Remediation of DNAPL Source Zones with Granular Iron: Laboratory and Field Tests

Abstract

Degradation of dissolved chlorinated solvents using granular iron is an established in situ technology. This paper reports on investigations into mixing iron and bentonite with contaminated soil for in situ containment and degradation of dense nonaqueous phase liquid source zones. In the laboratory, hypovials containing soil, water, bentonite, iron, and free-phase trichloroethene (TCE) were assembled. Periodic measurement of TCE, chloride, and degradation products showed progressive degradation of TCE to nondetectable levels. Subsequently, a demonstration was conducted at Canadian Forces Base Borden near Alliston, Ontario, Canada, where, in 1991, a portion of the surficial aquifer was isolated and free-phase tetrachloroethene (PCE) was introduced. Using a drill rig equipped with large-diameter mixing blades, three mixed zones were prepared containing 0%, 5%, and 10% granular iron by volume. The bentonite was added to serve as a lubricant to facilitate injection of the iron and to isolate the contaminated zone. Analysis of core samples showed reasonably uniform distributions of iron through the mixed zones. Monitoring over a 13-month period following installation showed, relative to the control, a decline in PCE concentrations to virtually nondetectable values. Reaction rates in the laboratory tests were similar to those reported in the literature, while the rate in the field test was substantially lower. The lower rate may be a consequence of mass transfer limitations under the static conditions of the field test. Results indicate that mixing iron and bentonite into source zones may be an effective means of source-zone remediation, with the particular advantage of being relatively immune to effects of geologic heterogeneity.

ZVI-Clay remediation of a chlorinated solvent source zone, Skuldelev, Denmark: 1. Site description and contaminant source mass reduction

“…An additional amount of ZVI or an alternative method of ZVI addition could also be applied to better meet the design criterion. The concurrent addition of ZVI and clay in the drilling fluid has been used at other sites (Bozzini et al, 2006;Olson et al, 2012;Shackelford et al, 2005;Wadley et al, 2005).…”

“…ZVI-Clay soil mixing is an emerging in situ remediation technology for chlorinated solvent source zones (Bozzini et al, 2006;Olson et al, 2012;Ovbey et al, 2010;Shackelford et al, 2005;Wadley et al, 2005). The technology delivers a reactive agent, zero-valent iron (ZVI), and a stabilizing agent, bentonite clay, to the subsurface via soil mixing.…”

Effects of Several Surfactants and High‐molecular‐weight Organic Compounds on Decomposition of Trichloroethylene With Zerovalent Iron Powder

“…ZVI powder is a commonly used reagent for the reductive dechlorination of TCE and PCE, and it is frequently used in practical methods for treating polluted groundwater, such as methods involving a permeable reactive barrier [15]. ZVI is an inexpensive and effective material for the reductive degradation of a wide range of organic contaminants including TCE, and several studies of its basic chemistry [16][17][18][19][20][21][22][23], its practical applications [24,25], and improvement of the efficiency by modification of the ZVI Figure 1.…”

Combining Low-Energy Electrical Resistance Heating with Biotic and Abiotic Reactions for Treatment of Chlorinated Solvent DNAPL Source Area

“…Installation via trenching or physical mixing has been implemented (Wadley et al 2005;ITRC 2005) but is not relevant for some situations. ZVI can be emplaced in an aquifer as either nanoscale or micron-scale particles.…”