WestCoastJustin says they're 2.7 inches. That's small enough you could probably use a large pair of bolt cutters.

They thought there might be copper wires in there that they could sell for scrap. :P

Other than sheer criminal mischief, this is the most likely explanation.

A coworker once saw some workers in the Philippines use a bulldozer to drag 500 meters of copper phone cable out of the ground so they could sell it on the black market.

H2/O2 torch probably. Or perhaps a "jaws of life" hydraulic scissors style setup. Probably not any sort of electrical blade, I imagine cavitation and/or the viscosity of water would become an issue there.