GH22A-02 - Groundwater arsenic hotspots in Ayeyarwady (Irrawaddy) delta of Myanmar – implications for rural water supplies

Myanmar is following the example of its neighbors, which removed widespread mortality linked to (surface) water-borne diseases by utilizing pathogen-free groundwater in rural areas. However, there is a significant knowledge gap about the rural water quality. The Ayeyarwady delta, which spreads over three administrative regions and homes ca. 12 million people, is similar to other Asian deltas with regards arsenic concentrations in groundwater being a widespread threat to human health. The ongoing government program of ‘safe water for all by 2030’ may be in jeopardy if the occurrences of unsafe arsenic levels in tubewells and areas that are at-risk due to sparse data are not constrained promptly. In other Asian deltas, reductive dissolution of iron minerals under anoxic aquifer conditions, fueled by organic carbon, is the main mechanism for producing high levels of arsenic in groundwater. Hydrology of pathways of organic carbon within aquifers are therefore important control on arsenic hotspots in a large polluted region. Here, we analyze NASA Shuttle Radar Topography Mission 30m digital elevation model data and satellite imagery to identify drainage density variation across the entire Ayeyarwady delta. Eighty private wells (up to 215 m deep) are sampled along a 170 km traverse in length running from western limit to eastern end of the delta. The data show that arsenic hotspots are located where drainage density is relatively high, i.e. areas with abundant organic carbon with pathways to underlying aquifers. However, in comparison with other Asian deltas, the magnitude of arsenic concentrations in groundwater is relatively lower along with the number of high arsenic (>50 μg/l) wells. A similar pattern is found in the national screening data, in which only 8% (n=123962) of the wells exceed 50 μg/l (the local regulatory limit). It is also apparent that some hydrogeochemically-similar wells are polluted while others are safe, which demonstrates the importance of improving local hydrobiogeochemical understanding. A blanket-screening program (at least in hotspot areas) would be an important first step in minimizing the threat to public health.