Separating baseline conditions from anthropogenic impacts: example of the Damour coastal aquifer (Lebanon)

Abstract

A new structured approach is presented to derive groundwater baseline conditions, in this case for a dolomitic limestone aquifer suffering from salinization and other anthropogenic impacts. It builds on the HydroChemical System Analysis (HCSA) to map different groundwater bodies (hydrosomes) and hydrochemical zones within them, each of which show significant differences in baseline conditions. It also comprises a rigorous elimination scheme for samples affected by bias or pollution. The method is applied to the Damour coastal aquifer system, south of Beirut (Lebanon). Concentrations of Cl, Cl/Br, 2 H, 18 O and Ca/Sr were used to discern five hydrosomes and to determine mixing ratios. The dominant hydrochemical facies was (sub)oxic, calcareous and salinized, indicating a very low reduction capacity of the aquifer system, strong dissolution of dolomitic limestone and clear traces of seawater encroachment. The method proposed was capable of filtering out baseline conditions for 16 main constituents, 64 trace elements and two isotopes. Séparer conditions originelles et impacts anthropiques: l'exemple de l'aquifère côtier de Damour (Liban) Résumé Nous présentons une nouvelle approche structurée de détermination des conditions originelles des eaux souterraines, ici pour un aquifère calcaire dolomitique subissant une salinisation et d'autres impacts anthropiques. Il s'appuie sur l'Analyse de Système Hydrochimique pour cartographier différentes structures d'eaux souterraines (hydrosomes) et des zones hydrochimiques en leur sein, chacune d'elles montrant des différences importantes de ses conditions originelles. Il comprend également un système d'élimination rigoureuse des échantillons affectés par des biais ou par la pollution. La méthode a été appliquée au système aquifère côtier de Damour, au sud de Beyrouth (Liban). Cl, Cl/Br, 2 H, 18 O et Ca/Sr ont été utilisés pour identifier cinq hydrosomes et déterminer des coefficients de mélange. Le faciès hydrochimique dominant est suboxique, calcaire et salé, indiquant une très faible capacité de réduction du système aquifère, une forte dissolution du calcaire dolomitique et des traces évidentes d'intrusion d'eau de mer. La méthode proposée a été capable de retrouver les conditions originelles pour 16 constituants principaux, 64 éléments traces et deux isotopes.

Problems and promise of managed recharge in karstified aquifers: the example of Lebanon

“…According to a survey conducted in 2011, wells within about 350 m from the channel (Figure S3, Supplementary Material) intercept bank-filtrated water as confirmed by δ 18 O (the ratio of oxygen-18 and oxygen-16) and chloride for a mixture of three end-members (river, local rain and infiltrated ocean water). These wells receive > 50% river water contribution (Khadra & Stuyfzand, 2014), summing up to a total discharge of about 3300 m 3 /d, a value that was corroborated by 3-D numerical modeling (Khadra & Stuyfzand, 2018).…”

Cadmium Background Levels in Groundwater in an Area Dominated by Agriculture

“…They can explain elevated contents of potential pollutants and possible sources of components in groundwater. Several approaches to groundwater classification and source separation exist (e.g., Khadra and Stuyfzand ; Liesch et al ; Hepburn et al ).…”

“…Bivariate statistics, such as correlation analysis, were performed in some studies to reveal the same behavior and thus the origin of trace metals in groundwater (Liesch et al ; Lu et al ). More advanced techniques include multivariate statistics, such as cluster analysis (Flem et al ), factor analysis (Huang et al ), and multicriteria evaluation (Banning et al ; Khadra and Stuyfzand ). According to Hinsby et al (), potential outliers can be identified by, for example, using ionic balance or indicator parameters such as nitrate.…”

Mitigation of saltwater intrusion by ‘integrated fresh-keeper’ wells combined with high recovery reverse osmosis

“…It is a main source of water providing one third of Beirut and its suburbs demands, and has been extensively pumped since 1991 with a total abstraction rate of about 13.5 Mm 3 /year. A description of the hydrogeological setting of this area is available from Khadra and Stuyfzand (2014). Upconing was recorded at different spots.…”

“…2). Recharge to the aquifer was variable on monthly basis according to rainfall data (Table S2, Supplementary Material) (Meteorological Service 2010) with a 40% infiltration coefficient; chloride concentration of recharge water was assigned a constant value of 30 mg/L as deduced from average chloride in rainfall (11 mg/L) and average evapo-concentration factor in the study area (Khadra and Stuyfzand 2014). Noteworthy that SEAWAT sets the recharge to the uppermost active (wet) layer.…”