Groundwater offers an important source for drinking water around the world; however, groundwater quality is under increasing pressure and is particularly vulnerable in karst areas. Total organic carbon (TOC) is significantly related to groundwater quality and when not removed by water treatment processes can give rise to the formation of disinfection by-products trihalomethanes (THMs) above the level of compliance. This study investigated the source of organic matter giving rise to the THM exceedances in a groundwater supply in a karst area. Results highlighted that source water for this groundwater supply was prone to surface water infiltration linked to rainfall events; was not accurately captured in the zone of contribution (ZoC); had inadequate treatment of natural organic matter (NOM) and suffered THM exceedances in 45% of sampling events. THMs were mostly represented by chloroform and caused by terrestrial delivered reprocessed organic matter. This work will support water managers tasked with decision-making.
Keywords: Drinking water; Granular activated carbon; Groundwater; Karst; Source protection zones; Trihalomethanes.