Bioremediation of chlorinated aliphatic hydrocarbon (CAH) compounds commonly found at contaminated sites has been an area of focus in recent years. The cometabolic transformation of CAH compounds is important at sites where the redox condition does not favor natural attenuation or populations of indigenous microorganisms are relatively low. At sites where the ground-water system is aerobic, monitored natural attenuation strategies will not meet remediation objectives, or both, enhanced bioremediation via cometabolism is an option. Models are needed to simulate cometabolism in an effort to improve performance and design. The SEAM3D Cometabolism Package was designed to address this need. The objective of this report is to model field data to determine the ability of SEAM3D to simulate the performance of cometabolism. A ground-water flow and transport model was designed based on reported parameters used in the field experiments at Moffett Field. Electron donor and acceptor breakthrough curves were also simulated in an effort to calibrate the model. Several data sets describing the cometabolism of CAHs were used in the cometabolism modeling for calibration to field data. The cometabolism modeling showed areas of best fit calibration with modification to the model parameters reported for the pilot tests at Moffett Field. The overall performance of the SEAM3D Cometabolism Package described in this report establishes validation of the model using field experiment results from the literature. Additional model validation is recommended for other contaminants. / Master of Science

Numerical models (GMS MODFLOW, SEAM3D, and SEAM3D Interface) were applied to simulate groundwater flow, petroleum hydrocarbon compound (PHC) transport and biodegradation, and the transport and biotransformation of chlorinated ethenes at Site FT-002 Plattsburgh Air Force Base (PAFB), NY. Site FT-002 was contaminated with waste jet fuel and chlorinated ethenes used as a fire source during fire fighting training. The results of groundwater analysis indicated that the aquifer exhibited aerobic, nitrate reducing, ferrogenic, sulfate reducing and methanogenic conditions due to the biodegradation of the PHCs. Additional groundwater analysis showed the biotransformation of TCE to DCE, VC, and ethene. A numerical model was developed to simulate and assess the extent to which reductive dechlorination and direct anaerobic oxidation were responsible for the biotransformation of the chlorinated ethenes. Reductive dechlorination accounted for the 100%, 98.3%, and 97.5% of the biotransformation of TCE, DCE, and VC respectively. Direct anaerobic oxidation accounted for 1.7% and 2.5% of the biotransformation of DCE and VC respectively. Though direct anaerobic oxidation only accounted for a small percentage of total biotransformation it was necessary to fully develop the biotransformation of the DCE and VC in the ferrogenic zone. This study focused on the mechanisms responsible for the biotransformation of chlorinated ethenes, specifically reductive dechlorination and direct anaerobic oxidation. By further defining the NAPL source and initial conditions it could be used as a tool to accurately predict the monitored natural attenuation (MNA) of the FT-002 contaminant plume. / Master of Science

Groundwater parameter analysis, microcosm experiments, and microcosms modeling were undertaken to assess the potential of Monitored Natural Attenuation as a remediation strategy at Site 12 at the Naval Amphibious Base (NAB) Little Creek. Site 12 was contaminated with PCE waste disposed by a former dry cleaning facility. In the groundwater analysis, contaminant characteristics and redox indicators were evaluated to assess the reductive dechlorination potential of Site 12. The results of the groundwater analysis indicated that Site 12 exhibited sulfate-reducing and methanogenic conditions which provide the required environment for reductive dechlorination. However, Site 12 only demonstrated partial reductive dechlorination to cis-1,2-DCE and possible anaerobic oxidation of cis-1,2-DCE and VC to CO₂. Microcosms were designed to further evaluate the extent of microbial degradation of the chlorinated ethenes at Site 12 and to provide concentration versus time data for the estimation of chlorinated ethenes' biodegradation rates. The extent of degradation in the microcosms was consistent with the groundwater data. However, ethene production was not observed and the quantity of TCE measured for two of the microcosms differed substantially when compared to the groundwater data. The microcosm model used SEAM3D to simulate the results of the microcosm experiments (concentration versus time data) to estimate the biodegradation rates of PCE and its daughter products. The SEAM3D reductive dechlorination package, based on Monod kinetics, predicted for the MLS12-Shallow microcosm maximum specific utilization rates for PCE, TCE, cis-1,2-DCE and VC at 0.4, 0.42, 0.05, and 0.25 day⁻¹, respectively and half saturation coefficients for PCE, TCE, cis-1,2-DCE and VC at 0.41, 0.01, 0.07, and 0.02 mg/L, respectively. The results of this study suggest that while the groundwater environment provides the necessary conditions for reductive dechlorination, Site 12 is not an efficient system for reductive dechlorination. This lack of efficiency may stem from sparse microbial populations capable of reducing cis-1,2-DCE or the system may contain levels of PCE which inhibit the further reduction of cis-1,2-DCE. Based on the observed inhibitory relationship between PCE and cis-1,2-DCE and VC production, source removal would reduce the PCE levels and encourage further reductive dechlorination at Site 12. Therefore, the recommended first step for a monitered natural attenuation-based remediation strategy at Site 12 should be source removal. / Master of Science

A numerical model is presented to describe solute transport in groundwater coupled to sorption by plant roots, translocation into plant stems, and finally evapotranspiration. The conceptual model takes into account both Root Concentration Factor, RCF, and Transpiration Stream Concentration Factor, TSCF for chemicals which are a function of Kow. A similar technique used to simulate the solute transport in groundwater to simulate sorption and plant uptake is used. The mathematical equation is solved using finite difference technique to solve for the concentration at any grid cell with respect to time. The new package is integrated into SEAM3D to create a new SEAM3D Plant Uptake Package, or PUP. The model is then verified by comparing results for root sorption in one side to the SEAM3D Reaction Package, and results for plant uptake to the SEAM3D Source Sink Mixing Package. The verification results showed an excellent match, which led to using the new package in a series of design application scenarios to evaluate phytoremediation effect. Hypothetical design scenarios included: 1) the effect of a phytoremediation system dimensions, 2) the effect of phytoremediation plant density or maximum ET rate, 3) the effect of out-flux of the phytoremediation with respect to the natural aquifer in-flux, and 4) the effect of using a phytoremediation system when the source of contamination is removed. For all the previous study cases, the results evaluate the effect on: 1) contaminant concentrations downstream the source (expressed in plume length at a concentration 1% of the source concentration), 2) solute mass removal from the aquifer, and 3) mass-flux changes at different cross-sections downstream the contaminant source. The results indicating the followings: 1) the width of the phytoremediation system, WET, has a limited effect on the solute mass-removal; 2) high tree density close to the contaminant source has a greater effect on solute mass removal relative to uniform density of trees planted over the entire plume; 3) the width of the ET area will have only a slight effect on the mass removal if the TSCF value is small; 4) as the value of TSCF gets lower, the efficiency of solute mass uptake is lower, and thus the solute concentration in groundwater is higher regardless of the quantity of water transpired; 5) dynamic steady-state plume dimensions (specially the plume length) are affected by the groundwater in-flux, which will control the dimensions and density of a phyto system; 6) splitting the phyto system into two halves does not have the same outcome of having one piece of area closer to the contamination site; 7) using a phyto system after the contamination source is removed led to increasing the solute concentration in the areas of the trees and decreases the concentration in the areas downstream the trees. The alternative model gives more options for simulation of solute mass uptake by plants by making use of field and lab data between the solute dissolved concentration in groundwater C, and solute mass in tree's core M to select a modeling category of three: Linear (ISO-1), Freundlich (ISO-2), and Langmuir (ISO-3). Each modeling option depends on the designer selection according to the fitted equation parameters between, C and, M. In terms of conservative results, ISO-1, and ISO-2 give less mass removal results than ISO-3 in case of sources with low concentrations. ISO-2, and ISO-3 give less mass removal results than ISO-1 in case of sources with high concentrations. / Ph. D.

Following the DWH oil spill event, crude oil reaching the shoreline of Gulf of Mexico produced petroleum oil deposit with a range of distinct geometries, including sphere tar balls and horizontal tar sheets. Numerical models were developed based on the Deep Water Horizon oil spill conditions to evaluate the influence of deposit geometry on long term persistence of residual NAPL oil. Two extreme deposit geometries were modeled in this study: the horizontal tar sheet and the spherical tar ball. Both two-dimensional modeling approach and three-dimensional modeling approach were applied to compare two contrasting geometries. The two-dimensional model results showed that sheet geometry deposits exhibited a greater obstruction to groundwater flow relative to the spherical deposits and induced a larger sulfate reducing zone downgradient of the NAPL source, resulting in significantly greater sulfate-based biodegradation of benzene. Three-dimensional models were constructed to assess the influence of key geometry parameters on oil deposit fate and persistence. Three parameters affecting deposit's geometric structure were recognized, including the upper horizontal area of the sheet deposit, the thickness of the sheet deposit, and the radius of the sphere deposit. The three-dimensional model results suggested that thickness of the sheet deposit and radius of the sphere deposit were important geometry factors impacting the fate and long term persistence of residual NAPL oil in the coastal environment. However, the influence of deposit geometry differed depending on the solubility of the different NAPL components. When high solubility compound and low solubility compound both exist in the oil deposit, the influence of deposit geometry on benzene degradation was significant, while the influence on naphthalene was almost negligible. / Master of Science

For a numerical or analytical model to be useful it should be ensured that the model outcome matches the observations or field measurements during calibration. This process has been typically done by manual perturbation of the model input parameters. This research investigates a methodology for using non linear parameter estimation technique (the Marquardt-Levenberg technique) with the multi component reactive solute transport model SEAM3D. The reactive multi-component solutes considered in this study are chlorinated ethenes. Previous studies have shown that this class of compounds can be degraded by four different biodegradation mechanisms, and the degradation path is a function of the prevailing oxidation reduction conditions. Tests were performed in three levels; the first level utilized synthetic model-generated data. The idea was to develop a methodology and perform preliminary testing where "observations" can be generated as needed. The second level of testing involved performing the testing on a single redox zone model. The methodology was refined and tested using data from a chlorinated ethenes-contaminated site. The third level involved performing the tests on a multiple redox zone model. The methodology was tested, and statistical validation of the recommended methodology was performed. The results of the tests showed that there is a statistical advantage for choosing a subgroup of the available parameters to optimize instead of the optimizing the whole available group. Therefore, it is recommended to perform a parameter sensitivity study prior to the optimization process to identify the suitable parameters to be chosen. The methodology suggests optimizing the oxidation-reduction species parameters first then calibrating the chlorinated ethenes model. The results of the tests also proved the advantage of the sequential optimization of the model parameters, therefore the parameters of the parent compound are optimized, updated in the daughter compound model, for which the parameters are then optimized so on. The test results suggested considering the concentrations of the daughter compounds when optimizing the parameters of the parent compounds. As for the observation weights, the tests suggest starting the applied observation weights during the optimization process at values of one and changing them if needed. Overall the proposed methodology proved to be very efficient. The optimization methodology yielded sets of model parameters capable of generating concentration profiles with great resemblance to the observed concentration profiles in the two chlorinated ethenes site models considered. / Ph. D.