Fig. 1: Regional and site map with tritium (3H) and arsenic (As) distribution.
From: Arsenic contamination of Bangladesh aquifers exacerbated by clay layers
a Map of the field area and the focus site M. The small symbols denote the wells 45–90 m deep, surveyed in 2012–13 and color corded according to their As concentration measured using the ITS Arsenic Econo-Quick kit37,70. The large symbols denote the surrounding (2 km radius) community wells installed <90 m deep within a clay-capped low-As aquifer36 and are color coded to reflect the highest measured 3H concentrations in tritium units (TU), as reported in Mihajlov et al.48. The enlarged inset map of site M displays sampled multi-level well nest locations, an additional coring location, and the location of community well (CW12) where arsenic concentrations rose twice prior to reinstallation at a greater depth. b Time-series of As concentrations in groundwater at the well cluster M-Middle from 2011 to 2017 (41 m) or from 2011 to 2016 (other depths); 2011/2012 average As concentrations plotted on Fig. 3e are also shown.
