Results

GROUNDWATER QUALITY

OTHER AQUIFERS - CHLORIDE

Figure 15. Map showing trends for chloride concentrations in groundwater of aquifersother than the Coastal aquifer during 1984–98.

Trends in chloride for aquifers other than the Coastal aquifer during 1984–98 are shown in figure 15. Concentrations in most wells were about constant. Significant decreases occurred in 29 percent of the wells, and increases occurred in only 18 percent. The largest changes were confined in two locations on the western side of the Jordan Valley. In both locations, there were large increases and decreases in nearby wells.

Time-series plots of chloride concentrations for selected wells representing trends in the most significant aquifers are shown in figure 16. A consistent effect of the high precipitation in 1992 is not indicated in these plots, so selection of a time period spanning that year was considered appropriate.

Cretaceous aquifers

In the Tulkarm area, chloride concentrations generally increased during 1984–98. The trend for IHS well 19515201 (WQ–8), tapping the Upper Cenomanian/Turonian aquifer, was an increase of 19 mg/L per year during 1984–98, but most of this increase occurred after 1990. This probably results from irrigation and disposal of untreated sewage in the upgradient recharge area. For some wells in this area, the increase of chloride concentration occurred primarily between 1992 and 1993 and can be explained by the leaching of chloride from the soil to the aquifer by heavy rain.

Farther south, chloride concentrations were about constant or decreasing. In IHS well 17114501 (WQ–9), chloride decreased steadily, with a trend of –2.0 mg/L per year. This well pumps from the Cenomanian aquifer near the contact with the overlying Coastal aquifer. There is indirect evidence that water in the Coastal aquifer in this location is less saline than water in the Cenomanian. If this is indeed true, then increased pumpage would draw more water from the less saline aquifer and chloride concentrations in the pumped water would decrease.

Figure 16. Graphs showing mean annual concentrations of chloride for selected locations in aquifers other than the Coastal aquifer during 1984–98.

Another area of increasing chloride concentra-tions was west of Jerusalem. The trend for IHS well 13414601 (WQ–10) was 4.9 mg/L per year, but the primary increase occurred from 1990 to 1995. This well is affected by a syncline that contains saline water. As pumping increases, more water is drawn from the syncline, and chloride in the pumped water increases.

IHS well 11513701 (WQ–11) shows the effects of dilution in an area not much impacted by anthropogenic activity. Chloride concentrations in the well decreased 3.7 mg/L during 1984–98, but almost all the change happened immediately following the high precipitation year of 1992. After 1993, chloride increased steadily but was still less than previous concentrations.

IHS well 7412901 (WQ–12) is near Be’er Sheva, at the southern extent of the Upper Cenomanian/Turonian aquifer. Chloride concen-trations increased 4.2 mg/L per year. This change probably was due to leakage of saline water from adjacent aquifers as a result of increases in the pumping rate of the well. Reduced pumping rates for other wells in the area were followed by decreases in chloride concentration.

MWI well 2 (WQ–16) is located in the Yarmouk Basin and penetrates the B2/A7 aquifer. Chloride concentrations decreased 0.98 mg/L per year during 1984–98, although primarily after 1992. This may be due to dilution following high precipitation.

MWI well 8 (WQ–17) is located in the Amman-Zarqa Basin and also penetrates the B2/A7 aquifer. The trend in chloride concentration was 4.1 mg/L per year, but the annual changes were highly nonlinear. Concentrations increased through 1988, then decreased through 1995, and then increased again. This trend may result from a complex interaction of overpumping, dilution from high precipitation in 1992, and leaching from agricultural areas.

Tertiary aquifers

PWA well 17–20/044Q (WQ–13) is representative of the general trend of the chloride content in the Eocene aquifer of the Northeastern Basin. Wells in this basin are surrounded by areas of agricul-tural irrigation, which can increase the mineral content of the soil. Well WQ–13 is shallow and is affected by recharge from surface land use. The trend in chloride concentration was 6.6 mg/L per year during 1984–98, but almost the entire increase occurred between 1992 and 1993, prob-ably because of the leaching of chloride by the high precipitation of 1992. Chloride concentra-tions in the well decreased after 1995.

Jordan Valley aquifers

The Al-Jiftlik area, near PWA well 20–17/016 (WQ–14), is one of the primary agricultural areas in the western Jordan Valley. There is intensive irrigation and application of fertilizers and pesticides, all of which can increase mineral content of the soil and unsaturated zone. In addition, the Pleistocene water-bearing formations include lacustrine marl and evaporites, which can contribute salinity to water in the aquifer. Well WQ–14 draws water from the Pleistocene aquifer. Chloride concentration increased 24 mg/L per year during 1984–98. This increase might be due to leaching of chloride as a result of agricultural activities.

PWA well 19–17/027 (WQ–15) is south of the Al-Jiftlik agricultural area. Chloride concentration in water from this well decreased 28 mg/L per year during 1984–98, although much of this change occurred after the high precipitation year of 1992. In this area, there are connections between the Jordan Valley alluvium and the underlying Eocene aquifer. Water from the Eocene aquifer could be diluting the salinity of the alluvial aquifer in this area. In addition, the allu-vial aquifer receives recharge from Wadi Fari’a, which is another potential source of dilution. Chloride concentrations for wells in this area vary according to distance from the wadi and thick-ness of the alluvial deposits.

Farther south, in the Jericho area, there is a similar pattern. Chloride concentrations have increased in wells affected by agriculture, Pleistocene deposits, and overpumping. In other wells, lower chloride concentrations may have been caused by dilution due to recharge from the mountain aquifer or surface-water runoff.

Basalt aquifers

MWI well 17 (WQ–18) is located in the Azraq Basin and penetrates the Basalt aquifer. Chloride concentration increased 9.7 mg/L per year during 1984–98, and the rate of increase seemed to accelerate throughout this period. The increase probably is due to overpumping, which draws more saline water from formations that contain high concentrations of salt.