الفهرس 
I. IntroductionOnly 14 pages are availabe for public view
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Abstract
Ten groundwater samples were collected with pH 6.79 which indicates slightly acidic. The mean value of electric conductivity is 6.41 for the groundwater samples which is under the permissible limits of WHO. The large variation in electric conductivity is mainly attributed to geochemical process like ion exchange, reverse exchange, evaporation, silicate weathering, rock water interaction, sulphate reduction and oxidation. T.D.S values are under the permissible limit of 2000 mg/l and all the collected samples are considered as fresh ground water (T.D.S < 1000 mg/l). The cations of southwestern Sinai groundwater samples indicate average as Na+ (176.56 mg/l), Mg2+ (108.11mg/l), Ca2+ (102.15 mg/l) and K+ (8.23 mg/l), while the anions reveal average values as Cl- (451.06 mg/l), HCO3 (204.53 mg/l), CO3 2- (125.82 mg/l) and SO4 2- (113.45 mg/l), respectively. The mean values of the cations in order of abundance were Na+ >Mg2+> Ca2+> K+, while the anions reveal order of abundance as Cl->HCO3 - >CO3 2 - > SO4 2-. The mean concentrations of most parameters are below WHO recommended limits with the exception of one sample has odd values of some parameters like Ca2+ and Mg2+, Sodium Absorption Ratio (SAR), Percent Sodium (Na%), Residual Sodium Carbonate (RSC), Potential Salinity (PS), clarified that the ground waters in the studied area were safe and suitable for irrigation. The study of the hydrochemistry of Summary - 147 - groundwater shows that for cations concentrations, Ca-Mg type of water predominated in most samples. On the other hand, anion concentrations indicate that chloride type of water predominated in the studied area. Most of the collected groundwater samples belong to the Ca - Mg- Cl mixed type, followed by Ca2+- Mg2+- Cl−- SO4 2- water type and one sample belongs to Na+- K+ - Cl−- SO4 2- water type. The activity concentrations of 238U range between 338 and 25413 mBq/l, 234U activity concentrations range between 425 and 35560 mBq/l. The 234U/238U ratios range between 0.029 and 1.49. The lowest ratio represents a flashflood sample which has very low 234U. Part (2) Eight groundwater samples were collected with pH 5.98 suggesting acidic conditions. EC is a measure of salt content in water, and changes in its concentration signify water quality deterioration. The mean value of EC is 6.14 μS/cm for El Bahariya Oases, which is under the permissible limits of WHO. The large variation in EC is mainly attributed to geochemical processes like ion exchange, reverse exchange, evaporation, silicate weathering, rock water interaction, sulphate reduction and oxidation. T.D.S values are under the permissible limit of 2000 mg/l and all the collected samples are considered as fresh ground water (T.D.S < 1000). Based on hardness, the groundwater samples of El-Bahariya could be classified as soft water with the exception of Summary - 148 - two samples from El-Bahariya Oases (BF.1, BF.5) are classified as moderately hard. The average values of cations are Ca2+ (68.51 mg/l), Mg2+ (37 mg/l), Na+ (33.55 mg/l) and K+ (17.68 mg/l) and anions Cl- (170.44 mg/l), HCO3 - (150.75mg/l), CO3 2- (108.5 mg/l) and SO4 2- (17.33 mg/l) , respectively. The mean values of the cations in order of abundance was Ca2+ >Mg2+> Na+ > K+, while the anions reveal order of abundance as Cl- > HCO3 - > CO3 2 - > SO4 2- with one exception. The mean concentrations of most cations and anions are below WHO recommended limits with the exception of some samples has odd values of some parameters like Ca2+ and Mg2+ . Also, other parameters such as Sodium Absorption Ratio (SAR), Percent Sodium (Na%), Soluble Sodium Percentage (SSP), Residual Sodium Carbonate (RSC), Residual Sodium Bicarbonate (RSBC), Permeability Index (PI), Potential Salinity (PS), Magnesium Hazard (MH), Magnesium Ratio (MR) and Exchangeable Sodium Ratio (ESR) clarify that the ground waters in the studied samples were safe and suitable for irrigation. The study of the hydrochemistry of groundwater shows that for cation concentrations, Ca-Mg type of water predominated in most samples with the exception of one sample lie in the fields of Na- and Mg-type of water. On the other hand, anion concentrations indicate that chloride type of water predominated. Most samples of El-Bahariya belong to the Ca - Mg- Cl mixed type, followed by Ca2+- Mg2+- Cl−- SO4 2- water type. It was also noticed that alkaline Summary - 149 - earth elements exceeded alkalies concentrations and weak acids exceeded the strong acid elements. Gibbs diagrams illustrate that the chemical weathering of rock-forming minerals influencing the groundwater quality by means of dissolution of rocks through which water is circulating was the most valid conditions. The activity concentrations of 238U in four samples range between 78.3 mBq/l and 151 mBq/l, 234U activity concentrations range between 109.6 mBq/l and 181.2 mBq/l. The 234U/238U ratio ranges between 1.09 and 1.39 which occur because of the α- recoil.