Isotopic Tracking of Hanford 300 Area Derived Uranium in the Columbia River

Our objectives in this study are to quantify the discharge rate of uranium (U) to the Columbia River from the Hanford Site's 300 Area, and to follow that U down river to constrain its fate. Uranium from the Hanford Site has variable isotopic composition due to nuclear industrial processes carried out at the site. This characteristic makes it possible to use high-precision isotopic measurements of U in environmental samples to identify even trace levels of contaminant U, determine its sources, and estimate discharge rates. Our data on river water samples indicate that as much as 3.2 kg/day can enter the Columbia River from the 300 Area, which is only a small fraction of the total load of dissolved natural background U carried by the Columbia River. This very low-level of Hanford derived U can be discerned, despite dilution to < 1 percent of natural background U, 350 km downstream from the Hanford Site. These results indicate that isotopic methods can allow the amounts of U from the 300 Area of the Hanford Site entering the Columbia River to be measured accurately to ascertain whether they are an environmental concern, or are insignificant relative to natural uranium background in the Columbia River

Review of Techniques to Characterize the Distribution of Chromate Contamination in the Vadose Zone of the 100 Areas at the Hanford Site

The purpose of this report is to identify and evaluate the state-of-the-art techniques for characteriza¬tion of chromate contamination in the vadose zone of the 100 Areas at the Hanford Site. The techniques include direct techniques for analysis of chromium in the subsurface as well as indirect techniques to identify contamination through geophysical properties, soil moisture, or co-contaminants. Characteri¬zation for the distribution of chromium concentration in the vadose zone is needed to assess potential sources for chromate contamination plumes in groundwater at the 100-D, 100-K, and 100-B/C Areas

Longitudinal relations between teaching-related motivations and student-reported teaching quality

Teaching-related motivations are often assumed to influence teaching quality; however, the empirical evidence regarding the directionality of such influences is scarce. The present study thus examined the reciprocal links between teaching-related motivations (self-efficacy and enthusiasm for teaching) and student-reported teaching quality (classroom management, learning support, and cognitive activation). Two-level cross-lagged panel analyses across three time points (with an initial sample of 165 secondary- level mathematics teachers and their 4273 students) revealed no significant cross-lagged effects when teachers' stable inter-individual differences are taken into account. Our findings suggest that teachers' motivations are remarkably stable over time

Isotopic Tracers for Biogeochemical Processes and Contaminant Transport: Hanford, Washington

Our goal is to use isotopic measurements to understand how contaminants are introduced to and stored in the vadose zone, and what processes control migration from the vadose zone to groundwater and then to surface water. We have been using the Hanford Site in south-central Washington as our field laboratory, and our investigations are often stimulated by observations made as part of the groundwater monitoring program and vadose zone characterization activities. Understanding the transport of contaminants at Hanford is difficult due to the presence of multiple potential sources within small areas, the long history of activities, the range of disposal methods, and the continuing evolution of the hydrological system. Observations often do not conform to simple models, and cannot be adequately understood with standard characterization approaches, even though the characterization activities are quite extensive. One of our objectives is to test the value of adding isotopic techniques to the characterization program, which has the immediate potential benefit of addressing specific remediation issues, but more importantly, it allows us to study fundamental processes at the scale and in the medium where they need to be understood. Here we focus on two recent studies at the waste management area (WMA) T-TX-TY, which relate to the sources and transport histories of vadose zone and groundwater contamination and contaminant fluid-sediment interaction. The WMA-T and WMA-TX-TY tank farms are located within the 200 West Area in the central portion of the Hanford Site (Fig. 2). They present a complicated picture of mixed groundwater plumes of nitrate, {sup 99}Tc, Cr{sup 6+}, carbon tetrachloride, etc. and multiple potential vadose zone sources such as tank leaks and disposal cribs (Fig. 3). To access potential vadose zone sources, we analyzed samples from cores C3832 near tank TX-104 and from C4104 near tank T-106. Tank T-106 was involved in a major event in 1973 in which 435,000 L of high activity waste leaked to the vadose zone over a seven-week period. Other nearby tanks (T-103 and T-101) are also suspected of having leaked or overfilled. Pore water from these cores was analyzed for U and Sr isotopic compositions. Increasing {sup 99}Tc concentration in monitoring well 299-W11-39 (to 27,000 pCi/L in 2005) near the northeast corner of the WMA-T area prompted the emplacement of a series of new wells, 299-W11-25B, W11-45 (down gradient), and W11-47 (Fig. 3), during which depth discrete samples were collected below the groundwater surface. The depth profile from W11-25B revealed high {sup 99}Tc concentrations peaking at 182,000 pCi/L at {approx}10 m below the water table (Dresel et al. 2006). We obtained aliquots for isotopic analysis of groundwater samples produced by purge-and-pump sampling during the drilling of W11-25B, -45 and -47. In addition we have analyzed groundwater samples from monitoring wells in the vicinity of WMA T-TX-TY

High-precision uranium isotopic analysis for environmental forensics using MC-ICPMS: Demonstration studies at the Hanford Site, Washington

The contrasts in isotopic composition between natural and anthropogenic uranium and the wide variation in the composition of different processed uranium sources, promotes the measurement of uranium isotopic composition as a fingerprint and tracer of uranium contamination in the environment. Previous studies mainly have focused on the use of only one of the isotope ratios of U, e.g., 234U/238U, 238U/235U or 236U/238U. We measure all three of these ratios in environmental samples in order to better distinguish, characterize, identify and apportion U sources. For our U isotopic measurements, we employ an IsoProbe (GV Instr. Inc.) multiple-collector ICP source magnetic sector mass spectrometer. U isotopic compositions are measured simultaneously using a combination of Faraday cups (for 235U and 238U) and a Daly photomultiplier ion counting system (for 234U and 236U in two separate analyses). U is separated from samples (e.g., vadose zone pore water, groundwater, rock/soil samples) prior to introduction to the MC-ICPMS via a desolvation system. At 7E-11 amps of 238U ions, a single analysis of a 20ppb U solution uses ~10ng of sample U. For correction of instrumental mass fractionation, we use bracketing analyses of a natural secular equilibrium U standard. This allows us to avoid the use of a double 233U-236Uspike for mass fractionation correction that would compromise our ability to measure 236U/238U. We also use the standard analyses for Daly/Faraday gain and for peak-tail correction of the 236U analyses. Typical precision for 238U/235U is ?0.05% 2s, while for 234U/238U it is ?0.15% 2s. Precision for 236U/238U is ?0.15% 2s down to the 10-7 range where precision degrades by a factor of ten. The limit for 236U/238U measurement is about 2x10-8, only ~five times higher than accelerator MS. For 1ppb U, this represents 5x107 atoms 236U per liter water.We will present three ongoing studies at the Hanford site as a demonstration of our techniques: (1) investigation of groundwater and vadose zone contamination in the B-BX-BY WMA (Christensen et al. (2004) Env. Sci. Tech., in press) (2) signatures of vadose zone contamination in waste cribs near U-Plant and (3) investigation of U contamination of the Columbia River

High-precision uranium isotopic studies at the Hanford Site, Washington using MC-ICPMS

Uranium from nuclear industrial activities covers a wide range of 235U/ 238U and 236U/238U due to variable combinations of isotopic enrichment and use in nuclear reactors. In addition, the irradiation of 232Th produces 233U and thus a signature separate from variable burn-up of different U fuel types. Natural background uranium in groundwater and porewater has essentially constant 235U/238U, virtually zero 236U/238U and 233U/238U, but variable 234U/238U due to alpha recoil effects. The contrasts in isotopic composition between natural and processed uranium, as well as the wide compositional range of processed uranium, provides the means to trace contaminant uranium in the environment and delineate the sources and history of contamination. We have developed techniques of high precision measurement of uranium isotopes using an ICP source multiple collector magnetic sector mass spectrometer (MC-ICPMS) (IsoProbe, GV Instruments Ltd.).U isotopic compositions are measured simultaneously using a combination of Faraday cups (for 235U and 238U) and a Daly photomultiplier ion counting system (for 234U, 236U and 233U in separate measurements). U is separated from samples prior to introduction to the MC-ICPMS via a desolvation system. A single analysis of a 20ppb U solution uses ~10ng of sample U. We use bracketing analyses of a natural secular equilibrium U standard to correct instrumental mass fractionation, establish Daly/Faraday gain, and account for peak-tailing on 236 /sup>U. This allows us to avoid the use of a 233U-236U double spike for mass fractionation correction that would compromise our ability to measure 236U and 233U. The lower limit for 236U/238U measurement is about 2x10-8. For 1ppb U in a water sample, this represents 5x107 atoms 236U per liter.As demonstrations of our techniques we will present data from several ongoing studies at the Hanford Site, where decades of nuclear related activities have left significant local U contamination, including: (1) investigation of the connection between groundwater and vadose zone contamination in the B-BX-BY Waste Management Area (WMA) (Christensen et al. (2004) Env. Sci. Tech., 38:3330) (2) behavior of vadose zone U contamination in a core from the T WMA (3) sourcing, apportioning and tracing the contribution of the Hanford Site to the U flux of the Columbia River

High-precision uranium isotopic studies at the Hanford Site, Washington using MC-ICPMS

Uranium from nuclear industrial activities covers a wide range of 235U/ 238U and 236U/238U due to variable combinations of isotopic enrichment and use in nuclear reactors. In addition, the irradiation of 232Th produces 233U and thus a signature separate from variable burn-up of different U fuel types. Natural background uranium in groundwater and porewater has essentially constant 235U/238U, virtually zero 236U/238U and 233U/238U, but variable 234U/238U due to alpha recoil effects. The contrasts in isotopic composition between natural and processed uranium, as well as the wide compositional range of processed uranium, provides the means to trace contaminant uranium in the environment and delineate the sources and history of contamination. We have developed techniques of high precision measurement of uranium isotopes using an ICP source multiple collector magnetic sector mass spectrometer (MC-ICPMS) (IsoProbe, GV Instruments Ltd.).U isotopic compositions are measured simultaneously using a combination of Faraday cups (for 235U and 238U) and a Daly photomultiplier ion counting system (for 234U, 236U and 233U in separate measurements). U is separated from samples prior to introduction to the MC-ICPMS via a desolvation system. A single analysis of a 20ppb U solution uses ~10ng of sample U. We use bracketing analyses of a natural secular equilibrium U standard to correct instrumental mass fractionation, establish Daly/Faraday gain, and account for peak-tailing on 236 /sup>U. This allows us to avoid the use of a 233U-236U double spike for mass fractionation correction that would compromise our ability to measure 236U and 233U. The lower limit for 236U/238U measurement is about 2x10-8. For 1ppb U in a water sample, this represents 5x107 atoms 236U per liter.As demonstrations of our techniques we will present data from several ongoing studies at the Hanford Site, where decades of nuclear related activities have left significant local U contamination, including: (1) investigation of the connection between groundwater and vadose zone contamination in the B-BX-BY Waste Management Area (WMA) (Christensen et al. (2004) Env. Sci. Tech., 38:3330) (2) behavior of vadose zone U contamination in a core from the T WMA (3) sourcing, apportioning and tracing the contribution of the Hanford Site to the U flux of the Columbia River

Determining flow, recharge, and vadose zone drainage in an unconfined aquifer from groundwater strontium isotope measurements, Pasco Basin, WA

Strontium isotope compositions (87Sr/86Sr) measured in groundwater samples from 273 wells in the Pasco Basin unconfined aquifer below the Hanford Site show large and systematic variations that provide constraints on groundwater recharge, weathering rates of the aquifer host rocks, communication between unconfined and deeper confined aquifers, and vadose zone-groundwater interaction. The impact of millions of cubic meters of wastewater discharged to the vadose zone (103-105 times higher than ambient drainage) shows up strikingly on maps of groundwater 87Sr/86Sr. Extensive access through the many groundwater monitoring wells at the site allows for an unprecedented opportunity to evaluate the strontium geochemistry of a major aquifer, hosted primarily in unconsolidated sediments, and relate it to both long term properties and recent disturbances. Groundwater 87Sr/86Sr increases systematically from 0.707 to 0.712 from west to east across the Hanford Site, in the general direction of groundwater flow, as a result of addition of Sr from the weathering of aquifer sediments and from diffuse drainage through the vadose zone. The lower 87Sr/86Sr groundwater reflects recharge waters that have acquired Sr from Columbia River Basalts. Based on a steady-state model of Sr reactive transport and drainage, there is an average natural drainage flux of 0-1.4 mm/yr near the western margin of the Hanford Site, and ambient drainage may be up to 30 mm/yr in the center of the site assuming an average bulk rock weathering rate of 10-7.5 g/g/yr