The impact of domestic wastewater effluent on karst aquifers

Karst aquifers are exceptionally vulnerable to pollution (as a result of rapid recharge of water from the surface and strong aquifer heterogeneity) and may be impacted by multiple contamination sources. In rural and suburban areas, human wastewater effluent and agricultural sources are mostly considered among the most significant threats to groundwater quality. The main wastewater treatment options for rural and suburban communities which lack access to centralized wastewater treatment are split between septic tanks, latrines and other improved on-site wastewater treatment systems. Previous studies have found that the effectiveness of on-site wastewater treatment systems in treating domestic wastewater varies widely, depending on local soil attenuation capabilities, system design, installation and maintenance. Consequently, the potential impacts of such wastewater effluent, especially in cases of inadequate performance of these decentralized treatment systems, are microbial and chemical pollution of aquifers and/or surface water. As karst groundwater is a major source of drinking water for at least one-quarter of the world’s population it makes protection and management of karst aquifers extremely important. This paper presents the results of research being conducted using a range of methodologies in order to determine and quantify domestic wastewater pollution impacts on karst springs. A number of karst springs in Ireland have been sampled over time for quantification and identification of microplastic particles using Fourier-transform infrared spectroscopy (FTIR), for the analysis of fluorescent whitening compounds (FWCs; well-known indicators of human contamination since their origin is mostly from laundry detergents), and for the analysis and interpretation of specific anion ratio signatures (e.g. Cl:Br). A significant correlation between microplastic particle counts and detected FWCs signals at different karst springs has been found which suggests the majority of found microplastic particles to be from wastewater effluent and helps to understand the contribution of household-derived contaminants to this environmental problem. Moreover, some limitations were found in terms of the capability of Cl:Br ratio method in determining human wastewater impacts on karst aquifers.