Nearly 1,000 feet into the passageway, made up of adjacent rings each composed of concrete slabs weighing some 4 tons each, the air is thin. Oxygen roars in through a tube, providing relief for those working on the project's edge. Workers crawl along scaffolding, crouching under an Erector Set of tanks and pipes that pump out water and hurl the deep-earth's rock and mud to the surface.
Their task is to prevent large portions of Mexico City, one of the world's most populous megacities, from catastrophic flooding. The area's growing population has placed demands on water supplies that are simply unsustainable. Its 20 million residents have laid down an urban jungle that obstructs water from naturally filtering into the ground.
Today, the city is sucking up water from the natural aquifers at twice the rate they are being replenished. The result: Mexico City is sinking, in some areas up to 16 inches a year, threatening its entire infrastructure. This includes the city's deteriorating drainage system, whose capacity has diminished by 30 percent since 1975 while the area's population has doubled.
"It's an alarming situation," says Felipe Arreguin, the technical general subdirector at Mexico's National Water Commission (Conagua), which is building the drainage tunnel. "We are taking [out] so much water, the city is sinking. What if an entire block were to go under?"