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Author: Sarayu Gottipati Publisher: ISBN: Category : Soil remediation Languages : en Pages : 252
Book Description
Persistence of Non aqueous phase liquids (NAPLs) in the subsurface at residual saturations eventually contributes to undesirable groundwater contamination. Proper characterization of subsurface NAPL, its location, composition and distribution, is essential for the chosen remediation technology to be effective. It is also desirable to assess the performance of remedial actions at NAPL-contaminated sites in order to verify the technoeconomic viability of the selected method. The unique properties of radon-222 gas make it a good indicator for organic phase liquids. It is ubiquitous in the subsurface, chemically inert, radioactive, and most importantly, partitions into NAPLs. This research explores the practicality of using radon to indirectly monitor the progress of NAPL remediation efforts. The effectiveness of surfactant flushing in remediating NAPL contamination was also studied in the process. Preliminary studies were conducted using micro-columns to evaluate the efficiency of the surfactant selected for the study, triton. These studies show that triton is more effective at higher concentrations in solubilizing residual soltrol and its solubilizing capacity is greatly enhanced after batch equilibration. These observations suggest that surfactant solubilization of NAPLs is rate-limited rather than instantaneous. These studies also indicate the adverse effect of aged NAPL on surfactant solubilizing capacity. Two independent methods, total organic carbon analysis and HDPE strip test, were also designed for analyzing the aqueous and sand samples and estimating the level of cleanup achieved. Since triton proved to be effective in micro-column studies, the remediation of the soil columns was performed by flushing triton through the columns in a sequential batch mode. The soil columns employed in the study had been previously packed and used by Hopkins (1994). The influence of the decrease in residual soltrol saturations on breakthrough of radon was observed. The gradual cleanup of columns at various initial residual soltrol saturations (1.0%, 5.0%, and 8.0%) through surfactant flushing was well reflected by radon. The aqueous radon concentrations increased and the retardation of radon lessened as residual soltrol was removed from the columns. The linear equilibrium partitioning model of radon was used to estimate the initial residual NAPL saturation in each column and the subsequent saturations as the remediation proceeded. The saturation estimates were based on retardation factors obtained from maximum aqueous radon concentrations and breakthrough of radon. These estimates correlated fairly well with those based on TOC analyses and HDPE strip tests, supporting radon's capability of detecting and quantifying NAPLs, and monitoring the progress of NAPL remediation. The results of this study demonstrate the potential of radon as a tracer for evaluating the performance of NAPL remediation techniques. This study also substantiates the ability of surfactants to enhance NAPL recovery from subsurface. However, clogging problems have been encountered, which are believed to be caused by surfactant micelles, while sampling columns. Hence, careful selection of appropriate surfactant, among other criteria, is essential to get maximum benefits of surfactant-enhanced NAPL remediation technology.
Author: Sarayu Gottipati Publisher: ISBN: Category : Soil remediation Languages : en Pages : 252
Book Description
Persistence of Non aqueous phase liquids (NAPLs) in the subsurface at residual saturations eventually contributes to undesirable groundwater contamination. Proper characterization of subsurface NAPL, its location, composition and distribution, is essential for the chosen remediation technology to be effective. It is also desirable to assess the performance of remedial actions at NAPL-contaminated sites in order to verify the technoeconomic viability of the selected method. The unique properties of radon-222 gas make it a good indicator for organic phase liquids. It is ubiquitous in the subsurface, chemically inert, radioactive, and most importantly, partitions into NAPLs. This research explores the practicality of using radon to indirectly monitor the progress of NAPL remediation efforts. The effectiveness of surfactant flushing in remediating NAPL contamination was also studied in the process. Preliminary studies were conducted using micro-columns to evaluate the efficiency of the surfactant selected for the study, triton. These studies show that triton is more effective at higher concentrations in solubilizing residual soltrol and its solubilizing capacity is greatly enhanced after batch equilibration. These observations suggest that surfactant solubilization of NAPLs is rate-limited rather than instantaneous. These studies also indicate the adverse effect of aged NAPL on surfactant solubilizing capacity. Two independent methods, total organic carbon analysis and HDPE strip test, were also designed for analyzing the aqueous and sand samples and estimating the level of cleanup achieved. Since triton proved to be effective in micro-column studies, the remediation of the soil columns was performed by flushing triton through the columns in a sequential batch mode. The soil columns employed in the study had been previously packed and used by Hopkins (1994). The influence of the decrease in residual soltrol saturations on breakthrough of radon was observed. The gradual cleanup of columns at various initial residual soltrol saturations (1.0%, 5.0%, and 8.0%) through surfactant flushing was well reflected by radon. The aqueous radon concentrations increased and the retardation of radon lessened as residual soltrol was removed from the columns. The linear equilibrium partitioning model of radon was used to estimate the initial residual NAPL saturation in each column and the subsequent saturations as the remediation proceeded. The saturation estimates were based on retardation factors obtained from maximum aqueous radon concentrations and breakthrough of radon. These estimates correlated fairly well with those based on TOC analyses and HDPE strip tests, supporting radon's capability of detecting and quantifying NAPLs, and monitoring the progress of NAPL remediation. The results of this study demonstrate the potential of radon as a tracer for evaluating the performance of NAPL remediation techniques. This study also substantiates the ability of surfactants to enhance NAPL recovery from subsurface. However, clogging problems have been encountered, which are believed to be caused by surfactant micelles, while sampling columns. Hence, careful selection of appropriate surfactant, among other criteria, is essential to get maximum benefits of surfactant-enhanced NAPL remediation technology.
Author: Publisher: ISBN: Category : Languages : en Pages : 5
Book Description
The objective of this research is to develop a unique method for using naturally occurring radon-222 as an inexpensive partitioning tracer for locating and quantitatifying nonaqueous phase liquid (NAPL) contamination in the subsurface, and assessing the effectiveness of NAPL remediation. Laboratory, field, and modeling studies are being performed to evaluate this technique, and to develop methods for its successful implementation in practice.
Author: Publisher: ISBN: Category : Languages : en Pages : 3
Book Description
The objective of this research is to develop a unique method of using naturally occurring radon-222 as a tracer for locating and quantitatively describing the presence of subsurface NAPL contamination. The research will evaluate using radon as an inexpensive, yet highly accurate, means of detecting NAPL contamination and assessing the effectiveness of NAPL remediation. Laboratory, field, and modeling studies are being performed to evaluate this technique, and to develop methods for its successful implementation in practice. This report summarizes work that has been accomplished after 1-year of a 3-year project. The research to date has included radon tracer tests in physical aquifer models (PAMs) and field studies at Site 300 of the Lawrence Livermore National Laboratory, CA, and Site 100D at Hanford DOE Facility, WA. The PAM tests have evaluated the ability of radon as a tracer to monitor the remediation of TCE NAPL contamination using surfactant treatment, and oxidation with permanganate. The surfactant tests were performed in collaboration with Dr. Jack Istok and Dr. Jennifer Field and their EMSP project ''In-situ, Field-Scale Evaluation of Surfactant Enhanced DNAPL Recovery Using a Single-Well-Push-Pull Test.'''' This collaboration enabled the EMSP radon project to make rapid progress. The PAM surfactant tests were performed in a radial flow geometry to simulate the push-pull-method that is being developed for surfactant field tests. The radon tests were easily incorporated into these experiments, since they simply rely on measuring the natural radon present in the subsurface fluids. Two types of radon tests were performed: (1) static tests where radon was permitted to build-up to steady-state concentrations in the pore fluids and the groundwater concentrations were monitored, and (2) dynamic tests were the radon response during push-pull surfactant tests was measured. Both methods were found to be useful in determining how NAPL remediation was progressing.
Author: Publisher: ISBN: Category : Languages : en Pages : 98
Book Description
Nonaqueous phase liquids (NAPL), including chlorinated solvents, aromatic hydrocarbons, and other volatile organic chemicals (VOC), are common contaminants at Department of Defense (DoD) and other federal and non-federal sites. Residual or pooled NAPL contamination provides a long-term source of contamination as it slowly dissolves into groundwater. A major obstacle preventing cost-effective soil and groundwater cleanup at many DoD sites is the current inability to accurately and inexpensively locate and quantify NAPL contamination. This final report describes the use of naturally occurring radon-222 (Rn) as a partitioning tracer for locating and quantifying NAPL contamination in the subsurface and for monitoring changes in NAPL quantities resulting from remediation activities. Radon-222 possesses unique physical properties that make it a useful natural partitioning tracer for detecting and quantifying NAPL. Rn is produced in the subsurface by the continuous decay of naturally occurring radium-226. In the absence of NAPL contamination, the aqueous Rn concentration quickly reaches a site-specific equilibrium value determined by the mineralogy and porosity of the geologic formation. In the presence of NAPL, however, the Rn concentration is substantially reduced due to partitioning of Rn into the organic NAPL phase. Moreover, the reduction in Rn concentration of groundwater in contact with a NAPL phase is quantitatively correlated with the quantity of NAPL present, as described by simple equilibrium models. Thus, the method is based on measuring Rn in groundwater samples from existing monitoring wells.
Author: Brian M. Davis Publisher: ISBN: Category : Radon Languages : en Pages : 432
Book Description
This study investigated the use of radon-222 as an in situ partitioning tracer for quantifying nonaqueous phase liquid (NAPL) saturations in the subsurface. Laboratory physical aquifer models (PAMs), field experiments, and numerical simulations were used to investigate radon partitioning in static (no-flow) experiments and in single-well, 'push-pull' tests conducted in non-contaminated and NAPL-contaminated aquifers. Laboratory push-pull tests in a wedge-shaped PAM and field push-pull tests in a NAPL-contaminated aquifer showed that radon was retarded in the presence of NAPL, with retardation manifested in increased dispersion of radon extraction phase breakthrough curves (BTCs). An approximate analytical solution to the governing transport equation and numerical simulations provided estimates of the radon retardation factor (R), which was used to calculate NAPL saturations (S[subscripts n]). Laboratory static and push-pull tests were conducted in a large-scale rectangular PAM before and after NAPL contamination, and after alcohol cosolvent flushing and pump-and-treat remediation. Radon concentrations in static tests were decreased due to partitioning after NAPL contamination and increased after remediation. Push-pull tests showed increased radon retardation after NAPL contamination; radon retardation generally decreased after remediation. Numerical simulations modeling radon as an injected or ex situ partitioning tracer were used to estimate retardation factors and resulted in overestimations of the likely S[subscripts n] in the PAM. Radon partitioning was sensitive to changes in S[subscripts n] in both static and push-pull tests. However, the test results were sensitive to test location, sample size, test design, and heterogeneity in S[subscripts n] distribution. Numerical simulations of hypothetical push-pull tests conducted in a NAPL-contaminated aquifer were used to investigate the influence of homogeneous and heterogeneous S[subscripts n] distributions and initial radon concentrations on radon BTCs and resulting S[subscripts n] calculations. Both of these factors were found to affect radon BTC behavior. A revised method of plotting and interpreting radon BTCs combined with numerical simulations modeling radon as an in situ partitioning tracer (incorporating initial radon concentrations into the model as a function of S[subscripts n]) were used to re-analyze laboratory and field push-pull test BTCs. This method reduced the overestimation of calculated S[subscripts n] values from laboratory tests.
Author: Publisher: ISBN: Category : Languages : en Pages : 5
Book Description
Naturally occurring 222-radon in ground water can potentially be used as an in situ partitioning tracer to characterize dense nonaqueous phase liquid (DNAPL) saturations. The static method involves comparing radon concentrations in water samples from DNAPL-contaminated and non-contaminated portions of an aquifer. During a push-pull test, a known volume of test solution (radon-free water containing a conservation tracer) is first injected (''pushed'') into a well; flow is then reversed and the test solution/groundwater mixture is extracted (''pulled'') from the same well. In the presence of NAPL radon transport is retarded relative to the conservative tracer. Assuming linear equilibrium partitioning, retardation factors for radon can be used to estimate NAPL saturations. The utility of this methodology was evaluated in laboratory and field settings.
Author: Omar Snowden Hopkins Publisher: ISBN: Category : Dense nonaqueous phase liquids Languages : en Pages : 188
Book Description
Radon-222 gas has unique properties allowing it to be used as an indicator for the presence of organic phase liquids in the saturated zone. It naturally occurs in soils. It is radioactive, making quantitative detection straight forward. A noble gas, it is chemically inert and does not react with aquifer media. Finally, radon has an affinity to concentrate in nonaqueous phase liquids. A proposed linear equilibrium partitioning model was tested by batch equilibration with the pore fluid to establish the deficit in aqueous radon concentrations that results from its partitioning into the residual saturation of the organic phase (Soltrol-220). Five sets of experiments were run on columns with 0.0, 1.0, 2.5, 5.0, and 8.0 percent residual soltrol fractions. The model was found to accurately represent the partitioning process. A one-dimensional physical model was run to see if the data from the partitioning experiments could be successfully applied to predict the aqueous radon concentrations in a more complex situation. The results indicate that radon-222 has great potential to be used as a means of detecting and quantifying the presence of residual organic phase liquids in the saturated zone.
Author: Sarayu Gottipati
Author: Sarayu Gottipati
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Author: Godage B. Wickramanayake
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Author: Brian M. Davis
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Author: Omar Snowden Hopkins