(Photo: flickr.com/mtaphotos)

In the aftermath of Hurricane Sandy, it became clear that the MTA's worst fears were realized: not only were many of the subway tunnels flooded, but they'd become inundated with salt and brackish water scooped up in the storm surge and funneled into the subway system.

The MTA has gotten parts of the system in Manhattan and Queens up and running, but pumping water out of stations dotted around Brooklyn along the East River will take some time. Seven subway tunnels beneath the East River have flooded, leaving switches and signals "likely damaged." MTA chairman Joseph J. Lhota said in an earlier press conference that the subway system "has never faced a disaster as devastating as what we experienced last night."

Furthermore, salt water can be much more harmful to equipment than fresh water. PopSci explains:

Salt has chemical properties that make it react with, and alter the composition of, iron, steel, zinc, concrete, wire insulation, and more--nearly all the building blocks of the manmade environment. It not only corrodes wires that can transmit electricity, it also conducts a charge itself, which means that it can both wear away our safety insulations, causing outages, and increase the chance of an accidental shock. When coated with salt, metal can transfer a jolt, too.

In the short term, that means big safety problems. We've already seen power outages and extensive clean-up efforts--which were triggered, at least in part, by salt.

In the long term--maybe not even that long term; "weeks or months or years," Apfelbaum says--it can mean serious, corrosive damage to infrastructure.

We better get used to waiting in those long shuttle lines.