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Tsunami's impact on well water a concern for MIT

The Indian Ocean tsunami's impact on Sri Lanka's drinking water and soil is the focus of an expedition this week by an MIT professor and colleagues from Florida and the Colorado School of Mines.

Upon hearing that the water in Sri Lanka's drinking wells has become too salty to drink as a result of ocean water infiltrating freshwater aquifers, the three whipped together a proposal to the National Science Foundation to study the situation in real time. The NSF supports rapid response disaster teams that can be dispatched quickly to affected areas.

"We know anecdotally that wells have been affected, but how many? And how far inland? We're hoping to get data on these kinds of questions," said Charles Harvey, an associate professor in MIT's Department of Civil and Environmental Engineering, who will keep a log while on the trip. The team, which left for Sri Lanka Feb. 11, has also heard that salty soil is affecting vegetation.

Harvey's colleagues on the trip are Tissa Illagasekera, principal investigator for the expedition, and Jayantha Obeysekera of the South Florida Water District. Hydrologist Illagasekera asked Harvey to join the team because of the latter's work on arsenic in Bangladesh drinking water. Obeysekera was asked because Florida has many issues concerning the intrusion of salty ocean water into coastal freshwater supplies.

Harvey and colleagues also want to explore whether the salinization is a long-term problem, or whether the salty water will be flushed out in June during the Monsoon season.

Harvey further notes that because salt water is denser than fresh, the salty layer currently on top is unstable. "So conceivably that layer could sink deep into the ground, which is good because the peoples' wells are not that deep."

On the other hand, he said, the initial intrusion of salt water would cause chemical reactions in which the sodium from the salt leaves the water and sticks to sediments, switching places with other elements like calcium. As a result, once fresh water is restored by the monsoon or gravity, the sodium could chemically react again, leaving the sediments and desorbing back into the fresh water. "So you could have salty water again," Harvey said. "It wouldn't be as salty as at first, but there could still be a lingering problem."

Based on the data the researchers collect during this expedition, they hope to return to Sri Lanka again in May, this time with other experts. For example, Harvey expects the May team will include someone familiar with the effects of salinization on tropical plants.

A version of this article appeared in MIT Tech Talk on February 16, 2005 (download PDF).

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