1. APHA, AWWA, WEF, 1992. Standard methods for the examination of water and wastewater. American Public Health Association, American Water Works Association and Water Environment Federation. 18th ed., New York, USA.
2. The Hydrolysis of Cations;Baes,1976
3. Chromium redox mechanisms in soils: should we worry about Cr(VI)?;Bartlett,1997
4. Precipitation, reduction and complexation;Beszedits,1986
5. EMA, 1988. National Atlas of Ethiopia. Ethiopian Mapping Authority. Addis Ababa, 79p.