Jökull - 01.12.2007, Page 77

A hot water drill with built-in sterilization
Table 2. Microbial growth and cell counts in samples collected during the drilling test on Langjökull. –
Niðurstöður ræktunar á sýnum úr borkerfinu, sem tekin voru við prófun á Langjökli.
Sampling location PCA at 30!C PCA at 7!C
Surface snow + +++
Snowmelter ++ +++
S1 – before entering filters ++ +++
S2 – after filtering in system +++ +++
S3 – after going through UV 2 CFU/ml +++
S4 – entering hose 3 CFU/ml +++
S4 – entering hose (2nd sample) 1 CFU/ml +++
Out of drill tip nozzles <1 CFU/ml +++
S1–S4: Sampling outlets indicated in Figure 1. The 500 ml samples were run through filters with a 0.45 µm pore size prior to culturing at
7!C. + : microbial growth +++ : substantial microbial growth.
Location of drill holes: March 18: 64! 36.209’N, 20! 24.656’W, 1220 m.a.s.l. March 19: 64! 37.688’N, 20! 27.180’W, 1300 m.a.s.l.
Drill test and biological analysis of drilling water
The hot water drill was tested under optimal field
conditions on the Langjökull ice cap on June 18–19
2005 (Figure 2). The test was conducted in collabo-
ration with the microbiological laboratory at the En-
vironment and Food Agency (Umhverfisstofnun) in
Reykjavík, with the aim of investigating whether full
decontamination of the meltwater could be achieved
during drilling. For sterilization purposes, all parts of
the drilling system between units 2A and 2H in Fig-
ure 1 were filled with 35 liters of 95% ethanol on the
day before departure to the ice cap. The ethanol was
emptied from the system into a container before the
start of drilling.
Two test boreholes were drilled on Langjökull us-
ing the 32-mm wide drill stem. A drill stem tip with
seven 0.8 mm wide holes (Figure 3, left) was used in
the first attempt and a depth of 80 m was reached in
2.5 hrs. The drilling direction then appeared to devi-
ate from the vertical and when the drill stem had been
pulled to the surface, one of the holes in the drill tip
was found to be blocked. During operations at this
site, 500 ml samples were collected from the surface
snow, the snow melter, from the four sampling outlets
S1–S4 within the system (Figure 1), and from the drill
tip. Table 2 lists the samples, which were collected
into pre-sterilized bottles and stored at temperatures
below 5!C for laboratory analysis.
Figure 3. Three different drill tips. Left and cen-
ter: Multi-hole tips (diameters 32 mm and 40 mm),
hole width 0.8 mm. Right: Single-hole tip (diameter
40 mm). Hole width: 1.5 mm. – Þrír mismunandi
spjótsoddar á bræðsluborinn.
During the second drilling, a drill tip with a sin-
gle, 1.5 mm wide hole was used, resulting in steady
penetration to 110 m depth in 2 hrs and 15 minutes,
corresponding to an average speed of 50 m/hr. The
hose was centered in the hole throughout the drilling,
indicating that no deviation from the vertical had oc-
curred. The snowmelter produced 500 l/hr, which was
sufficient to keep up with the measured discharge of
water through the high pressure pump (450 l/hr). The
temperature of the water emerging from the drill head
at surface level was 95!C and in total 1100 liters of
water were used to drill to 100 m depth. Numbers on
fuel consumption are given below Table 1.
In the laboratory, the 500 ml samples were run
through sterile filters with a 0.45 µm pore size. The
filters were placed on plate count agars (PCA) and
cultured at 7!C for 3 days. In addition, centrifuged
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