Petroleum-contaminated Sites Research Articles

Application of a GIS-Based Modeling System for Effective Management of Petroleum-Contaminated Sites

A GIS-aided simulation (GISSIM) system is developed for effective management of petroleum-contaminated sites in this study. The GISSIM contains two components: an advanced three-dimensional (3D) numerical model, and a geographical information system (GIS). The modeling component undertakes simulation for the fate of contaminants in subsurface unsaturated and saturated zones. The GIS component is used in three areas throughout the system development and implementation process: (1) managing spatial and nonspatial databases; (2) linking inputs, the model, and outputs; and (3) providing an interface between the GISSIM and its users. The system is applied to a North American case study. Concentrations of benzene, toluene, and xylenes in groundwater under a petroleum-contaminated site are dynamically simulated. Conditions of the contamination in different time stages under a variety of remediation scenarios are predicted. Reasonable outputs have been obtained and presented graphically. Implications of the modeling outputs have been analyzed based on the local environmental regulations. They provide quantitative and scientific bases for further assessment of site-contamination impacts and risks, as well as decisions of practical remediation actions. GISSIM is useful for both industrial and government sectors to make informed decisions on waste management, pollution control, site remediation, and environmental impact assessment.

Sensitivity analysis of a soil leachability model for petroleum fate and transport in the vadose zone

Risk-based assessment methods are commonly used at petroleum-contaminated sites. In South Carolina, the Soil Leachability Model (SLM) is used to calculate site-specific target levels (SSTLs) for soils that may leach contaminants to groundwater. The SLM is a series of analytical equations that is based upon the Green and Ampt equation to predict infiltration rates and accounts for equilibrium partitioning and first-order biodegradation of the contaminant as it travels to groundwater. To reduce costs, many soil property inputs to the model are estimated using regression equations that relate textural classification to these physical properties. It was not known what effect errors in these inputs might have on the SSTLs computed with the SLM. Thus, a sensitivity analysis was performed to determine the influence of parameter variability on benzene and naphthalene SSTLs computed for three soil types and two groundwater depths. The results of this study indicate that SSTLs computed with the SLM are very sensitive to organic carbon content and biodegradation half-lives for sand, loam, and clay, saturated hydraulic conductivity for loam and clay and most soil input parameters for clay. Overestimation of organic carbon content or underestimation of biodegradation half-lives in sand, loam or clay, or underestimation of the saturated hydraulic conductivity in loam or clay can result in SSTLs that are orders of magnitude too large, and therefore, potentially unconservative.

An intelligent decision support system for management of petroleum-contaminated sites

Groundwater and soil contamination resulted from LNAPLs (light nonaqueous phase liquids) spills and leakage in petroleum industry is currently one of the major environmental concerns in North America. Numerous site remediation technologies have been developed and implemented in the last two decades. They are classified as ex-situ and in-situ remediation techniques. One of the problems associated with ex-situ remediation is the cost of operation. In recent years, in-situ techniques have acquired popularity. However, the selection of the optimal techniques is difficult and insufficient expertise in the process may result in large inflation of expenses. This study presents an expert system (ES) for the management of petroleum contaminated sites in which a variety of artificial intelligence (AI) techniques were used to construct a support tool for site remediation decision-making. This paper presents the knowledge engineering processes of knowledge acquisition, conceptual design, and system implementation. The results from some case studies indicate that the expert system can generate cost-effective remediation alternatives to assist decision-makers.

Detection of catabolic genes in indigenous microbial consortia isolated from a diesel-contaminated soil

Bioremediation is often used for in situ remediation of petroleum-contaminated sites. The primary focus of this study was on understanding the indigenous microbial community which can survive in contaminated environment and is responsible for the degradation. Diesel, toluene and naphthalene-degrading microbial consortia were isolated from diesel-contaminated soil by growing on selective hydrocarbon substrates. The presence and frequency of the catabolic genes responsible for aromatic hydrocarbon biodegradation ( xylE, ndoB) within the isolated consortia were screened using polymerase chain reaction PCR and DNA–DNA colony hybridization. The diesel DNA-extract possessed both the xylE catabolic gene for toluene, and the nah catabolic gene for polynuclear aromatic hydrocarbon degradation. The toluene DNA-extract possessed only the xylE catabolic gene, while the naphthalene DNA-extract only the ndoB gene. Restriction enzyme analysis with HaeIII indicated similar restriction patterns for the xylE gene fragment between toluene DNA-extract and a type strain, Pseudomonas putida ATCC 23973. A substantial proportion (74%) of the colonies from the diesel-consortium possessed the xylE gene, and the ndoB gene (78%), while a minority (29%) of the toluene-consortium harbored the xylE gene. 59% of the colonies from the naphthalene-consortium had the ndoB gene, and did not have the xylE gene. These results indicate that the microbial population has been naturally enriched in organisms carrying genes for aromatic hydrocarbon degradation and that significant aromatic biodegradative potential exists at the site. Characterization of the population genotype constitutes a molecular diagnosis which permits the determination of the catabolic potential of the site to degrade the contaminant present.

Petroleum Hydrocarbon Monitored Natural Attenuation: Essential Framework for Remedial Managers

Abstract Monitored natural attenuation (MNA) is an attractive remedy for petroleum-contaminated sites. However, to use MNA as a partial or total site remedy, the remedial manager must first present unequivocal evidence that natural attenuation will occur at the site and will meet public and regulatory concerns. A considerable body of scientific evidence of natural attenuation exists, as does a small library of American Society for Testing and Materials and U.S. Environmental Protection Agency documentation on use of MNA. This article clearly and succinctly presents the background of MNA, guides the new remedial manager through the process, discusses the pros and cons of MNA alone and in combination with other low-cost remedies (primarily source removal), and outlines regulatory and public concerns and how to meet them.

Thermal Insulation Systems for Bioremediation in Cold Regions

Bioremediation of petroleum-contaminated soils in cold regions is hampered by low temperatures, frozen soils, and short summers. Extreme environmental conditions limit remedial efforts to a few technologies. Bioventing and combined air-sparging and soil vapor extraction have shown promise in subarctic regions. Expensive thermal desorption or encapsulation of organically contaminated soil is practiced in arctic Alaska and Canada, in lieu of successful bioremediation. Thermal insulation systems have recently been developed for innovative bioremediation efforts in cold regions. Commercially available insulation, electrical heating elements, and construction materials have been uniquely packaged to enhance bioremediation at two petroleum-contaminated sites in Alaska. Thermally enhanced bioventing successfully remediated hydrocarbon contamination in the vadose zone at a subarctic site within two years. Preliminary results from an oxygenated and fertilized biopile, actively warmed and covered with a thermal insulation system, shows promise at an arctic site. A guide for thermal insulation system design for bioremediation application in cold regions is developed.

Risk assessment of a petroleum-contaminated site through a multi-phase and multi-component modeling approach

An integrated simulation and risk-assessment approach is proposed, which includes a multi-phase and multi-component modeling system for simulating flow and transport of petroleum constituents in the subsurface and a fuzzy relation analysis (FRA) model for assessing environmental risks under uncertainty. Outputs of the simulation modeling were directly input into the FRA model to comprehensively evaluate integrated risk due to transport of multiple petroleum constituents in groundwater system to receptors of concern. Application of the integrated simulation and risk-assessment approach to a petroleum-contaminated site indicates that reasonable solutions have been generated. They are useful for providing decision-support for management and remediation of petroleum-contaminated sites.

Performance of air sparging systems: a review of case studies

Fluor Daniel GTI (now IT Corporation) has compiled a database of 49 completed in-situ air sparging case studies. Air sparging is a commonly used remediation technology which volatilizes and enhances aerobic biodegradation of contamination in groundwater and saturated zone soil. The air sparging database was compiled to address questions regarding the effectiveness and permanence of air sparging, and to provide predictive indicators of air sparging success to aid in optimization of existing and future air sparging systems. In each case study, groundwater concentrations were compared before sparging was initiated, just before sparging was terminated, and in the months following shutdown of the sparging system. The case studies included both chlorinated solvents and petroleum hydrocarbon contamination, and covered a wide range of soil conditions and sparge system parameters. In many cases, air sparging achieved a substantial and permanent decrease in groundwater concentrations. Successful systems were achieved with both chlorinated and petroleum contamination, both sandy and silty soils, and both continuous and pulsed flow sparging. In other cases, however, a significant rebound of groundwater concentrations was observed after sparging was terminated. Rebound sometimes required 6 to 12 months to develop fully. Rebound was more frequently observed at sites contaminated with petroleum hydrocarbons than with chlorinated solvents. Petroleum-contaminated sites were more likely to rebound when initial groundwater contamination levels were high enough to suggest the presence of LNAPL or a smear zone of residual LNAPL. Rebound at petroleum sites appeared to be minimized by a high density of sparge wells addressing the entire source area and a high sparge air injection rate. In some cases, rebound appeared to be related to a rising water table.

Bacterial adhesion to soil contaminants in the presence of surfactants

It has been proposed that addition of surfactants to contaminated soil enhances the solubility of target compounds; however, surfactants may simultaneously reduce the adhesion of bacteria to hydrophobic surfaces. If the latter mechanism is important for the biodegradation of virtually insoluble contaminants, then the use of surfactants may not be beneficial. The adhesion of a Mycobacterium strain and a Pseudomonas strain, isolated from a creosote-contaminated soil, to the surfaces of highly viscous non-aqueous-phase liquids (NAPLs) was measured. The NAPLs were organic material extracted from soils from two creosote-contaminated sites and two petroleum-contaminated sites. Cells suspended in media with and without surfactant were placed in test tubes coated with an NAPL, and the percentages of cells that adhered to the surface of the NAPL in the presence and absence of surfactant were compared by measuring optical density. Test tubes without NAPLs were used as controls. The presence of either Triton X-100 or Dowfax 8390 at a concentration that was one-half the critical micelle concentration (CMC) inhibited adhesion of both species of bacteria to the NAPLs. Both surfactants, when added at concentrations that were one-half the CMCs to test tubes containing previously adhered bacteria, also promoted the removal of the cells from the surfaces of the NAPL-coated test tubes. Neither surfactant was toxic to the bacteria. Further investigation showed that a low concentration of surfactant also inhibited the growth of both species on anthracene, indicating that the presence of a surfactant resulted in a reduction in the uptake of the solid carbon source.

Integrated environmental risk assessment for petroleum-contaminated sites - a North American case study

Development of petroleum industries is associated with a number of environmental concerns. Among them, soil and groundwater contamination by petroleum products is of major concern. In this study, an integrated risk assessment approach is proposed for evaluating environmental risks derived from petroleum-contaminated sites. The proposed approach is composed of (i) a hydrocarbon spill screening model (HSSM) which is used for simulating immisicible flow of released hydrocarbons in vadose zone, formation of lens in capillary fringe, dissolution of pollutants at water table, and transport of the pollutants to receptors, and (ii) a fuzzy relation analysis (FRA) model which is developed for comprehensively evaluating risks caused by a number of pollutants with different impact characteristics, based on the HSSM results. This hybrid HSSM-FPA approach was applied to a case study for a petroleum-contaminated site in western Canada, where soil and groundwater was contaminated by industrial wastes containing benzene, toluene, ethylbenzene and xylenes (BTEXs). The results suggest that the HSSM-FRA can provide insight into the potential risk to the receptor of concern downward the acquifer and can serve as a basis for further remediation-related decision analysis.

Assessing Human Exposure to Benzene at Petroleum-Contaminated Site

Entry of volatile organic compounds into buildings is often considered when evaluating air exposure pathways during remedial investigation of petroleum-contaminated sites. This paper presents two approaches used to evaluate human exposure to benzene inside a former gasoline station converted into a strip mall in Manitoba, Canada. Passive air sampling was used to measure benzene in indoor air several times over a two-week period. Soil-to-indoor air vapor transport and worker exposure were modeled to evaluate the potential impact from entry of benzene into the mall. Because these transport models lack field validation and their results can be highly dependent on the sophistication of the models, several models were used. Benzene levels inside the mall were comparable to average levels observed inside Canadian residences. It was not apparent that air inside the mall had been impacted by subsurface contamination at the time of sampling. Modeling of benzene exposure arising from soil vapor entry suggested low incremental exposure for workers compared to what they would receive by inhalation of air inside typical residences. Soil contamination was allowed to remain in place based on these findings.

Integrated environmental risk assessment for petroleum-contaminated sites — A North American case study

Development of petroleum industries is associated with a number of environmental concerns. Among them, soil and groundwater contamination by petroleum products is of major concern. In this study, an integrated risk assessment approach is proposed for evaluating environmental risks derived from petroleum-contaminated sites. The proposed approach is composed of (i) a hydrocarbon spill screening model (HSSM) which is used for simulating immisicible flow of released hydrocarbons in vadose zone, formation of lens in capillary fringe, dissolution of pollutants at water table, and transport of the pollutants to receptors, and (ii) a fuzzy relation analysis (FRA) model which is developed for comprehensively evaluating risks caused by a number of pollutants with different impact characteristics, based on the HSSM results. This hybrid HSSM-FPA approach was applied to a case study for a petroleum-contaminated site in western Canada, where soil and groundwater was contaminated by industrial wastes containing benzene, toluene, ethylbenzene and xylenes (BTEXs). The results suggest that the HSSM-FRA can provide insight into the potential risk to the receptor of concern downward the acquifer and can serve as a basis for further remediation-related decision analysis.

Modification of Heterotrophic Plate Counts for Assessing the Bioremediation Potential of Petroleum-Contaminated Soils

Bioremediation is becoming an accepted treatment option for the remediation of petroleum-contaminated sites. Instrumental in implementing bioremediation is the characterization of bacteria capable of degrading the contaminants of interest. A wide variety of techniques have been reported in the literature but they often involve volatile solvents or petroleum mixtures as substrates and thus are difficult to use. Standard heterotrophic plate counts are often required by environmental regulations to be included as part of contaminated site investigations and assessments. Standard heterotrophic plate count techniques were found in this study to be unable to detect changes in population sizes in contaminated and uncontaminated soils. A more specific assay using benzoate, a metabolite of many BTEX compounds, was also used. This technique was capable of detecting differences in population size between contaminated and uncontaminated soils and benzoate is thus a better substrate to use when characterizing petroleum-contaminated soils. Furthermore, the data (population size vs. contaminant concentration) fit a hyperbolic model well. Such a model could be used to monitor population size with respect to contaminant concentration as well as population size outside the contaminant plume to further assess the progress of bioremediation at a contaminated site.

A comparison of microbial community characteristics among petroleum-contaminated and uncontaminated subsurface soil samples

Measurements of microbial community size, including total cell counts and specific degrader enumerations, were conducted on subsurface soil samples from both petroleum-contaminated and pristine aquifers. Samples were collected from both uncontaminated and contaminated areas of the petroleum-contaminated sites. In pristine and uncontaminated samples, total cell counts (acridine orange direct counts) were related to depth. The deeper samples contained smaller total microbial populations. However, indices of microbial activity varied considerably from sample to sample and probably reflect soil and site heterogeneity. Exposure to petroleum contamination apparently altered the microbial community structure. In samples exposed to low levels of contaminants as vapors and/or dissolved phases (ppb concentrations), and not free product, the toluene-specific degrader populations were larger at greater depths, and the numbers of amino acid-specific degraders were highly correlated to the numbers of decane-specific degraders, indicating that petroleum-adapted microbial communities were present in the contaminated samples. In highly contaminated samples, total microbial population densities decreased with increasing depth; however, microbial activity tended to increase with depth. These results indicate that petroleum contaminants exert toxic effects on the active microbial community at high exposures and enrich specific degraders at ppb levels of dissolved contaminants.

Experimental linkage issues of petroleum site bioremediation

Bioremediation of petroleum-contaminated sites is expected to be a cost-effective remediation technology. However, many potential users of the technology expect the reliability of this technology to be similar to other candidate technologies for widespread consideration. In particular, candidate technologies should possess the property of reliable experimental linkage — there should be reasonable confidence that experiments done at one scale can be reliably related to another. An important example is bench-scale treatability studies that should result in linkages with commercial-scale operations. In this respect comparison of bioremediation to other candidate technologies reveals that bioremediation is in an early stage of its evolution. It is being pursued at a variety of sites and scales with practitioners from a variety of disciplines. Integration of activities between disciplines and an ability to quantitatively compare results at different sites and scales is proceeding. This paper addresses a number of physical, chemical, biological, analytical, and statistical issues regarding the successful comparison of results between experiments.

Enumeration of phenanthrene-degrading bacteria by an overlayer technique and its use in evaluation of petroleum-contaminated sites.

Bacteria that are capable of degrading polycyclic aromatic hydrocarbons were enumerated by incorporating soil and water dilutions together with fine particles of phenanthrene, a polycyclic aromatic hydrocarbon, into an agarose overlayer and pouring the mixture over a mineral salts underlayer. The phenanthrene-degrading bacteria embedded in the overlayer were recognized by a halo of clearing in the opaque phenanthrene layer. Diesel fuel- or creosote-contaminated soil and water that were undergoing bioremediation contained 6 x 10(6) to 100 x 10(6) phenanthrene-degrading bacteria per g and ca. 5 x 10(5) phenanthrene-degrading bacteria per ml, respectively, whereas samples from untreated polluted sites contained substantially lower numbers. Unpolluted soil and water contained no detectable phenanthrene degraders (desert soil) or only very modest numbers of these organisms (garden soil, municipal reservoir water).

Field evaluation of benzopyrene hydroxylase induction as a monitor for marine petroleum pollution.

Fish from petroleum-contaminated sites in the marine environment have elevated levels of benzopyrene hydroxylase activity in liver and gill tissue. This sublethal response appears to be a practical biological monitor for marine petroleum pollution.