer. This process involved an exhaustive field sampling program that required overcoming significant logistical hurdles related to both the site location and local politics. Ivan and his colleagues combined radiocarbon (14C) dating of dissolved inorganic carbon in groundwater with the measurements of dissolved noble gases and tritium (3H) concentrations to evaluate groundwater ages.

The dataset resulting from these efforts successfully demonstrated that the aquifer can be differentiated into discrete depth zones, each bearing unique chemical profiles and ages. These findings establish both a rigorous protocol for differentiating portions of the region's aquifer while also yielding key data for the future positioning of groundwater monitoring and extraction systems in this vital water source.

Abstract

More than 100,000 community wells have been installed in the 150–300 m depth range throughout Bangladesh over the past decade to provide low-arsenic drinking water (<10 µg/L As), but little is known about how aquifers tapped by these wells are recharged. Within a 25 km2 area of Bangladesh east of Dhaka, groundwater from 65 low-As wells in the 35–240 m depth range was sampled for tritium (3H), oxygen and hydrogen isotopes of water (18O/16O and 2H/1H), carbon isotope ratios in dissolved inorganic carbon (DIC, 14C/12C and 13C/12C), noble gases, and a suite of dissolved constituents, including major cations, anions, and trace elements. At shallow depths (<90 m), 24 out of 42 wells contain detectable 3H of up to 6 TU, indicating the presence of groundwater recharged within 60 years. Radiocarbon (14C) ages in DIC range from modern to 10 kyr. In the 90–240 m depth range, however, only five wells shallower than 150 m contain detectable 3H (<0.3 TU) and 14C ages of DIC cluster around 10 kyr. The radiogenic helium (4He) content in groundwater increases linearly across the entire range of 14C ages at a rate of 2.5 × 10−12 ccSTP 4He g−1 yr−1. Within the samples from depths >90 m, systematic relationships between 18O/16O, 2H/1H, 13C/12C, and 14C/12C, and variations in noble gas temperatures, suggest that changes in monsoon intensity and vegetation cover occurred at the onset of the Holocene, when the sampled water was recharged. Thus, the deeper low-As aquifers remain relatively isolated from the shallow, high-As aquifer.

More Information

For more information regarding the article, please visit: Water Resources Research

For more information on low-arsenic aquifers, contact Ivan Mihajlov at This email address is being protected from spambots. You need JavaScript enabled to view it..