Scenes of caustic red sludge surging through pastoral Hungarian villages last week evoked a familiar blend of human pathos and righteous anger that most of us had shelved shortly after the BP well was capped. Then the news cycle turned over and our attention moved elsewhere. But as emergency workers in western Hungary slog through ankle deep rivers of toxic red muck to clear roads and contain the growing mess, the hardest job hasn’t even started: the cleanup of an estimated 30 million cubic feet of alkaline mud covering some 16 square miles of Hungarian countryside.

So far, nine people have died and more than 100 have sought medical treatment in the immediate aftermath of the industrial calamity – the “red mud,” as it’s known, is a byproduct of the aluminum production process – but the larger impact of the massive toxic spill will be measured in decades rather than weeks. That’s because the sludge – rich in inorganic salts, toxic metal oxides, and highly basic sodium hydroxide – isn’t the kind of stuff emergency workers can simply mop up. With pH levels as high as 13 in some places (seven is neutral; pH 13 is as caustic as bleach or engine cleaner), the toxicity of the metallic components take a backseat to the salts and spiking pH levels that could potentially make the land unusable for decades.

“The deposition salts and the high pH are going to render the land unproductive for agriculture,” says Dr. David Dzombak, a professor of civil and environmental engineering at Carnegie Mellon University. “It’s going to kill the plants that are there now, and even if you just want to re-plant grass or have a city park or landscaping, you won’t be able to until you do something to address those impacts.”

The first step in addressing those impacts is isolating and removing the source of the contamination. For a swath of territory approaching the size of the island of Manhattan, that’s going to be a very expensive first step for Hungary.

“You have to do physical removal,” says Wei-xian Zhang, professor of civil and environmental engineering at Lehigh University. “Then there are different remediation technologies to recover or clean up the small amounts of residuals left after the physical removal.”

The removal process is already somewhat underway in Hungary, though not really in earnest. Workers in Hungary are now working to clear roadways and make way for emergency vehicles and the eventual larger cleanup effort. But as the situation shifts from emergency response to land remediation, workers will try to recover and deal with as much of the sludge as possible, a volume estimate to be anywhere from 25 million to 35 million cubic feet.

Crews will have to shovel all that red mud – some of which will have dried into a hardened mass that scatters toxic, breathable particulate matter on the wind – into trucks for removal to a specially engineered landfill for proper storage, a costly undertaking. Then, site by site, engineers will have to decide how much topsoil has been contaminated – and to what degree – and answer the tough question inherent in pretty much all land remediation projects: how clean is clean enough? Topsoil deemed to be too contaminated would also be removed to a landfill. There are ways to wash soil – stripping it of its contaminants and returning it to the ground – but again high costs make such techniques more or less unfeasible for a disaster area the size of Hungary’s.

“The best thing for them to do is to build a landfill near the site and try to remove the topsoil and move it into a landfill,” Zhang says. “If you can, you move 95 percent and treat the remaining 5 percent.”