Published on: December 3, 2025, 3:01 PM
Research agency Tauw has investigated various scenarios to reduce the levels of the harmful substance HCH in the Twente Canal. This was commissioned by the municipality of Hengelo and Rijkswaterstaat.
The HCH pollution originates from the former Stork Chemie factory, which produced a pesticide in the mid-20th century. The research agency has described concrete scenarios. Two scenarios appear most feasible: a reactive mat with activated carbon on the waterbed and an activated carbon screen in the land soil.
Tauw will further develop these two scenarios and a combination of the two. The goal is to bring the water quality in the Twente Canal within the standards of the Water Framework Directive.
Eleven scenarios
Tauw conducted research aiming to reduce HCH levels in the long term (20-30 years) to comply with the Water Framework Directive. By 2027 at the latest, all surface waters must meet the European standards for chemical substances, including the Twente Canal.
Tauw identified a total of eleven scenarios. These eleven were outlined and assessed based on costs, feasibility (both in execution and time), and social impact. Six scenarios were eliminated based on this.
Five scenarios remain plus a so-called reference measure where all soil contamination is removed. None of the scenarios achieve compliance with the standard in the short term.
Possible solution against HCH
Based on the research, the involved parties decided to further develop two possible scenarios: a reactive mat on the waterbed and an activated carbon screen in the land soil. A combination of the scenarios is also being investigated.
- A reactive mat on the waterbed contains activated carbon to which HCH adheres very well. Such a mat on the bottom of the Twente Canal and in the Strootbeek captures more HCH from the groundwater than currently happens via the natural silt layer.
- With activated carbon, a vertical screen is made in the land soil using injections. Contaminated groundwater flows through this. These injections remove part of the HCH from the groundwater. As a result, less HCH ends up in the Twente Canal. This measure resembles the other solution (a reactive mat on the waterbed). The difference is that the activated carbon injections in the land soil (along the canal) are applied instead of on the waterbed.
Removing the source of HCH
Tauw also investigated what completely removing the HCH source in the soil and additional groundwater purification would mean. The costs would amount to over 500 million euros, mainly due to very high indirect costs. Unfortunately, this is currently not a feasible option.
Follow-up
The municipality and Rijkswaterstaat will have the possible scenarios further developed in follow-up research. Tauw is expected to complete this research in the second quarter of 2026. With the information from this in-depth study, a final choice between the remaining scenarios can be made.
Background
In January 2024, elevated HCH levels were measured at the official measurement point Wiene. Therefore, it was decided to flush the Twente Canal from the Eefde lock. After flushing the canal, the HCH levels at the Wiene measurement point dropped back to pre-peak levels. The values again meet the standard there.
The cause of the temporary peak was dredging activities in 2023 carried out by Rijkswaterstaat and the municipality of Hengelo. The water between the Delden lock and Hengelo lock does not meet the Water Framework Directive (WFD) standard and has never met it since the WFD was introduced. To comply with the directive, measures must be taken with long-term effects.
