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. / Graduation date: 2003

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. / Graduation date: 1995

Tetrachloroethene (PCE) is a major groundwater contaminant that often persists as dense, nonaqueous phase liquids (DNAPLs) in subsurface environments. Dissolved-phase PCE plumes emanate from DNAPL source zones, which act as continuous sources of contamination for decades. Removal of DNAPL source zones is crucial to achieve lasting remedy of contaminated aquifers. This research explored the contributions of the microbial reductive dechlorination process (i.e., anaerobic bioremediation) to PCE-DNAPL source zone remediation, either in isolation or as a polishing step for the removal of residual DNAPL remaining after application of surfactant enhanced aquifer remediation (SEAR), an emerging physical-chemical source zone treatment. Specific objectives of this research were to: (1) evaluate the ability of microorganisms to dechlorinate in the presence of PCE-DNAPL and at high dissolved-phase PCE concentrations expected near/in DNAPL source zones, (2) assess the distribution and activity of key dechlorinating populations during bioenhanced PCE-DNAPL dissolution in continuous-flow column experiments, (3) determine the influence of Tween 80, a biodegradable surfactant commonly used in SEAR, on the microbial reductive dechlorination process, (4) design and optimize quantitative real-time PCR (qPCR) protocols to detect and enumerate key dechlorinating populations (e.g., Geobacter lovleyi, Sulfurospirillum multivorans), and (5) explore the effects of oxygen on Dehalococcoides viability and biomarker quantification. This research demonstrated that microbial dechlorinating activity within DNAPL source zones promotes bioenhanced dissolution although many dechlorinating isolates cannot tolerate saturated PCE concentrations. Application of newly designed qPCR protocols established a direct link between dissolution enhancement and the distribution of relevant dechlorinating populations in the vicinity of PCE-DNAPL. The limited and reversible impact of Tween 80 on key dechlorinators supported the feasibility of a treatment train approach of SEAR followed by microbial reductive dechlorination to remediate PCE-DNAPL source zones. Finally, experiments with oxygen-exposed, Dehalococcoides-containing cultures suggested limitations of using Dehalococcoides DNA and RNA biomarkers for monitoring bioremediation at field sites. These findings advance the scientific understanding of the microbial reductive dechlorination process and are relevant to environmental remediation practitioners. The advantages and current shortcomings of PCE-DNAPL source zone bioremediation, as well as recommendations for future research, are discussed.

Thesis (Ph. D.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 113-127). Also available on the World Wide Web.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 418-432). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisors: Daene C. McKinney and Gary A. Pope. Vita. Includes bibliographical references.

[Truncated abstract] To date, many subsurface contaminant modelling studies have focused on increasing model complexity and measurement requirements to improve model accuracy and widen model application. However, due to the highly complex and heterogeneous nature of flow in the subsurface, the greater benefit in model development may lie in decreasing complexity by identifying key processes and parameters, simplifying the relationships that exist between them, and incorporating these relationships into simple models that recognise or quantify the inherent complexity and uncertainty. To address this need, this study aims to identify and isolate the key processes and parameters that control dense nonaqueous phase liquid (DNAPL) and aqueous phase migration through single, onedimensional fractures. This is a theoretical representation which allows the study of processes through conceptual and mathematical models. Fracture systems typically consist of multiple two-dimensional fractures in a three-dimensional network; however, these systems are computationally and conceptually demanding to investigate and were outside of the scope of this study. This work initially focuses on DNAPL migration in single, one-dimensional fractures. The similitude techniques of dimensional and inspectional analysis are performed to simplify the system and to develop breakthrough time scale factors. This approach relies heavily on the limitations of the equation used for the analysis and on the difficulty in representing variable aperture scenarios. The complexity of the conceptual model is then increased by embedding the fracture in a two-dimensional, porous matrix. ... These tools can be readily applied by the field investigator or computer modeller to make order-of-magnitude estimates of breakthrough times, reduce or target measurement requirements, and lessen the need to employ numerical multiphase flow models. To determine the implications of the results found in the one-dimensional studies to applications at the field scale, the complexity of the conceptual model was increased to a single, two-dimensional, planar fracture embedded in a three-dimensional porous matrix. The focus of this study was not DNAPL breakthrough times but the relative importance and interaction of different mass transport processes and parameters on plume migration and evolution. Observations clearly show that estimates of the size, location and concentration of the plume is highly dependent on the geologic media, the temporal and spatial location and resolution of measurements, and on the history, mass and location of the DNAPL source. In addition, the processes controlling mass transport (especially matrix diffusion and back diffusion) act in combination at the field scale in ways not always expected from an analysis of processes acting individually at smaller spatial and temporal scales. Serious concerns over the application of the common '1% Rule of Thumb' to predict DNAPL presence and the use of remediation efforts that rely largely on natural attenuation are raised. These findings have major implications for the field worker and computer modeller, and any characterisation, monitoring or remediation program development needs to be sensitive to these findings.

Light Non-Aqueous Phase Liquids (LNAPLs) are used throughout the world for numerous applications, the most well-known being automotive fuels, such as petrol and diesel. The widespread production, distribution, storage and use of LNAPLs results in the ubiquitous occurrence of spillage to ground (Geller et al, 2000). Considering the hazardous nature of most LNAPLs due to their explosive and toxic characteristics, releases of LNAPLs to ground have well documented human health and ecological consequences. The occurrence of leaking underground and above-ground storage tanks at service stations and consumer installations is a common cause of contamination; and is described in literature for various countries of the world (Dietz et. al., 1986; Moschini et al, 2005; Mulroy and Ou, 1997; Harris, 1989; The Institute of Petroleum, 2002). Little failure data are however available for the South African context. In addition to this, data concerning the location and characteristics of sites storing LNAPLs in South Africa is similarly scarce. The study analysed data from three sources, namely the eThekwini Fire and Emergency Services data, GIS data and data from a local consultancy, in order to determine whether certain factors increased contamination risk posed by these facilities. The results indicated that contamination may be a result of numerous factors, but primarily line and tank failure. The type of installation was also found to have a significant influence on whether a site would be contaminated or not. In addition to the above, the results indicated that certain circumstances increase the severity of loss. The results indicated the need for more investigation to be performed into contamination as a result of LNAPL loss to ground, and the need for protective measures to be implemented for high risk sites where the likelihood and severity of a potential loss is high. Focus should then be centred on the probability of failure of non-ferrous pipework and GRP tanks to ensure adequate protective mechanisms are in place in the event of a failure of this newer infrastructure. In addition, a review of regulatory control of LNAPL storage in South Africa and the eThekwini Municipality, with reference to the international context, indicated the need for a specific department within the local government structure that manages LNAPLs with the objective of reducing contamination incidents. The continued use of underground storage of LNAPLs will always present a risk of failure/contamination due to the unseen nature of the installations and related infrastructure. It is this risk that requires regulatory management. Details of contaminated sites in South Africa should be within the public domain. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.

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