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Research Projects

 

 
 

Transport and Retention of Nanoparticles in Saturated and Unsaturated Soils
Widespread production and application of nanomaterials is expected to increase dramatically over the next decade. Increases in production and dissemination will inevitably lead to the release of nanoscale particles into the environment, either from industrial sources or through disposal in municipal waste. The current understanding of nanomaterial fate and transport in subsurface environments is quite limited.  For example, knowledge of how nanoparticles interact with soil matrices must be expanded in order to mechanistically assess whether or not the transport of these materials in the saturated zone may be modeled using classic colloid filtration theory.  Because pathways for contamination of aquifers typically include migration through variably saturated soils, it is also important to understand the migration of nanoparticles under unsaturated soil conditions. Research in the IMPES laboratory is focused on developing mathematical models to predict the transport behavior of nanoparticles under both saturated and unsaturated conditions. 

 
     
 

Encapsulation of Active Ingredients Employed in Subsurface Remediation using Oil-in-Water Emulsions
Considerable emphasis is now being placed on delivery of remedial amendments within the contaminanted subsurface environment. In situ transformation of contaminants requires that the limiting reagent (e.g., iron metal in abiotic reductive dechlorination or electron donor in metabolic reductive dechlorination) be co-located with the contaminant mass.  Poor delivery (i.e., an inability to co-locate contaminant and amendment) causes technologies to fail in reducing contaminant concentrations.  In addition, controled release of amendments (e.g., alkalinity) may be necessary to maintain the local transformation of contaminants. Encapsulation of the remedial amendments within oil-in-water emulsions is a novel approach that may facilitate delivery and release while minimizing non-target reactions. Research in the IMPES laboratory is focused on developing kinetically stable oil-in-water emulsions that may serve as delivery vehicles for active ingredients.  While stability of the emulsion encapsulants is necessary, it is not a sufficient condition for application.  Thus, IMPES laboratory research also aims to develop constitutive relationships associated with the influence of emulsion rheology and interfacial processes on droplet transport and amendment release.   

 
     
 

Fate of Pharmaceuticals during Nitrification
Reduction of nutrient discharges is a priority for the environmental engineering and science community.  The community is, however, also being asked to address the potential threats posed by emerging contaminants in the aquatic environment.  Pharmaceuticals are particularly concerning emerging contaminants given the explosion in development and use of these chemicals over the last 30 years.  Interestingly, studies suggest that pharmaceuticals may be better removed in wastewater treatment plants that are designed to meet stringent regulations on nutrient discharge.  The potential synergy between nutrient control and microconstituent attenuation motivates specific emphasis on understanding biotransformation of pharmaceuticals by nitrifying organisms. We aim to elucidate rates and metabolites of pharmaceutical attenuation by nitrifying organisms in order to develop modeling tools that can predict pharmaceutical degradation within the context of enhanced nutrient removal.

 
     
 

Managed Underground Storage - Understanding Fate and Transport of Emerging Contaminants through the Water Reuse Process
The influence of anthropogenic chemical mixtures present within the environment at low concentration is one of the great challenges facing water scientists and engineers in the 21st century.  This challenge is amplified by the increasing importance of water reuse in satisfying growth in water demand.   Managed underground storage is becoming an important aspect of water reuse.  Yet, the current status of scientific knowledge is insufficient to determine the implications – to the certainty necessary to preserve human and ecosystem health – of recharging aquifers with water containing low concentrations of pharmaceuticals.  The 2008 National Research Council report on managed underground storage highlights the need to develop science-based criteria for proper stewardship of groundwater resources through the water reuse process.  We aim to aid the establishment of these science based criteria by understanding of the coupled physical, chemical and biological processes controlling the transport of low concentration mixtures comprising compounds of emerging concern.  

 
     
 
Mechanisms Controlling Emulsion Transport within Porous Media
Emulsion-based technologies hold great promise for localized delivery of remedial amendments within the subsurface environment.  Perhaps the most important aspect in implementing emulsion-based remedial technologies relates to transport of the oil droplets.  A number of studies report either effective or ineffective (pore clogging) emulsion transport through various media of differing permeability. Research in the IMPES laboratory is aimed at elucidating the mechanisms responsible for the disparity in observed behaviors.  With respect to delivery of remedial amendments, transport of the emulsion encapsulants is but one aspect requiring investigation.  Research efforts also seek to mechanistically describe those interactions between emulsion droplets and entrapped NAPL that permit targeted delivery within the subsurface environment.  Experiments at the pore and continuum scales are employed to develop and validate constitutive relationships implemented within multiphase compositional simulators.    
 
     
 
Development and Application of Mathematical Models to Quantify Dechlorination in DNAPL Source Zones
Recent laboratory studies have demonstrated that even without the use of aggressive mass removal technologies, metabolic reductive dechlorination within DNAPL source zones may enhance contaminant dissolution and decrease source longevity.  Research under this project is directed at incorporating metabolic reductive dechlorination kinetics into an existing multiphase, compositional simulator (MISER) so that the refined model may be used to systematically evaluate and rigorously quantify the benefits of metabolic reductive dechlorination on source-zone concentrations, mass flux, and source longevity.  These investigations are important for: (i) improving the fundamental understanding of the effects of metabolic reductive dechlorination on a source zone at the field-scale; (ii) developing guidance for determining when source zone bioremediation may be beneficial, and (iii) optimizing site-specific implementation strategies for source-zone bioremediation. 
 
     
 
Fate and Transport of Reductive Dechlorination Products within DNAPL Source Zones
Reactive technologies aimed at cleaning up aquifers contaminated by nonaqueous phase liquids frequently produce multiple degradation products which may or may not represent an overall reduction of the risk posed to human health.  Understanding the fate and transport of these degradation products within a multiphase subsurface environment is critical given the interest in applying enhanced dissolution for remediation of sites contaminated by chlorinated solvent NAPLs.  Assessing the fate and transport of degradation products in multifluid subsurface environments requires knowledge of the interplay between physical, chemical, and biological processes.  At the center of this interplay is availability of degradation products influencing contaminant fate. Availability is influenced by the kinetics of mass transfer processes active in multiphase subsurface environments.  This research project integrates laboratory experiments and mathematical modeling to explore how kinetics of interphase mass transfer influences rates of degradation and degradation product accumulation in NAPL source zones containing chloroethenes.  
 
     
 

Utilization of Upscaled Mass Transfer Coefficients for Estimation of DNAPL Source-Zone Mass Discharge
The difficulty in characterizing NAPL source-zone architecture at the field-scale, coupled with the computational cost of numerical field-scale dissolution simulations for heterogeneous source-zones, has motivated the development of simplified modeling approaches which utilize “upscaled” parameters to account for the effect of spatial variations in NAPL saturations on source-zone mass discharge.  Upscaled modeling methods typically incorporate rate-limitations resulting from flow by-passing and irregular saturation distributions using a single, lumped, upscaled mass transfer coefficient.  Employment of a single, upscaled mass transfer coefficient enables the prediction of source-zone mass discharge and source longevity using simple analytic solutions to the contaminant transport equation.  Research in the IMPES laboratory is evaluating the utility of these conceptually attractive, upscaled models for prediction of mass discharge from nonuniform, three-dimensional dense NAPL source-zones.  

 
     
 

Development and Evaluation of Protocols which Reduce the Uncertainty in Estimates of Mass Discharge
Mass flux emanating from contaminant source areas in aquifer environments, both prior and subsequent to remediation activity, is strongly influenced by the presence of aquifer heterogenenity across a variety of scales.  Research in the IMPES laboratory is using 3-D numerical simulations of DNAPL source zones and discharge data collected from field sites to develop and evaluate sampling protocols designed to quantify and estimate the uncertainty of near source zone contaminant discharge.  Enhanced sampling protocols will permit intelligent stagewise sampling and facilitate more accurate assessment of the benefits of source-zone treatment.

 
     
 
Refinement and Simulation of the Density Modified Displacement Method for Efficient Treatment of DNAPL Source Zones
The density modified displacement method is an innovative remediation technology which provides efficient recovery of DNAPLs while mitigating the risks associated with downward DNAPL migration.  The DMD method can be envisioned as a two step process.  Initially, in situ alcohol partitioning results in the conversion of DNAPL into LNAPL (click here for TCE-NAPL time lapse).  A subsequent displacement flood with a low-interfacial tension surfactant solution provides for recovery of the mobilized free-product LNAPL (click here for TCE-NAPL time lapse).  Inherent to the DMD process are  thermodynamic considerations which control alcohol partitioning, surfactant phase behavior, and interfacial tension reduction.    Research in the IMPES laboratory is focused on refinement of the DMD process for potential application at the pilot-scale and simulation of the spatially and temporally varying solute-dependent interfacial processes occurring during the DMD method.  
 
     
 
Development and Laboratory Validation of a Multicomponent Reactive Transport Model for Prediction of the Performance of Permeable Reactive Barriers
This project entails modeling the transformation of arsenic and cadmium species in an iron sulfide barrier system. While knowledge of the detailed thermodynamic and kinetic descriptions allow contaminant reduction, mineral precipitation/dissolution, and parent and product species transport to be incorporated within the model, variations in chemical and physical conditions within a barrier often exacerbate the difficulties associated with accurate simulation of barrier effectiveness.  Thus, model development is also focused on including natural alterations to the barrier chemistry and porosity.  Application of the model will facilitate more robust designs for permeable reactive barriers designed to treat heavy metal contaminated groundwater.  
 
     

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