SummaryThis report. presents results a€ an In Situ Redox M~~p u~~i~n (EM) Field Injection W~~h~~w a~ Test performed at the 100-H Area of the U.S. Department of Energy's (DOE's) Hanford Site in Washington State in Fisc& Year I996 by researchers at Pacific Northwest National Laboratoq (PNNL), The test is part u€ the overall ISIiM project, the purpose of which is to determine the potential for remediating contaminated groundwater with a technology based on in situ manipulation of subsurface reduction-oxidation (redox) conditions. The ISRM technology would be used to treat subsurface contaminants in groundwater zones at DOE sites.Subsurface &~~~~~~ at DUE sites occur in both the vadose md its not the vadose-saturated zone. It's the vadose zone ;ind GW-saturated zone. and ~o~~~w a t e r -s~~~e d zones. Some groundwater plrrmes at DUE sites are already dispersed over areas covering sqwe miIes and can be difficult to treat using excavation or pump-and-treat methods. Some contarninant plumes may be suuccessfulIy treated by ISM4 methods. Researchers are determining if these methods can be created by controlling the redox potential of the unconfined aquifers in which the contaminants reside. The concept requires creating a permeable treatment barrier in the subsurface by injecting reagents and/or microbial nutrients into the srrbsrrrface. The reagents and nutrients are selected to make the aquifer r&=clng, thereby destroying ur ~~~~~~~~~~ specific redox-sensitive ~~n~~~i~~n~~, located hEBdreds of feet below &e gmsd, This type a€ dispersed, inaccessib5zle ~u~~~~~~ isThe concept relies on the fact that unconfined aquifers are usually oxidizing environments; therefore, most o€ the mobile contaminants in these aquifers are mobile under oxidizing conditions. If the redox potential of the aquifer can be made reducing, then a variety of contaminants can be treated.The goal o€ I S M is to create a permeable treatment zone in the subsurface for remediating redox-sensitive contaminants in the groundwater. The permeable treatment zone must be created just downstream of the contaminant plume or c~~~~~ source through the injection of reagents m&or microbial nutrients to alter the redox potential of the aquifer fluids and sediments.~~~~~~~~~ pfumes migx-atkg tk-oqgh this ~~~p~~~r e~ zone will then be deseoyed or immobilized.Three field experiments have been conducted at the site: a full-scale bromide tracer experiment, a mini ~j t~j o~~t~ ~j~r~#~~~t~~r~w~ experiment, and a full-scale d~~~o n~~ ~~j~~~~w~t~ experiment, All the major objectives of the ISRM field test were achieved. These objectives included demonstrating the feasibility of reducing the aquifer sediments, determining how long the reducing conditions can be maintained, determining tfie natnre and severity o€ m y secondary effects, and developing a methodology for evaluating I S M technologies in general.Twenty-one thousand gallons of buffered sodium ditfiionite solution were successfully injected into the unconfined aquifer at the Hanford 100-H Area in September 1995. No ...

Geothermal steam used for power production contains significant quantities of volatile mercury. Much of this mercury escapes to the atmosphere as elemental mercury vapor in cooling tower exhausts. Mercury emissions from geothermal power plants, on a per megawatt (electric) basis, are comparable to releases from coal-fired power plants.

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...

No abstract

Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.