At Deonar dumping site, toxicology indicators four times safety limit: Study

According to the study, the average BOD in the leachate was 390 milligram per litre (mg/l) — the permissible limit is 100 mg/l (land) and 30 mg/l (water). Similarly, the average COD was 1,002 mg/l, while the permissible limit is 250 mg/l (water); the average TDS level was 6,550 mg/l, while the permissible limit is 2,100 mg/l (see box).

BOD indicates the amount of dissolved oxygen required by microorganisms to break down organic matter present in a water sample; COD refers to the amount of oxygen required to chemically oxidise organic matter; TDS refers to total concentration of all dissolved substances, including inorganic salts, minerals, and organic matter.

While the study was commissioned by the BMC in 2023, as a first step towards reclaiming the landfill, the report was made public last month after the civic body floated a Rs 2,368 crore tender to clean up the site by a process of bioremediation within three years. The study was carried out by NETEL India Limited, in a joint venture with NM Consultants-SKW Soil and Surveys.

According to the study, ‘inert waste’, which includes construction debris and non bio-degradable material, comprises 30-50% of the waste. “This type of waste poses challenges for disposal and management due to its… low degradation rate,” the report says.

Speaking to The Indian Express on the significance of the findings, Dr Tuhin Banerji, a PhD research scholar at IIT Bombay and former scientist at the National Environmental Engineering Research Institute (NEERI), said the high BOD, COD and TDS levels indicate that the entire area is severely contaminated.

“The leachate contaminates the soil and water severely. The high BOD, COD and TDS levels indicate that the whole area is contaminated, (making it unsuitable) for human habitation, at present. Any living organism, be it micro-organisms, animals or plants will not survive in such conditions, since the process of nutrient uptake will affect organisms across the food chain in a similar manner,” he said.

Saying that the level of contamination could be controlled by increasing the green cover around the dumping ground, Banerji said: “The High Court had recommended implementation of a green belt across the periphery… to control pollution levels. The green belt uses specific trees to absorb pollutants from soil, creating a barrier and preventing the pollutants from entering other areas.”

“The process of bioremediation needs to be done in a proper way to make it habitable for humans. No shortcuts should be taken,” he said. Saying that the average time for completing the bioremediation was a “minimum of five years”, he said the three-year target set by the authorities was “less, if seen under a scientific lens”.

When contacted, Kiran Dighavkar, Deputy Municipal Commissioner, solid waste management, said: “In the tender document that was floated for clearing the waste pile from the dumpsite last month, it has been clearly mentioned that the methodology of ideally processing the legacy waste, including the leachate, should be ideated by the contractor who will be awarded the contract. After the contractor submits the proposal, we (BMC) will analyse it and, if required, a peer review process will be carried out through a reputed agency. After we approve the methodology, work will start on the ground.”

Dighavkar said the contractor for this work would be finalised by June 23, following which the work order would be issued. “Before the monsoon season ends, the selected contractor will have to finalise the methodology and mobilise manpower, so that the work of bio-remediation can immediately begin after monsoon gets over,” he said.

“The primary challenge is in the manner of logistics. The leachate particles, along with every component of solid waste, will be treated scientifically, following which a residue will be extracted. Usually, these residues are used by cement factories. However, there is no cement factory available near Mumbai; the nearest factory is at least 500 km away. So the process of transporting the residue or deciding what to do with it is going to be a challenge,” said a civic official.

“Secondly, the maximum component of waste present there is either inert or non-recyclable, which is also a challenge. But we will have to achieve the process with bio-remediation, since this is the certified methodology of landfill reclamation as prescribed by the Government of India,” the official said. Bioremediation involves treating garbage with microorganisms that flourish in air and sunlight.

In October 2024, the state government had allocated 124 acres of the 311-acre Deonar landfill for the Dharavi Redevelopment Project (DRP), which is being carried out by the Navbharat Mega Developers Private Limited (NMDPL) — a special purpose vehicle set up through a joint venture between the Adani Group (80%) and the state housing department’s Slum Rehabilitation Authority (20%).

At present, the Deonar dumping ground houses 1.85 crore metric tonnes (MT) of legacy waste piled up in 40-metre-high mountains.

On April 11, The Indian Express had reported that around 6,200 kg of methane is generated from the landfill every hour, making Deonar one of the top 22 methane hotspots in the country, according to a CPCB report.