Shortage of water is among the most serious problems facing Israel today. The problem is exacerbated by the deteriorating quality of much of its water resources due to industrial, agricultural and municipal pollution, as well as over-exploitation of its limited reserves.
Israel's total renewable fresh water resources equal approximately 1600 MCM per year. About 2/3 of these water sources are provided by three major reservoirs -- Lake Kinneret (Sea of Galilee), the coastal aquifer, and the inland, mountain aquifer (Yarkon-Taninim aquifer). These sources have utilizable water yields of 470, 300, and 240-300 MCM, respectively. The remaining aquifers are smaller and are generally exploited locally. They are located in parts of the Galilee and the Carmel mountain regions in the northern part of the country, and in several parts of the Arava and Negev regions in the southern part of the country.
The coastal aquifer extends along 120 kilometers of Israel's Mediterranean coast, underlying the coastal plain. Its width varies between 7 and 20 kilometers, and the thickness of the unsaturated zone varies from 4 to 98m, averaging 34 m. The aquifer is composed of sandstone and sand layers of Pliocene-Pliestocene age . The eastern half of the aquifer is uniform and phreatic. Toward the west it is partially divided by intervening clay layers into subaquifers of which the lower ones are confined. About one third of Israel's population and a major part of its industry and agriculture are concentrated in the region overlying the coastal aquifer. Serious degradation of water quality in this aquifer is caused by salination, nitrates, fuels and toxic organic compounds.
Salination of the coastal aquifer has resulted mainly from sea water intrusion and from the gradual accumulation of dissolved salts from irrigation water and other sources. Overpumping has exacerbated the problem, since the lowered groundwater levels have resulted in further encroachment of the seawater interface as well as preventing the flushing of contaminants into the sea. Additional causes of salination are from the import of water from the National Water Carrier and other groundwater basins, irrigation by sewage effluents and groundwater recharge.
A practical model has been developed in Israel which predicts the position of the saltwater-freshwater interface in the coastal aquifer for planning purposes. The model should help in decision making related to exploitation of the aquifer.
Over the past 25 years, average chloride concentrations have increased from 110 to 150 mg/l. The average increase today is about 1 mg/l/yr. According to estimates of the Hydrological Service, 10% of the wells have already reached salinity levels exceeding 250 mg/l, a concentration unsuitable for unrestricted irrigation. Within 25 years, over half the wells are expected to exceed permitted salinity levels.
Nitrate concentrations in the coastal aquifer have increased considerably over the last several decades. Since 1950, average nitrate concentrations in wells have increased from 30 mg/l to 40-50 mg/l today. Some 17% of current groundwater production exceeds levels of 70 mg/l, and nearly 60% exceed recommended levels of 45 mg/l. A study of nitrate trends in the aquifer through 1981 has shown that nitrate levels in wells appeared to be leveling off in the 1970's in which the average rate of increase declined to 0.13 mg/l per year. However, a more recent trend study showed that the average rate of increase rose to 0.67 mg/l per year during the 1980's, an increase of five fold over the previous decade. There was no apparent reason for the phenomenon.
Nitrate contamination of the aquifer is considered to be caused primarily by intensive use of fertilizers in agriculture and irrigation with sewage effluents. However, some researchers have theorized that most of the nitrate contamination observed in recent years in the aquifer is the result of nitrogen mineralization from oxidation of organic matter in the soil brought about by the intense cultivation of the virgin soils above the aquifer in the late 1920's - early 1930's period. The reclamation of swamps over the aquifer resulting in decomposition of soils rich in organic matter during the latter part of the last century is also considered to have contributed significantly to the nitrate contamination.
Groundwater contamination of fuel was discovered at numerous sites during the last several years. Two major leaks, one at the Ashdod oil refineries in March 1992 and one at the Israel Electric Corporation facilities in Ramat Hovav in January 1994, were responsible for most of the contamination . Most of the remaining sites consisted of small-scale leaks caused by damage to pipelines by mechanical equipment or by corrosion of old pipelines, especially near the Haifa oil refineries. Over the past few years, bioremediation methods have been successfully used to treat and rehabilitate sites contaminated by fuel.
A survey to assess the degree of pollution by organic contaminants in well water of the coastal aquifer was initiated by the central laboratory of the Mekorot Water Company in 1991. The survey monitors 18 compounds derived from industrial sources, nine pesticides and four trihalomethanes. Of the 468 wells tested so far throughout the country, 108 wells (23%) showed trace-level concentrations and 13 (2.8%) revealed at least one substance which exceeded the standard in at least one test. The most prevalent pollutant discovered (over 60%) was trichloroethylene. All of the contaminated wells, most of them situated in the highly-industrialized Haifa Bay and Holon (near Tel-Aviv) areas, were known to be polluted previously and have been taken out of service for drinking water purposes. Data accumulated will serve as a baseline for future changes in water quality.
Because of the deterioration of both quantity and quality of the coastal aquifer, the mountain aquifer is becoming the main supplier of drinking water in the country. However, this deep limestone aquifer is especially prone to contamination due to its karstic nature and the quick transit of pollutants through it. Although salinity does not constitute a problem today, over exploitation can lead to a rapid rate of saline water infiltration into the aquifer from surrounding saline water sources.
During the past 50 years, several changes made in the catchment basin of Lake Kinneret have modified the balance of the lake's ecosystem. Draining of the Hula wetlands in the 1950's caused sediments and nutrients, especially nitrates, to flow directly into the lake. Increased agricultural activity in the lake's watershed area have led to contamination by pesticides, fertilizers and cowshed wastes. Effective management of the lake and its watershed over the last 20 years has reduced salinity, bacterial and dissolved nitrogen concentrations, and in the number of incidents of pesticide contamination. On the other hand, a gradual rise in total nitrogen concentrations, a decrease in zooplankton growth, and an increase in algal biomass have been noted.
*Portions of this information were obtained from "The Environment in Israel",Ministry of the Environment, .State of Israel, Jerusalem, 1994.
This information will be available in the near future.
Stuart Wollman is a consultant environmental hydrologist located in Jerusalem, Israel. He has 15 years of experience in both the U.S. and Israel, which includes analysis of groundwater, soil, unsaturated zone, and surface water contamination; fate and transport modeling; exposure and risk assessment; water resources engineering and computer applications. Inquiries may be sent to stuart@shani.net.
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