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contact with the contaminated salty formations that originate at greater depths. Recent drillings in the Jordan Valley show that salinity increases with depth. Salinity data obtained from one well in Jericho indicates that the chloride content increased from 380mg/l at 30 m depth to over 2,000mg/l at a depth of 162m. Increased salinity levels can also be a result of the flushing of soluble salts from the soil zone by excess irrigation water. Nitrate concentration in groundwater is naturally low but can reach high levels as a result of agricultural runoff, runoff from garbage dumps, or contamination from human or animal wastes. The toxicity of nitrate to humans is mainly attributable to its reduction to nitrite, with young infants being the most susceptible population . The PWA has adopted the World Health Organization’s upper limit of 50mg/l as (NO3) with 70mg/l deemed acceptable to PWA in the absence of any better quality water source. The nitrate standards are designed to prevent health risks from methemoglobinemia (blue baby syndrome), which in acute cases can cause premature death and disability. Nitrate concentrations in West Bank water sources have at time reached problematic concentrations (e.g., greater than 50mg/l) especially in newly urbanized areas. High levels have been measured in Qalqilia, Tulkarem, Jenin, and Nablus in the north, Ramallah and Jericho in the center, and the Beit Jala-Hebron region in the south. However, these hotspots appear to be comparatively localized and water in the vicinity is generally of better quality (SUSMAQ 2003). Total dissolved solids (TDS) can have an important effect on the taste of drinking water. The palatability of water with a TDS level of less than 600mg/l is generally considered to be good; drinking water becomes increasingly unpalatable at TDS levels greater than 1,200mg/l. The presence of high levels of TDS may also be objectionable to consumers owing to excessive scaling in water pipes, heaters, boilers , and household appliances. The PWA acceptable limit is 1,000mg/l, while up to 1,500mg/l is acceptable in the absence of any better source. Problem levels tend to be encountered only toward the boundaries of the West Bank, in other words, down-dip within each of the West Bank aquifer basins. This suggests that while urbanization plays a part in the creation of high TDS concentrations, down-dip water-rock interaction must also be a contributory cause (SUSMAQ 2003). Sulfate is not a serious problem anywhere in the West Bank. All water resources except for one are below the “taste” level of 250mg/l. Yet, trends suggest that there may be reason for concern, as there are some sites where SO4 concentrations are now higher than in the past. These findings might simply be anomalous analytical artifacts, but they may well be the result of changes in pumping regimes (for example, where groundwater is strongly layered in terms of quality) or simply the flushing over time of pockets of poor-quality water in gypsiferous strata. Figure 1.4 shows maps for chloride, nitrate, sulfate, and TDS values across the West Bank, respectively. In the northern part of the West Bank, recent deep drilling of wells penetrating very thick layers of Senonian chalk reveals processes of ion exchange between bituminous shale and limestone, serving to increase the concentration of fluoride and amjad aliewi 22 decrease the levels of calcium and magnesium. The high level of fluoride constitutes a major health risk. Water Quality in the Gaza Coastal Aquifer Groundwater in the Gaza segment of the coastal aquifer is generally of poor quality , characterized by medium to high salinity levels. Very few parts of this aquifer still have high water quality. These few reasonable segments of the aquifer are located along the extreme north and extreme south of the Gaza Strip (figure 1.5). In the whole of the coastal region, aquifer quality remains a critical issue as the values of nitrates and chlorides are frequently extremely high. Chloride (salinity) affects usability for irrigation and water supply. Intensive exploitation of groundwater in the Gaza Strip during the past 30 to 40 years has disturbed the natural equilibrium between fresh and saline waters and has resulted in increased salinity in most areas. In Gaza City, chloride values in several wells are increasing at rates up to 10mg/l per year. Sources of chloride that can be documented or inferred within the Gaza Strip are seawater intrusion, lateral inflow of brackish water from Israel in the...

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