A risk-based approach to how clean is clean

Clearly defined remedial action objectives are a key factor in successful remediation programs. Chemical-specific cleanup criteria are critical components of remedial action objectives. A common risk-based approach can be applied for developing cleanup criteria for remediations under CERCLA, RCRA, and TSCA. This approach involves four steps: identify regulatory requirements; identify chemical-specific cleanup guidelines from previous cleanups; evaluate site-specific risk considering mitigating factors for a given site; select the final cleanup criteria based on information from the first three steps. To describe this approach, this paper presents a case study on a PCB cleanup conducted under TSCA. An objective risk-based approach was used to capitalize on the flexibility built into EPA's PCB cleanup guidelines. EPA granted an exemption to the stated policy on the basis of competing risk factors using a comparative risk-assessment approach. Similarly, risk assessment can be used to take advantage of regulatory flexibility in the selection of applicable or appropriate and relevant requirements (ARARs) under CERCLA, or in the selection of media protection standards under RCRA.     

Adaptive sampling and analysis programs for contaminated soils

Adaptive sampling and analysis programs (ASAPs) provide a cost-effective alternative to traditional sampling program designs. ASAPs are based on field analytical methods for rapid sample turnaround and field-based decision support for guiding the progress of the sampling program. One common objective of ASAPs is to delineate contamination present in soils, either to support feasibility studies or remedial action designs. An ASAP based on portable gas chromatograph/ mass spectrograph (GC/MS) technologies developed at Tufts University combined with decision support tools created at Argonne National Laboratory was used to delineate explosives contamination in soils at Joliet Army Ammunition Plant, Joliet, Illinois. Tufts' GC/MS technologies provided contaminant-specific identification and quantification with rapid sample turnaround and high sample throughput. Argonne's decision support tools estimated contamination extent, determined the uncertainty associated with those estimates, and indicated where sampling should continue to minimize uncertainty. In the case of Joliet, per sample analytical costs were reduced by 75 percent as compared to the cost of off-site laboratory analyses for explosives. The use of an ASAP resulted in a much more accurate identification and delineation of contaminated areas than a traditional sampling program would have with the same number of samples collected on a regular grid. While targeting explosives contamination in soils at Joliet, the ASAP technologies used in this demonstration have much broader application.     

Characterizing soils contaminated with heavy metals: A uranium contamination case study

To stem rising remediation costs for soils contaminated with hazardous metals, increased emphasis is being placed on the development of in-situ and ex-situ treatment technologies. Often, a lack of basic information on the chemical and physical characteristics of the soil and contaminants hampers treatability studies used to design these technologies. This article proposes and demonstrates a characterization program to meet these information needs, employing standard analytical techniques coupled with advanced spectroscopy and microscopy techniques. To support treatments involving physical separation strategies, the program uses standard analytical techniques to characterize the soil and the association of contaminants with different soil fractions (e.g., size and density fractions). Where chemical treatments are required, spectroscopy and microscopy methods are employed to yield quantitative information on the oxidation state and speciation of the contaminant. Examples demonstrate the use of measured soil and contaminant characteristics in the screening of alternative treatment technologies and in the selection of soils for use in treatability studies. Also demonstrated is the use of these characterization tools in the design and optimization of treatment strategies and in support of risk assessment determinations.     

Electroremediation: A study of the influence of buffering behavior in contaminated soils

This article presents the results of an experimental study conducted to evaluate the behavior of two types of andisol soils found in Tenerife, Canary Islands, Spain. The soils were evaluated in relation to their buffering capacity when confronted with acid and alkaline fronts generated during electroremediation treatment. The study was conducted using a cell, which established a continuous flow of distilled water through electrode chambers to remove H⁺ and OH^? generated during electrolysis. The results indicate that the soils had sufficient buffer capacity to support variations in pH independent of the maintenance of flow of solution in the electrode chambers. Although the mechanism of migration was not affected, the flow of water favored the movement of ions by diffusion monitoring of the electrolytic current allowed for a real‐time parameter to act as an indicator of the quantity of ions available in regions near the electrodes. © 2004 Wiley Periodicals, Inc.     

Soil washing for volume reduction of radioactively contaminated soils

The Office of Radiation and Indoor Air of the U.S. Environmental Protection Agency has demonstrated a soil washing plant for the treatment of radioactively contaminated soils from two Superfund sites in New Jersey. The plant employs unit operations that are widely used in the processing of minerals and coal. These operations were examined and tested to determine how they would apply to volume reduction of these contaminated soils. In this context, they are considered to be innovative candidates for remediation of other sites with large volumes of soil contaminated with low-level radioactivity. Laboratory testing of soil characteristics and behavior in unit processes is used to assess the applicability of volume reduction/chemical extraction (VORCE) technology to specific sites.     

Treatability studies as a remedial option screening tool for contaminated soils

As the limitations of site remedial technologies become more apparent and greater experience in their field implementation and effectiveness is gained, increased emphasis is placed on development of a structured technology selection process. Ideally, this selection process should yield the most cost-effective technology, which will accomplish cleanup goals in the shortest time frame. Although laboratory treatability studies comprise an essential component of this process, very little has been written about the methodology of designing, executing, and assessing the value of their results. This article presents practical considerations for environmental professionals who use treatability results in technology selection or others who execute such studies.     

Disposal of contaminated sediments/soils in MSW landfills: Need to consider the true cost

A disturbing trend among governmental agencies is the remediation of so‐called “nonhazardous” contaminated sediments/soils by deposition in minimum‐design Subtitle D municipal solid waste (MSW) landfills or landfills with equivalent design. This is done despite the fact that, in terms of protection of public health and environmental quality, the designation “nonhazardous” is misleading at best, and the fact that minimum‐design Subtitle D landfills as being allowed will not ensure protection of groundwater quality for as long as the buried wastes remain a threat. Although acknowledged in the regulatory documentation and exposed in the writings of a few in the scientific/engineering community, the environmental and public health issues that will inevitably be faced at minimum‐design Subtitle D landfills are underplayed, and even misrepresented, to the public. Discussion of relevant issues, as well as remarkable omissions, characterized the October 2004 United States Army Corps of Engineers (US ACE)/United States Environmental Protection Agency (US EPA)/Sediment Management Work Group (SMWG) conference,” Addressing Uncertainty and Managing Risk at Contaminated Sediment Sites.” This article addresses many of those neglected issues. © 2005 Wiley Periodicals, Inc.     

Assessing the potential of using phytoremediation for pyrene‐contaminated soils

Forage crop species representing two biologically distinct families (legumes and grasses) were evaluated on soil spiked with 100 mg/kg of pyrene to determine the potential effectiveness of the rhizospheres of these plants for phytoremediation. In this experiment, pyrene dissipation could not be attributed to the presence of plants. Pyrene dissipation was also not related to rhizosphere biological activity, such as microbial counts and enzyme activity. Planting with reed canarygrass and switchgrass significantly increased the microbial counts in soil; however, the differences in the microbial counts were not correlated to the levels of pyrene dissipation. Reed canarygrass rhizosphere had significantly higher dehydrogenase activity compared to the switchgrass rhizosphere, but this difference in soil dehydrogenase activity was not related to pyrene dissipation. In general, the use of plants was not effective in causing pyrene transformation; however, the presence of vegetation on polycyclic aromatic hydrocarbon–contaminated soils could play a significant role in limiting the spread of contaminants (erosion, leaching) and enhancing ecosystem restoration. © 2004 Wiley Periodicals, Inc.     

Treatment of mercury‐contaminated soils with activated carbon: A laboratory,field, and modeling study

A series of laboratory batch leaching tests was conducted to evaluate the performance of different activated carbons in stabilizing mercury in soils. Based on the results of these experiments, an amendment application rate of 5 percent powdered activated carbon (PAC) was selected for in situ field application at a former industrial facility. A geochemical model was also developed to simulate the interactions between mercury and activated carbon in vadose‐zone soils. Modeling was used to (1) better understand possible mercury sequestration mechanisms and (2) predict the in situ performance of PAC. Model results indicate dissolved mercury concentrations observed in batch tests are consistent with equilibrium partitioning of mercury between dissolved organic matter, soil organic matter, and PAC. Activated carbon is predicted to reduce dissolved mercury concentrations via two mechanisms: (1) the formation of stable mercury complexes on PAC surfaces and (2) the direct adsorption of dissolved organic matter that would otherwise be available for mercury dissolution. Study results demonstrate PAC effectiveness for site soils with mercury concentrations below 200 mg/kg. © 2010 Wiley Periodicals, Inc.     

In Situ flushing of contaminated soils from a refinery: Organic compounds and metal removals

This article demonstrates the applicability of in situ flushing for the remediation of soil contaminated with petroleum hydrocarbons at a Mexican refinery. The initial average total petroleum hydrocarbon (TPH) concentration for the demonstration field test was 55,156 g/kg. After six weeks of in situ flushing with alternate periods of water and water/surfactant, an average concentration of 1,407 mg/kg was reached, achieving a total removal efficiency of 98 percent. At the end of the process, no hydrocarbons such as diesel; gasoline; benzene, toluene, ethyl benzene, and xylene (BTEX); or petroleum aromatic hydrocarbons (PAHs) were found. Iron washing achieved a removal efficiency of 70 percent, and for vanadium, the removal efficiency was 94.4 percent. The volume of soil treated was 41.6 m³ (38 m²), equivalent to 69.5 tons of soil. A rough calculation of the process costs estimated a total cost of $104.20/m³ ($114.00/m²). Our research indicates that there are a few studies demonstrating in situ flushing experiences under field conditions where both organic (TPH, diesel, gasoline, PAHs, BTEX) and metal (iron and vanadium) removals are reported. © 2004 Wiley Periodicals, Inc.     

A steady-state approach for evaluating the impact of solute transport through composite liners on groundwater quality

New adaptations of analytical equations for predicting the impact of solute transport through composite landfill liners on groundwater quality for steady-state conditions are presented. Analytical equations are developed for evaluating average concentration and mass flow rate in an underlying aquifer resulting from diffusion of volatile organic compounds (VOCs) through intact composite liners and transport of inorganic constituents through defects in composite liners. The equations are applied to evaluate the effectiveness and equivalency of composite liners having either a 0.6 m-thick compacted soil liner or a 6.5 mm-thick geosynthetic clay liner (GCL) overlying an intermediate attenuation layer and an aquifer having horizontal flow. Example analyses for designing composite liners meeting particular performance criteria are also provided. The analytical equations are relatively simple to apply and can be used for preliminary design and analysis, to evaluate experimental results, and to possibly verify more complex numerical models for evaluating the impact of landfills on groundwater quality if consistency of the assumptions of the analytical equations and the more complex numerical models can be specified.     

A system dynamic modeling approach for evaluating municipal solid waste generation,landfill capacity and related cost management issues

As planning for sustainable municipal solid waste management has to address several inter-connected issues such as landfill capacity, environmental impacts and financial expenditure, it becomes increasingly necessary to understand the dynamic nature of their interactions. A system dynamics approach designed here attempts to address some of these issues by fitting a model framework for Newark urban region in the US, and running a forecast simulation. The dynamic system developed in this study incorporates the complexity of the waste generation and management process to some extent which is achieved through a combination of simpler sub-processes that are linked together to form a whole. The impact of decision options on the generation of waste in the city, on the remaining landfill capacity of the state, and on the economic cost or benefit actualized by different waste processing options are explored through this approach, providing valuable insights into the urban waste-management process.     

土壤氰化物污染生物修复技术研究进展

综述了植物修复、微生物修复和生物联合修复等土壤氰化物污染生物修复技术的降解机理、降解途径及降解影响因素的研究进展,探讨了氰化物生物修复技术的发展趋势和应用前景。指出基于提高修复时效和针对土壤复合污染类型的多技术融合研究、基于提高微生物耐受性和降解效率的菌株固定化及菌根真菌-植物联合技术研究以及基于工程化应用为导向的现场试验研究是未来研究的重点领域,为土壤氰化物污染的综合治理和修复提出了新思路。     

Solvent extraction and soil washing treatment of contaminated soils from wood preserving sites: Bench‐scale studies

Bench‐scale solvent extraction and soil washing studies were performed on soil samples obtained from three abandoned wood preserving sites included in the National Priority List. The soil samples from these sites were contaminated with high levels of polyaromatic hydrocarbons (PAHs), pentachlorophenol (PCP), dioxins, and heavy metals. The effectiveness of the solvent extraction process was assessed using liquefied propane or dimethyl ether as solvents over a range of operating conditions. These studies have demonstrated that a two‐stage solvent extraction process using dimethyl ether as a solvent at a ratio of 1.61 per kg of soil could decrease dioxin levels in the soil by 93.0 to 98.9 percent, and PCP levels by 95.1 percent. Reduction percentages for benzo(a)pyrene (BaP) potency estimate and total detected PAHs were 82.4 and 98.6 percent, respectively. Metals concentrations were not reduced by the solvent extraction treatment. These removal levels could be significantly improved using a multistage extraction system. Commercial scale solvent extraction using liquefied gases costs about $220 per ton of contaminated soil. However, field application of this technology at the United Creosote site, Conroe, Texas, failed to perform to the level observed at bench scale due to the excessive foaming and air emission problem. Soil washing using surfactant solution and wet screening treatability studies were also performed on the soil samples in order to assess remediation strategies for sites. Although aqueous phase solubility of contaminants seemed to be the most important factor affecting removal of contaminants from soil, surfactant solutions (3 percent by weight) having nonionic surfactants with hydrophile‐lipophile balance (HLB) of about 14 (Makon‐12 and Igepal CA 720) reduced the PAH levels by an average of 71 percent, compared to no measurable change when pure deionized water was used. Large fractioza of clay and silt (<0.06mm), high le!ezielsof orgaizic contami‐ nants and hzimic acid can makesoil washing less applicable.     

A comprehensive approach to plume stability

This article defines and presents a systematic approach to groundwater plume‐stability assessment. Qualitative and quantitative methods that have been used to assess plume stability at National Priority List sites undergoing optimization are reviewed. Example case studies are included to illustrate the advantages of combining multiple analysis methods. Relevant statistical methods include identifying normal data distributions, detection frequencies, coefficients of variation, individual well trends, and rates of change at individual monitoring locations. Trend estimates for total plume mass and center of mass provide a broader picture of plumewide processes. Deterministic methods, such as quantitative mass‐balance approaches, may be useful for larger plumes. Qualitative assessments include evaluations of the conceptual site model, source strength, attenuation mechanisms, and hydrogeology. Because groundwater plumes are always dynamic, the determination of plume stability has to include qualitative steps relating the rate and magnitude of change to the goals and objectives of the program and the time frame over which critical management decisions are to be made. The assessment of plume stability is, therefore, presented as a process that should involve both qualitative and quantitative steps for determining the acceptability of variability in groundwater contaminant concentrations. © 2010 Wiley Periodicals, Inc.     

A new method for evaluating the sewage sludge pyrolysis kinetics

A new method to simplify calculation the kinetics model is applied to sewage sludge pyrolysis based on the assumption that volatile run out as soon as it formed and during temperature arising process in this study. Difference method widely used to solve math problems is conducted to calculate kinetics parameters. Pyrolysis experiments are carried out at heating rates of 10, 15, 20, and 50 °C/min. All the TG curves are divided into three parts which are beginning decomposition temperature range, main decomposition temperature range, and final decomposition temperature range. The second one is employed to determine the parameters for more than 70% of the total mass loss occurs in this range. According to the developed method, the react order, reaction energy and pre-exponential factor are obtained, which are in the range of 3.9–4.1, 82.3–109.2 kJ/mol and 7.7 × 10⁶–2.8 × 10⁹/min, respectively, which are in the range of that reported previously. As a comparison experimental data with calculated data, the well fitting results indicate that this method is appropriate for simulating sludge pyrolysis kinetics.     

A carbon-13 method for evaluating degradation of starch-based polymers

A new method for evaluating biodegradability of starch-based and certain other polymer blends uses the pre- and postexposure stable carbon isotope composition of material coupled with weight loss data to determine which components have degraded. The naturally occurring stable isotope of carbon.¹³C, is enriched in corn starch (¹³C, approx. –11) compared to petroleum-derived synthetic polymers (¹³C, approx. –32). Results on starch-synthetic polymer blends indicate that the ¹³C signatures of these blends are near-linear mixtures of their component ¹³C. Values of a ¹³C for starch-synthetic polymer blends exposed to biologically active laboratory soil and artificial seawater conditions are depleted in¹³C compared to unexposed samples, suggesting loss of the starch component. Combined with weight loss data for the exposed samples, the ¹³C values are statistically consistent with models requiring loss of the soluble component glycerin, followed by loss of starch, then petrochemical polymer, or simultaneous loss of starch and petrochemical polymer. Replicate ¹³C analyses of starch-synthetic polymer blends increase the statistical power of this relatively inexpensive, accessible technique to discriminate between degrading components.     

A multiobjective modeling approach to locate multi-compartment containers for urban-sorted waste

The location of multi-compartment sorted waste containers for recycling purposes in cities is an important problem in the context of urban waste management. The costs associated with those facilities and the impacts placed on populations are important concerns. This paper introduces a mixed-integer, multiobjective programming approach to identify the locations and capacities of such facilities. The approach incorporates an optimization model in a Geographical Information System (GIS)-based interactive decision support system that includes four objectives. The first objective minimizes the total investment cost; the second one minimizes the average distance from dwellings to the respective multi-compartment container; the last two objectives address the “pull” and “push” characteristics of the decision problem, one by minimizing the number of individuals too close to any container, and the other by minimizing the number of dwellings too far from the respective multi-compartment container. The model determines the number of facilities to be opened, the respective container capacities, their locations, their respective shares of the total waste of each type to be collected, and the dwellings assigned to each facility. The approach proposed was tested with a case study for the historical center of Coimbra city, Portugal, where a large urban renovation project, addressing about 800 buildings, is being undertaken. This paper demonstrates that the models and techniques incorporated in the interactive decision support system (IDSS) can be used to assist a decision maker (DM) in analyzing this complex problem in a realistically sized urban application. Ten solutions consisting of different combinations of underground containers for the disposal of four types of sorted waste in 12 candidate sites, were generated. These solutions and tradeoffs among the objectives are presented to the DM via tables, graphs, color-coded maps and other graphics. The DM can then use this information to “guide” the IDSS in identifying additional solutions of potential interest. Nevertheless, this research showed that a particular solution with a better objective balance can be identified. The actual sequence of additional solutions generated will depend upon the objectives and preferences of the DM in a specific application.     

The Triad approach: A catalyst for maturing remediation practice

Many individual scientific and technical disciplines contribute to the multidisciplinary field of remediation science and practice. Because of the relative youth of this enterprise, disciplinary interests sometimes compete and conflict with the primary goal of achieving protective, cost‐effective, efficient projects. Convergence of viewpoints toward a more mature, common vision is needed. In addition, cleanup programs are changing under the influence of Brownfields initiatives and the needs of environmental insurance underwriters. Investigations and cleanups increasingly need to be affordable, yet transparent and defensible. Disciplinary goals and terminology need to better reflect real‐world site conditions while being more supportive of project needs. Yet, technical considerations alone will not ensure project success; better integration of human factors into project management is also required. The Triad approach is well placed to catalyze maturation of the remediation field because it emphasizes (1) a central theme of managing decision uncertainty; (2) unambiguous technical communications; (3) shortened project life‐cycles and multidisciplinary interactions that rapidly build professional expertise and provide feedback to test and perfect programmatic and field practices; and (4) concepts from “softer” sciences (such as economics, cognitive psychology, and decision theory) to capture important human factors. Triad pushes the cleanup industry toward an integrated, practical, second‐generation paradigm that can successfully manage the complexities of today's cleanup projects. © 2004 Wiley Periodicals, Inc.