Description

In the framework of the REGROUND project, a contaminated site in north of Spain was remediated using ColFerroX technology.  The site was used historically for the production of nitrogen based products such as fertilizers. Waste materials (e.g. slag from furnaces, wastes from coal-washing and partially burned pyrites and pyrite ashes reach with heavy metals) were dumped on the surface. The contaminants eventually leached into the groundwater and were transported towards the neighboring sites and to a downstream river.

Contamination levels were high in both groundwater and sediment phases. Dissolved concentrations of 20-45 mg/L for zinc, 1-20 mg/L copper, 50-3000 µg/L arsenic, 100-700 µg/L lead were measured among others. Metal contaminants were also present in the sediment phase as high as several grams per kg of solid weight.

The aim of the study was to demonstrate the applicability of the ColFerroX technology to immobilize heavy metals at an industrial site in realistic dimension.

ColFerroX

Despite high levels of contamination in both GW and sediment, the laboratory results shows efficient immobilization of the mobile contamination, as well as reduced leaching (if any occurs).

Fast breakthrough if no particle is added
Breakthrough is delayed and mitigated using ColFerroX particles

A barrier of 22 m wide was installed using 9 injection points in two rows. Normal monitoring wells were placed upstream and downstream the barrier to record the pollutant concentrations before and after the barrier. Injection was carried out at low pressure (<1 bar). A total volume of ca. 105 m3 was injected within 5 days. No daylighting or pressure buildup was observed during the injection. Particle delivery to the intended radius was confirmed by later coring and sediment analysis.

Results

Reduction in all toxic metal concentrations was observed after applying the ColFerroX technology (day 0). An exemplary case for Zinc is shown. Zinc concentrations were reduced from 20-50 mg/L to below the threshold value of 5 mg/L in downstream values. The pH-values changed from 4 to 8 at some wells. Effective immobilization of toxic metals was observed across the pH-values at this highly contaminated site.