Summary

Comprehensive investigations of the former Mitholz ammunition depot (1947 explosion) confirm significant contaminant pollution in the ejection zones. Approximately 350,000 m³ of heavily to very heavily contaminated material is stored in the debris cone in front of the cliff. No operational restrictions are required for current pasture use. The complex material management requires optimizations to the project planning. The project completion date has been postponed from 2045 to 2047.

Persons

  • Federal Council (responsible authority)

Topics

  • Remediation of contaminated sites
  • Ammunition disposal
  • Soil protection
  • Environmental geotechnics
  • Infrastructure planning

Clarus Lead

The two-year delay signals the technical complexity involved in remediating war-era contaminated sites in Switzerland. With a staggered approval strategy (railway December 2026, road 2029), efforts are being made to disentangle construction workflows and build up capacities for ammunition disposal step by step. The establishment of a test facility and blast bunker from summer 2026 marks a turning point from the planning stage to practical testing.

Detailed Summary

Technical investigations since 2022 comprised systematic soil sampling, material samples from excavation trenches, and exploratory drilling. The results confirm that the ground surface from 1947 is partially heavily contaminated. The zone to the south and southwest is particularly critical, where natural events (flooding, debris flows) and construction of the avalanche protection tunnel have buried contaminated soil layers several meters deep.

The presumed heavily contaminated blast site with approximately 30 blast craters (1948) is today covered several meters deep by debris flows and the Stägebach sediment trap. Further investigations are necessary for this zone. The largest quantities of contaminated material are located in the debris cone east of the national highway: 350,000 m³ of contaminated material, approximately 50–60% of the debris cone – a volume that would fill the Swiss Parliament building in Bern three times over.

Despite this contamination, the project management determined that there is no hazard to soil, groundwater, and streams. No operational restrictions are required for current pasture use with grass and pasture management. Remediation is only required for shooting ranges and bullet traps. Material management should be concentrated on already contaminated areas to protect the western valley side. Additional interim storage areas will be planned within the railway loop and require a revision of the sectoral plan fact sheet.

Key Statements

  • Contaminant pollution in ejection zones confirmed by technical investigations; no acute hazard to groundwater and streams
  • 350,000 m³ of heavily contaminated material in the debris cone requires specialized treatment and reuse
  • Project completion date postponed by two years (2045 → 2047) due to staggered approval procedures and capacity building
  • Test facility and blast bunker planned from summer 2026 for testing triage and disposal procedures

Critical Questions

  1. Evidence/Data Quality: How representative are the soil samples for the overall contamination of the debris cone, and what uncertainty margin exists in the estimate of 350,000 m³ of contaminated material?

  2. Conflicts of Interest: Who bears the costs for specialized material treatment and reuse, and are there financial incentives to deposit material on-site rather than dispose of it externally?

  3. Causality/Alternatives: Why was the staggered approval procedure optimization only undertaken now, and what alternatives to interim storage within the railway loop were examined?

  4. Feasibility/Risks: What capacity does the planned test facility have, and how is it ensured that ammunition disposal does not become a bottleneck?

  5. Environmental Protection: How is contaminated excavated material protected from leaching and groundwater contamination during transport and interim storage?

  6. Timeline: What buffer time is included in the new completion date of 2047 for unforeseen discoveries or technical problems?

Source Directory

Primary Source: State Visit Poland – Mitholz Ammunition Depot: Investigation Results and Project Optimizations – news.admin.ch, 28.05.2026

Verification Status: ✓ 28.05.2026

This text was created with the support of an AI model. Editorial responsibility: clarus.news | Fact-checking: 28.05.2026