High levels of chemicals led to change in colour of water in Vellore Fort moat

A series of tests carried out by the T.N. Water Supply and Sewerage Board, on the request of the ASI, has found that high levels of ammonium, nitrate and phosphate led to the colour change; The report has been sent to the ASI’s Chennai Circle, which might seek the govt.’s intervention into the issue

High levels of ammonium, nitrate, and phosphate had given the water in the moat of the 16th Century Vellore Fort a yellowish colour. This was found through a series of tests conducted by the Tamil Nadu Water Supply and Sewerage Board (TWAD), after the Archaeological Survey of India (ASI) decided to investigate the reasons for the change in the colour of water.

The Department of Fisheries has been using the water in the moat for fish farming for many years. On an average, around 50,000 fish are present in the moat for breeding every year. The TWAD conducted the tests at its laboratory here. The report has been submitted to ASI.

Unfit for consumption

Vellore Collector V.R. Subbulaxmi has been apprised of the findings of the study report, a copy of which is available with The Hindu. “Water samples collected from the moat by the ASI have high levels of ammonium, nitrate and phosphate. Such contamination makes the water unfit for domestic consumption. Low-cost water treatment methods should be explored to clean the moat,” K. Nithiyanantham, Executive Engineer (EE), TWAD (Vellore), told The Hindu.

According to the findings, the water samples had 2.90 milligrams per litre (mg/L) of ammonium as against the permissible limit of 0.5 mg/L. The levels of nitrate and phosphate were 0.28 mg/L and 0.68 mg/L respectively. However, as per the norms, the permissible limit of nitrate and phosphate in water for domestic consumption should be zero. The report also observed that there was 60 mg/L of fecal coliform in the samples, making the water “bacteriologically contaminated”.

The TWAD officials said that the colour change was also due to the presence of phytoplankton, also known as microalgae, that depend on sunlight for survival. They asserted that the water colour changes when microalgae react to sunlight.

The officials further said that the microalgae might have been carried by the wind to the moat, or through water seepage from contaminated ponds and streams nearby, over the years. Low-cost treatment using carbon should be done as seepage of the contaminated water in the moat might affect borewells and small waterbodies.

The moat runs about 3 km around the Fort, and has an average depth of 29 feet. The ASI officials said they do not have the power to undertake water treatment and other developmental work. The TWAD report has been sent to the ASI’s Chennai Circle, which might seek the State government’s intervention into the issue.

Published - November 08, 2024 12:25 am IST