The green tribunal’s directive to biomine landfill sites at Okhla, Bhalswa and Ghazipur has prompted experts to question the risks involved in the process. Sidharth Ravi probes the pros and cons of the proposed exercise

The infamous garbage hills of Delhi — at Okhla, Bhalswa and Ghazipur — will soon be “biomined” in order to have them cleared.

The landfills are proposed to be dug up and the garbage, after processing, would either be recycled, or sent to fill up the abandoned Bhatti Mines on the border of south Delhi, or be used as road construction material. But without clarity on the toxicity levels of what will be dug up and sent to the mines, there remains a risk of contaminating a whole new area, especially if done without adequate safeguards.

A study by researchers at IIT-Delhi, recently published in the Journal of Hazardous, Toxic and Radioactive Waste — ‘Leachate Characteristics of Aged Soil-Like Material from MSW dumps: Sustainability of Landfill Mining’ — tackles exactly this question. Through multiple mined samples from three landfills in different parts of India, including the one at Okhla, the study determines the presence of dangerous levels of toxicity in the leachate (dark-coloured liquid produced when water seeps through garbage) produced from such excavated and processed landfill material.

The exercise of biomining and bioremediating the landfills was ordered by the National Green Tribunal in July. Based on the reported success of similar work carried out by the Indore Municipal Corporation at its landfill site, the tribunal instructed the three municipal corporations of Delhi to begin the project on their landfills by October 1. And finish clearing them within a year.

The cost of carrying out the work at all three sites, estimated at ₹250 crore by the court, has been set aside in an escrow account. The NGT has instructed that this amount would be forfeited if satisfactory progress is not shown within six months.

‘Capping’ ruled out

While passing the order, the NGT cited multiple reports of groundwater pollution, fire breakouts, festering of unhygienic conditions and an increase in air pollution caused by such landfills across the country. Taking cognisance of the hazards of such dump sites on public health and the environment, it was determined that they must be cleared at the earliest. To this end, the tribunal rejected the alternative of an engineered “capping” of the landfills.

According to the guidelines of the Central Pollution Control Board, presented to the NGT, “Capping of dump sites was not advisable as it would lead to generation of more leachate and methane gas which would further contaminate the already heavily contaminated groundwater.” Such capping could only be allowed in the complete absence of potential of biomining and bioremediation, the NGT observed.

The Indore example

The case of the Indore Municipal Corporation, which had reportedly cleared 15 lakh metric tonnes of a landfill site within one year through biomining, was cited to recommend the same. Asad Warsi, who assisted in the Indore model and presented the case to the tribunal, explained the process thus: the material after being excavated and aerated for decomposition was put through trommels (a large sieve tube) to segregate it. Construction and demolition material thus separated was sent to cement plants, while others like cloth and plastic were used as refuse-derived fuel. The remaining soil-like material was spread out over the area of the landfill.

While multiple studies have shown that such soil-like material constitutes 50%-60% of the landfill, in terms of volume it would be only about 30%, Mr. Warsi claimed.

The project carried out in Indore was also used to recommend similar works in Ahmedabad and Gurugram. However, the scale of work to be carried out in Delhi, where the three landfills have a combined capacity of 2.8 crore metric tonnes of garbage, spread over 152 acres of land, and the plan to fill the abandoned mines to attempt afforestation would be a first of its kind, said Mr. Warsi, who has been roped in as a consultant by the Delhi civic bodies.

‘Safeguards needed’

As part of the study, various tests for toxicity were performed on leachate produced in a lab from soil-like material, which was dried, mixed and screened after being from collected from landfills in Hyderabad, Delhi and Kadapa. Results of these tests were compared with water passed through regular soil, collected from 5 km around the landfill. The study showed that heavy metal concentration was up to 96% higher in the soil-like material. Other characteristics and elements such as hardness, calcium, magnesium, sulfates, chlorides, bromides, organic matter, alkalinity and ammoniacal nitrogen were all found to be in much higher concentration.

“We can expect that about 20% of the landfill will probably be toxic,” Mr. Warsi conceded. It would perhaps also be laden with heavy metals given the size of the city and the age of the landfills, he added. While the oldest landfill at Ghazipur has been operational since 1984, the one at Bhalswa has been operational since 1993 and the one at Okhla since 1994.

A lot of unchecked hazardous material not supposed to be dumped at landfills may have found its way here, he explained. This would affect the toxicity of the soil-like material which would be derived from the landfills. But to make sure it doesn’t contaminate the mine it is shifted to, safeguards such as sandwiching the material between layers of soil and geosynthetic clay liners would be undertaken, he said.

However, the quality of these liners, the difficulty of laying them inside a mine and the risk of leachate collecting at the bottom of the pit over time would have to be kept in mind, said experts.

Apart from this, Mr. Warsi also suggested that certain varieties of trees could be planted over the site to absorb toxic material. However, here too, the level of penetration of the roots into the soil and their ability to absorb heavy metals will have to be considered. In any case, Mr. Warsi said that the solution with the least environmentally hazardous impact had to be chosen.

While such techniques, possibly unaccounted for costs, may be deployed to safely dispose of the waste in the country’s capital, similar safeguards will also have to be kept in mind while dealing with biomining exercises set to start across the country. The NGT in its order has also directed all municipal corporations in the country to carry out similar projects, starting November 1, one month after the work commences in Delhi.