[ckissick]

As a geologist I've worked on tunnel jobs and jobs where we drilled over 950 vertical feet into granite in just a couple of days. The boys are about a kilometer down. With directional boring you can aim for your target very accurately.

You could define your target by performing a simple "seismic refraction survey". This is done by setting off very small explosive charges in shallow auger holes, where the boys are. Vibrations travel through the rock and are picked up by a network of geophones at the surface. The geophones detect the compression waves at different times, depending on their distance from the source of the wave. Simple geometry defines the location of the source. A good oil well driller could get those boys out in no time.