In Situ Bioremediation When Does it Work? (1993) / Chapter Skim
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Background Papers
Background Papers
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Background Papers
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This paper describes the information that regulators need to make their decision. Basically, this information comprises descriptions of the site, the specific cleanup process, and the overall approach to site cleanup.
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Also, the regulated community (potentially responsible parties) must realize that the cleanup process itself is but one facet of the overall site cleanup.
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The description of the cause of the release allows the regulator to identify its source and thus the most highly contaminated areas of the site. PROCESS DESCRIPTION The responsible party should provide a detailed description of the treatment process to be used.
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Such loss of permeability not only prevents delivery of the nutrients and oxygen necessary to sustain biological activity to clean up the soils or aquifer but may seriously hamper use of other technologies. OVERALL SITE CLEANUP DESCRIPTION A very important part of the description of the overall approach to site cleanup is the methodist to be used to prevent movement of the contaminants farther off site through the soil or to or through the ground water or other medium.
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In addition, if nutrients are added, they may also be contaminants and require monitoring. Nitrate, for example, is a chemical of concern that may have to be added to a biological treatment system as a nutrient or may be proposed as an electron acceptor in an anaerobic treatment process.
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, given enough dissolved oxygen in the ground water. With adequate site characterization, analysis, and monitoring, this type of intrinsic bioremediation can shrink plumes and control the migration of hydrocarbons.
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Evidence that this natural process is occurring has been obtained from laboratory and field observations. EVIDENCE FOR INTRINSIC BIOREMEDIATION OF AROMATIC HYDROCARBONS IN PLUMES It is now widely recognized that the most significant factor in the time-dependent decrease of BTEX compounds in aquifers is degrada
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It should be emphasized that laboratory and field data have confirmed that all BTEX compounds can be biodegraded under aerobic conditions (dissolved oxygen in ground water) in aquifer subsoils in which oxygen is the terminal electron acceptor.
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above background well levels. It is known that various ferric oxides in soil can be used (as electron acceptors)
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userfriendly ground water models that use monitoring well, hydrogeological, and soil microbiology data to predict the transport and fate of contaminants. Geochemical and biological indicators of in situ biodegradation in addition to BTEX and dissolved oxygen, such as the formation of carbon dioxide and other microbial metabolites as well as ferrous ion, may also help verify intrinsic biodegradation processes in aquifers.
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Pp. 207-231 in Proceedings of the Petroleum Hydrocarbons and Organic Chemicals in Groundwater Conference.
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A shift in paradigm emphasizing the ecological principles governing biodegradation instead of contaminant mass balances would greatly advance the understanding of bioremediation. INTRODUCTION I suggest that there are at least two conceptual approaches to hazardous waste bioremediation.
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Nonetheless, the emphasis in the ecological approach is not on quantification of pollutants but on whether principles are met, since it is known that biological communities respond according to these principles. The first part of this paper reviews basic ecological principles important to the evaluation and success of in situ bioremediation.
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112 JAMES M TIEDJE technique because resources are focused only on the target chemical.
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In contrast, in the vadose zone and aquifer soil, which are impoverished in organic matter, the total populations will be lower and hence
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It is useful to group chemicals into two classes of biodegradability: (1) those that support the growth of microbial populations and (2)
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growth substrates are almost always completely oxidized to carbon dioxide, leaving no toxic intermediates. Less than complete pollutant destruction by natural selection is usually due to limitation by some other resource, most commonly the electron acceptor.
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116 JAMES M TIEDJE THREE KEY QUESTIONS I suggest that the following key questions, in the indicated order of priority, are a basic guide to successful bioremediation: 1.
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The second issue is the availability of sufficient lifesustaining growth factors, such as nutrients, particularly nitrogen and phosphorus; appropriate electron acceptors; and perhaps other growth factors that might be contained in soil organic matter. Nutrient supply can be evaluated by considering whether the proper carbon-nitrogen-phosphorus (C:N:P)
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Such treatments overcome a rate limitation if the site is anaerobic. Alternative electron acceptors are possible, and nitrate is particularly attractive because of its high electron-accepting capacity in water, its leachability in soils, its low toxicity, and its low cost.
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and electron acceptors. At contaminated sites, this kind of evidence in the biological record would be strongly indicative of successful intrinsic bioremediation and its persistence as long as the conditions for natural selection can be ensured.
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Applied and Environmental Microbiology 56:782-787.
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Nashville, Tennessee SUMMARY Since the pioneering work by Dick Raymond during the 1970s and early 1980s, in situ bioremediation has been widely used to clean up aquifers contaminated with petroleum hydrocarbons. A need for better performance led to development of the use of hydrogen peroxide and direct injection of air into the aquifer as sources of oxygen, which was a critical problem in bioremediation.
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, and has been used almost as long as simple pump-and-treat technology. In situ bioremediation was one of the first technologies that was able to bring a site to closure by significantly and permanently reducing soil and ground water contamination, predating in situ processes such as soil vapor extraction and air sparging.
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During 1983-1986J several commercial in situ bioremediation projects using hydrogen peroxide as the oxygen source were implemented and in some cases reduced hydrocarbons (Frankenberger et al., 1989) and BTEX (benzene, toluene, ethylbenzene, xylenes)
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Concerns with hydrogen peroxide stability led to a search for other soluble electron acceptors. Several tests were conducted to evaluate nitrate as an alternate electron acceptor for degradation of monoaromatic (except benzene)
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Air sparging provides the same benefits to saturated zone treatment that soil vapor extraction has to vadose zone treat ment. CURRENT USES The application of bioremediation is continually changing.
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For volatile biodegradable contaminants, a combination of in situ bioremediation, air sparking, and/or vapor extraction may be the best strategy, provided the soil properties and site infrastructure permit. Designs that emphasize air sparging and vapor recovery are likely to lead to faster remediation than systems that emphasize bioremediation.
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Similarly, there is little evidence that nonindigenous microorganisms have been used successfully on a commercial scale for in situ bioremediation. With highly degradable substances, intrinsic bioremediation can be used as the final treatment when the contaminant load has been reduced to the point that the ambient nutrient levels and oxygen diffusion are sufficient to support biodegradation.
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Central requirements of in situ bioremediation are that the contaminants are biodegradable, that the appropriate microbial populations are present, and that the microbes are able to thrive. The understanding of metabolic pathways in biodegradation and of the factors that control microbial populations continues to grow, thus increasing the potential for bioremediation.
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There has been a plethora of laboratory investigations to identify beneficial microbial processes but relatively few field pilot studies demonstrating the efficacy of in situ bioremediation for recalcitrant compounds and little commercialization of novel microbial processes. Extensive field studies by researchers at Stanford University used stimulation of methanotrophs to cooxidize TCE under nearly ideal field conditions.
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BROWN, WILLIAM MAHAFFEY, AND ROBERT D NORRIS Site Assessment Limitations An important element of any field pilot program is that the site be well characterized and that statistically valid sampling plans be used during the site investigation and remediation.
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It would seem that monitoring methods that could provide direct evidence of the performance of in situ bioremediation processes would go a long way toward validating treatment effects early in the remediation process and even provide the mechanism for stimulus-response control of the process. Methods for on-line analysis of general metabolic end results, such as carbon dioxide production and oxygen consumption, are used fairly routinely.
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Typically, this process will leave behind residual contaminants and polymer/surfactant. The potential of using in situ bioremediation to treat these residuals (biopolishing)
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Application of new microbial processes requires better monitoring and mathematical modeling as well as improved subsurface engineering. Such advances will lead to better understanding and use of natural or enhanced in situ bioremediation.
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1989. In situ bioremediation of an underground diesel fuel spill: a case history.
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1986. Opportunities for bioremediation of aquifers contaminated with petroleum hydrocarbons.
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Requisite factors for successful application of in situ bioremediation include adequate aquifer permeability; a suitable microbial population; sufficient hydrodynamic control for plume containment and delivery of required electron donors, electron acceptors, and/or nutrients; and a complete monitoring system. Evaluating the progress of in situ bioremediation and proving that the microbes are responsible for contaminant degradation can be challenging because of the inaccessibility of the subsurface bioreactor, aquifer heterogeneities, and the wide range of potential contaminant fates.
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SUBSURFACE BIOREACTOR REQUIREMENTS Before applying in situ bioremediation to a contaminated aquifer, it is necessary to evaluate the feasibility of engineering a subsurface bioreactor at the specific site to carry out the biological degradations of interest. Engineering feasibility depends on a number of factors; principal among them are aquifer permeability, heterogeneity, and geochemical characteristics, as well as the nature and distribution of the contaminants.
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Permeability Adequate permeability for the transport of solutions delivering nutrients or other compounds required for stimulation of the desired microbial population within the subsurface bioreactor is essential to in situ bioremediation. Additionally, the aquifer must be sufficiently permeable that the increased microbial mass and volume will not cause extensive plugging of the aquifer pores, thus restricting further ground water movement.
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These results suggest that both permeability and pore size distribution must be considered in determining the feasibility of in situ bioremediation (Taylor and laffe, 1991~. Environmental Conditions It is important to analyze the environmental parameters inside the intended zone of biostimulation that could exert significant impact on microbial growth and degradation potential.
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AQUIFER PREPARATION Before applying in situ bioremediation, the source of contamination must be detected and mitigated, major accumulations of free product must be removed, and mechanisms for plume containment must be installed. Contaminants entering the subsurface partition into different phases due to sorption, volatilization, and dissolution processes.
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Hydrodynamic controls are used alone or in conjunction with physical controls. They are especially suited for use with in situ bioremediation since biostimulation amendments could be added with the control water.
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Many organic contaminants can be used as a primary substrate for microbial metabolism, in which case the contaminant serves as an electron donor and sometimes also as the major carbon source for the microbial cells. Therefore, some degradation reactions produce energy and usable carbon, resulting in microbial growth.
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However, the use of an alternate substrate also enables the degradation reaction to be maintained at contaminant concentrations below those required to support microbial growth and much lower than those possible for degradations in which the contaminant is used by the microorganisms as a primary substrate. Therefore, alternate substrates can increase the potential for attaining contaminant removal to regulatory levels.
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One such method, which has been shown in field studies to reduce localized plugging associated with cometabolic bioremediation, is alternating pulses of electron donor and electron acceptor in the reinfection water. Since both electron donor and acceptor are required for microbial metabolism, advective and dispersive processes within the aquifer must mix the nutrients before conditions promote microbial growth, causing cells to grow dispersed throughout the aquifer and producing a large biostimulation zone (Semprini et al., 1990~.
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However, in some cases the increased cost and potential explosion hazard associated with pure oxygen may more than offset its increased delivery efficiency. Application of hydrogen peroxide to in situ bioremediation is limited by its toxicity to microbes and its potential for causing aquifer plugging.
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Again, laboratory feasibility studies will be necessary to determine the tolerance range of the indigenous microbial population. The toxic effects of hydrogen peroxide on microbes have a side benefit that can be exploited through careful control of the injection stream.
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DETERMINING THE SUCCESS OF IN SITU BIOREMEDIATION Perhaps the biggest challenges associated with managing a subsurface bioreactor for in situ bioremediation are evaluating its progress
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Therefore, specific documentation of the successful application of in situ bioremediation for the destruction of aquifer contaminants is extremely rare. It has been asserted that true proof of in situ bioremediation requires convergent lines of independent evidence of microbial degradation in the field (Madsen, 1991~.
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5. In situ bioremediation of jet fuel was qualitatively demon
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CONCLUSIONS In situ bioremediation is the management of a subsurface bioreactor to carry out specific biological degradations of ground water contam~nants. Successful implementation should include a thorough aquifer characterization, removal of contaminant source and free product, plume containment, laboratory feasibility studies, installation and operation of biostimulation controls, and continuous monitoring.
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1992. Hydrogen peroxide use to increase oxidant capacity for in situ bioremediation of contaminated soils and aquifers: a review.
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Applied and Environmental Microbiology 54(1)
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This paper reviews modeling efforts, including BIOPLUME II. INTRODUCTION One of the aquifer remediation methods that has been gaining more widespread attention recently is bioremediation, the treatment of subsurface pollutants by stimulating the growth of native microbial populations.
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MODELING BIODEGRADATION PROCESSES The problem of quantifying biodegradation in the subsurface can be addressed by using models that combine physical, chemical, and biological processes. Developing such models is not simple, however, because of the complex nature of microbial kinetics, the limitations of computer resources, the lack of field data on biodegradation, and the lack of robust numerical schemes that can simulate the physical, chemical, and biological processes accurately.
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Basic assumptions incorporated into the model include a simulated particle-bound microbial population comprised of heterotrophic facultative bacteria in which metabolism is controlled by lack of an organic carbon electron donor source (substrate) , an electron acceptor (oxygen and/or nitrate)
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The major sources of oxygen, this research concluded, are transverse mixing, advective fluxes, and vertical exchange with the unsaturated zone. Rifai et al.
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The natural attenuation rate was calculated to be 0.95 percent per day. Spatial relationships between dissolved oxygen and total benzene, toluene,
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The results were remarkably consistent with field data on the presence of high or low levels of BTX and dissolved oxygen in several monitoring well samples.
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1987. Development and application of a model for simulating microbial growth dynamics coupled to nutrient and oxygen transport in porous media.
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Environmental Protection Agency Robert S Kerr Environmental Research Laboratory Ada, Oklahoma SUMMARY An operational definition for success of in situ bioremediation at field scale includes meeting regulatory goals for ground water quality in a timely fashion at a predictable cost.
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Experimental controls are usually unavailable during full-scale implementation of in situ bioremediation because the technology is applied uniformly to the contaminated area. As a result, performance monitoring that is limited to the concentration of contaminants in ground water over time, and perhaps the concentrations of nutrients and electron acceptors, cannot ensure that the biological process developed in the laboratory was responsible for contaminant removal at full scale.
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Lacking information on the structure of the data, Kennedy and Hutchins ran all three simulations and took the numerical average. Of 320 kg of benzene in the aquifer, only 22 kg was dissolved in the ground water; of 8800 kg of BTEX compounds, only 82 kg was dissolved; and of 390,000 kg of total petroleum hydrocarbons, only 115 kg was dissolved.
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Often the meter's response in the field headspace analyses has a strong correlation to the content of total petroleum hydrocarbons. In these cases, results from a limited number of expensive core analyses can be extrapolated to a large number of inexpensive field headspace analyses.
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(1989, in press) quantitatively described this effect in a pilot-scale demonstration of in situ bioremediation of a jet fuel spill using nitrate as the electron acceptor.
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To estimate the distribution of an individual BTEX compound between fuel and water, the published partition coefficients were multiplied by the ratio of the volume of JP-4 under the infiltration gallery to the volume of water in circulation. The distribution between oil and fuel was used to calculate the fraction of total material in oil or water.
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Ground water was amended with mineral nutrients and nitrate as an electron acceptor. Water was recirculated to an infiltration gallery installed above the JP-4 spill.
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Concentrations dropped below the analytical detection limit over a 2-day period. Concentrations of other BTEX compounds were not reduced (compare data for o-xylene in Figure 5)
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of BTEX Compounds in Ground Water After Bioremediation to the Cor~centrations Expected from the BTEX Content of the Residual Petroleum Hydrocarbons Concentration Concentration Concentration Prior to After Predicted from Compound Bioremediation Bioremediation Residual Benzene 760 <1 2 Toluene 4500 <1 15 Ethylbenzene 840 6 6 m,p-Xylene 2600 23 27 o-Xylene 1380 37 18 2.0 1.5 o -0.5 -1 .0 Start Nitrate Predicted PP7A : T -- _ ____ _. 1 1 1 1 1 1 1 1 1 1 -_ Stop Nitrate 1 0 20 40 60 80 100 120 140 160 180 200 Days Since Startup FIGURE 4 Bioremediation of a [P-4 jet fuel spill using nitrate.
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benzene removal, other BTEX compounds (such as o-xylene) would also have been removed because these other compounds have physical and chemical properties similar to those of benzene but are less readily biodegradable.
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As a result, concentrations of oilyphase material that are determined to be protective of ground water quality are low, on the order of 10 to 100 mg total petroleum hydrocarbon per kilogram of aquifer material (Bell, 1990~. Bioremediation, particularly innovative bioremediation that uses an electron acceptor other than oxygen, can remove the compounds of regulatory concern from the subsurface while leaving significant amounts of oily-phase hydrocarbons.
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Figure 6 shows the relationship between the garage, the work pit containing the leaking holding tank, and the approximate area of the spill. Remediation involved removal of separate oily phases, in situ bioremediation with hydrogen peroxide and mineral nutrients, and bioventing.
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N 20 meters FIGURE 6 Infrastructure at an in situ bioremediation project in Denver, Colorado. A holding tank in a work pit under a garage leaked petroleum hydrocarbons to the water table aquifer.
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The system was designed to sweep the ground water containing hydrogen peroxide and mineral nutrients through the spill to the recovery well. The system was operated from October 1989 to March 1992.
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of Hydrocarbon Contaminants in Ground Water Achieved by In Situ Bioremediation Benzene Total BTEX WellBefore During AfterBefore During After MOO-1 220 <1 <1 2030 164 <6 MOO-8 180 130 16 1800 331 34 MOO-2A ?
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Obviously, the materials with lower residual concentrations of hydrocarbons are more extensively weathered. Infiltration of hydrogen peroxide and mineral nutrients at an aviation gasoline spill in Michigan preferentially removed BTEX compounds from the oily-phase gasoline, leaving a total petroleum hydrocarbon residual low in aromatic hydrocarbons (Wilson et al., in press)
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The cross section runs through core boreholes depicted in Figure 6. TABLE 3 Vertical Extent of Total BTEX Compounds and Total Petroleum Hydrocarbons (mg/kg)
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and the extent of biological and chemical weathering (reduction in percentage of BTEX compounds in total petroleum hydrocarbons) in core material after bioremediation at the Denver site.
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Assume that the weathered material is weathered because it is in effective contact with moving ground water that supplied nutrients and electron acceptors, and the residual is not weathered because it was not in effective contact and the supply of nutrients and electron acceptors was inadequate. If partitioning between moving ground water and the weathered oily residual controls the concentration of hydrocarbons in the water, the 10-fold reduction in concentrations of benzene and BTEX compounds seen in the weathered core material (Table 3)
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As weathering progresses, aromatic hydrocarbons such as the BTEX compounds are restricted to regions with low hydraulic conductivity (panel C)
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As a result, the residence time of water in the spill area is longer, and the total amount of hydrocarbon transferred to the water is greater, although the supply of electron acceptor for biological destruction of the hydrocarbon is less (compare panels C and D in Figure 10~. These relationships are well illustrated by the performance of bioremediation at the Denver site (Table 5~.
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Oxygen consumption must have been limited by mass transfer of hydrocarbon to the ground water circulated through the spill. Relationship to Siting and Sampling Monitoring Wells No established procedures exist for determining under ambient conditions whether the mass transfer of hydrocarbons from oily residual material will exceed the supply of oxygen or other natural electron acceptors.
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If properly benchmarked by a limited number of laboratory analyses, field headspace techniques can provide a rapid and affordable estimate of total contaminant concentrations. · Simple ground water flow models can estimate the volume of water circulated through a spill during in situ bioremediation.
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A full scale field demonstration on the use of hydrogen peroxide for in-situ Bioremediation of an aviation gaso
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1987. A wireline piston core barrel for sampling cohesionless sand and gravel below the water table.
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