UNSATURATED ZONE AND GROUNDWATER CONTAMINATION BY ORGANIC POLLUTANTS IN A SEWAGE-EFFLUENT-IRRIGATED SITE

This study describes the distribution of organic pollutants from the ground surface, through the unsaturated zone, to the water table at a citrus grove irrigated by sewage effluent for about 20 years. The citrus grove, located in Israel, overlies an unconfined Coastal Plain aquifer about 2 km inland from the Mediterranean Sea. The distribution of organic compounds at the citrus grove is compared with two control sites receiving moisture from nonpolluted water sources (one in another citrus grove irrigated by ground water and the other in an uncultivated area receiving only precipitation). Overall, 10 analyses were performed. At the effluent-irrigated site, organic pollutants from the sewage had migrated through the 20 meter thick unsaturated zone to the water table; included in these were several pollutants, such as toluene and phthalates, that are considered to be biodegradable. Pollutant concentrations generally increased with depth. On the other hand, pollutant concentrations at the two control sites decreased significantly with depth through the unsaturated zone. The downward mobility of organic pollutants may be enhanced by the sewage itself. Because sewage effluent is considered to be a readily available source of irrigation water in many parts of the world, the results of this study suggest that what may seem to be a relatively simple solution to water scarcity problems may have potentially long-term and dangerous effects on ground-water quality.