Chapter 16 - A novel approach for identification of groundwater salinization sources

Abstract

The hierarchical cluster analysis (HCA) technique and geostatistical analysis with a new hybrid-based method called IEP-SF-HA-WT approach (ion exchange process–salinization/freshening–humidity/aridity–water type) have been used successfully to provide a new comprehensive understanding for the major factors and hydrogeochemical processes controlling the salinization of groundwater in a highly urbanized coastal region subject to multiple sources of groundwater salinization. This new approach was applied on 10 physicochemical variables for 257 wells using STATA/SE12 and Surfer software. HCA technique divided groundwater chemistry into eight distinct hydrogeochemical signature clusters influenced by anthropogenic and natural factors. Seawater intrusion (SWI) was the highest active contributor to groundwater salinization along the whole sea shoreline and has extended far inland (around 3.5 km), especially in the northern area of the Gaza Strip. The IEP-SF-HA-WT approach elucidates the predominance of Na-Cl (65%) (17%) Ca-HCO 3 type, and (9%) for both of Ca/Mg-Cl and Na-HCO 3 . Among the hydrogeochemical processes, it is found that the IEP was effective hydrogeochemical process all over the study where 56.4% of groundwater samples are influenced by reverse IEP field (surplus of Cl − ions) and (43.6%) impacted by direct IEP field (surplus of Na + ions). It reveals the low influence of Ca 2 + /Mg 2 + enrichment processes as carbonate dissolution. It elucidates dominance of evaporation process especially in the southern area which is close to Sinai desert, Egypt, where 74% of the groundwater samples were impacted by the high aridity/evaporation conditions. Nitrification process was effective and chief in the study area especially under highly populated urban areas where around 91.1% of the wells are nitrate polluted revealing the high existence of sewage invasion. The other recorded salinization factors were Eocene brackish water invasion from the east and saltwater up-coning from down-side. These results could be mainly attributed to the overexploitation and improper management of groundwater in the study area as a result of political conflict and strife in the region. This new integrated multitechnique research should be of benefit for effective utilization and management of the Gaza coastal aquifer system as well as for future work in other similar coastal aquifers systems.