Jökull - 01.12.2007, Side 73

Instruments and methods
A hot water drill with built-in sterilization:
Design, testing and performance
Thorsteinn Thorsteinsson1, Sverrir Óskar Elefsen1!, Eric Gaidos2, Brian Lanoil3,
Tómas Jóhannesson4, Vilhjálmur Kjartansson1, Viggó Þór Marteinsson5,6,!!,
Andri Stefánsson7 and Thröstur Thorsteinsson7
1Hydrological Service, Orkustofnun (National Energy Authority), Grensásvegi 9, IS-108 Reykjavík, Iceland
2 Department of Geology and Geophysics, University of Hawaii, Honolulu, Hawaii 96822, USA
3 Department of Environmental Sciences, University of California, Riverside, California, USA
4 Icelandic Meteorological Office, Bústaðavegi 9, IS-150 Reykjavík, Iceland
5 Environment and Food Agency, Suðurlandsbraut 24, IS-108 Reykjavík, Iceland
6 Prokaria, Gylfaflöt 5, IS-112 Reykjavík, Iceland
7 Institute of Earth Sciences, University of Iceland, Sturlugötu 7, IS-101 Reykjavík, Iceland
* Now at: Hönnun Consulting Engineers, Grensásvegi 1, IS-108 Reykjavík, Iceland
** Now at: Matís ohf., Skúlagötu 4, IS-101 Reykjavík, Iceland
thor@os.is
Abstract – A hot water drilling system designed to penetrate to subglacial lakes with a minimum risk of bio-
logical 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 pres-
sure 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 !C at
the surface to 33!C at 300 m depth; the typical thickness of ice-cover above subglacial lakes in the Vatnajökull
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.
INTRODUCTION
Hot water drilling in ice is a standard method in
glaciological research (Taylor, 1984; Iken et al., 1989;
Hubbard and Glasser, 2005 and references therein),
but its use in drilling to subglacial lakes has so far only
been carried out in Iceland. There, geothermal and
volcanic systems beneath temperate ice caps sustain
ice-covered lakes that regularly drain in jökulhlaups
(Björnsson, 2002). Lake Grímsvötn, a lake beneath
the Vatnajökull ice cap, was first accessed with a hot
water drill in 1990 (Björnsson, 1991) and during a
drilling operation in 1991 the lake temperature was
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