Results

GROUNDWATER QUALITY

OTHER AQUIFERS - NITRATE

Figure 17. Map showing trends for nitrate concentrations in groundwater of aquifers other than the Coastal aquifer during 1984–98.

Figure 18. Graphs showing mean annual concentrations of nitrate for selected locations in aquifers other than the Coastal aquifer during 1984–98.

Trends in nitrate for aquifers other than the Coastal aquifer during 1984–98 are shown in figure 17. Concentrations increased over a broad area in the northern part of the Western Mountain Basin along its boundary with the Coastal Basin. Farther south and east, concentrations generally were constant (or trends were insignificant).

Increases also were common in the Northeastern Basin and along the west side of the Jordan Valley. East of the Jordan Valley and Wadi Araba, nitrate concentrations were about constant, except in the vicinity of Amman. Time-series plots of nitrate concentrations for selected wells representing trends in the most significant aquifers are shown in figure 18.

Cretaceous aquifers

IHS well 19515201 (WQ–8), in the Tulkarm area, is affected by disposal of untreated sewage in the upgradient recharge area. In addition, this is an area of intense agricultural activity, and the land surface is connected to the Upper Cenomanian/Turonian aquifer by an extensive fracture system. Nitrate concentrations generally increased 3.5 mg/L per year during 1984–98, mostly after 1990. Farther south, in the undivided Cenomanian (IHS well 17114501, WQ–9), nitrate concentrations are much lower and were about constant during 1984–98. In the areas west of Jerusalem (IHS well 13414601, WQ–10) and near Be’er Sheva (IHS well 7412901, WQ–12), nitrate also was about constant. This is in contrast with the upward trends for chloride in both areas. The sources of the chloride increases probably are geologic rather than anthropogenic, which also would affect nitrate.

For MWI well 2 (WQ–16), the overall trend in nitrate concentrations was a decrease of 0.24 mg/L per year. However, during 1984–88, nitrate actually increased, possibly due to leaching of nitrogen fertilizer applied to upgradient agricultural areas. All the decrease occurred during 1992–97, after the year of high precipitation, and might be a result of dilution by greater recharge.

Nitrate concentrations were highly variable for MWI well 8 (WQ–17), in the Amman area, but there was an overall increase of 0.71 mg/L per year during 1984–98. This increase likely results from leaching of nitrogen fertilizer and from septic tanks.

Tertiary aquifers

Wells in the Northeastern Basin are affected by irrigated agriculture. PWA well 17–20/044Q (WQ–13) draws water from the Eocene aquifer, and it is representative of the upward trends for nitrate concentration in the basin. The increase in this well was 2.5 mg/L per year during 1984–98, with most of the change occurring after 1992. This increase could be attributed to leaching of nitrate that had accumulated in the soil and unsaturated zone. The source of nitrate is probably waste-disposal sites. Leaching to the aquifer would have accelerated after the high precipitation in 1992.

Jordan Valley aquifers

Nitrate concentrations increased for many wells on the west side of the Jordan Valley. Most wells in this area are shallow, unprotected, and very vulnerable to pollution from human and animal activities. Possible sources of these trends could include:

1. Intensive agriculture, including fertilizer and manure application;
2. Disposal of untreated sewage in the areas of Jericho and Wadi Al-Fari’a (near well WQ–15); and
3. Evaporite beds in the Pleistocene aquifer, which is the main water-bearing geologic unit in the Jordan Valley.

PWA well 20–17/016 (WQ–14) is located in the Pleistocene aquifer on the northern side of Al-Jiftlik agricultural area. The increase in nitrate concentration was a relatively steady 1.3 mg/L per year during 1984–98, probably as a result of contamination from fertilizer or manure. PWA well 19–17/027 (WQ–15) is located south of Al-Jiftlik and near Wadi Fari’a. The increase in nitrate concentration at this well was 1.2 mg/L per year. The most likely source for this increase is untreated sewage water passing through Wadi Fari’a.

Two Jordan Valley wells for which nitrate concentrations decreased were in areas where agricultural activity was relatively low and where significant underground recharge might occur. In addition, intensive well protection was in place at both wells.