Yamuna Monitoring Committee has directed the Delhi Jal Board to furnish a list of unauthorised colonies, along with their population, not covered under the utility's Interceptor Sewer Project (ISP) by July 15.

The National Green Tribunal (NGT)-appointed committee warned that if the DJB failed to do so, the matter will be raised before the National Green Tribunal. The DJB is in the process of installing "interceptor sewers" that will help reduce pollution in the Yamuna. Officials say 97 per cent of the work has been completed.

Earlier, sewage water from unauthorised colonies would run directly into the three main drains in the city — Najafgarh, supplementary and Shahadra — that flow into the river.

The ISP blocks waste water from unauthorised colonies and diverts it to nearby sewage treatment plants (STPs) that releases the treated effluent into the main drains, reducing pollution in the Yamuna.

"With regard to trapping of 108 drains under the ISP, the monitoring committee repeated a direction that had not been responded to for over 9 months. Information had been sought about the precise number of colonies and households that the ISP will cover...," read the minutes of a meeting conducted by the monitoring committee last month.

"The colonies left out of the ISP coverage and their population should also be given to show what remained to be trapped among the 1,797 unauthorised colonies," it said.

The DJB should also tell which colony's sewage will be diverted to which STP, the monitoring committee said.

Unless the link between the colony, the conveyance system and the designated STP is planned and shared vis-a-vis all unauthorised colonies, there can be no clarity on how the sewage from these colonies is proposed to be trapped, it said.

The DJB CEO has been asked to furnish related information in a  "comprehensible manner by July 15, failing which it will be communicated to NGT," the monitoring committee said.