A file image of the Numaligarh refinery in Assam
| Photo Credit: The Hindu
GUWAHATI
A refinery in eastern Assam’s Golaghat district has been discharging hazardous effluents into a tributary of the Brahmaputra River, endangering its fragile aquatic ecosystem, an environmental activist said.
In a letter to the Member-Secretary of the Central Pollution Control Board (CPCB) on April 2, Golaghat town-based Apurba Ballav Goswami sought a probe into the effluent treatment practices of the Numaligarh Refinery Limited (NRL) and its compliance with the board’s updated pollution standards.
He appended a report by a private biosciences laboratory analysing a water sample reportedly collected from the NRL’s effluent treatment plant on March 11.
“The results reveal an exceedance of CPCB effluent discharge standards for petroleum oil refineries under the Environment (Protection) Rules, 1986, and subsequent guidelines, with severe implications for aquatic life and the long-term health of the Dhansiri River,” the letter read.
Mr. Goswami said the analysis highlighted violations such as 18.0 mg/litre of biochemical oxygen demand (BOD), 142.0 mg/litre of chemical oxygen demand (COD), and 11.5 mg/litre of oil and grease. The CPCB limits are 15 mg/litre, 125.0 mg/litre, and 10 mg/litre, respectively.
He said the readings signal a potential pattern of pollution that threatens the Dhansiri River’s biodiversity and the communities that depend on it.
“High toxicity”
“The elevated BOD indicates excessive organic matter, depleting dissolved oxygen levels critical for aquatic organisms. Fish species such as mahseer and catfish, abundant in the Dhansiri, require oxygen levels above four-six mg/litre to survive. A BOD of 18.0 mg/litre risks creating hypoxic zones, leading to fish kills, the suffocation of benthic invertebrates, and the disruption of the river’s food web,” he wrote.
Mr. Goswami further said the high COD reflected a toxic cocktail of oxidisable pollutants from refinery processes, which can impair reproduction, stunt growth, and bioaccumulate in aquatic species, ultimately affecting predators like birds and mammals.
“The oil and grease content of 11.5 mg/litre, though seemingly modest, forms a surface sheen that blocks oxygen exchange, coats fish gills, and smothers aquatic plants, further compounding the ecological stress,” he said, requesting a thorough investigation into the NRL’s effluent discharge practices.
He also sought an assessment of the cumulative ecological impact of the discharge on Dhansiri’s aquatic life and water quality, including long-term monitoring of oxygen levels and biodiversity.
“Open to probe”
The NRL refuted the allegations, asserting the refinery does not discharge effluents in the Dhansiri, which is 12 km away.
“The generated effluents are treated in a modern effluent treatment plant within the refinery and the processed water is recycled for utilisation in the refinery. However, stormwater is occasionally discharged through a stormwater drain. The discharged storm water quality is closely monitored for compliance with statutory norms. The discharged storm water flows through several villages to meet the Kalioni River 6 km away,” an NRL spokesperson said.
He said that in light of the complaint to the CPCB, the refinery authorities collected storm water samples to test for pollution levels. “The results would be known in a few days,” he added.
The NRL also said it was committed to continuing compliance with pollution control and environmental protection norms. “We are open to a probe and will actively cooperate with the CPCB or any other agency,” the spokesperson said.
Established in 1993 according to the provisions of the Assam Accord of 1985, the NRL has a refining capacity of nine million metric tonnes per annum.
Published – April 03, 2025 04:08 pm IST