A hot water drill with built-in sterilization: Design, testing and performance

A hot water drilling system designed to penetrate to subglacial lakes with a minimum risk of biological contamination has been built and tested. The system uses a heat exchanger to melt snow in a plastic container and the meltwater is pumped through filters and a UV sterilization unit before entering a high pressure pump and heater. The drill hose is made of synthetic rubber and reinforced with high-tensile steel braids. The drill stem is made of stainless steel and is fitted with an exchangeable nozzle. The flow rate of the drilling water at full load is 450 l/hr. The drilling speed set by a winch can be varied between 1.5 mm/s and 1.5 cm/s. In tests of the sterilization efficiency of the system using snow and tap water spiked with bacteria, reduction of cell counts and attenuation of colony forming units to undetectable levels in the drilling water has been achieved. Calculations of heat loss in the drilling hose indicate that the temperature at the drill stem drops from 90 degrees C at the surface to 33 degrees C at 300 m depth; the typical thickness of ice-cover above subglacial lakes in the Vatnajokull ice cap, Iceland. Assuming a drilling speed of 25 m/hr the drill can produce a 300 m deep borehole with a minimum diameter close to 10 cm in 12 hours.