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Case study

Bro Tathan: what was settled before the public was asked?

A data-centre campus on the former RAF St Athan airfield in the Vale of Glamorgan brings several of this site’s themes together on one real site: public land, a US-headquartered operator, generators, contaminated ground, and a decision that no Environmental Impact Assessment was needed.

About this case study

Based on published sources only. It asks questions; it makes no allegation against any person or body.

What is on the public record

  • Vale of Glamorgan Council approved the application at committee for 120 MW of data capacity.[1]
  • The operator, Vantage Data Centers, is US-headquartered and holds a 999-year lease of the land from the Welsh Government. The campus is described as three buildings with 22 generators on a 27-acre site, with completion planned for 2027.[2]
  • The planning consultants’ own summary lists the site’s challenges as including PFAS soil contamination, wartime defence structures and protected dormouse habitat, and states that they successfully argued that the development did not require an Environmental Impact Assessment.[1]
  • In August 2026 Vantage announced plans for more than 1 GW of AI-ready capacity across Newport, Bridgend and Bro Tathan, welcomed by Welsh and UK ministers as part of the South Wales AI Growth Zone.[3]
  • We have not found the commercial terms of the lease published.

What the Council’s own file shows

In October 2026 the Council released its file on whether the site needed an Environmental Impact Assessment, in answer to a request made through WhatDoTheyKnow.[4]

  • In January 2022 the developer’s consultants asked whether an assessment was needed for a data centre on 11.3 hectares. Their request said water use would be “very slight”; it did not deal with electricity demand, cooling water or carbon.[4]
  • On 8 February 2022 a Council planner said informally that an assessment was “likely” to be needed. The consultants disputed this. Nine days later the Council decided that no assessment was needed, before several of its own consultees had replied.[4]
  • A month after that decision, the consultants’ own site survey reported likely PFAS ‘forever chemical’ contamination from fire-fighting foam, buried radium-containing objects, and a site over an aquifer draining to the Boverton Brook.[4]
  • The scheme approved in 2024 covered about 26.7 hectares, with 72 diesel generators able to produce 120 MW. Natural Resources Wales said the site boundary had included the “main” PFAS source area. The Council relied on the 2022 decision, calling the scheme “essentially the same”.[5]
  • The 2024 scheme promised 120 jobs, down from up to 216 described in 2022. Land kept by the Welsh Government was not covered by the clean-up plans submitted.[5]

These are facts from the Council’s documents. Nothing here suggests any wrongdoing; the question is whether the process looked at the things that matter most for a data centre.

Power for Bro Tathan

The data-centre planning documents say little about where the power will come from. Other public documents fill in part of the picture.

  • In May 2024 the Welsh Government asked suppliers to “design, construct, finance and operate a new 280MW high voltage power connection” at Bro Tathan, fed from National Grid’s substation at the former Aberthaw power station by 132 kV circuits to a new Bro Tathan substation, with bays for “large demand users on site”. It gave an indicative value of £60 million. The notice does not mention a data centre.[6]
  • In June 2026 Welsh Ministers applied to the Council for a 132 kV substation at Bro Tathan, described as serving the site, Cardiff Airport and the St Athan Enterprise Zone.[7]
  • In October 2026 National Grid began public engagement on two new substations beside its Aberthaw substations, known as Gileston substation, to connect solar, battery storage and data-centre developments that have asked for connections.[8]
  • On 23 October 2026 the Welsh Government began consulting on an “undergrounding-first” policy: new electricity lines from 11 kV to 132 kV would be underground by default.[9] The proposal covers lines, not substations, and does not cover the higher-voltage lines that are decided at UK level. Ministers expect to set out next steps in early 2027.[10]

Our reading: the power connection, the new substation and the data centre depend on each other, but they are being considered separately, and the 2022 screening decision looked at none of the power infrastructure. If the Welsh Government, as landowner, is paying for the connection, part of the cost of powering the data centre may fall on the public purse. The UK Government’s new Covenant expects data centres to cover the energy costs they create.[11]

Why it matters

Here the Welsh Government is at once the landowner, a promoter of the investment, and ultimately responsible for the planning and data-governance framework in which it is judged. Existing PFAS contamination in the ground meets new PFAS-related questions about fire suppression and cooling. And a campus of this scale, with 72 standby diesel generators, proceeded without a full Environmental Impact Assessment, on the strength of a decision taken in 2022 for a smaller site. None of this means a wrong decision was made. It does mean the questions deserve published answers.

Questions we will be asking

Answered: our first question, asking for the screening opinion, was answered when the Council released its file in October 2026 (above). These are the follow-up questions.

Ask: Vale of Glamorgan Council, Head of Sustainable Development

“Was a screening opinion adopted under the Town and Country Planning (Environmental Impact Assessment) (Wales) Regulations 2017 specifically for application 2023/00780/FUL, as distinct from reliance on the 2022 opinion for a smaller site? If so, please provide it and say whether it took account of the enlarged site of about 26.7 hectares, the former fire-training area identified by Natural Resources Wales as the main PFAS source area, and the 72 standby generators with a combined capacity of 120 MW.”

Follow-up: Not yet asked. A request via WhatDoTheyKnow for any screening record or officer notes for that application could follow.

Ask: Vale of Glamorgan Council and Natural Resources Wales

“What investigation and remediation of PFAS contamination in the soil at the Bro Tathan site has been required as a condition of consent, how will any contaminated material be handled during construction, and will monitoring results be published?”

Follow-up: Request the contaminated-land reports and any discharge-of-conditions submissions via WhatDoTheyKnow.

Ask: the Welsh Government

“How has the Welsh Government managed the potential conflict between its roles as freeholder of the Bro Tathan site, promoter of the South Wales AI Growth Zone, and body responsible for the planning and data-governance framework; and will the principal terms of the 999-year lease be published?”

Follow-up: A freedom of information request via WhatDoTheyKnow for the lease terms may meet a commercial-confidentiality exemption; the public-interest test would then be the point to argue.

Ask: the Welsh Government Cabinet Secretary responsible for the economy, as landowner

“The Council's report on application 2023/00780/FUL records that land at Bro Tathan retained by the Welsh Government is not addressed by the remediation strategies submitted. What assessment has the Welsh Government made of PFAS contamination of soil and groundwater on its retained land there, including the former fire-training area, what remediation is planned, and who will pay for it? And before granting the lease, what due-diligence, environmental and data-protection assessments did the Welsh Government carry out, and how did it keep its roles as landowner, promoter of the investment and regulator separate?”

Follow-up: Not yet asked. Requests via WhatDoTheyKnow to the Welsh Government for those assessments, and to Natural Resources Wales for any monitoring of PFAS in groundwater beneath the site and in the Boverton Brook, could follow.

Ask: the Welsh Government Cabinet Minister for Enterprise, Connectivity and Energy

“Has the high-voltage power connection at Bro Tathan described in notice C035/2024/2025 been contracted? If so, at what cost, who is paying for it, and what is Vantage Data Centers contributing? Will the 132 kV circuits from Aberthaw to Bro Tathan be underground, and will the proposed undergrounding-first policy apply to lines not yet consented when it takes effect?”

Follow-up: Not yet asked. A request via WhatDoTheyKnow for the contract award and business case for notice C035/2024/2025 could follow.

Ask: Vale of Glamorgan Council, Head of Sustainable Development

“Was the application by Welsh Ministers for a 132 kV substation at Bro Tathan (June 2026) screened under the Environmental Impact Assessment (Wales) Regulations 2017, and did that screening consider it together with the data centre approved under 2023/00780/FUL and the grid works proposed at Aberthaw?”

Follow-up: Not yet asked. A request via WhatDoTheyKnow for the screening record would follow if needed.

From the paper “Beyond Planning Permission”

The full text of the relevant sections of the paper, with its own numbered notes. Note numbers match the paper.

16. Bro Tathan: Public Land, a US Operator and Unresolved Governance Questions

One proposal illustrates several of the tensions discussed elsewhere in this appraisal with particular clarity.

Vale of Glamorgan Council has granted planning consent for a substantial data-centre campus at Bro Tathan, on the site of the former RAF St Athan airfield, to be developed by Vantage Data Centers under a 999-year lease of Welsh Government-owned land.187,188,189

Vantage is a US-headquartered operator, and the Welsh Government has indicated that the development forms part of a wider, multi-billion-pound programme across its South Wales campuses - including Newport, Bridgend and Bro Tathan - expected to exceed 1GW of AI-ready capacity, with Ministers publicly welcoming the investment as a source of high-skilled employment and as central to the South Wales AI Growth Zone.190

This arrangement places the Welsh Government in an unusually direct set of overlapping roles: it is the freeholder leasing the land, an active promoter of the investment through its AI Growth Zone and economic-development strategy, and, separately, ultimately answerable for the planning and data-governance framework within which the development is assessed.

The commercial terms of the lease itself do not appear to have been made widely public.191 Given that the same development places a US-headquartered operator's infrastructure on land owned directly by a devolved government, the sovereignty and jurisdiction questions considered in Sections 9 to 14 above - UK GDPR adequacy, exposure under the US CLOUD Act, and the adequacy of existing international transfer mechanisms - arise here in a sharper and more immediate form than in relation to data-centre development generally.

It would be preferable for the Welsh Government's position on these points, and on how it manages the potential conflict between its landowner and promotional interests on one hand and its regulatory and public-data responsibilities on the other, to be stated clearly and resolved before, rather than after, such developments are committed.

The same questions arise at Bro Tathan in relation to computing capacity (see 'Control of computing power, not only of data' in Section 12 above). The site forms part of the South Wales AI Growth Zone, and it is not known whether the lease, or any agreement connected with the Growth Zone, gives the Welsh or UK Government any right to reserve capacity on the site in an emergency, or any information about, or say over, the customers it serves and the work done there.

The author intends to put the following question in writing to the Welsh Government Cabinet Secretary responsible for the economy, as landowner:

'Does the lease to Vantage Data Centers at Bro Tathan, or any related agreement, give the Welsh or UK Government any right to reserve computing capacity in an emergency, or any information about, or control over, the customers served and the work carried out on the site?'

A request via WhatDoTheyKnow for the lease and related agreements could follow; commercial confidentiality is likely to be argued, but the public-interest test applies.

What the screening file shows (October 2026)

In October 2026 Vale of Glamorgan Council released, in response to the author's request via WhatDoTheyKnow, its file on whether the Bro Tathan data centre needed an environmental impact assessment.192 The documents, which are public on that site, add a good deal to the history set out above. What follows describes them; comments that are the author's own are identified as such.

In January 2022 the applicant's planning consultants, CarneySweeney, asked the Council on behalf of Vantage Data Centers for a screening opinion (whether an assessment was needed) and a scoping opinion (what it should cover) for a phased data centre of up to about 83,000 square metres on 11.3 hectares. The request said that the development 'is unlikely to have significant environmental impacts', that the use of water 'will be very slight', and that standby generators of 2.6 MW each would run only in emergencies and for about 18 hours a year of testing. It did not address the facility's demand for electricity, the water needed for cooling or its carbon emissions.193 The request described 11 generators for each pair of data halls, across up to six phases of two data halls each; read literally, that suggests up to 66 generators, whereas the Council's report later described three buildings with 11 generators each. Neither document states a total; this is the author's reading. The accompanying plan labelled the buildings 32 MW, 32 MW, 16 MW and 16 MW.194

On 8 February 2022 the Council's senior planner told the consultants informally, before consultation responses had been received, that 'it is likely that the proposals would require an EIA, although the scope of which may be relatively limited', covering landscape, heritage, transport, ground conditions, noise and air quality, and ecology. The consultants disputed that the same day and the next, relying on guidance in Welsh Office Circular 11/99 that assessment is 'more likely to be required' for industrial estates of more than 20 hectares, and saying that they were 'genuinely struggling to see' any likely significant effects.195

On 17 February 2022 the Council issued its screening opinion: an environmental impact assessment was not required. The officer's report noted that the wider allocated site 'cumulatively would far exceed the threshold' and that 'the accumulation of effects needs to therefore be carefully considered', but concluded that the effects would be of local significance only. It recorded that no comments had yet been received from the Council's highways, drainage, pollution control and ecology consultees, and it accepted that the generators 'would only be utilised in extreme circumstances'. Because no assessment was required, the accompanying request for a scoping opinion was closed without a response.196,197

A month later, on 14 March 2022, the consultants sent the Council a summary of their own Phase I environmental site assessment. It recorded that the southern part of the site had been used as a fire-training ground, that residual contamination of soil and groundwater 'is likely to be present beneath the site, including per- and polyfluoroalkyl substances (PFAS), used in fire-fighting foam', together with hydrocarbons and possibly asbestos, that nine buried radium-containing objects had been found, that the site lies over a Secondary A aquifer with drainage channels flowing to the Boverton Brook, and that the layout encroached on a flood-defence bund and a designated flood-storage area.198 The Council's land-quality advisers had already noted, on the scoping file, potential risks from 'made ground, radioactive material and fuel tanks'.199

The planning application eventually approved, 2023/00780/FUL, as amended in March 2024, covers about 26.7 hectares, of which about 12.6 hectares is the building and related development, with a building of 67,227 square metres and 72 diesel generators able to produce 120 MW in total. Natural Resources Wales initially said that it would object unless more information was provided on land contamination and protected species; it noted that the planning boundary then included 'an area known to be where firefighting practice of fighter jets took place and was the main perfluoroalkylated (PFAS) source area', and that 'all locations where PFAS has been detected exceed the adopted screening criteria'. The boundary was later redrawn to exclude most of the fire-training area, and the Council's advisers noted that land retained by the Welsh Government was 'not addressed by the remediation strategies submitted to date'. The application proposed 120 full-time jobs, against the 216 described in 2022; the report itself observed that a typical storage or industrial building of the same size would support about 1,003.200

On the question of assessment, the report relied on the 2022 opinion, describing the proposal as 'essentially the same use' and 'a building covering a similar area', 'largely commensurate in terms of the material considerations', and concluded that no assessment was required. Neither the 2022 screening report nor the 2024 committee report contains an assessment of the electricity the data centre would draw or of the water used for cooling.201

In the author's view, the file illustrates the points made in Section 2 and in the discussion of environmental assessment elsewhere in this appraisal. The decision that no assessment was needed was taken early, on the applicant's description of a smaller site, before the main consultees had replied and before the contamination of the site was set out; and it was then carried forward to a scheme on more than twice the area, with a known PFAS source area inside its first boundary and 120 MW of diesel generation. No impropriety is suggested by this appraisal, and whether the law required a fresh screening opinion is a question for others; legal remedies are not considered here. What the file does show is how the questions that matter most for data centres - power, water, chemicals and cumulative effect - can fall outside the process altogether.

The author intends to put the following question in writing to Vale of Glamorgan Council's Head of Sustainable Development: 'Was a screening opinion adopted under the Town and Country Planning (Environmental Impact Assessment) (Wales) Regulations 2017 specifically for application 2023/00780/FUL, as distinct from reliance on the 2022 opinion for a smaller site? If so, please provide it and say whether it took account of the enlarged site of about 26.7 hectares, the former fire-training area identified by Natural Resources Wales as the main PFAS source area, and the 72 standby generators with a combined capacity of 120 MW.' A request via WhatDoTheyKnow for any screening record or officer notes for that application could follow.

And to the Welsh Government Cabinet Secretary responsible for the economy, as landowner: 'The Council's report on application 2023/00780/FUL records that land at Bro Tathan retained by the Welsh Government is not addressed by the remediation strategies submitted. What assessment has the Welsh Government made of PFAS contamination of soil and groundwater on its retained land there, including the former fire-training area, what remediation is planned, and who will pay for it? And before granting the lease, what due-diligence, environmental and data-protection assessments did the Welsh Government carry out, and how did it keep its roles as landowner, promoter of the investment and regulator separate?' Requests via WhatDoTheyKnow to the Welsh Government for those assessments, and to Natural Resources Wales for any monitoring of PFAS in groundwater beneath the site and in the Boverton Brook, could follow.

Notes from the paper

  1. 187. CarneySweeney, Vantage Data Centre, Bro Tathan, Vale of Glamorgan — planning consent summary. https://www.carneysweeney.co.uk/projects/vantage-data-centre-bro-tathan-vale-of-glamorgan.html
  2. 188. Baxtel, Vantage: Bro Tathan CWL2 Data Center — site profile confirming the 999-year Welsh Government lease and US ownership. https://baxtel.com/data-center/vantage-bro-tathan-cwl2
  3. 189. Welsh Government, Bro Tathan — Cardiff Airport and Bro Tathan Enterprise Zone. https://www.gov.wales/bro-tathan
  4. 190. Vantage Data Centers, Vantage Data Centers and Nebius Expand UK AI Infrastructure with First Deployment in South Wales AI Growth Zone (2026). https://vantage-dc.com/news/vantage-data-centers-and-nebius-expand-uk-ai-infrastructure-with-first-deployment-in-south-wales-ai-growth-zone/
  5. 191. Baxtel, Vantage: Bro Tathan CWL2 Data Center — site profile confirming the 999-year Welsh Government lease and US ownership. https://baxtel.com/data-center/vantage-bro-tathan-cwl2
  6. 192. Vale of Glamorgan Council, response of 16 October 2026 (reference 00211434) to the author's request 'Screening of Datacentre at Bro Tathan' made via WhatDoTheyKnow on 11 September 2026, with 18 attachments. https://www.whatdotheyknow.com/request/screening_of_datacentre_at_bro_t
  7. 193. CarneySweeney for Vantage Data Centers, 'Environmental Impact Assessment - request for screening and scoping opinion', letter to Vale of Glamorgan Council (13 January 2022), applications 2022/00038/SC1 and 2022/00084/SC2, pages 3, 6 and 9. https://www.whatdotheyknow.com/request/screening_of_datacentre_at_bro_t/response/3594738/attach/html/17/220113%20EIA%20Screening%20Scoping%20Request.pdf.html
  8. 194. Scott Brownrigg, 'St Athan Data Centre Proposal: areas and dimensions' (December 2021), submitted with the screening request. https://www.whatdotheyknow.com/request/screening_of_datacentre_at_bro_t/response/3594738/attach/html/14/St%20Athan%20Data%20Centre%20Proposal%20Site%20Plan%20A1%20Updated.pdf.html
  9. 195. Email exchange between Vale of Glamorgan Council planning officers and CarneySweeney, 8 and 9 February 2022 ('RE: Data Centre, Bro Tathan'). https://www.whatdotheyknow.com/request/screening_of_datacentre_at_bro_t/response/3594738/attach/9/RE%20Data%20Centre%20Bro%20Tathan.html
  10. 196. Vale of Glamorgan Council, screening report 2022/00038/SC1 and decision notice of 17 February 2022. https://www.whatdotheyknow.com/request/screening_of_datacentre_at_bro_t/response/3594738/attach/html/3/2022%2000038%20Final%20Report%20202200038SC1.pdf.html https://www.whatdotheyknow.com/request/screening_of_datacentre_at_bro_t/response/3594738/attach/html/24/R%202022%2000038%20Decision%20Notice%20202200038SC1.pdf.html
  11. 197. Vale of Glamorgan Council, internal email closing scoping request 2022/00084/SC2. https://www.whatdotheyknow.com/request/screening_of_datacentre_at_bro_t/response/3594738/attach/19/2022%2000084%20SC2.html
  12. 198. CarneySweeney, email to Vale of Glamorgan Council of 14 March 2022, 'Data Centre, Bro Tathan', section 'A summary of the survey work being undertaken'. https://www.whatdotheyknow.com/request/screening_of_datacentre_at_bro_t/response/3594738/attach/html/25/R%20200322%201234.pdf.html
  13. 199. Shared Regulatory Services, land-quality memorandum on 2022/00084/SC2 (dated 2 February 2021 on its face; ref SRS/E/10875/22). https://www.whatdotheyknow.com/request/screening_of_datacentre_at_bro_t/response/3594738/attach/html/4/2022%2000084%20202200084SC2.pdf.html
  14. 200. Vale of Glamorgan Council, report to Planning Committee on application 2023/00780/FUL, Land North of Ffordd Bro Tathan (2024), including 'Need for Environmental Impact Assessment', the generators, staffing and the responses of Natural Resources Wales and Shared Regulatory Services. https://www.whatdotheyknow.com/request/screening_of_datacentre_at_bro_t/response/3594738/attach/html/20/Final%20Report%20202300780FUL%201%20compressed.pdf.html
  15. 201. Vale of Glamorgan Council, report to Planning Committee on application 2023/00780/FUL, Land North of Ffordd Bro Tathan (2024), including 'Need for Environmental Impact Assessment', the generators, staffing and the responses of Natural Resources Wales and Shared Regulatory Services. https://www.whatdotheyknow.com/request/screening_of_datacentre_at_bro_t/response/3594738/attach/html/20/Final%20Report%20202300780FUL%201%20compressed.pdf.html

Sources for this page

  1. CarneySweeney (the applicant’s planning consultants), project summary: Vantage Data Centre, Bro Tathan, Vale of Glamorgan. https://www.carneysweeney.co.uk/projects/vantage-data-centre-bro-tathan-vale-of-glamorgan.html
  2. Baxtel, site profile: Vantage Bro Tathan (CWL2). https://baxtel.com/data-center/vantage-bro-tathan-cwl2
  3. Vantage Data Centers, ‘Vantage Data Centers and Nebius expand UK AI infrastructure with first deployment in South Wales AI Growth Zone’ (13 August 2026). https://vantage-dc.com/news/vantage-data-centers-and-nebius-expand-uk-ai-infrastructure-with-first-deployment-in-south-wales-ai-growth-zone/
  4. Vale of Glamorgan Council, response of 16 October 2026 to the request 'Screening of Datacentre at Bro Tathan' (WhatDoTheyKnow), with the screening request, emails, screening report and decision. https://www.whatdotheyknow.com/request/screening_of_datacentre_at_bro_t
  5. Vale of Glamorgan Council, report to Planning Committee on application 2023/00780/FUL (2024), released with the same response. https://www.whatdotheyknow.com/request/screening_of_datacentre_at_bro_t/response/3594738/attach/html/20/Final%20Report%20202300780FUL%201%20compressed.pdf.html
  6. Welsh Government, prior information notice ‘Bro Tathan – High Voltage Power Connection’, ref. C035/2024/2025 (Find a Tender, 22 May 2024). https://www.find-tender.service.gov.uk/Notice/016186-2024
  7. Nation.Cymru, ‘Plans submitted for new substation on Ministry of Defence site’ (11 June 2026). https://nation.cymru/news/plans-submitted-for-new-substation-on-ministry-of-defence-site/
  8. Bro Radio, ‘National Grid shares plans for new Aberthaw substation development’ (5 October 2026). https://www.broradio.fm/news/local/national-grid-shares-plans-for-new-aberthaw-substation-development/
  9. Welsh Government, ‘Consultation on undergrounding-first policy for new electricity lines’ (23 October 2026). https://www.gov.wales/consultation-undergrounding-first-policy-new-electricity-lines
  10. Herald.Wales, ‘New power lines in Wales to go underground by default under major policy change’ (October 2026). https://herald.wales/national-news/politics/wales-new-power-lines-underground-default-policy-change/
  11. UK Government, Initial Proposal for a National Policy Statement for Data Centres (October 2026; England only). https://assets.publishing.service.gov.uk/media/6ae1c5937fe45a08a4036e4e/draft-national-policy-statement-for-data-centres.pdf

Based on section 16 of the paper, with additional material found while preparing this site. The PFAS soil contamination and the EIA screening point are not yet in the paper.