The Saq aquifer is the largest most productive and most developed
aquifer in the study area. Generally, it has a very large areal extension from
the Jordanian border as far south as latitude 24° 30' N and longitude 45° E,
with a surface area of about 6500 km2 (Jerais, 1986).
The thickness of this aquifer is variable but it changes according to
geologic formations. It ranges from 200 m to 500 m in south and east of
the study area, while in the northern part it ranges between 150 m and 500
m. However, in the central part of the area, its thickness varies between 450
m to 600 m (Tabuk Agricultural Development Company, personal
communications).
The Saq Formation rests directly on the crystalline rocks of the
Precambrian basement, and overlain by the lower part of the Qassim
Formation. The effective porosity of this aquifer generally exceeds 15%
with a range of 10 – 20% ( King Fahd University Staff, 1987) The isotopic
age of groundwater of the Saq aquifer varies between 22,000 and 28,000
before present, which indicates fossil water features (Edgell, 1997)