Tamil Nadu’s Pollution Control Board has been flouting norms for two decades to allow Sterlite Copper to operate its smelter in Thoothukudi with chimney stacks much shorter than is permitted, an environmental non-profit alleged on Monday. This has helped the Vedanta-owned company cut costs while “exposing the residents of Thoothukudi to grave harm”, the Chennai Solidarity Group claimed.

Guidelines prescribed by the Central Pollution Control Board required a 68-metre chimney stack when Sterlite made its first proposal to produce sulphuric acid in 1996, but the company managed with a 60-metre stack, the Chennai Solidarity Group found. In later years, with increasing production capacity, even higher chimney stacks were needed, but Sterlite continued with the same height, the nonprofit said.

The statutory height of chimney stacks is calculated using the production capacity of a plant. The company needed at least an 88-metre chimney stack for its capacity in 2006, the group’s report said.

In India, copper smelters are required to recover the sulphur dioxide they produce and convert it into useful products. Sterlite has two sulphuric acid plants in Thoothukudi.

For over two decades, activists in Thoothukudi have accused Sterlite of contaminating the region’s air and water resources. Since February, there have been large-scale protests in Thoothukudi, where the Sterlite runs the copper smelter with the capacity to produce 4.38 lakh tonnes of copper anodes per annum, or 1,200 tonnes per day.

Earlier this month, the state pollution board rejected the company’s application to renew its licence for the copper plant after its Consent to Operate expired on March 31. Sterlite Copper challenged the order before the Appellate Authority, whose chairperson, Justice T Sudanthiram, has since asked the board to reply to the plea by May 4.