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After intervals of groundwater immersion, polyacrylamide hydrogel-encapsulated solid specimens were retrieved, assayed non-destructively for uranium and other elements using x-ray fluorescence spectroscopy, and replaced in groundwater for continued reaction. Desorption dynamics of uranium from contaminated soils and other solids, when moved to uncontaminated groundwater, were fit to a general two-component kinetic retention model with slow-release and fast-release fractions of the total uranium. In a group of Oak Ridge soils with varying ambient uranium contamination (169-1360 mg/kg), the uranium fraction retained under long-term in situ kinetic behavior was strongly correlated (r2 = 0.89) with the residual uranium retained after laboratory sequential extraction of water-soluble and cation-exchangeable fractions of the same soils. To illustrate how potential remedial techniques can be compared to natural attenuation, thermal stabilization of one soil increased the size of its long-term retained fraction from 50 to 88% of the total uranium and increased the in situ retention half-life of the long-term retained fraction from 990 to 40,000 days. Hydrogel encapsulation presents a novel and powerful general method to observe many water-solids interactions in situ for a variety of aqueous media besides groundwater, with a variety of non-destructive analytical methods, and with a variety of solids besides contaminated soil.

Many geochemical reactions that control aqueous metal concentrations are directly affected by solution pH. However, changes in solution pH are strongly buffered by various aqueous phase and solid phase precipitation/dissolution and adsorption/desorption reactions. The ability to predict acid-base behavior of the soil-solution system is thus critical to predict metal transport under variable pH conditions. This studywas undertaken to develop a practical generic geochemical modeling approach to predict aqueous and solid phase concentrations of metals and anions during conditions of acid or base additions. The method of Spalding and Spalding was utilized to model soil buffer capacity and pH-dependent cation exchange capacity by treating aquifer solids as a polyprotic acid. To simulate the dynamic and pH-dependent anion exchange capacity, the aquifer solids were simultaneously treated as a polyprotic base controlled by mineral precipitation/ dissolution reactions. An equilibrium reaction model that describes aqueous complexation, precipitation, sorption and soil buffering with pH-dependent ion exchange was developed using HydroGeoChem v5.0 (HGC5). Comparison of model results with experimental titration data of pH, Al, Ca, Mg, Sr, Mn, Ni, Co, and SO4(2-) for contaminated sediments indicated close agreement suggesting that the model could potentially be used to predictthe acid-base behavior of the sediment-solution system under variable pH conditions.

Strontium-90 is a major hazardous contaminant of radioactive wastewater and its processing sludges at many Department of Energy (DOE) facilities. In the past, such contaminated wastewater and sludge have been disposed in soil seepage pits, lagoons, or cribs often under highly perturbed alkaline conditions (pH12) where 90Sr solubility is low and its adsorption to surrounding soil is high. As natural weathering returns these soils to near-neutral or slightly acidic conditions, the adsorbed and precipitated calcium and magnesium phases, in which 90Sr is carried, change significantly in both nature and amounts. No comprehensive computational method has been formulated previously to quantitatively simulate the dynamics of 90Sr in the soil-groundwater environment under such dynamic and wide-ranging conditions. A computational code, the Hydrologic Utility Model for Demonstrating Integrated Nuclear Geochemical Environmental Responses (HUMDINGER), was composed to describe the changing equilibria of 90Sr in soil based on its causative chemical reactions including soil buffering, pH-dependent cation-exchange capacity, cation selectivity, and the precipitation/dissolution of calcium carbonate, calcium hydroxide, and magnesium hydroxide in response to leaching groundwater characteristics including pH, acid-neutralizing capacity, dissolved cations, and inorganic carbonate species. The code includes a simulation of one-dimensional transport of 90Sr through a soil column as a series of soil mixing cells where the equilibrium soluble output from one cell is applied to the next cell. Unamended soil leaching and highly alkaline soil treatments, including potassium hydroxide, sodium silicate, and sodium aluminate, were simulated and compared with experimental findings using large (10 kg) soil columns that were leached with 90Sr-contaminated groundwater after treatment. HUMDINGER's simulations were in good agreement with dynamic experimental observations of soil exchange capacity, exchangeable cations, total 90Sr, and pH values of layers within the soil columns and of column effluents.

The objective of this preliminary investigation is to determine the effect of heating hardened Portland cement paste (the cementitious component of concrete) in aiding the removal of common radionuclide contaminants including 137 Cs, 90 Sr, 60 Co, and U. Direct volatilization of radionuclides during heating as well as subsequent behaviors during extractions were established over a range of temperatures up to the melting point of Portland cement paste. Techniques for spiking pulverized Portland cement paste with shorter-lived radioisotopes ( 134 Cs, 35 Sr, and 57 Co) and U were developed using gamma-ray spectroscopy to measure their activity nondestructively before and after heating. An extraction procedure (employing five sequential extractions each with water, followed by 0.1 N CaCl 2 , followed by 0.2 N HCl) for pulverized but fully hydrated Portland cement paste was adapted to contrast behaviors after thermal treatments. Complete volatility of 134 Cs was observed at temperatures of 1200°C or greater. Thus, decontamination of 137 Cs from cement paste would be feasible by direct heating. However, no volatility of other radionuclides was observed, and, thus, their potential for facilitated decontamination will likely depend on their extraction behavior following thermal perturbation. Both 134 Cs and 85 Sr were readily removed from cement paste during initial water-based extractions for final temperatures

A field test with a one-time emulsified vegetable oil (EVO) injection was conducted to assess the capacity of EVO to sustain uranium bioreduction in a high-permeability gravel layer with groundwater concentrations of (mM) U, 0.0055; Ca, 2.98; NO3(-), 0.11; HCO3(-), 5.07; and SO4(2-), 1.23. Comparison of bromide and EVO migration and distribution indicated that a majority of the injected EVO was retained in the subsurface from the injection wells to 50 m downgradient. Nitrate, uranium, and sulfate were sequentially removed from the groundwater within 1-2 weeks, accompanied by an increase in acetate, Mn, Fe, and methane concentrations. Due to the slow release and degradation of EVO with time, reducing conditions were sustained for approximately one year, and daily U discharge to a creek, located approximately 50 m from the injection wells, decreased by 80% within 100 days. Total U discharge was reduced by 50% over the one-year period. Reduction of U(VI) to U(IV) was confirmed by synchrotron analysis of recovered aquifer solids. Oxidants (e.g., dissolved oxygen, nitrate) flowing in from upgradient appeared to reoxidize and remobilize uranium after the EVO was exhausted as evidenced by a transient increase of U concentration above ambient values. Occasional (e.g., annual) EVO injection into a permeable Ca and bicarbonate-containing aquifer can sustain uranium bioreduction/immobilization and decrease U migration/discharge.

During vitrification of soil and soil:limestone mixtures, significant volatilization (> 10%) of the radioisotope [sup 137]Cs occurred particularly in the presence of small amounts ( 99% of the [sup 137]Cs by repeated amendment and treatment at 1000[degree]C. Amendment with sodium borate and subsequent heating to 1200[degree]C also stimulated significant volatilization of [sup 137]Cs. However, amendments up to 10% of other chemicals including carbonates, nitrates, phosphates, sulfates, fluorides, polystyrene, graphite, stainless steels, iron, zinc oxide, and antimony oxide did not increase [sup 137]Cs volatilization compared to unamended samples. The majority of the chloride-induced volatilization occurred between 800 and 1000[degree]C for sodium chloride-amended samples of both soil and soil:limestone mixtures. Thus, an effective and potentially efficient soil decontamination technique for [sup 137]Cs has been identified. 17 refs., 8 figs., 3 tabs.

An in situ passive sampling and gas chromatographic protocol was developed for analysis of the major and several minor fixed gases (He, Ne, H2, N2, O2, CO, CH4, CO2, and N2O) in groundwater. Using argon carrier gas, a HayeSep DB porous polymer phase, and sequential thermal conductivity and reductive gas detectors, the protocol achieved sufficient separation and sensitivity to measure the mixing ratio of all these gases in a single 0.5 mL gas sample collected in situ, stored, transported, and injected using a gastight syringe. Within 4 days of immersion in groundwater, the simple passive in situ sampler, whether initially filled with He or air, attained an equivalent and constant mixing ratio for five of the seven detected gases. The abundant mixing ratio of N2O, averaging 2.6%, indicated that significant denitrification is likely ongoing within groundwater contaminated with uranium, acidity, nitrate, and organic carbon from a group of four closed radioactive wastewater seepage ponds at the Oak Ridge Field Research Center. Over 1000 passive gas samples from 12 monitoring wells averaged 56% CO2, 32.4% N2, 2.6% O2, 2.6% N2O, 0.21% CH4, 0.093% H2, and 0.025% CO with an average recovery of 95 +/- 14% of the injected gas volume.

A simple in-situ passive dissolved gas groundwater sampler, comprised of a short length of silicone tubing attached to a gastight or other syringe, was adapted and tested for in-situ collection of equilibrium gas samples. Sampler retrieval after several days of immersion in groundwater allowed the direct injection of the sample onto a gas chromatograph (GC), simplifying field collection and sample handling over the commonly used "bubble stripping" method for H2 analyses. A GC was modified by sequencing a thermal conductivity (TC) detector followed by a reductive gas (RG) detector so that linear calibration of H2 over the range 0.2-200,000 ppmv was attained using a 0.5-mL gas sample; inclusion of the TC detector allowed the simultaneous quantification of other fixed gases (O2, CO2, He, and Ne) to which the RG detector was not responsive. Uptake kinetics for H2 and He indicated that the passive sampler reached equilibrium within 12 h of immersion in water. Field testing of these passive samplers revealed unusually large equilibrium gas-phase H2 concentrations in groundwater, ranging from 0.1 to 13.9%, by volume, in 11 monitoring wells surrounding four former radiological wastewater disposal ponds at the Y-12 plant in Oak Ridge, Tennessee.

We encapsulated radioisotope-spiked soil within a water-permeable polyacrylamide matrix cast in a small cylindrical geometry (approximately to 5 cm3) to measure the persistence of immobilized soil contaminants. As a proof-of-principle, soils contained within these permeable environmental leaching capsules (PELCAPs) were labeled with either 85Sr or 134Cs and were leached in both laboratory tests and continuously in situ with ground and streamwaters at two field sites on the Oak Ridge reservation. Groups of PELCAPs were retrieved, assayed nondestructively for radioisotopes via gamma spectroscopy, and then replaced in ground and surface water repeatedly over a 6-month period. PELCAPs that contained no soil readily and quantitatively leached either 85Sr or 134Cs into laboratory extractants or ground or surface water with effective diffusion coefficients (D(eff)) of (1.14 +/- 0.06) and (4.8 +/- 0.2) x 10(-6) cm2/s, respectively. PELCAPs containing untreated soil readily leached > 90% of 85Sr but < 1% of 134Cs during field leaching at both sites, whereas thermally treated soils quantitatively retained both isotopes under all conditions. Permeable polymer encapsulation methods, such as PELCAPs, offer the potential capability to conveniently test large numbers of soils and soil treatments for contaminant release and uptake under actual field environmental conditions.

Heating of fine sand-sized common mineral powders (quartz, feldspar, or calcite) or a soil (from the Department of Energy's Hanford site) up to 1000 degrees C, in contact with sorbed radioisotopes (85Sr, 57Co, 134Cs, or U), markedly increased each isotope's immobilization. A sequential extraction procedure was applied after heating the materials to assess the changes in each isotope's functional form among water-soluble, cation-exchangeable, acid-soluble, and residual phases. The overall immobilization effects were consistent with rapid high temperature ionic diffusion from the initially contaminated surfaces into the mineral matrices; subsequent diffusion out of mineral particles at ambient temperature, as measured by the sequential extraction behavior, would be such a slow process that the radionuclides may be considered sequestered from further potential environmental mobilization. In the Hanford soil, the effect was found to follow an Arrhenius-type relationship with treatment temperature up to 1000 degrees C for 57Co, 85Sr, and U, and immobilization was independent of previous thermal treatment of the materials. Although 134Cs exhibited its largest immobilization in the Hanford soil after heating to 1000 degrees C, the large immobilization of 134Cs at all temperature and even in unheated Hanford soil made it difficult to observe a strong temperature dependence. A general and promising technique for environmental remediation of contaminated soil by high-temperature heating without melting can be extrapolated directly from the empirical leaching information.

The objective was to clarify from the theoretical viewpoint the mechanical, diffusional, thermodynamic and electromagnetic aspects of the decontaminations problem, by means of developing a powerful computational model to evaluate the effect of a very rapid heating regime on the on the contaminated concrete walls or slabs. The practical objective was to assess the feasibility of the microwave heating scheme envisaged and determine its suitable parameters such as power and duration. This objective was complementary to, but separate from, the chemical and nuclear aspects of long-time processes that led to the contamination and various conceivable alternative methods of decontamination which were investigated by Dr. Brian Spalding of Oak Ridge National Laboratory, with whom the start-up phase of this project was coordinated.

Twelve soils from areas used for the disposal of low-level radioactive solid waste at the Oak Ridge National Laboratory were examined for their ability to adsorb trace levels of Sr. Radiostrontium adsorption, in the presence of normal soil Ca levels, was determined following the addition of LiOH, NaOH, KOH, NaCl, and Na-polyacrylate. With soils from C horizons, the average thermodynamic equilibrium constant for the Na-Ca(Sr) exchange reaction decreased from 0.063 to 0.00041 after treatment with 0.4 meq/g of NaOH, indicating a large increase in the selectivity for Ca(Sr) adsorption. With samples from A or B horizons, this effect was not observed due to the dissolution of soil organic matter; Na-polyacrylate interfered with the adsorption of Ca(Sr) in the same manner as the NaOH-solubilized soil organic matter. Selectivity differences between trace levels of Sr and the macroamounts of soil Ca were quite small ( Na > K.« less

In White Oak Creek watershed in eastern Tennessee, the radionuclides60Co,90Sr, and137Cs were retained by streambed gravels on different sites:60Co was associated with manganese in the hydrous oxide coatings on rocks and minerals;90Sr occurred primarily as an exchangeable cation although small amounts were held in a nonexchangeable form; and137Cs was held very selectively, presumably by illite in shale fragments composing the sediment. The distribution of radionuclides on sediments was size dependent: the 0.85–3.35 mm fine-gravel fraction was higher in radionuclide concentration than the sand fraction. An areal survey of radionuclide concentrations on streambed gravels from throughout the watershed, located numerous contamination sources. These radionuclide concentrations, when combined with both distribution coefficients of radionuclides between gravel and water and drainage area, were used to rank subsections of the watershed by their relative contribution to the overall contamination of the watershed. For90Sr, this ranking procedure agreed with the measured discharges of subsections of the watershed which are routinely monitored.

The leachability of radiostrontium from radioactive waste and through soil is one of the most salient problems with shallow-land burial as a disposal method. The continuous leaching of buried waste at the Oak Ridge National Laboratory (ORNL), for periods up to 30 years, by lateral ground water flow has led to the contamination of surrounding soils and streams with /sup 90/Sr. The goal of the present investigation was to evaluate methods to effect either the in situ fixation or reduced leachability of /sup 90/Sr in soil. Small columns of three soils, collected from the solid waste disposal areas at ORNL, were labeled with /sup 85/Sr as a convenient tracer for /sup 90/Sr. After this labeling, but prior to leaching, the soil columns were percolated with equivalent amounts of sodium salt solutions of hydroxide, fluoride, carbonate, phosphate, silicate, or aluminate. Leaching was then initiated with 0.1N CaCl/sub 2/ which was selected to qualitatively simulate ground water which contains Ca as the dominant dissolved cation. With two soils, high in indigenous exchangeable Ca/sup 2 +/, only 30 to 35% of the /sup 85/Sr could be leached from the carbonate-treated columns. Presumably, the /sup 85/Sr was coprecipitated with the nascent CaCo/sub 3/ formedmore » during this treatment. In contrast, >98% of the /sup 85/Sr was readily leached from all untreated soils. Other anions fixed variable but generally less /sup 85/Sr than the carbonate treatment. Thus, sodium carbonate appears to have a potential application to immobilize /sup 90/Sr in situ in contaminated soil.« less

A demonstration of In Situ Vitrification (ISV) technology for the stabilization of radioactively contaminated soil sites at the Oak Ridge National Laboratory (ORNL) was successfully completed during July 1987. This demonstration is the first application of the ISV process not performed at the Hanford Site, where the technology was developed and patented for the U.S. Department of Energy by Pacific Northwest Laboratory (PNL). The joint ORNL-PNL pilot-scale demonstration was performed on a 3/8-scale trench (2 m deep × 1 m wide × 10 m long) that was constructed to simulate a typical seepage trench used for liquid low-level radioactive waste disposal at ORNL from 1951 to 1966. In the ISV process, electrodes are inserted around a volume of contaminated soil, power is applied to the electrodes, and the entire mass is melted from the surface of the soil down through the contaminated zone, thus making a glassy-to-microcrystalline waste form that incorporates the contaminants. Gases produced during the melting are collected, treated, monitored, and released through an off-gas process trailer. In the ORNL demonstration, a 25,000-kg mass of melted rock approximately 1.2 m thick × 2.1 m wide × 4.9 m long was formed during 110 h of operation that consumed approximately 29 MWh of power. Data obtained on the operational performance of the test and waste-form durability will be used to assess the feasibility of applying the ISV technology to an actual waste trench.

The rates of CO/sub 2/ evolution from Douglas-fir (Pseudotsuga menziesii )Mirb.) Franco) needle litter, following application of divalent metal (Hg, Cd, Pb, Ni, Zn, and Cu) chlorides at rates of 10, 100, and 1000 ..mu..g/g and Ca chloride at 7, 68, and 683 ..mu..g/g, were monitored at 2- to 3-day intervals for 4 weeks; extractable enzymatic activities were also measured on additional samples at 1 day, 2, and 4 weeks following treatment. All metals except Pb inhibited respiration when applied at the highest level. Cellulase activity was depressed by treatments of 1000 ..mu..g/g of either Hg or Cd after 4 weeks but was not affected initially (1 day after). After 4 weeks, xylanase activity was also depressed by the 1000-..mu..g/g Hg treatment. Apparently these enzymatic activities declined due to decreased enzyme synthesis associated with inhibited microbial growth rather than by direct enzymatic inhibition. Although addition of Hg or Cu chlorides directly to litter extracts caused marked inhibition of most enzymatic activities, equivalent levels, when applied to the needle litter, produced no inhibitions in extracts after 1 day, except for invertase activity. Invertase activity was depressed at all intervals and ..beta..-glucosidase activity was elevated at all intervals by Hg at themore » 1000-..mu..g/g level. The level of extractable ninhydrin-reactive compounds was elevated by this Hg treatment at all intervals similar to the effect of fumigation of soil or litter. Regardless of treatment, cellulase and xylanase activities were correlated (r = 0.70, n = 192).« less

Assays for measuring the activities of cellulase, xylanase, mannase, amylase, ..beta..-glucosidase, invertase, and protease employing buffered suspensions of ground coniferous and deciduous leaf litter exhibited zero-order kinetics. Only a small percentage of the whole-litter activities of invertase, ..beta..-glucosidase, and protease were extractable into 0.05M potassium acetate, pH 5.0; however, extractable activities of cellulase and xylanase represented from 39 to 174% of the whole-litter activities indicating their soluble exocellar nature. Extractable protease and amylase activities were best correlated with the average daily rates of CO/sub 2/ evolution in a group of 90 leaf litter samples equally representing 18 coniferous species. Enzymatic activities were readily detectable in extracts of all samples but classification of the samples by species provided little differentiation in the distribution of either enzymatic activities or rates of CO/sub 2/ evolution. Mannase, cellulase, and xylanase activities were well-correlated with each other in all samples. Assays attempting to measure a pool of readily-metabolizable substances in litter by extractable reducing substances, ninhydrin-positive substances, glucose, and phenolics failed to show correlation coefficients >0.41 with rates of CO/sub 2/ evolution. Addition of D-(+)-catechin to litter extracts, up to levels equivalent to those observed in the group of samples, did not inhibit any carbohydrasemore » thus suggesting the lack of inhibition of litter-decomposing enzymes by the concentrations of phenolics present in these coniferous leaf litters.« less

Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) needle-litter was given treatments of varying biocidal severity including air-drying, oven-drying, fumigation with methyl bromide plus chloropicrin. autoclaving, and a control. The litter was inoculated with a small amount of fresh litter homogenate and monitored for CO2 evolution rate and extractable enzymatic activity during a 77-day incubation. Enzymatic activities assayed included cellulase. xylanase, mannase, amylase. invertase, β-glucosidase, protease, polyphenoloxidase and peroxidase. The concentrations of extractable ninhydrin-reactive compounds, glucose, and reducing substances were also determined. Air-drying produced a small, initial stimulation in respiration but had no effect on any enzymatic activity throughout the 77-day incubation except for an initial decrease in polyphenoloxidase and peroxidase activities. Oven-drying produced a substantial loss of all enzymatic activities initially but all carbohydrase and protease activities recovered to greater than control levels by 7 days; after a 1-day lag, oven-drying produced a pronounced stimulation in the rate of CO2 evolution. Autoclaving produced a 2-day lag in a less pronounced (compared to oven-drying) respiratory stimulation: initially all enzymatic activities were destroyed and only protease and β-glucosidase activities recovered to control levels. Fumigation produced a respiratory stimulation after a 9-day lag (probably due to residual chloropicrin) which coincided with a pronounced increase in cellulase. xylanase, mannase and amylase activities: initially, no activities except polyphenoloxidase and peroxidase were adversely affected by fumigation. During the entire incubation, the activities of cellulase. xylanase. mannase. amylase and invertase were highly correlated with each other regardless of treatment. After 77 days, the rates of CO2 evolution of all samples were correlated with the level of amylase and cellulase activity (r = 0.86 and 0.83, respectively). This observation points to the value of enzymatic assays for following the processes which release substrate for microbial assimilation from plant litter. The close association of polysaccharidase and protease activities with the flush of CO2 evolution following biocidal treatment, particularly oven-drying, indicates that the decomposition of carbohydrates and proteins released from microbial biomass or plant litter is a mechanism for this often-observed respiratory stimulation.