Parys Underground Group / Grwp Tanddaearol Parys

Dyffryn adda drainage adit

In 2001 the group decided to explore an old drainage adit to the North East of the mountain. The adit had not been entered for about 40 years. The flow of water out from the adit was very slow due to the build up of "Ochre" a thick mud formed by the oxidation of iron.The joint level at Dyffryn Adda was driven for 3000 feet into the mountain by the Parys and Mona mine companies around 1850 to help dewater the mines below the 45 fathom level.



Once the entrance had been cleared it was possible to wade through the thick mud and water. .
In the 19th century, when deep mining had ceased , a dam was constructed across the level to allow the stoops and levels in the mountain to flood up to the 25 fathom level of the mine. This allowed many millions of gallons of water to pond up behind the dam and absorb the copper minerals remaining in the worked out mineral veins. After many weeks work we where able to find the dame again. The concrete and valves were in a very poor state of repair. 
It was immediately realised that the hold up of  water behind the rotting dam was a great hazard to the people of Amlwch. A dewatering project was set up to try and deal with the problem.