Site Records


The Valley Works
North Wales

[Source: Andrew P Smith]

17/7/02. We have obtained this outline proposal from DEFRA (formerly the MAFF) on the immediate future of the Valley Works site. We also have a copy of the map (90k.gif click here) detailing which structures will be affected. This information is reproduced with the full permission of DEFRA.

DEFRA (outline proposal): Valley Factory, Rhydymwyn.


The former Ministry of Agriculture, Fisheries and Food (MAFF) Buffer Depot at Rhydymwyn closed in 1994 and now is completely unused. The Depot occupied the site and buildings of what had been the wartime Valley Factory site, where chemical warfare munitions had historically been produced and stored. A review of the site’s history to help determine the requirements to return the land to beneficial use was therefore carried out and the results presented to the local community at a public meeting in 1997, together with an outline of the proposed plans for further investigation.

The Department for the Environment, Food and Rural Affairs (DEFRA), has completed these investigations and will soon be carrying out a programme of works to:
a) improve the frontage of the site by demolition of the former administration area buildings and the carrying out of minor landscaping
b) demolish buildings in the vicinity of the Tunnel Entrances as required under the Chemical Warfare Convention
c) demolish clad buildings with the potential to be a physical hazard as fixings deteriorate
d) reduce the residual risk of buried toxic features by capping of pits and infilling of manhole chambers
e) provide additional groundwater monitoring wells to demonstrate lack of contaminant migration from burial pits

This document summarises the findings of the investigations and describes the planned works. Its aim is to bring the local community up to date with the latest understanding of the site and to start the process of building a consensus on the long term options for the land.

Site History

The Valley Factory at Rhydymwyn was developed on the site of a former lead mine between 1939 and 1940. It contained purpose built facilities for the wartime production of mustard gas, its storage in underground chambers, the filling of munitions with chemical agent and the assembly of filled munitions with explosive bursting charges and fuses. Later in the war, one of the buildings was used for gaseous diffusion experiments in support of the early atomic bomb project.

Mustard production on site ceased in April 1945 and between 1946 to 1948 the associated plant and facilities were decommissioned. Some re-usable items were transferred to other sites but most of the equipment appears to have been treated where possible (mainly by burning or boiling) and sent for scrap. However some toxic or incompletely decontaminated items were buried in disposal pits on the site and covered with bleach. The underground storage chambers continued to house bulk mustard supported by the facilities of a loading bay and the laboratories until 1958 when work started to remove the remaining stockpile. By April 1959 the entire stockpile had been sent for destruction and dismantling and decontamination of all the remaining pipework and equipment was completed by April 1960.

The Ministry Of Public Buildings and Works (later to become the Property Services Agency - PSA) assumed responsibility for maintaining the site in 1964. From the 1960’s the site was used as buffer depot for the storage of a variety of non-perishable foodstuffs such as sugar and flour. Transfer of responsibility from PSA to MAFF occurred in 1992 and the use of the site as a buffer depot ceased in 1994. The buildings have remained empty since 1994.

Results of Site Investigations

Site Environment

Although not of special ecological importance, the southern part of the site and the western hillsides are attractive and support a varied flora and fauna. Lack of public access has created a haven for wildlife, including grass snakes, badgers and bats. The derelict buildings are used by local bat populations as temporary feeding areas and may also provide features to help bats navigate between woodland on either side of the valley. Contrary to expectations, however, there has been little evidence of bats inhabiting the storage tunnels on the site.

The River Alyn (a tributary of the River Dee) runs through the site in a concrete culvert. Groundwater beneath the site is in the alluvial deposits of the valley floor and drains to the underground lead mine workings and the River Alyn. The primary consideration is whether it would be possible for potentially hazardous solvents used at the factory to be transported by the groundwater beneath the site to the river water or to the drainage tunnels for the underground mine workings. (Mustard is not a problem in this situation, since it rapidly degrades in water to a non-hazardous form). Traces of solvents are detected in some of the monitoring boreholes installed on the site, but the dilution available in the mines and the River Alyn is such that the low concentrations of contaminants identified present no realistic risk to users of water abstracted from either source. Samples for detailed chemical analysis are collected from the boreholes twice a year.

A caving expedition into the accessible lead mine workings beneath the site found no evidence of chemical warfare materials and no traces of solvent were detected in the water samples that were collected from them.


Those buildings known to have handled chemical warfare agent materials during the war have been tested and no hazardous chemical concentrations identified. Traces of mustard degradation product were only identified in the fabric of one building, the former Mustard Production Plant R3, and in the ventilation system of the former Chemical Weapon Filling Shed K5. A health physics survey has shown that no significant radiological hazard exists in Building 45 which was used for research in support of the UK’s wartime atomic bomb project.

Buried Objects

A magnetometry survey for buried objects has been carried out across all the accessible areas of the site and now provides the data for taking appropriate precautions during the ongoing management of the site. The widespread pattern of buried objects would tend to suggest the vast majority of these are due to the scattering of ferrous demolition debris. There are no obvious indications of formal munition burial trenches.

An investigation of 20 buried objects at the southern tip of the site, including some interpreted by the magnetometry to be similar in size and shape to potential munition types, only unearthed benign metallic objects (metal bars, buckets, paint tins, angle iron, pipes, etc).

Toxic Pits

The investigation of the toxic burial pit marked by “Headstones” north of the tunnel entrances found contamination with chemical warfare degradation product, dioxins, asbestos and heavy metals, which would result in the material being classified as special waste. Munition cases and components found and removed from this pit during the investigation were confirmed to be free from explosive or chemical contamination.

A copy of the previously lost original Reference Drawing produced in 1948 showing the position of the remainder of the Toxic Pits was obtained from a Private Archive. This adds considerably to the confidence in knowing the location of Toxic Pits, and also identifies the Decontamination Area and entire drainage system as potentially contaminated. However even this plan omits any reference to the area of disposal at the Southern Tip of the site.

Southern Tip

Tipped materials are present in the area at the southernmost end of the site from lead mine activities dating back to the 19th Century (shale, rock and mineral spoil), Second World War factory operations (pipes, pumps, drums, etc) and post war depot and workshop disposals (rubble, scrap, etc).

An area near to the bend in the former river course was found to contain large amounts of bleach, burnt material, mustard indicator powder and glassware. This has the strong appearance of a toxic burial area. Burnt material from the toxic burial and soil from the adjoining river bank were found to contain high dioxin concentrations and some carbon tetrachloride contamination was identified in a couple of soil samples. A groundwater monitoring borehole has been installed between the tip and the river and is monitored monthly.

No Second World War munitions were found. Some expended smoke generator cases were found but were of post war origin and probably relate to police or military training exercises. Asbestos, including amosite (brown) asbestos, was found in significant quantities in the area of tipping.

Lengths of sealed pipework were taken to Porton Down for inspection and analysis. No contamination was found and they were disposed of at Porton Down. Approximately 0.5 tonne of loose bleach was also removed to Porton Down for disposal.

Soil Gas Emissions Testing

A number of areas of the site were surveyed to ensure that there was no potential hazard to site workers due to chemical agent or solvent vapours. The areas tested were those with the greatest potential for mustard contamination, including some old burial pits. Air samples were also collected in the vicinity of the site perimeter as a control and to confirm the lack of air pollution hazard to the off-site population. No chemical agent vapours were detected in any of the samples and only minute traces of solvent vapours from some on-site areas were detected which were well within the appropriate safety levels. None of the results from the site perimeter samples showed any trace of airborne contamination.

Risk assessment calculations based on the theoretical release of mustard from a hypothetical munition buried just below the ground surface have shown that the exposure of an individual standing directly above to the resultant vapour would be well within acceptable risk thresholds due to the effects of dilution and dispersion. (It should be noted that the term mustard “gas” is a misnomer, mustard is in fact a liquid vesicant or blistering agent).

Mineworking Voids

Geophysical surveys carried out over the locations of Pryn and Footway Shafts and the surrounding area affected by lead mine workings did not detect any evidence of hazardous voids or subsidence features

Planned Works

The Department for the Environment, Food and Rural Affairs (DEFRA), has obtained a budget to carry out the following programme of works on the site over the next year.

Improving The Frontage Of The Site

This will entail demolition of the nine derelict former administration area buildings in the part of the site fronting the village. The existing security gatehouse and maintenance storage garage will be refurbished and site of the demolished buildings grassed over. A hawthorn hedge will be planted in front of the security fence to provide a visual screen.

Demolish Buildings In The Vicinity Of The Tunnel Entrances

The International Inspection Team that monitors implementation of the Chemical Warfare Convention has requested the demolition of eleven small derelict buildings and structures in the vicinity of the entrances to the former underground storage chambers. The site of the demolished buildings will be grassed over.

Demolish Clad Buildings

Most of the derelict buildings remaining on the site are of a sturdy brick and concrete construction and are not anticipated to collapse in the foreseeable future. However five buildings have a steel framework clad with corrugated iron or asbestos sheeting and it is anticipated that they could pose a physical hazard in the future as the fixings for the cladding deteriorate. These will therefore be dismantled and the steelwork and cladding removed off site.

The buildings concerned include the two large sheds opposite the entrances to the former underground storage chambers that were used to fill chemical munitions during the war. Contamination could potentially reside in the ventilation systems in these buildings, impregnated within porous gasket material, and specialist contractors will be employed to remove them and dispose of them off-site.

Capping Of Pits And Infilling Of Manhole Chambers

The burial pits and contaminated buried drains and pipelines that remain on the site are best left undisturbed provided that they are not causing pollution of water and are not easily accessible to inadvertent contact. Following consultation with the Environment Agency Wales, the existing system of monitoring and control will be improved. The pits that are not already covered by concrete will be capped with an impermeable membrane to reduce water infiltration and mounded over to prevent accidental intrusion. Additional groundwater monitoring wells will then be installed around them to confirm the current indications of lack of significant contaminant migration. Manhole chambers for the drainage and toxic pipeline system will be filled with concrete to prevent inadvertent access and to isolate each length of buried pipework.

Long Term Future For The Site

When the Buffer Depot closed in 1994, the initial aspiration was for the site to be restored to some beneficial use outside of government ownership. However it soon became apparent that there was a lack of market demand in the area for redevelopment of a property of this nature. The next aspiration was to restore as far as practicable the pre-factory environment of the site, but as the history of the site has become better understood this has been shown to be prohibitively expensive and potentially undesirable given the disturbance that would be caused. In addition, the long pre-war history of lead mining in the area means that a “natural” environment free from man derived contamination can never be recreated.

The two main long term options for the site would appear to be either doing the minimum of works by maintaining security on the site and letting nature continue to take over or alternatively to flatten and bury the site under a capping layer. The latter would be closer to what historically has been considered in the UK as a remedial scheme, for example in the treatment of much of the former coal industry. However it would be very expensive, disruptive, would destroy the current ecological and historical interest and would not significantly improve risk reduction or the value of the land. Even in a “remediated” state, the site would require securing against squatters and fly tippers and some ongoing maintenance of features such as the River Alyn culvert would need to continue.

The works currently proposed are a considerable commitment of financial resources and should help continue to maintain the site in a safe condition for many years to come. They would also allow access for parties interested in the history and ecology of the site to take place by agreement and the possibility of extending the gatehouse to provide a briefing room for visitors is being explored. Now that understanding of the site is more complete, DEFRA would like to open the debate on the long term future of the site and will be seeking the views of the local community once they have had an opportunity to consider the issues.

This information is reproduced with the full permission of DEFRA.

[Source: Andrew P Smith]

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Last updated 17th June 2002

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