Drilling down the dumps

-- SINCE July last year, the municipal
garbage dump at Gladokvarn, outside
Stockholm, has been yielding gas at the
rate of 22,000 in per day from gas wells
up to 20 in deep. The gas is carried via a
13 km-long pipeline to a 5 mw heating
plant which, in turn, supplies central
heating to the nearby Skogas housing
estate - enough to heat some 2,500
single-family houses.

It is a well known fact that household garbage, compacted over long periods of time, creates large quantities of
methane gas. Many attempts have been
made in the past to bring the gas to the
surface and harness it, not just for
commercial purposes but also to
prevent it from leaking into the
atmosphere and contributing to the
greenhouse effect.

The technical problems involved,
however, have been difficult to solve.
The main problem is to be able to drill
large and deep well holes through layer
upon layer of material containing such a
wide variety of waste. However, engineers in Sweden claim to have found
almost a complete answer.

The drilling at Gladokvarn was carried out by Svenska Borr AB, using an
Atlas Cop Geodrill 800E equipped with a
six-inch-hollow stem auger, a drilling
tool. The hollow stem auger is normally
used for soil investigation, groundwater
monitoring and well-drilling. The auger
has no trouble with small metal objects
and simply pushes larger objects aside.
Wood, concrete and stone can give
some problem by slowing the rotation
down, but generally speaking, it drills
right through without stopping.

During the first two weeks of
drilling through the compacted household waste consisting of every conceivable type of material, eight holes varying
from 15 in to 20 in deep were drilled.
The engineers soon learned to operate
the wireline system. The deepest hole
drilled was 22 in deep and was completed in less than 24 hours. Now almost
70 holes have been drilled, of which
about 50 are active.

The company claims that it is the
first in Sweden and probably one of the
first in Europe to use a hollow
stem auger for this type of work,
which although not problem-free, is
vastly superior to conventional drilling
in these circumstances.