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From garbage dump to Metro depot: Pune’s story

For Metro projects, land acquisition remains a perennial challenge. While the operational route itself can bypass this by tunnelling underground or being built on pillars that occupy the medians of roads, Metro depots, on the other hand, require a vast, on-surface land parcel.

In the urban areas where Metros typically come up, such land parcels are hard to come by. Depots are required for the regular maintenance and upkeep of trains and must therefore be within the Metro network. Acquisition of land from private parties is a complicated process, and even government land may not be available or sufficient. In this context, the transformation by the Pune Metro of an abandoned garbage depot into a plot of land fit for a Metro depot is a case study for such projects across the country.

Problem statement

The newly inaugurated Pune Metro will have three corridors. Land for the Vanaz to Ramwadi corridor was allocated at Vanaz municipal dumping ground – over 12.2 hectares of undulating land which served as a garbage depot before dumping operations stopped in 1990.

The garbage on this land consisted predominantly of municipal solid waste (MSW) heaped in stacks 10-12 metres high. The plot was home to pigs, stray dogs and rodents which thrived in these unsanitary conditions. The depot area also happens to be located amidst residential and commercial buildings, posing an environmental risk to Punekars.

Clearing the site for commencement of construction of the depot was a priority. However, the Pune Municipal Corporation was unable to provide an alternative space where the MSW could be transferred. Maha Metro Pune thus undertook the challenge of converting a garbage dump site into a world-class depot.

Preliminary decisions

A brainstorming session with all stakeholders to consider the options for clearing the site led to the following decisions:

  • Handling garbage is an environmentally sensitive issue, and the existing garbage cannot be removed from the site in its present condition.
  • Garbage needs to be handled in a scientific manner by testing and using a proven technology.
  • Physical and chemical analysis of 10 samples each to be done by a QCI-NABET accredited consultant.
  • Field trip required to an active legacy waste site for firsthand experience.

This field trip took the team to such a site in Mulund, Mumbai where they learned that waste needs to be stabilised and then segregated prior to disposal.

Results of analysis

The total waste comprised 3.8 tons with a specific gravity of 1.2 and a volume of 4,60,000 cubic metres.

Physical analysis of the legacy waste revealed that it consists of 14% biodegradable material, 39% recyclable RDF material (paper, cardboard, textile rags, plastic rubber etc.), 8% recyclable non-RDF material
(glass, metal etc.) and 39% inert construction and demolition waste.

Chemical analysis showed that 96% of the material passed through a sieve size of 4 mm. It also revealed a high content of potassium, nitrogen, phosphate and high organic carbon. The heavy metals were found to be well within acceptable norms, making it a rich soil conditioner.

The tests confirmed that the waste was in the stabilised form and safe to handle. The major requirement was to segregate this waste into various components and dispose of it as per guidelines.

Choosing the right solutions

The first step of waste management was screening, for which the in-house team experimented with multiple options. A vibratory machine of screen size 750mm x 1500mm with a sieve size of 10mm was operationalised. The sieved material was like fine-grain soil. The material left on the screen consisted of plastics, rubber, leather and C&D waste. The plastic material was flimsy, covered in dirt and of little value for R&D.

Based on this experience, a second Bed/Pit type of machine was procured. JCB was used for pouring garbage onto the sieve and the sieved material would collect in a pit.

The machines had a rated capacity of 30 cubic metres per hour but could only provide efficiency of 8-10 cubic metres per hour. This was due to almost 60% of the material being fine grained; the pit required frequent cleaning for which the machine needed to be shut down.

Another problem was that in case the JCB dropped a heavy load on the machine, it would tend to bounce off. Sometimes, the machine would stop operating due to heavy loading.

After due deliberation, a conveyor type of screening machine, like those used in quarries, was ordered, with a capacity of 40 cubic metres. The advantage of this machine was that the screened material was brought out by the conveyor and did not pose a risk in handling.

 

Screening and segregation

This was done at a central location and a barricade of green net was provided around the equipment to minimise dust particles from escaping to the atmosphere. During this phase, ragpickers were invited to collect anything of value to them.

The screened material was tested as per IS 2720 and found suitable for use as backfill.

Final fate of the waste

2,76,000 cubic metres (60%) of the waste material was sieved, of which 1,60,000 cubic metres (57%) was used as backfill for two depots. The balance was used for tree transplantation and as raw material for soil filling between metro piers.

The balance 40% inert material was used as backfill at a landfill site 20 km away.

A model to emulate

By using segregated waste at the depot site, Maha Metro avoided the use of landfill material (murum soil) which otherwise would have been sourced from mines to fill the site. This eliminated the need for the mining of 1,60,000 cubic metres of backfill material. Thus, apart from avoiding environmental damage, the strategy also helped the project save on costs, a win-win for everyone.

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