The extent of the danger is reflected in the Health Ministry data on the Tel Aviv district, which shows that since 1980, some 88 drilled wells used for potable water were closed - and that is more than half the available wells in the district.

Pressure on water carrier

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As a result of the closures, the dependence on water drawn from the National Water Carrier has risen significantly.

In many of the wells still in use, the process of contamination continues, even if the level as yet is still below the acceptable contamination standard for drinking water in Israel.

For example, in 18 active wells, scientists found arsenic (an extremely toxic material) in samples tested. In nine wells, heavy metals such as lead and chrome were found in test samples.

Some of the experts raised the possibility that drawing potable water from the coastal aquifer cease; this proposal, however, was rejected by most relevant authorities.

"I think that it is still possible to rescue the aquifer, but this will have to be an effort that includes all parties in the system, and I hope that this is not too much for the State of Israel to manage," Dr. Yeshayahu Bar-Or, the chief scientist at the Environment Ministry said yesterday.

One of the ways that the contamination problem could be countered is through the installation of purification equipment in each of the wells showing high levels of pollutants.

This was adopted in contaminated wells in Rishon Letzion and Ramat Hasharon.

Another option is to set up a number of large purification installations to which water drawn from various locations along the coastal aquifer will be piped for treatment.

At the Water Authority preparations are underway to set up a backup water supply system for communities in which their wells were closed due to contamination.

One such community, Bnei Dror in the Sharon region, has been without a local drinking-water supply as a result of contamination levels that exceeded the standard.

Professor Ronen also raised the problem of underground toxic gases that affect the water supply, even though it is not always easy to trace them.

This sort of contamination was discovered five years ago in the Israel Military Industries compound on the municipal boundary between Tel Aviv and Givatayim.