Rhydymwyn is a village in Flintshire, North Wales, located in the upper River Alyn valley. Once a district of Mold, it was recognised as a separate parish from 1865.
The geology of the area consists of a layer of extremely pure, and hence structurally sound, 200ft thick layer of limestone at depths ranging from surface to 900 feet.[1] The limestone holds other minerals, including lead, nickel and copper deposits, making it an ideal site for mining.
Due to the industrialisation of Northwest England, and it needs for mineral supplies, the mineral deposits in the Alwyn valley created a population explosion in various villages, including Rhydymwyn.
The new parish of Rhydymwyn was created on 31 March, 1865, comprising: parts of the townships of Gwysaney and Gwernaffield, formerly in the parish of Mold; parts of the townships of Cefn and Glust (or Llysdianhunedd), and the whole of the township of Dolfechlas, formerly in the parish of Cilcain; and part of the township of Caerfallwch, formerly in the parish of Northop. The foundation stone of the new parish church, dedicated to St. John the Evangelist, was laid on 1 August, 1861, and the church was consecrated on 17 September, 1864.[2]
In the autumn of 2000, local rainfall was exceptional in terms of intensity and duration. Between 28 October and 6 November, 68 homes and 8 businesses flooded in Rhydymwyn thanks to overflow from the River Alwyn. In 2002 and 2003, DEFRA's internal team in two phases created a flood alarm and protection scheme to protect the whole village and Valley Works, with a level of protection in excess of a flood with a 1% chance of occurring in any one year. The total cost for the scheme was £88, 000.[3]
Due to its unique geographic structure, the Alyn valley has been used by the UK government for storage of sensitive material for most of the twentieth century. This is in part due to a combination of factors, including old mine workings, and a very low population density; but with good road (A541) and railway (LNWR), transport links. With access to clean and fast flowing water, Rhydymwyn offered an ideal site for a munitions factory.[1]
Originally used for mining, the site known as "The Foundry" was closed after becoming uneconomic. Controlled by the UK Government, while the War Ministry was investigating chemical weapons the site was chosen as a UK site for chemical weapon production and storage.
In September 1938 the Ministry of Supply started construction of a purpose-built chemical weapons storage facility at the Valley Works. Operating under the guise of ICI - the site was in actual fact unique, as it was the only ammunitions factory which was purpose built; the UK’s other six big munitions factories were based in ICI factories. Incoming services were adequate, however waste disposal was difficult, and so miners from the Hendre Mine company HDUM Ltd were commissioned to build a 24 inch waste pipe. Laid in total secrecy the six miles to the River Dee estuary for the disposal of high level waste, arrangements for gaseous emissions were classified as an "acceptable risk to the local populous."[1]
In October 1939 HDUM miners began cutting four 30 feet wide, 8 feet high and 760 feet long tunnels into the hillside behind the former mine surface buildings. Connected to these are a set of four storage chambers at a depth of 140 feet below surface. The work was completed in October 1940.
The first chemicals arrived on 19 June, 1940 but production didn't start until January 1942, when staff from ICI Randle arrived to supervise the startup of the Valley production plant. From 1942 to 1945, the factory produced the UK's entire supply of mustard gas, which via secure Royal Air Force guarded train onto the nearby LNWR railway line, was distributed all over the UK to various airfields.
The site consisted of"[4]
After being shut in 1945, the site remained top secret and off of the local Ordnance Survey map. In the 1990s the European Union stored food stocks in the tunnels.[5]
Still permanently guarded today by owner DEFRA appointed private security guards, in 2003 under a ten year agreement the site was leased to North East Wales Wildlife. Made safe for access by local volunteers, the site is now a registered nature reserve and open to the public. The Welsh heritage NGO Cadw have proposed listing the remaining structures as a Grade Two listed building.[4]