Geostatistical Assessment of Groundwater Nitrate Contamination with Reflection on DRASTIC Vulnerability Assessment: The Case of the Upper Litani Basin, Lebanon

Abstract

Groundwater constitutes the largest single source of fresh water in many parts of the world and provides a risk buffer to sustain critical water demands during cyclic and prolonged dry periods, especially in semi-arid and arid regions. However, unprecedented socio-economical growths are threatening the viability of these precious resources through fast depletion of already critically low stocks accompanied by persistent degradation of water quality due to salinization, and contamination by pesticides and fertilizers, urban sewage and industrial waste. These circumstances are particularly true of the Upper Litani Basin (ULB), which houses over 500,000 of Lebanon's 4 million population and provides the bulk of the country's agricultural output. Uncontrolled urban, agricultural and industrial growths following a prolonged civil strife and foreign occupation have resulted in the deterioration of the quality of the basin's surface water and potentially its groundwater resources. An assessment study of groundwater quality conditions in the ULB was conducted in support of efforts to manage water quality in the basin. Geostatistical analysis of groundwater nitrate levels was conducted using data collected through an extensive basin-wide water quality survey sponsored by the USAID and covered two periods representing the summer and winter periods. The results of analysis include maps of nitrate contamination and probability of exceedance of drinking-water nitrate regulatory limit. The results indicate a significant, widespread and persistent nitrates contamination of groundwater in the ULB. Nitrate levels in groundwater exceed standard limits for drinking water in many parts of the basin. These findings were examined with respect to those of a DRASTIC groundwater vulnerability assessment conducted by the USAID BAMAS project. Comparative analysis of the two assessments shed the light on several issues related to the application and interpretation of DRASTIC scores and the groundwater nitrate contamination process.

Hot Spots and Persistence of Nitrate in Aquifers Across Scales

“…For instance, Assaf and Saadeh [24] analyzed groundwater nitrate-N levels using a geostatistical approach and demonstrated maps of the persistence of nitrate-N contamination in groundwater in Upper Litani Basin in Lebanon [24]. Similarly, a principal component analysis (PCA) and K-means clustering technique was used to analyze the temporal evolution of groundwater composition [25].…”

Chemometric evaluation of nitrate contamination in the groundwater of a hard rock area in Dharapuram, south India

“…Due to its mobility, it can travel long distances and pollute the groundwater easily (Assaf and Saadeh 2009). Nitrate contamination is predominant in the states of India such as Punjab, West Bengal, Andhra Pradesh, Tamil Nadu and Delhi, which have a major incidence of nitrate contamination.…”

Origines et modélisation de la minéralisation des eaux du Quaternaire d’Abidjan (Sud de la Côte d’Ivoire)

“…L'examen de l'allure du variogramme donne des renseignements sur la nature des variations. Aussi, ses paramètres que sont la portée (a), le palier (C) et l'effet de pépite (C 0 ) rendent compte de l' échelle d' investigation et de l' amplitude de ces mêmes variations (Assaf et Saadeh, 2008;Soro et al, 2004). Ceux-ci sont obtenus après ajustement du variogramme expérimental à une expression analytique ou modèle.…”