System Also Used to Explain the Saltiness of the Sea of Galilee


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REHOVOT, Israel -- October 31, 1996 -- A Weizmann Institute of Science groundwater sampling system, recently recognized by the US Environmental Protection Agency as useful sampling technology, tracks down microscopic particles that act as vehicles for the spread of groundwater pollutants, as reported in the current issue of Environmental Science and Technology.

The system, known as the multilayer sampler or MLS, has also been recently used to identify contaminated groundwater layers that can be effectively cleaned up by bacteria. Moreover, in an application that may be significant for Israel's water supply, MLS is now being employed to study salty fluxes in the fabled Sea of Galilee ("Kinneret" in Hebrew).

While many other water samplers are based on pumping, which distorts the natural flow and layering of the water, MLS leaves the natural conditions in the water intact. It is simply lowered into a lake, aquifer or water-filled sediment, where water -- together with contaminants and other microscopic particles -- seeps by diffusion into its membrane-covered cylindrical chambers.

"This makes MLS particularly suitable for mapping the precise distribution and flow of pollutants and other substances in the water," says Dr. Daniel Ronen of the Environmental Sciences and Energy Research Department, who invented the sampler together with the late Prof. Mordeckai Magaritz.

One of the system's first applications was to provide early warning of contaminants trickling down into the groundwater surface, before they sink to deeper levels of the aquifer where they become much harder to eliminate.

No More Free Rides

In the study reported in the October issue of Environmental Science and Technology, MLS has proved effective in sampling microscopic particles called colloids, such as clay minerals and various oxides, that facilitate the spread of pollution.

Hazardous materials such as organic contaminants, toxic metals and radioactive nuclides readily attach themselves to colloids, which are highly mobile, and get "free rides" over long distances, wreaking havoc on the environment.

"Monitoring colloids is therefore vital for effective pollution assessment, control and remediation. Contaminants attached to colloids significantly increase the concern about rapid pollution spread," says Ronen, who conducted this study with Ph.D. student Noam Weisbrod and Dr. Ronit Nativ of the Hebrew University of Jerusalem.

In experiments carried out in the Coastal Plain aquifer of Israel, the membranes covering the MLS chambers were provided with large pores allowing colloids to enter. After several days, the chambers were removed from the well, and the concentration and chemical composition of the trapped colloids and attached pollutants were analyzed.

In contrast, when water samples are obtained through an active process such as pumping, particles from the aquifer walls are sucked into the water, producing colloids that are not naturally present in the groundwater.

Are the Bacteria Doing Their Job?

In another study, reported in the August issue of Environmental Science and Technology, Ronen, his M.Sc. student Miri Rietti Shati, and Dr. Raphi Mandelbaum (of Israel's Volcani Research Institute) used MLS to determine the field conditions conducive to bacterial clean-up of contaminated groundwater.

For this purpose, bacteria were confined in the sampler's chambers, which were lowered into groundwater polluted with the widely used herbicide atrazine. The study, conducted in Israel's Coastal Plain aquifer, showed that the bacteria caused atrazine to degrade in particular layers of the aquifer. This will allow researchers to pinpoint the groundwater strata where bacteria are most likely to do their job.

In this and other studies, MLS furnished an accurate picture of distinct layers of water simultaneously because it consists of a rod outfitted with sampling chambers at different levels.

Salty Rain in the Sea of Galilee?

Israel's Sea of Galilee is a major tourist attraction. But many people who visit its historical sites and marvel at its beauty are unaware that this fabled lake also provides about a fourth of the country's water supply.

However, its waters are relatively salty, and in an effort to tackle this problem, the government has diverted nearby salty springs away from the lake. Yet the Sea of Galilee s chloride content remains relatively high -- about 220 parts per million -- and the source of this saltiness is yet to be clarified.

According to one theory, salt makes its way up from mineral deposits buried deep below the lake's bottom. If this is indeed the case, such reverse salty rain will be very difficult to control. Weizmann Institute scientists, in collaboration with a team headed by Dr. Ami Nishri from the Kinneret Limnological Laboratory, are now applying MLS to try and resolve this question. For this purpose, divers insert samplers at different sites into the lake's floor.

When the samplers fill up with the water from the surrounding sediment, they are removed and subjected to chemical analysis, which -- in combination with temperature measurements and hydraulic studies -- will make it possible to detect any upward salty streams and measure their flow. The Weizmann team in the Sea of Galilee study consists of Ronen, M.Sc. student Gil Dror, and consultant Dr. Mariana Stiller.

The sampler is manufactured under the brand name DMLS by Margan M.L.S. (1994) Ltd., Netanya, Israel, recently set up specifically for the system's production and worldwide commercialization. An exclusive marketing agreement for North America has been recently signed between Margan and Wheelabrator Clean Water Technologies Inc., New Brighton, Minnesota, and distribution may soon begin in Europe and the Far East.

Yeda Research and Development Co. Ltd., Weizmann Institute's technology transfer organization, has an agreement with Margan for the worldwide commercialization of the system.

The U.S. Environmental Protection Agency has recently recognized DMLS as useful for a variety of groundwater sampling applications, including determination of vertical distribution of chemical components and sampling in turbid water environments.

The EPA's groundwater monitoring guidance document that will include information on DMLS is expected to be posted soon in the Federal Register. Photos illustrating the use of MLS at the Sea of Galilee are available.

The Weizmann Institute of Science is a major center of scientific research and graduate study located in Rehovot, Israel.