Bayesian Saltwater Intrusion Prediction and Remediation Design under Uncertainty

Groundwater resources are vital for sustainable economic and demographic developments. Reliable prediction of groundwater head and contaminant transport is necessary for sustainable management of the groundwater resources. However, the groundwater simulation models are subjected to uncertainty in their predictions. The goals of this research are to: (1) quantify the uncertainty in the groundwater model predictions and (2) investigate the impact of the quantified uncertainty on the aquifer remediation designs. To pursue the first goal, this study generalizes the Bayesian model averaging (BMA) method and introduces the hierarchical Bayesian model averaging (HBMA) method that segregates and prioritizes sources of uncertainty in a hierarchical structure and conduct BMA for saltwater intrusion prediction. A BMA tree of models is developed to understand the impact of individual sources of uncertainty and uncertainty propagation on model predictions. The uncertainty analysis using HBMA leads to finding the best modeling proposition and to calculating the relative and absolute model weights. To pursue the second goal of the study, the chance-constrained (CC) programming is proposed to deal with the uncertainty in the remediation design. Prior studies of CC programming for the groundwater remediation designs are limited to considering parameter estimation uncertainty. This study combines the CC programming with the BMA and HBMA methods and proposes the BMA-CC framework and the HBMA-CC framework to also include the model structure uncertainty in the CC programming. The results show that the prediction variances from the parameter estimation uncertainty are much smaller than those from the model structure uncertainty. Ignoring the model structure uncertainty in the remediation design may lead to overestimating the design reliability, which can cause design failure

Stochastic Cost-Optimization and Risk Assessment of in situ Chemical Oxidation for Dense Non-Aqueous Phase Liquid (DNAPL) Source Remediation

This study involved development of a computer program to determine optimal design variables for in situ chemical oxidation (ISCO) of dense nonaqueous phase liquid (DNAPL) sites to meet site-wide remediation objectives with minimum life-cycle remediation cost while taking uncertainty in site characterization data and model predictions into consideration. A physically-based ISCO performance model computes field-scale DNAPL dissolution, instantaneous reaction of oxidant with contaminant and with readily oxidizable natural oxidant demand (NOD), second-order kinetic reactions for slowly oxidizable NOD, and time to reach ISCO termination criteria. Remediation cost is computed by coupling the performance model with a cost module. ISCO termination protocols are implemented that allow different treatment subregions (e.g., zones with different estimated contaminant concentrations) to be terminated independently based on statistical criteria related to confidence limits of contaminant concentrations estimated from soil and/or groundwater sampling data. The ISCO model was implemented in the program called Stochastic Cost Optimization Toolkit, which includes modules for additional remediation technologies that can be implemented serially or in parallel coupled with a dissolved plume model to enable design optimization to meet plume-scale cleanup objectives. This study focuses on optimization of ISCO design to meet specified source zone remediation objectives. ISCO design parameters considered for optimization include oxidant concentration and injection rate, frequency and number of soil or groundwater samples, and cleanup criteria for termination of subregion injection. Sensitivity studies and example applications are presented to demonstrate the benefits of proposed stochastic optimization methodology

Tetrachloroethylene migration and remediation by surfactant-alcohol in two-dimensional saturated layered sand laboratory experiment

Surfactant-alcohol remediation have been reviewed by many researchers as an innovative technology to remediate tetrachloroethylene (PCE) from the subsurface. However, the application of surfactant-alcohol remediation to layered sand conditions is still obscurity and its implementation is limited due to flow sensitivity to site characterization. The laboratory experiment was performed in assessing the efficiency of surfactant-alcohol remediation through two-dimensional (2-D) saturated layered sand contaminated with tetrachloroethylene (PCE) spill. The 2-D physical model consist of front clear glass for easy visualization of 2-D PCE migration and framed with aluminum material has been developed. The type of sand use is fine sand and coarse sand. The laboratory investigation of PCE remediation in 2-D saturated layered sand using three different surfactant solutions. The first solution consist of 4 % surfactant, the second solution consist of 8 % surfactant and the third solution consist of 4 % surfactant and 15 % n-butanol. The PCE migration has been captured and analyzed to evaluate the dominant mechanisms and efficiency of PCE remediation. The laboratory experimental results shows that the dominant mechanism of PCE remediation in 2-D saturated layered sand using surfactant-alcohol treatment is solubilization and mobilization mechanisms. The solubilisation mechanisms are govern by the properties of surfactant itself where the surfactant are soluble in water due to the oxygen atom that are capable in forming hydrogen bond with the water molecules. The oxygen atom in surfactant are the hydrophilic head which is water lover attach to water and the other atom with the hydrophobic tail which is water hate attach to PCE. The interfacial tension between PCE, water and sand are lod because the surfactant molecules are surround PCE. The addition of co-surfactant, n-butanol in surfactant solution help in the formation of microemulsion which increase the number of micelles thus increase the solubilisation and mobilization of PCE. The reduction of total density of the microemulsion result in the PCE migration to the upward direction following its low density compared to water density. This shows that the prevention of uncontrolled downward migration of PCE are possible. The effect of microemulsion in lowering the interfacial tension between PCE, water and sand has result in no residual PCE left at the PCE source zone. The results of this study shows that surfactant-alcohol are very efficient solution to remediate PCE in 2-D saturated layered sand

A New Approach to Groundwater Remediation Treatability Studies - Moving Flow-through Column Experiments from Laboratory to In Situ Operation

abstract: In situ remediation of contaminated aquifers, specifically in situ bioremediation (ISB), has gained popularity over pump-and-treat operations. It represents a more sustainable approach that can also achieve complete mineralization of contaminants in the subsurface. However, the subsurface reality is very complex, characterized by hydrodynamic groundwater movement, geological heterogeneity, and mass-transfer phenomena governing contaminant transport and bioavailability. These phenomena cannot be properly studied using commonly conducted laboratory batch microcosms lacking realistic representation of the processes named above. Instead, relevant processes are better understood by using flow-through systems (sediment columns). However, flow-through column studies are typically conducted without replicates. Due to additional sources of variability (e.g., flow rate variation between columns and over time), column studies are expected to be less reproducible than simple batch microcosms. This was assessed through a comprehensive statistical analysis of results from multiple batch and column studies. Anaerobic microbial biotransformations of trichloroethene and of perchlorate were chosen as case studies. Results revealed that no statistically significant differences were found between reproducibility of batch and column studies. It has further been recognized that laboratory studies cannot accurately reproduce many phenomena encountered in the field. To overcome this limitation, a down-hole diagnostic device (in situ microcosm array - ISMA) was developed, that enables the autonomous operation of replicate flow-through sediment columns in a realistic aquifer setting. Computer-aided design (CAD), rapid prototyping, and computer numerical control (CNC) machining were used to create a tubular device enabling practitioners to conduct conventional sediment column studies in situ. A case study where two remediation strategies, monitored natural attenuation and bioaugmentation with concomitant biostimulation, were evaluated in the laboratory and in situ at a perchlorate-contaminated site. Findings demonstrate the feasibility of evaluating anaerobic bioremediation in a moderately aerobic aquifer. They further highlight the possibility of mimicking in situ remediation strategies on the small-scale in situ. The ISMA is the first device offering autonomous in situ operation of conventional flow-through sediment microcosms and producing statistically significant data through the use of multiple replicates. With its sustainable approach to treatability testing and data gathering, the ISMA represents a versatile addition to the toolbox of scientists and engineers.Dissertation/ThesisPh.D. Civil and Environmental Engineering 201

Development and evaluation of models for assessing geochemical pollution sources with multiple reactive chemical species for sustainable use of aquifer systems: source characterization and monitoring network design

Michael designed a groundwater flow and reactive transport optimization model. He applied this model to characterize contaminant sources in Australia's first large scale uranium mine site in the Northern Territory. He identified the contamination sources to the groundwater system in the area. His findings will assist planning actions and steps needed to implement the mitigation strategy of this contaminated aquifer

Microbial ecology and biodegradation potential of a sulfolane-contaminated, subarctic aquifer

Thesis (Ph.D.) University of Alaska Fairbanks, 2019Contaminant biodegradation is one of many ecosystem services aquifer microbiota can provide to humans. Sulfolane is a water-soluble emerging contaminant that is associated with one of the largest contaminated groundwater plumes in the state of Alaska. Despite being widely used, the biodegradation pathways and environmental fate of sulfolane are poorly understood. In this study, we investigated the biodegradation of sulfolane by the microbial community indigenous to this contaminated subarctic aquifer in order to better understand the mechanisms and rates of loss, as well as the environmental factors controlling them. First, we conducted aerobic and anaerobic microcosm studies to assess the biodegradation potential of contaminated subarctic aquifer substrate and concluded that the aquifer microbial community can readily metabolize sulfolane, but only in the presence of oxygen, which is at low concentration in situ. We also investigated the impacts of nutrient limitations and hydrocarbon co-contamination on sulfolane biodegradation rates. To identify exactly which community members were actively degrading sulfolane, we combined DNA-based stable isotope probing (SIP) with genome-resolved metagenomics methods. We found a Rhodoferax sp. to be the primary sulfolane degrading microorganism in this system and obtained a near-complete genomic sequence of this organism, which allowed us to propose a new metabolic model for sulfolane biodegradation. Finally, we assessed the distribution of sulfolane-degrading bacteria throughout the contaminated subarctic aquifer by sequencing 16S rRNA genes from 100 groundwater samples and two sulfolane treatment systems and screening for the sulfolane degrader previously identified using SIP. This assessment revealed that sulfolane biodegradation potential is widespread throughout the aquifer but is not likely occurring under normal conditions. However, the sulfolane-metabolizing Rhodoferax sp. was the most dominant microbe in an effective experimental air-sparge system, suggesting that injecting air into the aquifer can stimulate sulfolane biodegradation in situ. These studies are the first to investigate sulfolane biodegradation potential in a subarctic aquifer. Through this work, we learn there are several important factors limiting biodegradation rates, we expand the known taxonomic distribution of sulfolane biodegradation, and we shed insights into the mechanisms underlying an effective in situ sulfolane remediation system.Alaska Department of Environmental Conservation and an Institutional Development Award (IDeA) from the National Institute of General Medical Sciences of the National Institutes of Health under grant number P20GM10339

Modeling long term Enhanced in situ Biodenitrification and induced heterogeneity in column experiments under different feeding strategies

Enhanced In situ Biodenitrification (EIB) is a capable technology for nitrate removal in subsurface water resources. Optimizing the performance of EIB implies devising an appropriate feeding strategy involving two design parameters: carbon injection frequency and C:N ratio of the organic substrate nitrate mixture. Here we model data on the spatial and temporal evolution of nitrate (up to 1.2 mM), organic carbon (ethanol), and biomass measured during a 342 day-long laboratory column experiment (published in Vidal-Gavilan et al., 2014). Effective porosity was 3% lower and dispersivity had a sevenfold increase at the end of the experiment as compared to those at the beginning. These changes in transport parameters were attributed to the development of a biofilm. A reactive transport model explored the EIB performance in response to daily and weekly feeding strategies. The latter resulted in significant temporal variation in nitrate and ethanol concentrations at the outlet of the column. On the contrary, a daily feeding strategy resulted in quite stable and low concentrations at the outlet and complete denitrification. At intermediate times (six months of experiment), it was possible to reduce the carbon load and consequently the C:N ratio (from 2.5 to 1), partly because biomass decay acted as endogenous carbon to respiration, keeping the denitrification rates, and partly due to the induced dispersivity caused by the well developed biofilm, resulting in enhancement of mixing between the ethanol and nitrate and the corresponding improvement of denitrification rates. The inclusion of a dual-domain model improved the fit at the last days of the experiment as well as in the tracer test performed at day 342, demonstrating a potential transition to anomalous transport that may be caused by the development of biofilm. This modeling work is a step forward to devising optimal injection conditions and substrate rates to enhance EIB performance by minimizing the overall supply of electron donor, and thus the cost of the remediation strategy.Peer ReviewedPostprint (author's final draft

Geochemical reactivity of subsurface sediments as potential buffer to anthropogenic inputs: a strategy for regional characterization in the Netherlands

Geochemical reactivity of subsurface sediments as potential buffer to anthropogenic inputs: a strategy for regional characterization in the Netherland