The IIT experts told a bench headed by NGT chairperson Justice Swatanter Kumar that with every 1 meter increase in the barrier height, no substantial drop in the sound pressure level was noticed during the study conducted by it.

“Air gap between the existing wall and the proposed additional construction on top of the existing wall should be effectively sealed, while allowing for the thermal expansion of the structure,” the IIT report said.

The report was filed in pursuance to the NGT’s direction to conduct a study after hearing a batch of pleas filed by the residents of South Delhi’s Vasant Kunj, NGO Society for Protection of Culture Heritage, Environment, Traditions and Promotions of National Awareness (Chetna) and others seeking directions to reduce noise level in the residential areas near the IGI airport here.

NGO Chetna president Anil Sood termed the report as an “eyewash” and said it was contrary to the IIT-Delhi’s earlier report which had said that the height of the barrier was found to have influence on noise attenuation.

He alleged that the report has been prepared at the behest of Delhi International Airport Limited (DIAL) which has been trying to put forward its own agenda. The NGT has fixed the matter for hearing on October 10.

The tribunal had in January directed the Ministry of Civil Aviation and aviation regulator DGCA to mull over the possibility of providing incentives to pilots who create least noise pollution while landing aircraft at this airport.

DGCA had earlier told the tribunal that all aircraft operating from India were compliant with noise standard requirements laid down by the International Civil Aviation Organisation (ICAO), a UN agency, in order to operate globally.

The NGT had expressed displeasure over the government’s failure to fix environmental norms on noise pollution and directed the Ministry of Environment, DGCA and the Central Pollution Control Board to convene a meeting and take a clear decision on the issue.