New Delhi, July 16 -- A new survey of the Yamuna has revealed an alarming truth: the Najafgarh drain, long known to be the river's biggest polluter, is pumping nearly twice the estimated volume of untreated sewage into the Yamuna. And a significant chunk of this pollution isn't even Delhi's doing - it originates in Gurugram. The revelation is part of an ongoing analysis by the Delhi government to assess untreated sewage flow into the Yamuna from the city's 22 major drains. According to Delhi water minister Parvesh Verma, fresh findings indicate that the Najafgarh drain alone now carries around 800 million gallons per day (MGD) of sewage into the river-up from previous estimates of 450 MGD. Even more striking is that nearly 250 MGD of that waste is believed to come from Gurugram, through drains such as Badshahpur, before entering Delhi's already overburdened drainage network. "This (the actual volume of sewage) is a serious discovery," Verma told HT. "We are mapping every drain and their catchment areas to understand where the sewage is coming from and how much of it is treated or untreated. The final report will be ready by September or October, and it will help us plan the treatment infrastructure accordingly." The most polluted 22km stretch of the Yamuna in Delhi, between Wazirabad and Okhla, receives effluents from dozens of drains, with Najafgarh and Shahdara being the most significant. Experts said the scale of the problem exposed by the new survey demands a complete re-evaluation of sewage treatment capacities and pollution control efforts across both Delhi and neighbouring Haryana. Meanwhile, officials of the Gurugram Metropolitan Development Authority (GMDA) confirmed that steps are being taken to stem the flow of sewage into the Najafgarh drain. A senior GMDA official said the authority is upgrading its two main sewage treatment plants (STPs) at Dhanwapur and Behrampore and constructing a new 350 million litres per day (MLD) STP in Sector 107. A common effluent treatment plant (CETP) for industrial wastewater is also under construction. Additionally, a new main pumping station of 665 MLD capacity will be set up at the Dhanwapur STP, along with additional treatment capacity of 100 MLD each at both existing plants. "Our aim is to recycle the maximum amount of sewage generated in the city and reduce the burden on downstream systems," the official said. On July 11, Union home minister Amit Shah chaired a high-level review meeting on the Yamuna, and directed that drone surveys be conducted of the Najafgarh and Shahdara drains. He also stressed on the need to double Delhi's STP capacity to 1,500 MGD by 2028 as part of a multi-pronged strategy for rejuvenating the Yamuna. Delhi currently generates about 792 MGD of sewage, but its 37 STPs can treat only 667 MGD, with only 565 MGD is actually being treated, according to the Delhi Economic Survey. This leaves a gap of 227 MGD -- wastewater that flows untreated into the Yamuna. Experts believe this shortfall is even greater when factoring in groundwater use, which remains largely untracked in sewage calculations. Verma said that with land scarcity in parts of Delhi, the city is now planning 40 decentralised STPs to ensure local treatment of wastewater, rather than relying solely on large centralised plants....