SAVING LIVES WITH A PIPER DIAGRAM IN SRI LANKA

A chronic kidney disease of unknown origin (CKDu) kills over 2,000 Sri Lankan’s annually, almost exclusively in groundwater-dependent areas of the country (“Dry Zone”). CKDu disproportionately affects older males in rural agricultural settings. The very strong geographic correlation between CKDu and Dry Zone indicates an environmental factor must be a major contributor to disease incidence. Some villages in the Dry Zone are relatively free of CKDu, and at least some of these utilize nearby springs rather than the deeper water wells used elsewhere. This suggests that variability in ground-water composition contributes to variability in CKDu incidence at a very local level. If true, then very simple tools such as Piper diagram groundwater classification may allow avoidance of apparently higher risk groundwaters, and incidentally guide the placement of village-scale reverse osmosis (RO) water treatment plants.

Dry Zone aquifers are composed of weathered metamorphic regolith, underlain by spheroidally weathered metamorphic rock, and finally fractured metamorphic rock at depths of 50-70 m. Groundwater is typically extracted from this depth. Thickness of the fractured rock aquifer is highly variable, forming quite localized groundwater basins. Those basins in turn can exhibit quite different hydrochemical facies, likely depending on the nature of the poorly exposed bedrock.

Results from a temporal monitoring network at a limited number of sites indicate two main groundwater types, CaMgHCO₃^- meteoric dominated waters with lower TDS, and more bedrock influenced NaCl waters with generally higher TDS. Very little mixing is observed between these two types, and in the study area, the MgHCO₃^- waters appear to be associated with the presence of granitic gneiss and reduced prevalence of CKDu. Conversely, NaCl waters are associated with the predominant charnockite lithology, and increased prevalence of CKDu. We propose analysis of waters from some 360 government-installed wells in the Dry Zone, with the idea of identifying zones of greater environmental risk for CKDu. Water from these areas could be avoided for consumption, and installation of small RO plants encouraged, hopefully reducing the risk of this growing yet mysterious disease in Sri Lanka.