Portions of this document may be illegible in electronic image products.Images are produced from the best available original document. SummaryThe feasibility of chemically treating sediments from the Ft. Lewis, Washington, Logistics Center .to develop a permeable barrier for dechlorination of trichloroethylene (TCE) was investigated in a series of laboratory experiments.The proposed remediation technology uses a chemical treatment to reduce existing iron in sediments, then relies on the ability of the ferrous iron to act as an electron .donor to dechlorinate organic contaminants. The effects of temperature, partial iron reduction, and flow on these redox reactions were also studied to ascertain how to achieve viable TCE dechlorination rates at the field scale. The fraction of reducible iron in Ft. Lewis sediments would create a reduced zone that would remain anoxic for -300 pore volumes. Because the kinetics of the reduction reaction are third-order, significant amounts of iron are reduced early in the reduction period. The reduction is slower at later times. Because the slower disproportionation reaction destroys the remaining dithionite, specific sedimentisolution contact times (32 h at 25°C, 100 h at 12°C) are needed to efficiently reduce 80% of the iron in the sediment.When the pH buffer concentration was less than four times the dithionite concentration, there was a significant loss in reduction efficiency along with a significant pH decrease and increased iron mobility. The long contact times needed for reduction at ambient aquifer temperature coupled with density effects of the solution at the field scale indicate that heated injections (with high concentration of pH buffer) can efficiently reduce the sediment zones of interest. Dithionite-reducedFt. Lewis sediments were shown to degrade TCE in Ft. Lewis groundwater at sufficiently fast rates (1.2 h to 19 h) during static and transport experiments to create a permeable barrier at the field scale. The TCE degradation rate can be calculated for all sediments from the product of the intrinsic degradation rate (0.0034/h pmol) and the mass of reduced iron (range of 12 pmol/g to 126 pmol/g; averaged = 63 pmol/g). Products of TCE dechlorination clearly show that 99.5% to 100% is occurring via reductive elimination, producing acetylene, ethylene, and chloroacetylene. The TCE degradation rate decreased up to 3 orders of magnitude in partially reduced sediment. This departure on fraction of reduced iron has significant implications, because uniform full sediment reduction is not possible at the field scale. Although minimally reduced sediment had nearly no TCE reactivity, X070 reduced sediment resulted in TCE reduction rates that were viable at the field scale (<65 h). The second-order dependence of the TCE dechlorination rate on the fraction of reduced iron demonstrates the significant role of the iron oxide surface (as a catalyst or for surface coordination) in addition to Fe**as the electron donor for TCE dechlorination to proceed. Reduced sediment barrier longe...
Pacific Northwest National Laboratory (PNNL) conducted a proof-of-principle test at the Fort Lewis Logistics Center to determine the feasibility of using the In Situ Redox Manipulation (ISRM) technology for remediating groundwater contaminated with dissolved trichloroethylene (TCE). ISRM creates a permeable treatment zone in the subsurface to remediate redox-sensitive contaminants in groundwater. The permeable treatment zone is formed by injecting a chemical reducing agent (sodium dithionite with pH buffers) into the aquifer through a well to reduce the naturally occurring ferric iron in the sediments to ferrous iron. Once the reducing agent is injected and given sufficient time to react with aquifer sediments, residual chemicals and reaction products are withdrawn from the aquifer through the same well used for the injection. Redox-sensitive contaminants such as TCE, moving through the treatment zone under natural groundwater flow conditions, are destroyed. TCE is degraded via reductive dechlorination within the ISRM treatment zone to benign degradation products (i.e., acetylene, ethylene). Prior to the proof-of-principle field test, the ISRM technology was successfully demonstrated in laboratory experiments for the reductive dechlorination of dissolved TCE using sediments from the Fort Lewis site. The Logistics Center was placed on the National Priorities List in December 1989 because of TCE contamination in groundwater beneath the site. A Federal Facilities Agreement between the Army, the U.S. Environmental Protection Agency, and the Washington State Department of Ecology became effective in January 1990, and a Record of Decision (ROD) was signed in September 1990. The major components of the ROD included installation of two pump-and-treat systems for the upper aquifer and further investigation of the lower aquifer and other potential sources of contamination. The pump-andtreat systems became operational in August 1995. Fort Lewis asked PNNL to provide technical support in accelerating Installation Restoration Program site remediation and significantly reducing site life-cycle costs at the Logistics Center. In support of this program, ISRM was selected as an innovative technology for bench and field-scale demonstration. Emplacement of the ISRM treatment zone was accomplished through a series of four separate dithionite injection tests conducted between November 10, 1998 and March 29, 2000. An extensive program of chemical monitoring was also performed before, during, and after each injection to evaluate the performance of ISRM. Prior to emplacement of the ISRM treatment zone, the site was extensively characterized with respect to geologic, hydrologic, and geochemical properties. Sediment core samples collected for the characterization studies were analyzed in bench-scale column tests at PNNL to determine reducible iron content. These site-specific hydrogeologic and geochemical data were used to develop the emplacement design of the pilot-scale (i.e., single injection well) ISRM treatment zone. Performance data...
Abstract. Theexperimental andtheoretical development of ion cyclotronradofrequency heating (ICRF)intoroidalmagnetically-confined plasmasrecentlyculminatedwith the demonstration of ICRFheatingof D-Tplasmas, firstin theTokamakFusionTestReactor(TFTR)and then in the Joint EuropeanTorus (JET). Variousheating schemesbased on the cyclotronresonances betweentheplasmaionsandtheappliedICRFwaveshavebeenused,includingsecondharmonic tritium, minoritydeuterium, minorityhelium-3,modeconversionat the D-T ion-ion hybrid layer,andandionBernstein waveheating. Secondharmonictritium heatingwasfirst shownto be effectivein a reactor-grade plasmain TFTR. D-minorityheatingon JET has led to the achievement of Q = 0.22,theratioof fusionpowerproducedto RFpowerinput,sustainedovera few energyconfinementtimes. In this paper, some of the key building blocks in the development ofrf heatingofplasmasarereviewedandprospectsfor the development of advanced methodsof plasmacontrolbasedontheapplication ofrf wavesarediscussed.
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