Bogota Metro Could Become Colombia’s First Urban Mining Laboratory

The construction of the first line of the Bogota Metro has led the attention of the capital’s residents to the future and to the benefits that this mass transit system will bring, a dream that will become a reality after 80 years of failed attempts. But little attention has so far been paid to the enormous volumes of waste the project has been generating.

A study by the National University of Colombia (UNAL) concluded that this megaproject offers an unprecedented opportunity to plan the use of these resources from the very beginning of construction. Metro Line 1 will make it possible to track the behavior of about 8.51 million tons of materials that will be moved during its construction.

This scale turns the project into a unique scenario for evaluating, for the first time in Colombia, how these materials can be reincorporated into new infrastructure projects through urban mining processes, instead of being treated as waste once construction is completed, reported the UNAL News Agency, Unimedios.

The multiple uses of fill materials and excavation material

Unlike traditional recycling, in this model the recovery of materials is planned from the design and construction stages of the project, making it possible to identify which resources will remain available as an “urban reserve” for the city, where they will be located, what value they will have once the project is completed, and how they can be reincorporated into new construction and industrial processes, thus reducing the extraction of raw materials and the generation of waste.

Applied to the first Metro line, which has now reached 80% completion, this model would make it possible to identify which materials can be reused and what obstacles prevent that from happening.

Of the nearly 8.51 million tons of materials that the project will move, 4.64 million tons consist of fill and excavation material, while 3.54 million tons are concrete, the same outlet added. These resources could be reused in structural fills, soil stabilization, new concrete, and other infrastructure projects, for example, instead of becoming waste, representing one of the greatest opportunities to promote urban mining in the country.

However, taking advantage of that potential depends not only on the amount of materials available, but also requires changes in the way projects are planned, in the regulations governing waste management, and in the demand for recovered materials, according to Andrea Sandoval Santos, who holds a master’s degree in Environment and Development from UNAL, as quoted by the agency.

The researcher analyzed these conditions and identified the potential for this megaproject to become the country’s first urban mining laboratory.

“The real challenge is to consolidate rules, markets, and mechanisms that make it possible to calculate available mineral reserves and reincorporate these materials into new productive cycles,” she explained to Unimedios, where she said that, to verify this potential, she analyzed which materials enter construction, in what quantities they are used, which become waste, and what their destination is when each stage of the project is completed.

Broad room to strengthen urban mining strategies

A review of the Environmental Management Plans, Construction Implementation Plans, and other documents from the Bogota Metro Company allowed the researcher to establish that the main waste stream generated during the initial stage of the project corresponds to excavation materials, which account for 85% of construction and demolition waste (debris).

These soils could be used in structural fills and soil stabilization processes instead of ending up in final disposal sites, that is, the authorized locations for permanently depositing waste that cannot be reused, provided they meet the required physical and chemical characteristics, as well as the technical standards established for each use.

Likewise, the expert found that only 2.96% of the material has been reused in situ, a figure that demonstrates the broad room that still exists to strengthen urban mining strategies and advance compliance with the recovery targets established for this type of project.

More than quantifying the available materials, the research identified that the main obstacle to implementing urban mining in Colombia is that construction and demolition waste continues to be managed as waste rather than as a potential source of raw materials for new projects.

Although there is a regulatory framework for its management, it focuses mainly on verifying compliance with recovery and disposal targets, but does not generate incentives to effectively reincorporate these materials into new infrastructure projects.

“Its management continues to respond largely to a logic of regulatory compliance,” Sandoval Santos added to Unimedios. “The goal is to avoid a sanction or meet a percentage required by the environmental authority, but not necessarily to take advantage of these materials as a source of raw materials for new projects.”

Colombia should move toward a model already proven viable worldwide

For that reason, the transition toward this model does not depend solely on having technologies to recycle concrete, asphalt, or stone materials, but also requires adjusting regulations, strengthening markets for recovered materials, and coordinating public entities, construction companies, waste managers, and communities so that the use of these resources becomes part of project planning and helps prevent social conflicts and the concentration of the value generated by these materials in the hands of a few actors.

What today represents a challenge for the first line of the Bogota Metro has already proven to be viable in other megaprojects. One example is the Brenner Base Tunnel, between Austria and Italy, which will be the longest underground railway tunnel in the world. There, about 30% of the excavated material is reincorporated into the project itself as aggregate for concrete and structural linings.

This experience demonstrates that excavation materials can stop being viewed as an environmental liability and become a source of raw materials for the infrastructure itself.

Based on these experiences, researcher Sandoval Santos argues that Colombia should incorporate urban mining from the planning stage of major projects, such as the future Metro Lines II and III in Bogota, taking advantage of the lessons learned from the first line rather than waiting until the waste has already been generated.

She also recommends strengthening coordination among public entities, construction companies, waste managers, and research centers to expand the use of recovered materials and thereby consolidate a market that makes their utilization viable.