Cerco de Almadenejos

A Pilot for the Remediation of Mercury-Contaminated Soils

Cerco de Almadenejos

The Cerco de Almadenejos (CDA), located in the small municipality of Almadenejos in the Ciudad Real region, is part of the Almadén mining district, known for being the largest mercury mine in the world.

This historic area, with a population of around 200 inhabitants, houses an ancient metallurgical plant from the 18th century, which was used for mercury extraction.

From 1794 to 1861, the CDA was a key center for cinnabar roasting, both from Almadén and Almadenejos, and is now declared a Bien de Interés Cultural (BIC), making it a valuable historical heritage site.

The site presents varying levels of mercury contamination in the soil, ranging from 40 mgHg/kg to up to 15,900 mgHg/kg, significantly exceeding the average contamination levels in Europe. This contamination generates a continuous source of mercury emissions in gas form, which disperse into the atmosphere through dust particles that can be carried by the wind to varying distances. Additionally, the area is also prone to generating contaminated water, which may occasionally reach public streams, further contributing to water contamination, especially affecting aquatic biota.

The challenge of addressing this issue is complicated by the historical and cultural value of the site, preventing drastic measures such as the demolition of the furnace ruins and the complete restoration of the soil. Due to its protected status, it is necessary to develop an innovative, cost-effective, and less invasive solution that improves the environment without compromising the conservation of cultural heritage.

To this end, the LIFE HERMES project is implementing a treatment for mercury-contaminated soils at the CDA, an innovative solution that adapts to the specific characteristics of this site. With a total area of 33,306 m², the treatment will focus on the first 50 cm of soil, where the highest mercury concentrations have been detected.

The soil at CDA is of a “loam” texture, with a high sand content and effective porosity, which promotes the circulation of air and water, ideal conditions for applying the selected remediation technologies. Preliminary studies conducted at the site confirm that the chosen technology is suitable for treating mercury contamination in these soils, allowing for a significant reduction in mercury levels and minimizing risks to the environment and public health.

In summary, the CDA represents a key pilot case for demonstrating how mercury contamination at sites of high cultural value can be addressed while maintaining a balance between heritage preservation and improving the natural environment. This project has the potential to offer replicable solutions for other sites affected by historical mining in Europe, contributing to environmental rehabilitation and the well-being of local communities.