Impact of an in-situ Cr(VI)-contaminated site remediation on the groundwater

Abstract

This study presents the latest results of the groundwater monitoring of a research project, which tested an innovative pump and treat method in combination with an in-situ remediation. This technique was assessed on an abandoned site in Austria, where two hot spots of hexavalent chromium (Cr(VI)) were located. For the in-situ remediation, a strong reducing agent (sodium dithionite) was injected into the underground to reduce Cr(VI) to Cr(III) by using different injection strategies. Throughout this treatment, part of the Cr(VI) is mobilized and not instantly reduced. To prevent a further spreading of the mobilized Cr(VI), the pump and treat method, which uses zero-valent iron to clean the groundwater, was installed downgradient of the hot spots. Based on the groundwater sample analyses, it was possible to distinguish different remediation phases, characterized by excess chromate and excess sulfite. During the excess sulfite conditions, Cr(VI) was successfully removed from the system, but after terminating the sodium dithionite injection, the Cr(VI) rebounded. Keywords Cr(VI) remediation. In-situ treatment. Sodium dithionite injection. Cr(VI) mobilization. Cr(VI) reduction. Rebound effect 2−), but this newly formed ion is rather unstable.

Recovery of Molybdenum, Chromium, Tungsten, Copper, Silver, and Zinc from Industrial Waste Waters Using Zero-Valent Iron and Tailored Beneficiation Processes

“…Also for Cr and W concentrations in the abrasion product and the concentration decrease in solution match quite well. After 25 h the Cr concentration increases again which can be interpreted as a rebound effect: Cr which had been adsorbed or precipitated is remobilized by desorption or dissolution [20]. This can be explained by an increase in Eh and O2 concentration in the final stage of the experiment.…”

Application of nanoscale zero-valent iron in hexavalent chromium-contaminated soil: A review

“…In vitro and plant experiments show that the application of CMC-nZVI to remove Cr(VI) from contaminated soil can significantly enhance the immobilization of Cr by converting Cr(VI) to Cr(III) [15], thereby reducing its bioavailability, leaching ability, and plant bioaccumulation, and finally realize the remediation of Cr(VI)contaminated soil [46]. As suggested by Zhang et al [46], the speciation of Cr in soil changes from relatively high availability (exchangeable) to relatively lower availability (carbonate binding and iron manganese oxide binding).…”

“…Ex situ remediation, however, will significantly increase the transportation cost, and there is also a risk of pollutant diffusion during transportation and transfer. Technologies for in situ remediation [15], such as phytoremediation, bacterial remediation, chemical flushing, and chemical reduction [16], are more promising because of the lower cost and higher efficiency [17]. Moreover, soil disturbance can be minimized, which is better for the subsequent application of soil.…”

Temporal filtering and time-lapse inversion of geoelectrical data for long-term monitoring with application to a chlorinated hydrocarbon contaminated site

“…Analysis of groundwater and soil samples, while the remediation is on-going, provides necessary quantification and can be used to monitor changes in the subsurface accurately (Sedlazeck et al 2020). The information provided is however localized at a point and often quite limited due to the cost related to the collection and analysis of the samples.…”