A cost study for enhanced sludge washing of high-level radioactive waste at the U.S. Department of energy Hanford Site

Enhanced Sludge Washing (ESW) with caustic has the potential to significantly reduce the amount of sludge-based underground storage tank (UST) high-level radioactive waste at the Hanford Site. The alternative to ESW is a simple sludge wash, a process that does not take advantege of recent dissolution development efforts. During the past several years, studies have been conducted to determine the remediation cost savings derived from the development and deployment of ESW. The tank waste inventory and ESW process performance continues to be revised as waste characterization, and ESW development efforts advance. This study provides a new cost savings estimate based upon the most recent waste inventory and ESW process performance revisions, an estimate of the associated cost savings uncertainty, and an estimate of the rate of return (ROR) on the investment in technology development. The revised remediation cost savings estimate due to ESW of all UST waste at Hanford is $4.8 billion ± $0.7 billion within 95 percent confidence in 1998 dollars. The ROR on investment was estimated to range from 100 percent to 130 percent. A sensitivity analysis indicated that it would be difficult to imagine a remediation scenario for which ESW did not yield a significant remediation cost savings and ROR.     

An Updated Cost Study for Enhanced Sludge Washing of Radioactive Waste

This article updates previous cost savings studies conducted to evaluate the use of enhanced sludge washing (ESW) of high‐level radioactive waste at the United States Department of Energy Hanford Site. The cost savings estimate was updated using stochastic analysis based on new information from the Independent Review of Hanford High Level Waste Volume and the more recent Tank Waste Remediation System Operation and Utilization Plan. It is estimated that implementation of ESW in the tank waste remediation system (TWRS) at the Hanford Site can save approximately $4.8 billion compared to the use of an alternative, simpler water wash. The simpler water wash dissolution was found to be 85 percent as effective as the ESW dissolution. Further, the updated remediation cost estimate of $4.8 billion savings is uncertain only within ±$1.6 billion at the 95 percent confidence interval. © 2002 Wiley Periodicals, Inc.     

In-situ bioremediation of hanford groundwater

The U.S. Department of Energy has generated liquid wastes containing radioactive and hazardous chemicals throughout the more than forty years of operation at its Hanford site in Washington State. Many of the waste components, including nitrate and carbon tetrachloride (CCl₄), have been detected in the Hanford groundwater. In-situ bioremediation of CCl₄ and nitrate is being considered to clean the aquifer. Preliminary estimates indicate that this technology should cost significantly less than ex-situ bioremediation and about the same as air stripping/granular activated carbon. In-situ bioremediation has the advantage of providing ultimate destruction of the contaminant and requires significantly less remediation time. Currently, a test site is under development. A computer-aided design tool is being used to design optimal remediation conditions by linking subsurface transport predictions, site characterization data, and microbial growth and contaminant destruction kinetics.     

Remediation and review: Developing groundwater strategy at the hanford site

The U.S. Department of Energy's (US DOE's) environmental challenges include remediation of the Hanford Site in Washington State. The site's legacy from nuclear weapons “production” activities includes approximately 80 square miles of contaminated groundwater, containing radioactive and other hazardous substances at levels above drinking water standards. In 1998, the U.S. General Accounting Office (US GAO), the auditing arm of Congress, concluded that groundwater remediation at Hanford should be integrated with a comprehensive understanding of the “vadose zone,” the soil region between the ground surface and groundwater. The US DOE's Richland Operations Office adjusted its program in response, and groundwater/vadose‐zone efforts at Hanford have continued to develop since that time. Hanford provides an example of how a federal remediation program can be influenced by reviews from the US GAO and other organizations, including the US DOE itself. © 2008 Wiley Periodicals, Inc.     

Using risk assessment to achieve cost-effective property transfers and site closures for former UST sites

Risk assessment has been increasingly applied as a tool in making risk management decisions that affect cleanup of contaminated sites, property transactions, and liability issues. As a site-specific evaluation, risk assessment takes into account the unique characteristics and intended future uses for site property in evaluating chemical concentrations which may remain in place without risk to public health and the environment. The results of a risk assessment can be used to determine reuse options for a property, facilitate site closure, and reduce liabilities (Copeland and Robles, 1994; Copeland et al., 1993a). This article describes the risk assessment process, the role of risk assessment in determining the need for remedial action and identifying site-specific cleanup goals, and the cost effectiveness of applying risk assessment in remedial decisions. Because of the prevalence of former UST sites throughout the United States, this article focuses on risk assessment and remediation of UST sites. However, the process can be applied at sites where other chemicals have been released. Three case studies are presented to illustrate the application of risk assessment in achieving cost-effective site closure at sites containing leaking underground storage tanks.     

Solidification/stabilization for remediation of wood preserving sites: Treatment for dioxins,PCP, creosote,and metals

This article discusses the use of solidification/stabilization (S/S) to treat soils contaminated with organic and inorganic chemicals at wood preserving sites. Solidification is defined for this article as making a material into a freestanding solid. Stabilization is defined as making the contaminants of concern nonmobile as determined from a leaching test. S/S then combines both properties. For more information on S/S in general the reader should refer to other publications (Connors, J.R. [1990]). Chemical fixation and solidification of hazardous wastes. New York: Van Nostrand Reinhold; US Environmental Protection Agency. [1993a]. Engineering bulletin solidification/stabilization of organics and inorganics (EPA/540/S‐92/015); Wiles, C.C. [1989]. Solidification and stabilization technology. In H.M. Freeman [Ed.], Standard handbook of hazardous waste treatment and disposal. New York: McGraw Hill) as this article addresses only wood preserving sites and assumes basic knowledge of S/S processes. For a more general discussion of wood preserving sites and some other remedial options, the reader may wish to refer to a previous EPA publication (US Environmental Protection Agency. [1992a]. Contaminants and remedial options at wood preserving sites [EPA/600/R‐92/182]). This article includes data from the successful remediation of a site with mixed organic/inorganic contaminants, remediation of a site with organic contaminants, and detailed treatability study results from four sites for which successful formulations were developed. Included are pre‐ and post‐treatment soil characterization data, site vaines. ileizdot‐ names (in some cases), treatment formulas used (generic aridproprietary), costs, recommendations, and citatioiis to inore detailed refer‐ en ces. The data presen ted iiidica te that dioxins, pentachlorophepi 01 (PCP), creosote, polycyclic aromatic hydrocarbom (PAHsI, and metals can be treated at moderate cost by the use of S/S techuologp.     

Evaluation of carbonization as a thermal pretreatment method for landfilling by column leaching tests

To evaluate carbonization as a thermal pretreatment method for landfilling, the releasing characteristics of organic and inorganic constituents from carbonization residue derived from shredded residue of bulky waste was investigated by means of batch and column leaching tests. Shredded residue of bulky waste itself and its incineration ash were tested together to compare pretreatment methods. In batch leaching tests at a liquid/solid ratio of 10, the release of organic carbon from carbonization residue was at a remarkably low level. Besides, carbonization contributed to immobilize heavy metals such as chromium, cadmium, and lead within its residue. In column tests, the discharges of organic constituents were lowest from carbonization residue under aerobic conditions due to microbial activity. The leaching of Cd, Cr, Pb, and Cu from carbonization residue was suppressed under anaerobic conditions; however, this suppression effect tended to be weaker under aerobic conditions. From the results showing that the total releasing amounts of organic and inorganic constituents from carbonization residue are so low as to be comparable to that of incineration ash, carbonization can be considered as one of the thermal pretreatment methods of organic wastes.     

Biogeochemical gradients as a framework for understanding waste‐site evolution

The migration of biogeochemical gradients is a useful framework for understanding the evolution of biogeochemical conditions in groundwater at waste sites contaminated with metals and radionuclides. This understanding is critical to selecting sustainable remedies and evaluating sites for monitored natural attenuation, because most attenuation mechanisms are sensitive to geochemical conditions, such as pH and redox potential. Knowledge of how gradients in these parameters evolve provides insights into the behavior of contaminants with time and guides characterization, remedy selection, and monitoring efforts. An example is a seepage basin site at the Savannah River Site in South Carolina where low‐level acidic waste has seeped into groundwater. The remediation of this site relies, in part, on restoring the natural pH of the aquifer by injecting alkaline solutions. The remediation will continue until the pH upflow of the treatment zone increases to an acceptable value. The time required to achieve this objective depends on the time it takes the trailing pH gradient, the gradient separating the plume from influxing natural groundwater, to reach the treatment zone. Predictions of this length of time will strongly influence long‐term remedial decisions. © 2008 Wiley Periodicals, Inc.     

Remediation,land use,and risk at Hanford

U.S. Department of Energy (US DOE) remediation responsibilities include the Hanford site in Washington State. Cleanup is governed by the Tri‐Party Agreement (TPA) between the US DOE as the responsible party and the U.S. Environmental Protection Agency and Washington State Department of Ecology as joint regulators. In 2003, the US DOE desired to implement a “Risk‐Based End State” (RBES) policy at Hanford, with remediation measures driven by acceptable risk standards using exposure scenarios based on the 1999 Hanford Comprehensive Land‐Use Plan. Facing resistance from regulators and stakeholders, the US DOE solicited public input on its policy. This led to a Hanford Site End State Vision in 2005 and a commitment that the TPA would continue to control remediation. This article describes how regulator and public participation modified RBES to an end‐state vision. © 2010 Wiley Periodicals, Inc.     

Comparison of mass balance, energy consumption and cost of composting facilities for different types of organic waste

Mass balance, energy consumption and cost are basic pieces of information necessary for selecting a waste management technology. In this study, composting facilities that treat different types of organic waste were studied by questionnaire survey and via a chemical analysis of material collected at the facilities.The mass balance was calculated on a dry weight basis because the moisture content of organic waste was very high. Even though the ratio of bulking material to total input varied in the range 0-65% on a dry basis, the carbon and ash content, carbon/nitrogen ratio, heavy metal content and inorganic nutrients in the compost were clearly influenced by the different characteristics of the input waste. The use of bulking material was not correlated with ash or elemental content in the compost. The operating costs were categorised into two groups. There was some economy of scale for wages and maintenance cost, but the costs for electricity and fuel were proportional to the amount of waste. Differences in operating costs can be explained by differences in the process characteristics.     

Citizen board issues and local newspaper coverage of risk,remediation, and environmental management: Six U.S. nuclear weapons facilities

We examined site‐specific advisory board (SSAB) minutes and local newspaper coverage of the Fernald, Hanford, Idaho, Oak Ridge, Rocky Flats, and Savannah River sites of the U.S. Department of Energy (US DOE) in order to determine the importance of risk‐related issues related to remediation and other forms of environmental management. About one‐third of SSAB issues were risk‐related, and these were disproportionately major issues at meetings. The media focused on risks associated with remediation and other forms of waste management. The analysis implies that contractors and government officials need to establish and maintain communications with advisory panels and accentuate these contacts well in advance of contemplated new actions. © 2008 Wiley Periodicals, Inc.     

Groundwater geochemistry diagnostics during in situ ERH remediation

In situ remediation represents a series of challenges in interpreting the monitoring data on remedial progress. Among these challenges are problems in determining the progress of the remediation and the mechanisms responsible, so that the process can be optimized. The release of organic pollutants to groundwater systems and in situ remediation technologies alter the groundwater chemistry, but outside of natural attenuation studies using inorganic chemical analyses as indicators of intrinsic biodegradation, typically little attention has been paid to the changes in inorganic groundwater chemistry. Smith (2008) noted that during an electrical resistance heating remediation that took place at a confidential site in Chicago, a two‐orders‐of‐magnitude increase in chloride concentrations occurred during the remediation. This increase in chloride resulted in a corresponding increase in calcium as a result of what is known as the common ion effect. Carbon dioxide is the gas found in highest concentrations in natural groundwater (Stumm & Morgan, 1981), and its fugacity (partial pressure) corresponds directly with calcium concentrations. Carbon dioxide at supersaturation in groundwater is capable of dissolving organic compounds, such as trichloroethene, facilitating removal of nonaqueous‐phase liquids at temperatures below the boiling point of water. One means of diagnosing these reactions is through the use of compound‐specific isotopic analysis, which is capable of distinguishing between evaporation, biodegradation, and differences in sources. The appropriate diagnosis has the potential to optimize the benefits from these reactions, lower energy costs for removal of nonaqueous‐phase liquids, and direct treatment where it is needed most. © 2010 Wiley Periodicals, Inc.     

Combining Ion‐exchange (IX) technology and biological reduction for perchlorate removal

Ion‐exchange (IX) resin is perhaps the most promising technology to remove the contaminant perchlorate (ClO₄^?) from waters. However, ion exchange is only a separation technology that transfers the perchlorate from waters to the waste solutions used to regenerate the resins. The waste solutions contain high perchlorate concentrations, and treatment technologies for these regenerant solutions are needed. In this article, we review the latest knowledge on perchlorate removal by ion‐exchange resins; propose three systems that combine ion‐exchange resins (for perchlorate removal) and biological reduction for treating the waste solutions resulting from resin regeneration; and discuss the challenges and research needed to fully develop the proposed technology. © 2002 Wiley Periodicals, Inc.     

Hanford remediation at 20 years: A glass half‐empty

The U.S. Department of Energy's (US DOE's) responsibilities for its former national nuclear weapons complex include remediation of the Hanford Site in Washington State. In 1989, the site's primary mission shifted from nuclear weapons material production to cleanup of the extensive radioactive and chemical contamination that represented the production legacy. Cleanup is governed by the Tri‐Party Agreement (TPA), between the US DOE, as responsible party, and the U.S. Environmental Protection Agency and Washington State Department of Ecology, as joint regulators. Nearly 20 years have passed since the TPA was signed, but the Hanford remediation is expected to require decades longer. This article covers the cleanup progress to date and challenges that remain, particularly from millions of gallons of highly radioactive liquid wastes and proposals to bring new wastes to Hanford. © 2008 Wiley Periodicals, Inc.     

Advances in photocatalytic remediation technology

The cost of remediation at hazardous waste sites is estimated at billions of dollars annually. It is imperative that more cost‐effective remediation technologies be developed, particularly to address the more complex megasites. Chlorinated hydrocarbons represent the major contaminants at many such sites. It has long been recognized that chlorinated hydrocarbons can be destroyed by photocatalytic oxidation. Traditional photocatalysts, however, have often shown inadequate destruction activity, a loss of activity over time, and poor selectivity, thereby producing substantial amounts of phosgene and chloroform by‐products. This article presents results obtained using novel photocatalyst compositions. The results demonstrate the ability to achieve high photocatalytic destruction activity for chlorinated hydrocarbons with full retention of activity over extended time periods and with complete elimination of phosgene and chloroform by‐products. © 2006 Wiley Periodicals, Inc.     

Using an integrated approach for quantifying VOC source areas for site remediation

Locating and quantifying free-phase volatile organic compounds (VOCs) in the subsurface represent one of the more difficult challenges facing hazardous waste site remediation programs. Successful remediation programs require reliable data on the size and extent of potential VOC contamination sources. Improving subsurface quantification of VOCs requires a large number of reliable low-cost samples. Satisfying this objective relies on improved sampling techniques, field analysis of samples, and a modified quality assurance program. This paper describes an integrated approach using conventional split-spoon samplers, microcore sampling, hexane extractions, and a field gas chromatograph with an autosampler as part of a technical demonstration for innovative remediation technologies. Using this approach, it was possible to delineate a subsurface source of free-phase VOCs at a cost of $15 per sample. The distribution of dense nonaqueous phase liquid determined by this sampling approach agreed with the conceptual model for the site.     

Feasibility of a monitoring system for detecting changes in dioxin concentrations of both in flue gas and fly ash in incineration plants

Surrogate measurements should be low in cost and quick to perform. To examine its feasibility, continuous surrogate monitoring was performed using an organic halogen compound (OHC) analyzer. Surrogates for dioxins (DXNs) from waste incinerators were examined by changing the operating conditions such as the atomized volume of activated carbon added and the temperature at the inlet of the dust collector. OHCs were measured along with DXNs in flue gas at the inlet and the outlet of the dust collector of two waste incinerators over five runs; the fly ash was sampled at the same time. Although the final flue gas concentration of DXNs at the incineration plants was below the regulation criteria, this does not mean complete reduction of DXNs. In addition, the de novo synthesis of DXNs inside the dust collectors was studied by analyzing the mass balance for DXNs concentrations in flue gas and fly ash. Semivolatile chlorinated organic compound concentrations at the outlet of the bag filter were basically well correlated with DXNs levels at the inlet of the bag filter in the test runs. When advanced flue gas treatment is applied by using a bag filter and lime/activated carbon adsorbent, DXNs that may be generated during flue gas cooling processes move to the fly ash, and this amount determines the mass balance of the entire system. It may be useful to monitor surrogate organic halogens for detecting changes in DXN concentrations of both flue gas and fly ash in incineration plants.     

Stable isotope signatures for characterising the biological stability of landfilled municipal solid waste

Stable isotopic signatures of landfill leachates are influenced by processes within municipal solid waste (MSW) landfills mainly depending on the aerobic/anaerobic phase of the landfill. We investigated the isotopic signatures of δ¹³C, δ²H and δ¹⁸O of different leachates from lab-scale experiments, lysimeter experiments and a landfill under in situ aeration. In the laboratory, columns filled with MSW of different age and reactivity were percolated under aerobic and anaerobic conditions. In landfill simulation reactors, waste of a 25 year old landfill was kept under aerobic and anaerobic conditions. The lysimeter facility was filled with mechanically shredded fresh waste. After starting of the methane production the waste in the lysimeter containments was aerated in situ. Leachate and gas composition were monitored continuously. In addition the seepage water of an old landfill was collected and analysed periodically before and during an in situ aeration.We found significant differences in the δ¹³C-value of the dissolved inorganic carbon (δ¹³C-DIC) of the leachate between aerobic and anaerobic waste material. During aerobic degradation, the signature of δ¹³C-DIC was mainly dependent on the isotopic composition of the organic matter in the waste, resulting in a δ¹³C-DIC of ?20‰ to ?25‰. The production of methane under anaerobic conditions caused an increase in δ¹³C-DIC up to values of +10‰ and higher depending on the actual reactivity of the MSW. During aeration of a landfill the aerobic degradation of the remaining organic matter caused a decrease to a δ¹³C-DIC of about ?20‰. Therefore carbon isotope analysis in leachates and groundwater can be used for tracing the oxidation–reduction status of MSW landfills.Our results indicate that monitoring of stable isotopic signatures of landfill leachates over a longer time period (e.g. during in situ aeration) is a powerful and cost-effective tool for characterising the biodegradability and stability of the organic matter in landfilled municipal solid waste and can be used for monitoring the progress of in situ aeration.     

Physicochemical mechanisms controlling the periodic release of flammable gases from hanford tanks

Hanford tanks contain more than 60 million gallons of high-level wastes produced by decades of extracting plutonium from irradiated uranium fuel. The wastes were concentrated to a thick slurry consistency by evaporation prior to storage to minimize space. The resulting concentrated waste properties introduced unanticipated, detrimental conditions affecting workers' and the public's health and safety and involving the release of potentially flammable gases. The released gases consist primarily of hydrogen, nitrous oxide, and ammonia. Dilution and sluicing were initially proposed to mitigate the flammable gas safety conditions. As a result of evaluations, the mechanisms and conditions that are thought to control the accumulation and spontaneous release of flammable gases were identified and confirmed. The technical rationale was established for developing operational approaches to mitigate the periodic generation of flammable gases in existing tanks and to avoid any reoccurrence of this serious safety problem during future waste management activities. The chemistry of the two highest risk tanks was examined to test the potential for reversing the conditions causing gas buildup and the consequences of sluicing without appropriate chemical conditioning. The identified mechanisms apply equally to the remaining flammable gas tanks at Hanford as well as to other waste tanks in the DOE complex, particularly those at Savannah River. Passive means of mitigating the flammable gas condition require less than 1:1 dilution, and sluicing wastes from tank 106-C can be accomplished without creating a flammable gas condition. Carbonate equilibria reactions and their effect on aluminum speciation are largely overlooked and provided the key for explaining the episodic release of flammable gases from tank wastes. The reaction of atmospheric carbon dioxide with a sodium hydroxide-rich waste solution produces carbonate precipitates. More importantly, this reaction lowers the pH of the waste and precipitates aluminum hydroxide as a gel. The wastes contain substantial amounts of complexing agents such as ethylene diamine tetraacidicacid (EDTA), hydroxy ethylene diamine triacidic acid (HEDTA), and their degradation products. These complexing agents stabilize the aluminum hydroxide gel together with chromium, manganese and iron hydroxides, and oxybydroxides under the resulting pH conditions. These complex species may coprecipitate and accumulate as a metastable layer in the middle and lower levels of th tank. The complexed aluminum hydroxide acts as a binding agent trapping other particulates in a microcrystalline mat. Microcrystalline particles such as sodium nitrite provide the structural strength for the mat. Once the gas accumulation below the gel layer achieves a critical buoyancy sufficient to rupture the microcrystalline mat, a gas release event occurs. The cycle of gas buildup and release continues each time the buoyancy of the trapped gas exceeds the hydrostatic pressure and the gels' plasticity modulus. Stokes Law predicts a particle settling rate in the tank of less than 50 days, well within the bistorical periodicity of GREs. Laboratory tests, forming the basis of a recent patent application, verify that large quantities of complexed aluminum hydroxide gel are produced by passing carbon dioxide through simulated waste solutions (Hobl, 1993) equivalent to those found in tank 101-SY. It was confirmed that a simple adjustment of pH witll redissolve the gel, thereby reducing viscosity and safely facilitating continuous flammable gas release. Additional experiments were undertaken to provide a basis for understanding the role of complexed aluminum hydroxides in the CO₂/NaOH/Al(OH)₃ (complexing agents)/NaAlO₂ system. This article examines a plausible mechanism for the periodic release of flammable gas and considerations for: (1) remediating existing flammable gas tanks through a combination of chemical treatment and mixer pumps; (2) diluting, combining, retrieving, and storing wastes; (3) preventing clogging of transfer lines; (4) sludge and soil washing; and (5) cribs, ponds, basins, and ground-water cleanup. This study provides a singificant breakthrough for tank waste management by explaining key mechanisms controlling episodic release of flammable gases. The breakthrough provides the bases for removing the tanks classified as flammable gas from the wathclist and has broad operational applications with a potential for billions of dollars in cost savings.