Bollocks the wavelengths are on the order of hundreds of meters, there is no way you get microwave like heating out of that. Even at 30 MHz you're still looking at 10 meters wavelength, 3 meters at 100 MHz.

This system operates according to TFA up to the end of the AM band at roughly 1600 KHz, so 180 meters and change.

The danger is more likely there because someone might enter the tunnel and hit the feeder, which depending on the design can carry considerable power.