CHENNAI: Ever swallowed the salt water you gargle with? Pose this question to the village folk of Andarmadam in Tiruvallur district and you may get thrown out.
Believe it or not, the people here have had no choice but to ‘drink’ saline groundwater for centuries. That is, until a Ph.D geology student from Anna University constructed a percolation pond, which stores rainwater. Now the only salty water you will see in the area is the from the happy tears of the people.
The project, which began four years ago for research fellow Raicy Mani Christy, has taken over Rs 35 lakh from the university, though the pond itself costs only Rs 20,000. “We have constructed a pilot pond of 8m by 8m breadth and width and 1.7m height. During rainfall the water will be stored in the pond and this fresh water will dilute the brackish water. Even if the pond is getting dried up, people can extract fresh water at least for two months,” said Raicy.
This is in a stark contrast to what she saw when she made her first trip to the village back in the summer of 2012. Not only was the drinking water saline and brackish, but primary crops such as paddy were being affected. The reasons were two-fold. “The groundwater salinity is due to marine transgression which is 20,000 years old,” the 27-year-old explained.
“When the water level is lower in the river, the saline water from Pulicat mixes and comes to the land. As a result, the river water becomes saline,” she said. To top it off, the one source of fresh water from the Arani river orginating in Andhra Pradesh had largely been extracted for the water needs of Chennai.
While the study found that groundwater in the adjoining villages is equally saline, it was discovered that some regions had fresh water floating above saline water. This occurs because the latter is slightly denser. So the solution, according to L Elango, Head of the Department of Geology is to introduce and thereby infiltrate fresh water into the ground. “Here the whole region is completely saline. But in one location we are promoting recharge. As a result, fresh water will enter into the formation,” he said.
“Fresh water will not completely mix with the saline water because the latter is a bit denser. Hence fresh water will float over the saline water,” he said.