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Public dossier The risks Spills have killed thousands of fish

Water

Digestate spills into rivers are the best-documented serious risk. At Châteaulin (France, 2020), about 180,000 people had tap-water restrictions for about 5 days.

What is known

Digestate is not toxic in the chemical sense, but it uses up a lot of oxygen and is rich in ammonium: a spill into a river kills fish through lack of oxygen and ammonia.

  • At Châteaulin in 2020, about 400 m³ of digestate reached the river Aulne upstream of a water intake; about 180,000 people in about 50 communes had water restrictions for about 5 days.
  • On the river Mole (England, 2019), a digestate leak during spreading killed about 15,600 fish along 4.7 km.
  • In Luxembourg, a 2018 inspection found 35 of 61 digestate tanks non-compliant; after a spill polluted three rivers in 2023, the government ordered a review of every permit.
  • In Bavaria, biogas plants caused between 24 and 36 water or soil pollution incidents a year from 2017 to 2021.

What reduces the risk

Retention basins, inspected tanks, and distance from watercourses and water abstractions. Castilla-La Mancha's draft decree proposes 250 m from groundwater abstractions; in England the standard permit is not available inside groundwater source protection zones. In Portugal the law requires digestate storage to be 10 m from watercourses and 25 m from abstractions.

In Guarda

The parcel boundary is about 352 m from an area local residents know as a water extraction zone; we could not find it in the official registers we checked. Part of the site is in the REN as an area at high risk of soil erosion by water. The area lies between the river Mondego and the Massueime stream, in the Côa basin; which watercourse drains the parcel and what aquifer lies beneath it is not known.

What to ask the promoter

  • How far are the tanks from watercourses, wells and the water extraction zone known to residents?
  • What retention basins are there, and for what volume?
  • Where will the digestate go, and on which land will it be spread?

Water: rain, groundwater and the water the plant could use

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Sources on this page

  1. 400 m³ de digestat dans l'Aulne à Châteaulin : Engie Bioz condamnée par la justice Splann! · 4 Dec 2023
  2. Incident de pollution par une installation de biométhanisation (comunicado) Gouvernement du Grand-Duché de Luxembourg · 1 Mar 2023
  3. North Devon company fined for pollution that devastated fish population Environment Agency (GOV.UK) · 29 Jul 2021
  4. Resposta a pergunta escrita, Drucksache 18/21909: incidentes de poluição de água e solo em centrais de biogás Bayerischer Landtag (parlamento da Baviera) · 2022
  5. Proyecto de Decreto sobre las plantas de transformación en biometano (documento de participación pública) Junta de Comunidades de Castilla-La Mancha (Espanha) · 2026 (projeto em consulta pública)
  6. SR2021 No 6: anaerobic digestion facility including use of the resultant biogas (installations) GOV.UK (Environment Agency) · 26 Feb 2026
  7. Portaria n.º 79/2022, de 3 de fevereiro (gestão de efluentes pecuários; o digerido de biogás é equiparado a efluente pecuário) Diário da República, 1.ª série, n.º 24 · 3 Feb 2022
  8. MOV.AP: medições sobre imagem de satélite, outubro de 2026 (distâncias do limite da parcela à zona de exploração de água, quintas e aldeias) MOV.AP · 16 Oct 2026
  9. MOV.AP: conhecimento local dos moradores sobre a «Zona de Exploração de água» a sul da parcela MOV.AP · transmitido ao site em 30.10.2026
  10. Ata da reunião ordinária da Câmara Municipal da Guarda de 19 de junho de 2026 (Ponto 18, Proposta VPCM n.º 10/2026) Câmara Municipal da Guarda · 19 Jun 2026
  11. Rocamondo (ponto de interesse) Visit Guarda (Município da Guarda) · consultado em 16.10.2026
  12. Rio Massueime Wikipédia · consultado em 16.10.2026

See all sources