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Project background

Dounreay Castle is situated outside the Dounreay licensed site, next to the coastline. The castle dates from the late 16th century, and is one of the few remaining examples of a Scottish Laird’s castle from that period. It has ‘scheduled monument’ status because of its high archaeological potential derived from its design, history, and local and national context.

Experiments involving radioactive liquids were conducted from the castle courtyard in the 1950s, using a temporary holding tank and pipeline. As a result of leakage and spillage, the courtyard became affected by radioactive contaminants. The tank and pipeline were removed but it was impossible to decontaminate the site conventionally, given its archaeological sensitivity.

Furthermore, contaminated drainage water had leaked through fractures in the Castle Gate drain, contaminating the coastal slope and beach area.

Key challenges

We started a project to characterise and remediate the area, in order to reduce the possibility of contamination migrating towards the marine environment. We needed to develop a solution for restoring the contaminated area while preserving the castle’s archaeological heritage.

Our approach

We began by taking samples from the castle and beach areas to establish the baseline condition of the site. After discussions with Historic Scotland, who are responsible for important historical monuments, we excavated the site in close co- operation with archaeological specialists. This allowed safe removal of contaminated material, and meant we could develop and record a detailed understanding of the site’s archaeological history.

An area of 900 m2 was excavated down to a maximum depth of 3m, creating 1,540 tonnes of low-level waste. This was safely transferred to the Dounreay site’s waste storage facilities, and the excavated areas were backfilled with non-contaminated fill from local farms and quarries, and segregated materials from site excavations.

Following the remediation, we carried out a radiological survey to confirm that we had met the remediation criteria.

The results

The remediation project was successfully completed in May 1998 and we replaced the fractured section of the Castle Gate drain. Remediation works allowed open access to the site for the first time in 40 years, and have helped to preserve an important feature of Scottish archaeological heritage. Post-remediation surveys have shown that levels of residual contamination do not present a significant health or environmental risk.