Results

GROUNDWATER QUALITY

COASTAL AQUIFER—NITRATE

Figure 13. Map showing trends for nitrate concentrations in groundwater of the Coastal aquifer during 1984–98.

Figure 14. Graphs showing mean annual concentrations of nitrate for selected locationsin the Coastal aquifer during 1984–98.

Information on nitrate in the Coastal aquifer is more limited than information on chloride. The PWA/Gaza did not have a record of nitrate data sufficient to analyze trends during 1984–98. Trends for 251 IHS wells that had adequate data are shown in figure 13. Similar to trends for chloride, most nitrate trends (62 percent) indicate increasing concentrations in the aquifer. The trends do not appear to have a spatial pattern; wells where concentrations increased or remained about constant exist throughout the extent of sites that had adequate data. A cluster of wells that had some of the largest increases is located in an agricultural area southeast of Tel Aviv. Time-series plots of nitrate concentrations in a few locations (fig. 14) illustrate some of these processes.

IHS well 21214302 (WQ–1) is in an agricultural area. The trend in nitrate concentration was a fairly steady increase of 1.1 mg/L per year during 1984–98. This probably resulted from infiltration of excess nitrogen in commercial fertilizer and manure.

Nitrate also increased in the production wells 20313903 (WQ–2A) and 20313901 (WQ–2B), although at different rates. Like chlo-ride, nitrate concentrations were much higher in well WQ–2A, but unlike chloride, nitrate did not decrease when the well was removed from production in 1991. This might indicate that the source of nitrate is different from the source of chloride that is affecting the well. On the other hand, the patterns of nitrate and chloride are similar in well WQ–2B.

The nitrate trend for IHS well 14212202 (WQ–3), in the urban area between Tel Aviv and Ashdod, is similar to the trend for well WQ–1, in an agri-cultural area, but it is more variable and the overall concentrations are lower.

Like chloride, nitrate in IHS well 10711501 (WQ–4) is affected by industrial contamination. Dilution is apparent during the 2 years following high precipitation in 1992. After that, nitrate concentrations more than doubled.