One of the processed used during the operation of the mine was precipitation. This involved storing water within the mine over the winter period and then letting it out into large areas called precipitation pits. The water in these pits collected a significant amount of dissolved copper while in the mine.
Scrap Iron was thrown into this solution and over the period of a few weeks the iron and copper reacted such that copper was precipitated out in the bottom of the pits and could be collected.
There is evidence that even when the main underground processing operation of the mine had ceased, some precipitation operations was still ongoing.
One area where the precipitation process was still going up until the 1940 was at Dyffryn Adda.
To maximise the amount of time that water within the mine had to dissolve in the water a concrete dam with drainage valves was constructed in dyffyn adda. Up until the 1940s the valves were regularly opened to drain water rich in copper out into the precipitation pits.
To maximise the amount of time that water within the mine had to dissolve in the water a dam with valves were constructed in dyffyn adda. Up until the 1940s the valves were regularly opened to drain water rich in copper out into the precipitation pits.
Unfortunately, the practise of draining the mine seemed to have stopped before 1950. By the time PUG entered the mines at the end of the 20th century the level within the mine had built up to such an extent that it had formed a large pool in the bottom of the open cast.
This was beginning to cause concern with the environmental agencies. In other mine locations around the UK a similar build-up of water behind a dam had been released, uncontrollable when the underground dam had weakened and failed over time.
It was decided to try and examine the concrete dam by gaining access from the Dyffyn Adda portal and trying to walk up the drainage adit until the dam wall was reached and could be inspected.
After many weeks of digging, a small crew eventually got to the downstream side of the concrete dam. From this area it could be seen that the concrete of the dam was beginning to crumble and that the Saunders values previously used for draining the mine were blocked.
The blocked valve and poor condition of the dam caused even more concern for the environmental agencies. It was decided that the main would need to be drained or pumped out to prevent catastrophic failure of the dam wall.
There was one shaft (Garrdd Daniel) which was just of the upstream side of the known position of the dam. It was hence decided to drill a hole in the top of that shaft to try and determine the level of water behind the dam. It was found that the level of the water was 15 metres below the shaft top.
To determine what sort of pollutants may be in the water it was arranged for a pump to be used to take a large sample of the water into a road tanker which could then be analysed. It was also hoped that by pumping out 6000 gallon of water and watching the level drop in the shaft that the total amount of water in the mine could be estimated.
However, the drop in the shaft level was insignificant. After much discussion it was realised that trying to pump the water out of the mine into a road tanker for disposal was not a feasible option due to the amount of water which could be held up in passage ways and caverns.
It was eventually decided that the only practical solution was to pump the water up the Gardd Daniel shaft, under the road via pipes in an existing draining ditch and discharge the water into the Afon Goch river which would then naturally discharge into the sea at Amlwch.
There were obviously environmental concerns about the amount of copper and other heavy metals which may be discharged this way, however on balance the risk of the dam wall collapsing and causing uncontrolled pollution and damage was deemed to be so great that discharge to sea over a number of days / weeks was thought to be the best option.
The pumping work started in 2003.
The quality of the water was monitored every day by engineers working on the project. Samples are also being taken and analysed by the Environmental Agency.
The water was been clear, with a pH of about 2.5. As you would expect the water contains both copper and zinc and traces of other metals.
The pumps removed around 50 litres per second of water from the mountain. The pumping operation took 8 weeks.