At a rate of 3 samples a year over 7 years (2008–2014), groundwater quality indicators for 294 samples from 14 groundwater supply wells located on the delta of Wadi Al-Arish, North Sinai (Egypt) were measured and analyzed. The prime objective was to characterize significant and sustained trends in the concentrations of the pH, TDS, Total Alkalinity, Fe2+, Mn2+, Zn2+, NO3−, K+, Pb2+, Al3+, and fecal coliform (FC). Detection and estimation of trends and magnitude were carried out applying the nonparametric Mann-Kendall and Thiel-Sen trend statistical tests, respectively. Geostatistical kriging implemented in ArcGIS 10× was appraised for the spatial distribution of the indicators and their sustained trends. Factor analysis was applied to identify significant sources of quality variation and their loads.Average contents of all indicators exceeded the permissible limits except for Mn. Violation of groundwater quality standards clarified emergence of FC (99.6%), Pb2+ (76.8%), TDS (60.2%), Al3+ (56.6%), NO3− (46.5%), Fe2+ (37.5%), and Mn2+ (14%). Out of the 14 wells, notable upward trends (deterioration) were significant (>95% level) for Mg2+ (100%), TDS (78.5%), NO3− (71.42%), Zn2+ (42.85%), pH (14.28%), K+ (14.28%), and 7.14% for Al3+ and FC. Ranges of attenuation rates (mg/l/year) varied for TDS (52.61–37.59), Mg2+ hardness (3.81–0.14), K+ (0.58–1), pH (0.004–0.027), total alkalinity (−1.89-13.18), NO3− (1.47–0.69), Al3+ (0.002–0.011), Fe2+ (−0.001-0.016), Mn2+ (−0.00004-0.01), Pb2+ (−0.00001-0.002), Zn2+ (0.049–0.018), and FC (5.25–22) in cfu/100 ml.Out of the 14 wells, well no. 9 showed the largest increasing attenuation rates (mg/l/year) that marked NO3− (1.47), K+ (0.58), pH (0.004), and Al3+ (0.002). TDS showed the largest rates of increase of 52.61, and 28.26 for well nos. 5 and 9, respectively. FC showed the highest rate of deterioration of 5.25 in well no. 10. Zn2+ recorded strong deterioration rates of 0.049, and 0.046 for well nos. 12 and 9, respectively. Four factors were found to explain 60.48% of the total variance of the quality variables and in particular, a significant load of TDS, Cl−, EC, SO42−, Na+, Ca2+, Mg2+, NO3−, K+, Pb2+ and Total Alkalinity in decreasing order of influence were identified. Variation in quality parameters originated from anthropogenic sources due to improper well head protection in the urban centers or from the agricultural wastes and the flash floodwater stagnation and intense evaporation in low relief areas.
Journal of African Earth Sciences – Elsevier
Published: Apr 1, 2018
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