A systematic approach to derive natural background levels in groundwater: Application to an aquifer in North Lebanon perturbed by various pollution sources

Abstract

Several efforts have recently emerged to develop methods capable of determining groundwater natural background levels (NBLs) due to their utmost importance in assessing water quality. A recently developed systematic approach to derive NBLs is the Khadra-Stuyfzand (KS) scheme. It has a clear and standardized flow with multi-steps to eliminate biased or contaminated samples, and hence it is capable of dealing with different pollution sources as well as saltwater intrusion. This method was applied to the Koura-Tripoli-Zgharta (KTZ) Miocene aquifer of coastal North Lebanon. It derived baseline conditions for 2 physical, 16 chemical, and 3 bacteriological parameters in addition to 8 trace elements, and 83 pesticides, polynuclear aromatic hydrocarbons, and volatile organic compounds. The results revealed the extent of anthropogenic shift from background levels, and delineated the main contaminated spots. In fact, the established groundwater baseline composition is typical of limestone aquifers with oligohaline-fresh, moderate alkalinity, calcium bicarbonate water, under freshening conditions. Nonetheless, this quality is locally degraded by microbial contamination due to wastewater disposal sites, saltwater intrusion, and minor nutrient loading from agricultural activities and/or urban development. The measured concentrations of major water ions and a variety of drinking water contaminants (e.g. nutrients, pesticides, hydrocarbons, and heavy metals) are below human health benchmarks, but the microbiological content at several spots has exceeded the permissible limits which renders the water unsuitable for domestic use, and calls for prompt mitigation measures.