Origin and geochemical evolution of groundwater in the nubian sandstone aquifer at east el-owienat area, western desert, Egypt

الملخص EN

East El-Oweinat area has potential for human activities and agricultural plans in a part of the great Western Sahara pertaining to the Southwestern territory of Egypt.

Such development will be solely dependent on water supply from the Nubian aquifer.

In the present study, the recharge sources of this aquifer are determined and evaluated through the assessment of groundwater quality. This study reveals that there are three water salinity classes within the fresh water zone; the first is the ultra-fresh water class (<500mg / l) which occupies the Southwestern parts of the studied area, the second is the fresh water class (500-700mg / l) which occupies the area Southeast and Northwest and, the third is the fairly fresh water class (>700-1500mg / l) which dominates the central and Western parts The study also, indicates that the groundwater in the study area is of mixed origin, possibly pure meteoric but affected by traces of marine deposited. The analyses of the environmental isotopes (18O, 2H and 14C) indicate that the groundwater is mainly formed in the polio post pluvial times (about 18,000 years ago) without any significant contribution of recent recharge.

In other words, the main bulk of groundwater is pale water and any recent recharge from South or West is considered not significant if compared to the huge amount of water reserved. The chemical composition of groundwater as indicated by the hydro chemical profiles displays more hydro chemical evolution in the Northeast and East directions while being less hydro chemically evaluated in the Southwest and West directions.

This confirms that the general flow of groundwater is from Southwest to Northeast direction which has been, hydrologic ally, proved by other authors in previous studies.

The results of this hydro chemical study support the previous hydrological studies which concluded that the subsurface water flow in the investigated aquifer is from SW to NE.

Moreover, the local recharge in the study area during the post pluvial times plays the most important role in influencing the water quality.

In addition, the isotopic analyses have proved a polio-water origin dominating the aquifer in the area, although a marine affinity has appeared in the hydro chemical faces.