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Information on Knotlow Cavern/Hillocks Mine and Caving on Mynydd Ddu

The following information was forwarded from Alan Wood: National Caving Association

Update On Pollution in Knotlow Cavern/Hillocks Mine

By John Gunn, Limestone Research Group (LRG), University of Huddersfield

In a previous report it was noted that, as of 24 February, there were no problems with 'bad air' anywhere in Knotlow and no visual evidence of water pollution apart from some pink growths in the level between the base of Fourways Shaft and what will henceforth be called the Knotlow Farm Engine Shaft to avoid confusion with other 'Engine Shafts'.  The LRG are retained by English Nature to provide a 'rapid response' capability whereby we visit the site as soon as possible after a report of pollution and repeat the air, sediment and water sampling.  However, the contract allows for a maximum of five visits which means that we have to have a definite reason to undertake sampling.  During April and May there were conflicting accounts from visitors to the system, some reporting no problems, others 'bad air.'  Following these, on 20 May, Paul Hardwick tested the oxygen, hydrogen sulphide and methane concentrations in air by lowering a meter down the three shafts:

  • Climbing Shaft
  • Chapel Dale Engine Shaft (also known as the 210' of simply as 'the' Engine Shaft)
  • Fourways Shaft (also known as Crimbo Hollow Engine Shaft)



No evidence of 'bad air' was obtained, and oxygen levels were >19%.  This was confirmed by a party who visited on 31 May and reported 'no smells' although visitors on 4th & 6th June reported 'bad smells'. This presented us with some difficulty as the air monitoring equipment, without which we cannot undertake any visit to the mine because of Health & Safety considerations, costs £120 to hire in, and it was decided not to undertake a full sampling visit until there was a certainty that there was a pollution problem.  This visit was made on 29 July by John Gunn and Dave Nixon when we also hired in a carbon dioxide meter which proved to be extremely useful. As on 20 May, the oxygen, hydrogen sulphide and methane, plus carbon dioxide concentrations in air were measured by lowering the meters down the three shafts with the following results:

  • Climbing Shaft: oxygen> 20%; carbon dioxide <0.5%
  • Chapel Dale Engine Shaft: carbon dioxide >0.5% @ -20m & >1.0% @ -35m. oxygen >19% to base.
  • Fourways Shaft: carbon dioxide >0.5% @ -20m & > 1.0% @ -25m. oxygen> 19% to base.



The lids of the two deep shafts were left open to aid ventilation and we descended the climbing shaft making continuous measurements as we proceeded.  The carbon dioxide meter has two alarm levels, the first at 0.5% and the second at 1.0%.  The first alarm level was triggered while descending the 2nd pitch into Pearl Chamber (S2) and the second between Pearl Chamber and 'The Chain' (S3) oxygen levels were declining and the alarm level of 19.0% was triggered at S4, the junction between the level which continues through two low, wet squeezes to the Bung Series and a series of climbs down to the Waterfall Pitch.  At this point there was also an intermittent bad smell but after due consideration we decided, somewhat reluctantly that a relatively swift trip down to Waterfall Chamber was justified both to measure the gas concentrations and to obtain water samples for the Environment Agency.

However, the risks involved in a trip down the north crosscut to the base of Fourways Shaft were not considered to be justifiable and a rapid exit was made.  The following day [30th July] a return was made with breathing apparatus and David Nixon descended Fourways Shaft.  The 1evelleading to Knotlow Farm 'Engine Shaft' was found to be grossly polluted but the Chapel Dale Level was essentially pollution free so that at the foot of 'Fourways Shaft' the oxygen concentrations were slightly higher and the carbon dioxide concentrations slightly lower than in the upstream part of the mine (Table 1).  Hydrogen sulphide and methane concentrations were zero throughout the mine.

Our current thoughts are that polluted water, with a high content of organic material, is entering the mine from the Knotlow Farm 'Engine Shaft' and from a bedding plane near the top of the Waterfall Pitch.  One litre water samples were collected from a number of sites and are being analysed by the Environment Agency.  Officers from the Environment Agency are visiting farms in the area in an effort to determine where the pollution is coming from and it is hoped that the results of the water analyses will provide an indication as to whether sewage or silage is the major constituent.  However, it is important to understand that the derogation of the air quality is an indirect result of the water pollution since it appears to be due to oxidation of the organic matter which is deposited in the cave.  Hence, although the pollutant inputs may be sporadic the foul air will be more persistent, a factor likely to be exacerbated by the poor natural ventilation in the mine.  Consideration is being given to how the organic material may be flushed out of the system more rapidly and to how ventilation might be improved as well as to the question of the ultimate source of the material.

Given the low oxygen and high carbon dioxide cavers are strongly advised not to attempt to enter Knotlow until further notice.  The Environment Agency has posted warning notices on all entrances, including the entrances to Hillocks and to Whalf Mine as a precaution although no direct measurements have been made in these parts of the system.

Caving on Mynydd Ddu

The following was published in a South Wales Caving Club Newsletter, which you might find of interest. The area concerned is that over and beyond Dan-yr-Ogof and has a real potential to yield many miles of as yet undiscovered (not for want of trying) cave.

Access for Caving on Mynydd Ddu (The Black Mountain)

An open letter to cavers

This letter is being circulated widely in the caving community.  The National Park Authority wishes to agree with cavers; access and conservation arrangements for Mynydd Ddu and its caves.  This letter, which is intended to stimulate debate, outlines the legal requirements for managed access and suggests how this might be delivered. Comments from individuals and organisations are welcome, and should be sent to the address at the end of this letter. Every person or organisation submitting comments will be invited to attend an informal meeting towards the end of the year.

The Area

Mynydd Ddu is the area of upland lying broadly between the Upper Swansea Valley, in the east and the community of Trap in the west.  It extends to almost 15,000 hectares, and includes an important limestone outcrop, an area which must provide one of the greatest opportunities for cave exploration in Britain.

Survey work completed by local cavers in 1997 identified 296 sites of speleological significance, three quarters of which were visited, photographed and described.  Twenty five of these were recorded as being in a dangerous condition, most of which are abandoned digs.  The Park Authority is now obliged to undertake works to these to render them safe.  Offers of assistance from cavers - particularly if you have a guilty feeling about some of these digs - are invited.

The same survey has also collated a very comprehensive bibliography, and made many recommendations to improve access and conservation management.  Paper copies of the survey are held by the South Wales Caving Club and National Park Authority.  This should prove to be an important exploration & conservation tool, and arrangements will be made for its transfer to digital media to make it accessible and maintainable.

Ownership and Management

The whole area is 'common land' - land over which 'commoners' have rights (such as grazing) which they share 'in common' with others.  There are several graziers associations that represent the interests of many of the commoners.

The National Park Authority owns about 12,000 hectares of the area and manages a further 2,000 hectares on behalf of Dwr Cymru.  This letter relates to land that is owned and managed by the National Park Authority. The Authority manages the area according to its purposes set out in the 1995 Environment Act.  These are: to conserve and enhance natural beauty, wildlife and cultural heritage and to promote opportunities for understanding and enjoyment of the Park's special qualities.

It is also relevant to note that as landowner the Authority has a duty of care to all users of the area, and an associated liability if it is negligent in exercising that duty. Being a publicly funded organisation the Authority must manage its liabilities so as to protect itself - and the public purse - from damage claims.  Most of the area is designated under the Wildlife & Countryside Act as a "Site of Special Scientific Interest" SSSI, and this requires the landowners to ensure that the interest of the site is not damaged.

Caving is formally recognised by the Authority as an appropriate activity in the Park setting, and the Authority therefore has a duty to promote the enjoyment and understanding of caves.  It must also look after the interests of commoners, and exercise a duty of care to visitors.  Finally it must ensure the conservation of the area, and ensure that the SSI is not damaged.


Legal rights of access are provided by public rights of way.  ‘De facto’ access, or that of long standing tradition or custom, is also established.  The National Park Authority as a matter of policy allows open access on foot for quiet, informal enjoyment.  ‘De facto’ access does not extend to access for caving or digging, and these activities are only lawful if conducted with the consent of the landowner.

A New Approach

Historically the Park authority has made a number of false starts in trying to manage the issue of cave access and conservation, and is aware that some cavers view its motives with suspicion.  The following arrangements satisfy the remit of the National Park Authority, maximise accessibility, minimise bureaucracy and recognise the critical role played by cavers in the management of cave exploration and conservation.  The new approach should form the basis of a more productive relationship between the caving community and environmental organisations.

The National Park Authority proposes:

To declare a “standing permission” for all cavers to visit (on foot) all sites of speleological interest on Mynydd Ddu, on condition that:

i.                    Cavers follow the NCA advice and code of conduct regarding conservation of the cave environment.

ii.                  Cavers have their own 3rd party liability insurance, and undertake all such activities entirely at their own risk.

iii.                 Nothing is done that damages the rights of commoners.

To make widely available (at least possible cost to users) the Mynydd Ddu Cave Survey, and to put in place and fund arrangements for its maintenance by cavers.

To declare a ‘standing permission’ for all cavers to conduct exploration activity in caves and on the surface, on the condition that : I, 11, 111 – As I, ii, iii above.

iv.                 That digging and other exploration activity is recorded at the outset with the Mynydd Ddu Cave Survey (details may be held with restricted access if requested) and the survey is regularly updated through the duration of the activity. Detail of location and persons responsible will be needed.

v.                   ‘Between visits’ any works are left entirely safe and secure, and pose no threat to people, stock or other animals.

vi.                 When complete the site is left permanently safe and secure.

To annually review the impacts of exploration activity, to ensure that legal requirements of the SSI designation are not being breached.

To hold an open meeting do that the success of these access and conservation arrangements may be discussed.

Subject to views of the caving community and other interested parties, the National Park Authority intends that the new approach should be effective from 1s January 2000. Please forward comments to:

Jon Young – Brecon Beacons National Park Authority, Brecon, Powys