DNAPL Research Articles

Accumulation of DNAPL waste in subsurface clayey lenses and layers

Chlorinated solvents like trichloroethylene (TCE) and tetrachloroethylene (PCE) are prevalent groundwater contaminants being detected more than half of the Superfund Sites. They are introduced into the subsurface due to improper disposal of hazardous wastes containing these chlorinated dense non-aqueous phase liquids (DNAPL). DNAPL wastes sink in the subsurface and form pools on clay layers. Further transport into the underlying clay layer is dominated by diffusion due to the low permeability of these soils and results in accumulation of contaminants therein overtime through diffusion. However, field evidence reported that mass storage of solvents in such zones was higher than what can be attributed to simple diffusion. To evaluate this finding, mass storage of TCE in a hypothetical aquitard after 30 years of diffusion was calculated. The diffusion coefficient reported in the field study resulted in mass storage of 137.7 g in this hypothetical aquitard whereas the mass calculated using the measured diffusion coefficient of TCE from pure solvent into water-saturated clayey soil was 25–65% of it (35.0–89.4 g). The calculated mass storage was even lower (8.2 g) if the measured diffusion coefficient of TCE from DNAPL waste into waste-contacted soil was used. So, mass of TCE accumulated through sole diffusion was not able to explain the one observed in the field. This excess mass in the field might be the mass of DNAPL entered into the cracks which were reported to form in clay layers as a result of the direct contact between water saturated clay and DNAPL waste. Mass of TCE in the cracks was calculated using reported average crack size and an assumed crack depth, and it appeared that cracks filled with DNAPL could increase the stored mass up to a minimum of 334 g which could easily account for the enhanced mass storage observed in the field.

Quantification of Uncertainties from Image Processing and Analysis in Laboratory-Scale DNAPL Release Studies Evaluated by Reflective Optical Imaging

Subsurface DNAPL (dense non-aqueous phase liquid) contamination from (un-) intentional spilling typically leads to severe environmental hazards. A large number of studies have demonstrated the relevance of DNAPL source zone geometry for the determination of contaminant plume propagation in groundwater. Optical imaging represents a promising non-invasive method for identifying DNAPL saturation without disturbing multiphase flow dynamics. However, workflow and image analysis methodologies have not been sufficiently developed or described for general application to related experimental efforts. For example, the choice of dye(s) used for phase colorization affects image processing and can bias final estimations of DNAPL saturations. In this study, we perform a series of DNAPL migration and entrapment studies in transparent tanks that are filled with three different types of porous media. Different dyes are used and raw images are acquired. Subsequently, these are used to evaluate a suite of image processing and analysis approaches, which are organized into a workflow. Our approach allows for us to identify key image processing and analysis steps that introduce the most error. Applicable dye configurations led to uncertainties of up to 41% depending on the selection of processing steps. Based on these findings, it was possible to delineate a flexible framework for image processing and analysis that has the potential for transfer and application in other tank experiment setups.

Soil and Groundwater Pollution Assessment and Delineation of Intensity Risk Map in Sulaymaniyah City, NE of Iraq

Groundwater and soil pollution caused by (PAHs) spills, mostly from the oil industry and petrol stations in urban areas, represent a major environmental concern worldwide. However, infiltration into groundwater is decreasing due to the natural attenuation processes of PAHs in the vadose zone, which protect invaluable groundwater resources against contamination. This study was conducted to evaluate the effect of improper management of the petroleum industry on the groundwater and soil surrounding the petrol station and an oil refinery unit and, furthermore, to prepare the polluted risk intensity (PRI) map. Fifty-one soil samples and twenty-five water samples were analyzed for Light Non-aqueous Phase Liquid (LNAPLs), and one soil sample for Dense Non-Aqueous Phase Liquid (DNAPLs); furthermore, six soil samples analyzed for Tetraethyl Lead (TEL) analysis. The results showed that seventeen wells were polluted with LNAPLs and the soils were highly contaminated with different DNAPLs components and mainly was in the form of Polycyclic Aromatic Hydrocarbons (PAHs). Seven factors introduced to the GIS platform to produce PRI map, which is the distance to source, depth to water table, slope, lineaments, lithology, soil, and recharge rate. The final map revealed that the eastern and western parts of the study area are at a very high-risk level, whereas the center is at a very low to low-risk level.

Online surrogate multiobjective optimization algorithm for contaminated groundwater remediation designs

This paper proposes an online surrogate model-assisted multiobjective optimization framework to identify optimal remediation strategies for groundwater contaminated with dense non-aqueous phase liquids. The optimization involves three objectives: minimizing the remediation cost and duration and maximizing the contamination removal rate. The proposed framework adopts a multiobjective feasibility-enhanced particle swarm optimization algorithm to solve the optimization model and uses an online surrogate model as a substitute for the time-consuming multiphase flow model for calculating contamination removal rates during the optimization process. The resulting approach allows decision makers to find a balance among the remediation cost, remediation duration and contamination removal rate for remediating contaminated groundwater. The new algorithm is compared with the nondominated sorting genetic algorithm II, which is an extensively applied and well-known algorithm. The results show that the Pareto solutions obtained by the new algorithm have greater diversity and stability than those obtained by the nondominated sorting genetic algorithm II, indicating that the new algorithm is more applicable than the nondominated sorting genetic algorithm II for optimizing remediation strategies for contaminated groundwater. Additionally, the surrogate model and Pareto optimal set obtained by the proposed framework are compared with those of the offline surrogate model-assisted multiobjective optimization framework. The results indicate that the surrogate model accuracy and Pareto front achieved by the proposed framework outperform those of the offline surrogate model-assisted optimization framework. Thus, we conclude that the proposed framework can effectively enhance the surrogate model accuracy and further extend the comprehensive performance of Pareto solutions.

Mechanisms of mass transfer enhancement by phase-transfer catalysis for permanganate oxidizing dense non-aqueous phase liquid (DNAPL) TCE

Phase transfer catalysts (PTCs) have been shown to be effective in lowering the limitation of mass transfer between aqueous oxidant MnO4− and NAPLs in in-situ chemical oxidation (ISCO) technologies for remediation of NAPLs. This work researched the effects of pentyltriphenylphosphonium bromide (PTPP, used as the representative PTC) for the enhancement of TCE oxidation, the extent of different treatment effects contributions and generalizability of phase transfer. Experimental results revealed that MnO4− exchanged with Br− in PTPP by ion exchange mechanism and then transferred to NAPL phase due to biphasic nature of PTPP-MnO4-. PTPP enhanced TCE dissolution in aqueous phase but had no significant effect on TCE solubilization. Enhanced TCE dissolution gradually weakened after 2.0 h and disappeared after 5.5 h, while the percentage of MnO4− in phase transfer was 14.8% at 7.5 h, which indicated that dissolution acceleration was only effective at initial stage of reaction (0–2.5 h). Therefore, persistent phase transfer process played the leading role in TCE remediation enhancement. Moreover, for different NAPL phase, more effective phase transfer could be achieved in NAPLs with higher solubility and weaker hydrophobicity. The best-fit polynomial relationship (R2 = 0.992) existed between the percentage amount of MnO4− transferred and the solubility of NAPL.

Partitioning of chlorinated organic compounds from dense non-aqueous phase liquids and contaminated soils from lindane production wastes to the aqueous phase

Hexachlorocyclohexane (HCH) and mainly the γ-HCH isomer, namely lindane, were extensively produced and used as pesticides. Huge amounts of wastes, solids and liquids, were disposed of in the surroundings of the production sites. The liquid residuum was a complex mixture of chlorinated organic compounds, COCs, from chlorobenzene to heptachlorocyclohexane. This Dense Non-Aqueous Phase Liquid, DNAPL, migrated by density through the subsurface to greater depths, being trapped or adsorbed into the soil in this movement posing a significant risk to the groundwater. Knowledge of the partitioning in water of COCs in DNAPL is a key issue to determine its fate in the environment. However, there are no data in literature for the partitioning and/or solubility of many of the COCs in this DNAPL, such as pentachlorocyclohexene, hexachlorocyclohexene and heptachlorocyclohexane despite them constitute about 13–30% of the mole fraction of the DNAPLs. In this work, the partitioning to water of COCs in free and those adsorbed onto soil has been studied. In addition, measured and predicted aqueous concentrations of each COC in the DNAPL mixture have been compared. To do this, the solubility of a compound that is a solid crystal when pure at P = 298 K and P = 1 atm has been evaluated considering the approach of sub-cooled liquid state of solid organochlorines. Samples were obtained at Sabiñanigo landfills and soils used had several grain sizes. Transformation in alkaline media of COCs had a positive environmental impact.

Hydrogeochemical Model Supporting the Remediation Strategy of a Highly Contaminated Industrial Site

Delineation and understanding the geology and the hydrogeology of a contaminated site, considering its chemical and its biological aspects, are fundamental requirements for successful environmental remediation. The aim of this research is to provide some evidence about the effectiveness of a hydrogeochemical geodatabase to facilitate the integrated management, representation and analysis of heterogeneous data, enabling the appropriate selection, design and optimization of an effective remediation strategy. This study investigates a new technology for the remediation of a dense non-aqueous phase liquid aged source zone, with the aim of enhancing in situ bioremediation by coupling groundwater circulation wells with a continuous production system of electron donors. The technology was verified through a pilot test carried out at an industrial site highly contaminated by chlorinated aliphatic hydrocarbons. The multidisciplinary conceptual model confirmed a complex hydrogeological situation, with the occurrence of active residual sources in low permeability layers. The pilot test results clearly demonstrate a significant mobilization of contaminants from the low permeability zone, and the possibility of favoring the in situ natural attenuation mechanisms based upon biological reductive dechlorination. Different information related to the hydrogeochemical sphere must be integrated and taken into consideration when developing a reliable remediation strategy for contaminated sites.

Long-term mass flux assessment of a DNAPL source area treated using bioremediation

This study assessed the long-term effectiveness of bioremediation as a remedial strategy for a chlorinated, ethene dense, non-aqueous phase liquid (DNAPL) source area, consisting of a higher- and a lower-permeability zone at Alameda Point, California. The evaluation was performed over 3.7 years after cessation of active source area bioremediation using passive flux meters (PFMs), push-pull tracer tests, and soil cores. PFMs showed that total chlorinated ethene molar discharge emanating from the source area remained relatively unchanged pre-and post-bioremediation, but molar discharge compositions shifted from trichloroethene (TCE) and cis-1,2-dichloroethene (cis-DCE) to vinyl chloride (VC) and ethene dominated during post-remedial monitoring. First-order rate constants, derived from PFM data at the edge of the source area and describing the complete dechlorination of TCE at 3.7 years following active bioremediation, were approximately 1.05 yr−1, which was over three times lower than the rate 3.6 yr−1 determined using compound stable isotope analysis (CSIA). Soil cores and push-pull tracer test data showed that DNAPL volume estimates were relatively unchanged pre- and post-bioremediation due to the remaining presence of DNAPL in the lower-permeability zone. These data suggest biotransformation processes are continuing in the higher-permeability zone, whereas DNAPL in the lower-permeability zone continues to serve as a significant source of groundwater contamination. The results suggest that it will take many years under current conditions to attain the United States Environmental Protection Agency (EPA) Maximum Contaminant Levels (MCLs) cleanup objectives.

Experiments and sensitivity coefficients analysis for multiphase flow model calibration of enhanced DNAPL dissolution

Multiphase flow modeling is often used for the comparison and optimization of subsurface nonaqueous phase liquid (NAPL) remediation schemes. The calibration of such models is a challenging task due to the lack of detailed data describing the initial NAPL spatial distribution and the processes governing the fate and transport of NAPLs in porous media. In this study laboratory scale experiments were conducted to evaluate reagent-enhanced dense nonaqueous phase liquid (DNAPL) solubilization in saturated heterogeneous media. The DNAPL consisted of both pooled and residual saturation forms. To gain insight into the influence of various input parameters on effluent concentrations, the multiphase flow program was used to compute the sensitivity coefficients of key parameters, relating to the flow, flushing solution properties, soil parameters, NAPL distribution and mass transfer coefficient. The sensitivity coefficients were, in turn, used to aid in the model calibration and to underline the difficulties associated with the calibration of multiphase flow models, most notably the non-uniqueness of the calibration process when complete information is lacking. To alleviate this uncertainty and provide additional constraints, the conducted flushing experiments were jointly used to calibrate the multiphase flow model. The results of the model calibration suggest that the interphase mass transfer coefficient is dependent on the properties of the reagent aqueous solution used for DNAPL remediation, most notably the viscosity and interfacial tension.

Characterizing scales of hydrogeological heterogeneity in ice-marginal sediments in Wisconsin, USA

Creating a geological framework for hydrogeological investigations in ice-marginal settings is challenging, as the dynamic nature of ice margins results in heterogeneous sediments and complex geometries that are difficult to characterize geologically and hydraulically. In this study, a multi-scale and multi-tool approach was used to develop a robust and hydraulically calibrated conceptual model of a site in Wisconsin (USA), which constrains the subsurface geologic and hydraulic heterogeneity onsite and can be utilized offsite and in similar settings. Facies analysis, including detailed logging of sediment cores integrated with geophysical surveys, was used to reconstruct the glacial history of the site and to identify key sedimentation styles. Depth-discrete multilevel monitoring wells were used to measure hydraulic head and to explore the relationship between hydraulic conditions and stratigraphy. Results indicate that hydraulic and geological heterogeneity do not necessarily coincide, as hydraulic head profiles of the heterogeneous sediments showed little head change with depth. The minimal observed hydraulic heterogeneity in this complex geologic system is likely due to relatively small and spatially limited differences in hydraulic conductivities, limited water-table relief, and minimal natural or induced transience to enhance local head differentials. Hydraulic data were also used to provide new insights on the style and scale of geologic heterogeneity known to influence permeability within ice-marginal sediments; this is especially relevant at the study site where fine-scale bedding (millimeters to tens of centimeters scale) and lateral continuity of units (meters to hundreds of meters scale) influence water recharge and dense nonaqueous phase liquids migration and distribution.

One-at-a-time sensitivity analysis of pollutant loadings to subsurface properties for the assessment of soil and groundwater pollution potential.

Chemical leak was numerically simulated for four chemical substances: benzene (light non-aqueous phase liquid (NAPL)), tetrachloroethylene (dense NAPL), phenol (soluble in water), and pentachlorophenol (white crystalline solid) in a hypothetical subsurface leak situation using a multiphase compositional transport model. One metric ton of chemical substances was assumed to leak at a point 3.51m above the water table in a homogeneous unconfined aquifer which had the depth to water table of 7.135m, the hydraulic gradient of 0.00097, the recharge rate of 0.7mm/day, and the permeability of 2.92 × 10-10m2. For comparison, surface spill scenarios, which had a long pathway from source to the water table, were simulated. Using the model results, point-source pollutant loadings to soil and groundwater were calculated by multiplying mass, impact area, and duration above and below the water table respectively. Their sensitivity to subsurface properties (depth to water table, recharge rate, porosity, organic carbon content, decay rate, hydraulic gradient, capillary pressure, relative permeability, permeability) was analyzed, with changing each parameter within acceptable ranges. The study result showed that the pollutant loading to groundwater was more sensitive to the subsurface properties than the pollutant loading to soil. Decay rate, groundwater depth, hydraulic gradient and porosity were influential to pollutant loadings. The impact of influential parameters on pollutant loadings was nonlinear. The dominant subsurface properties of pollution loadings (e.g., decay rate, groundwater depth, hydraulic gradient, and porosity for groundwater) also affect the vulnerability, and the subsurface pollutant loadings defined in this study are dependent on chemical properties as well, which indicates that the influential hydrogeological and physicochemical parameters to pollutant loadings can be used for pollution potential assessment. The contribution of this work is the suggestion that the sensitivity of pollutant loadings can be used for pollution potential assessment. Soil and groundwater pollution potential of chemicals are discussed altogether for leak scenarios. A physics-based model is used to understand the impact of subsurface properties on the fate and transport of chemicals above and below the water table, and consequently their impact on the pollutant loading to soil and groundwater.

The influences of ionic strength and permeability on DNAPLs representative elementary volume in porous media

Dense nonaqueous phase liquids (DNAPLs) have led to widely distributed groundwater contamination due to their widespread applications and accidental spills. To investigate influences of two factor-ionic strength and permeability on the representative elementary volume (REV) of DNAPL, four experiments are conducted in two-dimensional (2D) porous media to investigate perchloroethylene (PCE) migration and associated REVs. The permeability and ionic strength of four experiments are set as different schemes. PCE migration and REVs are estimated by moment analysis and the criteria of the relative gradient error (εgi). Results suggest that the permeability and ionic strength are of significant effects on REVs of PCE. Higher permeability of porous media can promote the vertical infiltrate rate of PCE in aquifer. Simultaneously, higher ionic strength can lower the second moments of PCE plume and increase the GTP of PCE mass. More importantly, higher permeability has increased the REV of PCE saturation (So) with absolute errors of 1.35 mm and 2.71 mm under conditions of low and high ionic strength. Besides, higher permeability has decreased the REV of PCE-water interfacial area (AOW) with absolute errors of 2.76 mm and 1.09 mm under conditions of low and high ionic strength. What’s more, ionic strength has no apparent effects on So-REV sizes when permeability is high (absolute error equals to 0.16 mm between low and high ionic strength). However, high ionic strength can decrease the minimum REV sizes of So when permeability is low (absolute error is 1.52 mm). Moreover, high ionic strength can increase minimum REV sizes of AOW with absolute errors of 1.49 mm and 1.01 mm under conditions of high and low permeability. These findings can improve the understanding of DNAPLs behaviors in subsurface environment under complex condition.

The fate of DNAPL contaminants in non-consolidated subsurface systems – Discussion on the relevance of effective source zone geometries for plume propagation

Dense non-aqueous phase liquids, i.e., DNAPLs and the evolving contaminant plumes in aquifers provide significant potential to pose hazards affecting both environment and human health. Therefore, a proper assessment of contaminant spreading within the subsurface is critical. This includes a sufficient characterization of governing parameters describing both the subsurface and the contaminant itself. Thereby, knowledge on the contaminant source zone and especially the source zone geometry, i.e., SZG is critically required, yet very uncertain. This study identifies current limitations and open research questions in the formation and shape determination of source zone geometry, as well as its relevance for contaminant plumes. Our literature review reveals that existing characterization methods are subject to data interpretation uncertainties, while the application of these methods on field scale is limited by technical demands and accompanied efforts. In a next step, methods to implement increased source zone information into calculation methods are discussed. By means of an exemplary application of selected assessment tools, i.e., plume response models, results clearly proof the relevance of SZGs for site assessment. However, existing plume response models consider over-simplified geometries that may compromise their suitability. Our findings identify the demand for improved characterization of complex SZGs and the need to better evaluate the dependency of DNAPL migration on system properties and external influences. With emphasized knowledge on the most relevant SZG features, the delineation of "effective" SZGs allowing for straightforward implementation into plume response models and an adaption of the latter to incorporate more information on SZGs should be possible.

Enhanced reductive dechlorination of trichloroethene in an acidic DNAPL impacted aquifer

A field pilot test was conducted using an emulsified vegetable oil (EVO) and colloidal magnesium hydroxide [Mg(OH)2] formulation to enhance reductive dechlorination of dense non-aqueous phase liquid (DNAPL) trichloroethene (TCE) in an acidic (pH < 4), heterogeneous aquifer. The field test consisted of i) a single well injection test to evaluate Mg(OH)2 distribution and ii) installation of two EVO-Mg(OH)2 permeable reactive barriers (PRBs; PRB-1 & PRB-2) at varying distances downgradient of the DNAPL source area. Distribution of Mg(OH)2 was observed up to 2.3 m away from the injection point within a permeable coarse sand layer; however, Mg(OH)2 transport in the overlying clayey-silty sand was minimal. Downgradient of the PRBs, colloidal Mg(OH)2 increased the pH of the coarse sand to levels appropriate for biological reductive dechlorination (pH >∼5); however, some settling of Mg(OH)2 in the injection wells generated persistent high pH (∼9–10) within the PRBs. A redesigned suspension of colloidal Mg(OH)2 was tested and proved to be more effective at raising aquifer pH without an excessive rise in pH within the PRBs. At PRB-1 (located closest to the DNAPL source area), limited TCE biodegradation was observed due to the influx of high TCE concentrations (up to 400 mg/L) and inhibition of dechlorinating bacteria. At PRB-2 (located 25 m downgradient of the DNAPL source area), TCE concentrations were much lower (13–26 mg/L) and production of cis-1,2-dichloroethene (cDCE) and some vinyl chloride (VC) was observed. Subsequent bioaugmentation with a commercial dechlorinating culture at PRB-2 improved conversion of cDCE to VC and ethene at downgradient monitoring wells over the duration of the study. These results emphasize the importance of PRB location (relative to the DNAPL source), base selection for pH adjustment, source strength, and local heterogeneities for the design and long-term performance of ERD in acidic DNAPL-impacted aquifers.

In-situ reductive degradation of chlorinated DNAPLs in contaminated groundwater using polyethyleneimine-modified zero-valent iron nanoparticles

Zero-valent iron nanoparticles (ZVIN) have found applications in many strategies for on-site soil and groundwater decontamination. A number of studies have reported the prospective utilization of ZVIN in the reduction of chlorinated organic compounds such as dense non-aqueous phase liquids (DNAPLs) in groundwater. Due to their bioaccumulation and carcinogenesis, DNAPLs in groundwater are a human health hazard and pose environmental risks. Therefore, decontamination of these contaminants is necessary. This study presents the in-situ remediation of trichloroethylene (TCE), perchloroethene (PCE), and 1,2-dichloroethene (1,2–DCE) DNAPLs through the direct injection of polyethylenimine (PEI)-coated ZVIN (PEI–ZVIN composite materials) to facilitate the reduction of contaminants in low-permeability media. A field test was conducted at the premises of a petrochemical company, situated in the Miaoli County of Northern Taiwan that discharged significant amounts of DNAPLs. After in-situ injection and one-day of reaction with groundwater contaminants, ZVIN was further characterized to examine its efficacy in the reduction of pollutants. After the direct injection of PEI–ZVIN, a notable reduction in the concentration of DNAPLs was recorded with conversion from toxic to non-toxic substances. Use of resistivity image profiling (RIP) technique suggested similar conductivity data for the PEI-coated ZVIN suspension and groundwater samples. X-ray absorption near edge structure (XANES) and X-ray absorption fine structure (EXAFS) studies depicted that the oxidation of ZVIN and PEI–ZVIN was occurring after the reductive reaction with contaminated groundwater. The reacted samples had bond distance values of 1.98, 2.00, 1.96, and 1.94 Å. Combining floating surface-coated ZVIN and RIP technique seems promising and environmentally attractive.

Application of Mixed-Integer Nonlinear Optimization Programming Based on Ensemble Surrogate Model for Dense Nonaqueous Phase Liquid Source Identification in Groundwater

Groundwater contamination source identification (GCSI) is critical for taking effective measures to protect groundwater resources, assess risks, mitigate disasters, and design remediation strategies. Simulation–optimization techniques have been effective tools for GCSI. However, previous studies have applied individual surrogate models when replacing simulation models, rather than making efforts to combine various methods to improve the approximation accuracy of the surrogate model over the simulation model. In this study, the kernel extreme learning machine (KELM) model was proposed to enhance the surrogate model, and to approach GCSI problems, especially those of dense nonaqueous phase liquid-contaminated aquifers, more effectively. In addition, a kriging model and a support vector regression (SVR) model were built and compared with the KELM model, and various ensemble surrogate (ES) modeling techniques were applied to establish four ES models. Results showed that the KELM model was more accurate than the kriging and SVR models; however, the ES models performed much better than the three individual surrogate models. The most precise ES model increased the certainty coefficient (R2) to 0.9837, whereas limiting the maximum relative error to 13.14%. Finally, a mixed-integer nonlinear programming optimization model was established to identify the groundwater contamination source in terms of location and release history, and simultaneously assess aquifer parameters. The ES model developed in this article could reasonably predict the system response under given operation conditions. Replacement of the simulation model by the ES model considerably reduced the computation burden of the simulation–optimization process and simultaneously achieved high computation accuracy.

Method Development for DNA and Proteome SIP Analysis of Activated Sludge for Anaerobic Dichloromethane Biodegradation.

Dichloromethane (DCM) is a toxic, dense non-aqueous phase liquid (DNAPL) that pollutes groundwater in all industrialized countries. Fortunately, DCM can be used as the sole source of energy and organic carbon by anaerobic microorganisms and be transformed to benign end products such as acetate, formate, and bicarbonate. However, knowledge around the phylogenetic diversity of anaerobic microorganisms capable of DCM metabolism is limited. The genes and enzymes involved and details of the reaction mechanism are not known. Stable isotope probing (SIP) is a technique used to identify microbes involved in assimilation of elements. The isotopically labeled substrate can be recovered in DNA and protein (i.e., DNA-SIP and protein-SIP) which enables identification of both the microbial taxa and their respective proteins involved in the substrate degradation. Therefore, by applying a combination of SIP techniques with molecular approaches (i.e., Illumina Miseq sequencing and metaproteomics), DCM degrading organisms can be identified and characterized in a manner independent of anaerobic enrichment cultures. In our research, activated sludge from wastewater treatment plant was fed with unlabeled and 13C-labeled DCM, respectively. Here, we provide protocols and technical notes for DNA and protein extraction from activated sludge and present analysis pipelines for downstream molecular techniques.

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.

The Human Health Risk Assessment Based on Process Simulation and Uncertainty Analysis

Water resource is an important part of human living and production. With the modernization of cities, the problem of groundwater contamination is becoming more and more serious. It is outstanding to effectively assess the risk of groundwater contamination to human health. This paper proposes a human health risk assessment method based on the simulation of contaminant transport process and parameter uncertainty analysis. The method combines health risk assessment with groundwater contaminant transport processes and applies the TOUGH2 program to simulate the temporal and spatial distribution of contaminant in groundwater. In order to improve the accuracy of the assessment results, the influence of the uncertainty of the transport model on human health risk assessment is taken into account. And the key parameter (e.g., the permeability) of the transport model is inversed by Markov chain Monte Carlo simulation method. Based on a sandbox experiment, the human health risk exposed to a typical dense non-aqueous phase liquids contaminant tetrachloroethylene (PCE) is evaluated by considering the parameter uncertainty of the PCE transport model, which confirmed that the method can provide decision-making information for the management and prevention of contaminated sites.

Experimental and Numerical Modeling of DNAPL Mass Discharge from the Elliptic Pool in Saturated Homogeneous Sandy Soil

"The present study aims to study the dissolution and mass transport of trichloroethylene (TCE) as Dense Non Aqueous Phase Liquid (DNAPL) in saturated porous media." A rectangular Perspex tank of internal dimensions (150cm length 20cm width and 40 cm height) used to represent the model aquifer. The tank was packed with homogenous soil (Karbala sand)"."Unidirectional flow at five different interstitial velocities (0.9, 1.8, 2.34, 2.7, and 3.6) cm/hr assumed to study the process. The average mass transfer coefficient" was determined for each velocity .Their values were increased with increasing the velocity reaching a limit value" .A conservative tracer is used to obtain the longitudinal and transverse aquifer dispersivities"."An elliptic shape of (TCE) pool was used to carry out the dissolution processes. Steady state dissolved (TCE) concentrations at downstream were collected from ten ports with two different depths under five interstitial velocities". Two linear relationships are created from an elliptic trichloroethylene pool: these relationships were between the average Peclet number in x-direction (Pe*x(e)) with the overall Sherwood number (Sh*(e )), and the other between the average Peclet number in y-direction (Pe*y(e) ) with the overall Sherwood number (Sh*(e))". A numerical modeling was achieved using COMSOL software.