Preventing harm from chlorinated solvents

A contaminated site in north-eastern Hungary belonging to a multinational manufacturing company was contaminated with volatile organic compounds in the form of chlorinated solvents present as a dissolved plume and dense non-aqueous phase liquids (DNAPL). The plume had migrated 300 m into a residential area. Exposure can lead to short- or long-term health effects, depending on how it enters the body and the amount. Short-term side effects include dizziness, fatigue, headaches and skin rashes. Long-term side effects include chronic skin problems and damage to the nervous system, kidneys or liver.

The insidious nature of the material means that there is no practical method for removing contaminated sources. The manufacturing company feared remediation would cost millions of euros but would be futile because of the nature of the material. So, it wanted to convince the local environmental authority that it could mitigate the risks to human health and the environment without trying to remove the contamination sources.

The company asked BGT Hungaria Környezettechnológiai Kft. (BGT Hungaria) to perform human health and environmental risk assessments and develop a remediation design for the site. (In 2014, RSK acquired a 100% shareholding in BGT Hungaria.) It advocated adopting the US Environmental Protection Agency’s technical impracticality approach and the environmental authority agreed. This approach focused on mitigating the risks to human health and the environment. Using on-site dye tests and cone-penetration test membrane interface probe campaigns, BGT Hungaria investigated the DNAPLs. The plume was defined through hydrodynamic and contaminant-transport modelling. The study quantifies and predicts physical, chemical and biological processes. The data enabled BGT Hungaria to construct a conceptual site model.

The conceptual site model was a key element in determining the risk mitigation strategy. BGT Hungaria designed a pump-and-treat system to prevent plume-front migration. Sentinel wells in uncontaminated areas check for plume expansion and vapour intrusion monitoring systems in residential areas enable intervention measures, such as soil depressurisation systems, to be applied, should these be required to protect human health.

For 10 years, the mitigation measures have contained the plume and protected humans and the environment. The adoption of a technical impracticality approach has saved the manufacturing company millions of euros. Monitoring is ongoing: BGT Hungaria analyses samples and the data are uploaded to a GIS system, which enables easy analysis and interrogation of a decade of data.