nZVI injection into variably saturated soils: Field and modeling study.
Nano-scale zero valent iron (nZVI) has been used at a number of contaminated sites over the last decade. At most of these sites, significant decreases in contaminant concentrations have resulted from the application of nZVI. However, limited work has been completed investigating nZVI field-scale mobility. In this study, a field test was combined with numerical modeling to examine nZVI reactivity along with transport properties in variably saturated soils. The field test consisted of 142L of carboxymethyle cellulose (CMC) stabilized monometallic nZVI synthesized onsite and injected into a variably saturated zone. Periodic groundwater samples were collected from the injection well, as well as, from two monitoring wells to analyze for chlorinated solvents and other geochemistry indicators. This study showed that CMC stabilized monometallic nZVI was able to decrease tricholorethene (TCE) concentrations in groundwater by more than 99% from the historical TCE concentrations. A three dimensional, three phase, finite difference numerical simulator, (CompSim) was used to further investigate nZVI and polymer transport at the variably saturated site. The model was able to accurately predict the field observed head data without parameter fitting. In addition, the numerical simulator estimated the mass of nZVI delivered to the saturated and unsaturated zones and distinguished the nZVI phase (i.e. aqueous or attached). The simulation results showed that the injected slurry migrated radially outward from the injection well, and therefore nZVI transport was governed by injection velocity and viscosity of the injected solution. A suite of sensitivity analyses was performed to investigate the impact of different injection scenarios (e.g. different volume and injection rate) on nZVI migration. Simulation results showed that injection of a higher nZVI volume delivered more iron particles at a given distance; however, the travel distance was not proportional to the increase in volume. Moreover, simulation results showed that using a 1D transport equation to simulate nZVI migration in the subsurface may overestimate the travel distance. This is because the 1D transport equation assumes a constant velocity while pore water velocity radially decreases from the well during injection. This study suggests that on-site synthesized nZVI particles are mobile in the subsurface and that a numerical simulator can be a valuable tool for optimal design of nZVI field applications.
Department of Civil and Environmental Engineering, The University of Western Ontario, 1151 Richmond Street, London, ON N6A 5B9, Canada.
Ahmed I A
AI
Chowdhury
Department of Civil Engineering, Lassonde School of Engineering, York University, 4700 Keele St., Toronto, ON M3J 1P3, Canada.
Magdalena M
MM
Krol
Department of Civil and Environmental Engineering, The University of Western Ontario, 1151 Richmond Street, London, ON N6A 5B9, Canada.
Christopher M
CM
Kocur
Department of Civil and Environmental Engineering, The University of Western Ontario, 1151 Richmond Street, London, ON N6A 5B9, Canada.
Hardiljeet K
HK
Boparai
Department of Chemistry and Chemical Engineering, Royal Military College of Canada, Kingston, ON K7K 7B4, Canada.
Kela P
KP
Weber
Department of Civil Engineering, University of Toronto, 35 St. George St., Toronto, ON M5S 1A4, Canada.
Brent E
BE
Sleep
Department of Civil and Environmental Engineering, The University of Western Ontario, 1151 Richmond Street, London, ON N6A 5B9, Canada. Electronic address: docarroll@eng.uwo.ca.
Denis M
DM
O'Carroll
D002266:Carboxymethylcellulose Sodium / Q000737:chemistry; D003198:Computer Simulation; D052918:Environmental Restoration and Remediation / Q000379:methods*; D060587:Groundwater / Q000032:analysis; D007501:Iron / Q000737:chemistry; D053768:Metal Nanoparticles / Q000737:chemistry; D008962:Models, Theoretical; D009864:Ontario; D012987:Soil / Q000737:chemistry; D012989:Soil Pollutants / Q000032:analysis / Q000737:chemistry; D014240:Trichloroethanes / Q000032:analysis / Q000737:chemistry; D014783:Viscosity; D014874:Water Pollutants, Chemical / Q000032:analysis*; D060986:Water Wells
D012987:Soil; D012989:Soil Pollutants; D014240:Trichloroethanes; D014874:Water Pollutants, Chemical; D007501:Iron; D002266:Carboxymethylcellulose Sodium
CompSim; Field study; Nano-scale zero valent iron; Numerical simulation