Context
Environmental consultancies are often expected to meet regulatory requirements while offering technically sound and highly competitive pricing to win contracts. To reduce costs, studies are sometimes optimized by limiting field investigations. While these studies may be “administratively” acceptable to authorities, they can lack technical depth. This becomes critical when moving toward remediation works, as these gaps increase uncertainty, reduce treatment effectiveness, prolong timelines, and raise costs—often leading to a loss of client trust.
This case study focuses on a large chlorinated solvent remediation project. The initial remediation plan proposed six injection barriers across the plume. After reviewing the data and conducting a pilot test, Injectis facilitated a collaborative discussion with the remediation firm and the end client. It was agreed that a targeted recharacterization (Remedial Design Characterization (RDC)) was essential to redesign the remediation plan and optimize cost and effectiveness. EniSSA quickly performed this using advanced MIP-GC/MS technology (of EniSSA). The revised design allowed for more precise injections, focused on treatment of an extended source zone, reducing costs by nearly 25% (€100k) and increasing target achievement by over 40%. Trust and collaboration were key.
Reaction
In this case, the selected remediation approach is Enhanced Reductive Dechlorination (ERD), which stimulates the anaerobic biological degradation of chlorinated solvents. The subsurface is composed of low to very low permeability soils, with progressively less sandy clays extending down to 8 m-bgl. The natural presence of organic matter further supports favorable conditions for ERD. These native conditions already promote microbial anaerobic activity, so, the addition of a carbon source was selected to promote bacteria growth which stimulate and accelerate the degradation process. Given the low permeability and clay-rich nature of the soils, the injection will be carried out using SPIN® technology, which enables precise, low-pressure reagent delivery in such difficult lithologies. A pilot injection test was conducted in collaboration with VEOLIA, the remediation contractor, who selected glycerin as the carbon source. The test showed promising results, with a significant and rapid decrease in contaminant concentrations, falling below the target thresholds. This confirmed the effectiveness of the selected strategy and reagent under site-specific conditions.
Reagent
Glycerin was selected by VEOLIA for the pilot injection test due to its key advantages: it is cost-effective, easy to inject, and rapidly biodegradable, which allows for quick observation of short- to medium-term biological activity. These characteristics make it particularly well-suited for pilot-scale testing. However, for full-scale remediation, a longer-lasting solution is required. The objective is to maintain strongly reducing conditions over time, allowing sustained dechlorination. Additionally, since the superficial horizons (2–4 m bgl) are more permeable, a solid carbon source is essential to prevent the reagent from being washed away by groundwater flow. EHC®(Evonik) meets these criteria. It combines micron-scale zero-valent iron (mZVI, 40%) and a solid organic carbon source (50–70% w/w). The ZVI induces rapid chemical reduction and helps quickly establish strongly reducing conditions, while the solid carbon ensures a slow, long-term release. With SPIN® technology enabling successful ZVI injection even in low-permeability soils, this combined approach proved effective and reliable for the site.
Location: Wallon Brabant, Belgium
Geology: Sandy clay
Pollutant(s): TCE (150 μg/L) DCE (1.500 μg/L) CV (300 μg/l). Soils 5 mg/kg.ms residual concentrations of TCE after excavation (120 mg/kg.ms excavated)
Reaction: ISCR +ERD (Enhanced Reductive Dechlorination)
Reagent(s): EHC® (Evonik)
Application type: Grid and Barrier application
Surface/length: 800 m²
Number of points: 63
Depth interval: 2,0 – 7,0 m-bgl
Dosage: Between 250 and 400 l/m