Chennai: When former CM Jayalalithaa inaugurated Rs 1,928-crore Hogenakkal Combined Water Supply Scheme in May 2013, it was like a dream come true for people of parched and fluoride-affected districts of Dharmapuri and Krishnagiri. The reality is different. The Cauvery river water that is flowing into Hogenakkal from Karnataka is getting polluted with 593 MLD (millions of litres per day) of ‘untreated or partially treated’ sewage water generated by Bengaluru city on a daily basis.

Reliable sources in the state government told Deccan Chronicle that the Chief Secretary of Tamil Nadu K. Gnanadesikan issued an order to the Tamil Nadu Pollution Control Board (TNPCB) last month to check the facts and initiate urgent measures. The TN government is also planning to write to the Karnataka government seeking explanation on the rationale behind releasing sewage into the fresh waters coming into Tamil Nadu.

As per directives, TNPCB authorities did water sampling this week and the results are worrisome. The Bio-chemical Oxygen Demand (BOD) test carried out for five days on water samples collected from the upstream of the Cauvery river where the pollutants are allegedly joining the fresh waters show a steep rise in pollutants levels, in fact 10 times higher than the normal range. The average acceptable BOD range is 3 milligrams per litre, but it was recorded at 29 mg per litre, which confirms the fact that the sewage water that is let out is not properly treated or not treated at all. BOD is often used as a robust surrogate of the degree of organic pollution of water, sources highlighted.

The saving grace is that the sewage water from the point of joining Cauvery river till it reaches Hogennakkal has to travel a few kilometers during which a natural purification process takes place and minimises the threat. Still, the matter is of grave concern. “We are proposing to set up an automated water quality monitoring system in Hogenakkal, which will provide real time data on the quality of water and measure of all major pollutants. The government has instructed us to take necessary measures, relating to the issue, on top priority,” a TNPCB official told DC on condition of anonymity.

Ironically, the issue would not have cropped up if not for the astonishing revelation made by Karnataka minor irrigation minister Shivaraj Tangadagi on the floor of Legislative Council recently. The minister was quoted as saying that Bengaluru uses 1,950 MLD of water of each day, of which 1,482 MLD drains into Tamil Nadu through various river courses.

Out of the total 1,482 MLD discharge, 889 MLD of sewage water enters TN though South Pennar river identified as Dakshina Pinakini in Kannada and Thenpennai in Tamil. The sewage enters through Hosur before flowing into Kelavarapalli reservoir in Krishnagiri district, whose waters are used for irrigation and even for drinking water needs after treatment. The remaining 593 MLD of sewage water flows into TN through the Arkavathi river, which joins Mekedattu leading to Hogenakkal. “We are concerned about this 593 MLD which directly affected the Hogenakkal drinking water supply scheme”, another official said.