IMPACT OF THE REUSE OF DOMESTIC WASTE-WATER FOR IRRIGATION ON GROUNDWATER QUALITY

Egypt planned to reclaim large areas in both the Eastern and Western d esert fringes of the Nile Delta with an increasing use of sewage efflu ent from Greater Cairo. The Gabal el Asfar farm which has been irrigat ed with raw to primary treated sewage effluent for a period of seventy five years was selected as a pilot area to investigate the groundwate r quality. This farm covering 3000 feddan (1250 ha), is located in the sandy area northeast of Cairo. The main objective of the study was to assess the impact of agricultural application of sewage effluent on g roundwater quality. Observation wells were constructed and field and l aboratory measurements were carried out in and around the Gabal el Asf ar area. The water balance and mass balances have been assessed. The s tudy yielded useful recommendations to decrease the impact on groundwa ter quality and possible risks in Gabal el Asfar, concerning 1) type a nd amount of pollution from sewage effluent, 1) design criteria to con trol possible spreading of pollutants, and finally 3) the use of groun dwater in the area. The following comprises the main conclusions: Irri gation with sewage effluent had a positive impact on salinity of the i nitially brackish groundwater. On the contrary, groundwater quality is negatively affected from sewage effluent with regard to nitrogen cont ents (ammonium and nitrate), phosphate, heavy metals and faecal colifo rms. The drinking water limit for nitrate is sometimes exceeded. Moreo ver, faecal coliforms are found in water from all shallow handpumps in the area. The general suitability of the groundwater is therefore lim ited while the use of handpumps for drinking water purposes should be avoided. High boron contents of sewage effluent indicate a risk for cr ops sensitive to boron. The accumulation of heavy metals and phosphoru s in the soil adversely affects the soil system. Pretreatment of sewag e effluent in Gabal el Asfar should be improved to limit the pollution of the aquifer. Industrial discharge in sewage effluent should be avo ided. Groundwater recharged by sewage effluent is mainly collected by drains in or at the borders of the area, so spreading of pollutants ou t of the area is largely controlled.