The National Rivers Authority (now the
Environment Agency) commissioned Simon
Hughes and I to tackle the problem. This
we did in 5 stages:
1. Create large lagoon to catch any
sudden surges during works. The lagoon
was floored with hundreds of tons of
powdered limestone.
2. Remove scree above and behind the dam
in order to expose it properly.
3. Pump out clear water sitting on top of
ca. 0.5m of ochre, liming the discharge
every 15 minutes thus raising the pH from
2.5 to 5.5. This stage went on on a 24-7
basis.
4. Pump out ochre into the large lagoon
and bury with powdered limestone.
5. Remove dam and repair broken lagging.
Some aspects of this utterly messy but
ultimately successful job are illustrated
below. |
Opening up the adit mouth and setting up
pumps. A considerable amount of scree had
to be cleared off the back of the adit.
The excavator dug well back to allow for
further landslides, this permitting
access to a "porthole" into the
water at the back of the dam. A
submersible pump was lowered just under
the surface of the water, to avoid
stirring up the ochre below. A digital pH
meter was installed in the mine
discharge, a large stash of agricultural
lime was placed just upstream and we were
ready to go. |
A view up the adit during pumping. The
dam lies ahead in the darkness. While
pumping was ongoing the adit floor up to
the dam was cleared of debris. |
Once the water and ochre had been pumped
well down, work commenced on tackling the
dam, a mixture of fine shale, soil and
soft ochre. In this image the dam is
half-removed. The burst lagging where the
shale came in is above and to the left of
the dam. |
Beyond the dam lay the inky depths of the
mine which was explored for a short
distance. However, dangerous roof
conditions and bad air made a full
inspection of the mine impossible. This
image is taken a short way in. Note the
square timbering and copious amounts of
ochre in places - it covered the floor,
walls and roof. Ochre itself is however
less toxic than the mine water with its
loading of heavy metals - a classic case
of the highly visible pollution being
aesthetically displeasing while the
apparently "clear" water is in
fact the real rogue! |
The lagging on the level portal was
replaced. Note that this was a temporary
job designed to tackle an environmental
emergency: we made it clear at the time
that a longer-term solution must be found
and implemented. However, the adit should
not let in any more scree for a few tens
of years. |
Here, one of the NRA
excavators is spreading lorryloads of
powdered limestone over the ochre pumped
from the mine into the big lagoon. The
ochre in turn was pumped onto a powdered
limestone bed. This image also shows the
rusty mine-tips. |
Here the No 9 job is nearing completion.
The words "Keep Out - bad air"
were added to the mine door after this
photo was taken. In front of the door are
the remains of a mine-wagon which was
found buried in shale and winched out of
the way. The water was set to discharge
via a pipe from this small settling
lagoon.
Although we went home happy after
completing this work, Nature was to have
a nasty surprise for us, some distance
away, which 6 months after this photo was
taken was to transform the site's
appearance once again. |
