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Alyamani, M.S.,(2006 ) Effect of wastewater disposal from areas of high residental density in absence of sewer networks on groundwater quality oh shallow aquifer in Wadi Fatimah basin. Western Province of Saudi Arabia.

Proj.No ( 201/426 ( ، King Abdulaziz Uni., Jeddah.

SUMMARY

The aim of the present research is to study the groundwater quality in four selected sites where residences are serviced by the traditional cesspool systems. The selected sites are Alsail Alkabir (site 1), AlMadiq (site 2), Turfah-Ar ryan (site 3) and Abu Hisani -Al Khayf - Abo Urwah area (site 4). These sites are located within Wadi Fatimah basin in the western part of Saudi Arabia. The results of the chemical analyses of groundwater indicate that high NO₃^- concentration is a widespread pollutant that possessing a serious threat to the public health. The average NO₃^- concentrations in the four sites 1, 2, 3 and 4 were 252, 171, 146 and 191 mg/l respectively which obviously exceeded the maximum contaminant level (MCL) of 45 mg/l as well as the average background (16.3 mg/l) of the NO₃^- concentration in the low residential density and low agricultural activities within the Wadi Fatimah basin.. Thus, the chemical analyses results show that the higher NO₃^- levels almost marked the groundwater in site (1).than the other sites. To differentiate the potential sources of NO₃^- in the groundwater, the relationships between NO₃^-/Cl^- , Na⁺/Cl^- and Na⁺ +NO₃^- /Cl^- were developed. However, the relationship between NO₃^- and Cl^- indicates that positive relationship was observed in site (1) whereas the relationship between Na⁺ and Cl^- was a weak. In the three other sites this is not the case, the two relationships were completely different from that observed in site (1), where a weak relationship between NO₃^- and Cl^- , while a strong relationship between Na⁺ and Cl^- . This condition observed may indicate that in site (1) both NO₃^- and Cl^- ions might have the same source, while in the other three areas both elements have different sources. In site (1), leakage of wastewater disposal to groundwater is more likely the main source of both elements since these two ions are associated with groundwater pollutant by cesspool effluents. The effect of cesspool effluents on groundwater

might be depicted from the highest value of nitrate contents in well no. 11. This well almost located in close proximity to potential point waste source (Al Meqat Mosque) in Alsail Alkabir area which is annually visited by several thousands of pilgrims before starting the pilgrimage journey and Omerah to Makkah, the holy city. On the other hand, in the three sites, two possible sources for NO₃^- and Cl ions in the groundwater. Nitrate probably derived form intensive uses of animal and chemical fertilizers in these areas, while Cl concentrations may derive from halite as evaporitic salt in the sediments which in turn leaching through recycling of irrigation water processes. Although, halite salt was not detected by XRD analyses, but it can not be ruled out as the sole source of Cl in the groundwater.

This can be depicted from the strong relationships between Na and Cl of the groundwater in the three areas. The bacteriological analyses results were negative by means non of any type In the present investigation, recommendations were given to avoid and/or minimize the effects of pollution processes by wastewater disposal on groundwater.

of bacteria was detected in the groundwater samples even in samples with the highest NO₃^- concentrations (site 1), suggesting that residence time in fractured and weathered bed rocks was sufficient for bacterial die-off.