Contaminant hydrology Research Papers - Academia.edu (original) (raw)

Supercritical fluid extraction with CO2 was applied to the analysis of traces of pendimethalin, a herbicide of the dinitroanilines group, in four different natural soils. The Supercritical Fluid Extraction (SFE) method was compared with... more

Supercritical fluid extraction with CO2 was applied to the analysis of traces of pendimethalin, a herbicide of the dinitroanilines group, in four different natural soils. The Supercritical Fluid Extraction (SFE) method was compared with the classical Soxhlet and shaking methods in terms of ease to run, extraction efficiency, selectivity and reproducibility. The influence of the physico-chemical properties of the soil matrix on herbicide extraction was then evaluated with the SFE method. The supercritical fluid extraction system used in the present study was found to be much easier to run than the other two methods, less time consuming and requires fewer operations as it was optimized for on-line sample clean up. SFE is the most selective of the three tested methods as fewer co-extracts are obtained in the final samples. SFE with CO2 is particularly powerful because pendimethalin is highly hydrophobic. However, this makes pendimethalin a poor choice for a selectivity study of SFE as it is very rapidly extracted at any CO2 density. Pendimethalin extraction with supercritical CO2 was found to be almost complete with average recoveries of 96–99%, similarly to Soxhlet but with a much lower standard deviation (8–10%). The performance of SFE was shown to be unaffected by soil parameters except soil water content. It is demonstrated indeed that extraction efficiency is not linearly related to soil water content, and optimal recovery was found for water contents ranging from 2 to 15% depending on the type of soil. Soil water increases extraction efficiency because water acts as a modifier of the supercritical fluid and increases the penetration of the fluid inside the soil particles (clay swelling). In contrast to SFE and Soxhlet, the efficiency of the shaking method appeared to be partial and strongly dependent on soil properties. Although initial developments should be needed, the various benefits of SFE-CO2 make this method attractive compared to traditional methods.

The application of a DC electric field down gradient to the contaminated zone in the subsurface can create an electrokinetic barrier. The electrical potential gradient causes the movement of ions which in turn imposes a viscous drag on... more

The application of a DC electric field down gradient to the contaminated zone in the subsurface can create an electrokinetic barrier. The electrical potential gradient causes the movement of ions which in turn imposes a viscous drag on the pore water. In clayey soils, this viscous drag can generate a high enough pore water pressure capable of counteracting the ground water gradient. This phenomenon can be used effectively as a barrier to prevent contaminant migration. A finite element model was developed to simulate the contaminant migration in soil under coupled hydraulic, electrical and chemical gradients. The model is also capable of predicting the associated changes in the soil like the pore water pressure, pH and voltage gradient as a function of time and distance from the electrode. This model was validated using the w experimental data presented by Yeung Yeung, A.T., 1990. Electro-kinetic barrier to contaminant x transport through compacted clay. PhD Thesis, University of California, Berkeley, 260 pp. . The results indicate very good agreement between the experimental and simulated results. The model predications show that when the anode is placed down gradient of the cathode, the cation migration could be completely arrested. However, the anions were found to move faster in the direction of the ground water flow and reduce the effectiveness of the barrier. This could be avoided by carefully designing the placement of the electrodes. If the contaminant of interest is either a cation or an anion, a simple double row of anode and cathode electrode arrangement could serve as an effective barrier. On the other hand, if the contaminant includes both anions and cations, then a triple-row configuration of electrodes need to be implemented. The model ) Corresponding author. 0169-7722r00r$ -see front matter q 2000 Elsevier Science B.V. All rights reserved.

This study shows that acidic and alkaline wastes co-disposed with uranium into subsurface sediments have significant impact on changes in uranium retardation, concentration, and mass during downward migration. For uranium co-disposal with... more

This study shows that acidic and alkaline wastes co-disposed with uranium into subsurface sediments have significant impact on changes in uranium retardation, concentration, and mass during downward migration. For uranium co-disposal with acidic wastes, significant rapid (i.e., hours) carbonate and slow (i.e., 100 s of hours) clay dissolution resulted, releasing significant sediment-associated uranium, but the extent of uranium release and mobility change was controlled by the acid mass added relative to the sediment proton adsorption capacity. Mineral dissolution in acidic solutions (pH 2) resulted in a rapid (b 10 h) increase in aqueous carbonate (with Ca 2+ , Mg 2+ ) and phosphate and a slow (100 s of hours) increase in silica, Al 3+ , and K + , likely from 2:1 clay dissolution. Infiltration of uranium with a strong acid resulted in significant shallow uranium mineral dissolution and deeper uranium precipitation (likely as phosphates and carbonates) with downward uranium migration of three times greater mass at a faster velocity relative to uranium infiltration in pH neutral groundwater. In contrast, mineral dissolution in an alkaline environment (pH 13) resulted in a rapid (b10 h) increase in carbonate, followed by a slow (10 s to 100 s of hours) increase in silica concentration, likely from montmorillonite, muscovite, and kaolinite dissolution. Infiltration of uranium with a strong base resulted in not only uranium-silicate precipitation (presumed Na-boltwoodite) but also desorption of natural uranium on the sediment due to the high ionic strength solution, or 60% greater mass with greater retardation compared with groundwater. Overall, these results show that acidic or alkaline co-contaminant disposal with uranium can result in complex depth-and time-dependent changes in uranium dissolution/precipitation reactions and uranium sorption, which alter the uranium migration mass, concentration, and velocity.

Landfill gas, originating from the anaerobic biodegradation of the organic content of waste, consists mainly of methane and carbon dioxide, with traces of volatile organic compounds. Pressure, concentration and temperature gradients that... more

Landfill gas, originating from the anaerobic biodegradation of the organic content of waste, consists mainly of methane and carbon dioxide, with traces of volatile organic compounds. Pressure, concentration and temperature gradients that develop within the landfill result in gas emissions to the atmosphere and in lateral migration through the surrounding soils. Environmental and safety issues associated with the landfill gas require control of off-site gas migration. The Ž numerical model TOUGH2-LGM Transport of Unsaturated Groundwater and Heat-Landfill Gas . Migration has been developed to simulate landfill gas production and migration processes within and beyond landfill boundaries. The model is derived from the general non-isothermal multiphase flow simulator TOUGH2, to which a new equation of state module is added. It simulates the Ž migration of five components in partially saturated media: four fluid components water, atmo-. Ž . spheric air, methane and carbon dioxide and one energy component heat . The four fluid components are present in both the gas and liquid phases. The model incorporates gas-liquid partitioning of all fluid components by means of dissolution and volatilization. In addition to advection in the gas and liquid phase, multi-component diffusion is simulated in the gas phase. The landfill gas production rate is proportional to the organic substrate and is modeled as an exponentially decreasing function of time. The model is applied to the Montreal's CESM landfill site, which is located in a former limestone rock quarry. Existing data were used to characterize hydraulic properties of the waste and the limestone. Gas recovery data at the site were used to define the gas production model. Simulations in one and two dimensions are presented to ) Corresponding author. Tel.: q1-418-654-2682; fax: q1-418-654-2615. Ž . Ž . E-mail addresses: mnastev@nrcan.gc.ca M. Nastev , rene.therrien@ggl.ulaval.ca R. Therrien , Ž . rlefebvre@inrs.uquebec.ca R. Lefebvre . 0169-7722r01r$ -see front matter q 2001 Elsevier Science B.V. All rights reserved.

Key attributes of the source zone and the expanding dissolved plume at a trichloroethene (TCE) site in Australia were evaluated using trends in groundwater monitoring data along with data from on-line volatile organic compound (VOC)... more

Key attributes of the source zone and the expanding dissolved plume at a trichloroethene (TCE) site in Australia were evaluated using trends in groundwater monitoring data along with data from on-line volatile organic compound (VOC) samplers and passive flux meters (PFMs) deployed in selected wells. These data indicate that: (1) residual TCE source mass in the saturated zone, estimated using two innovative techniques, is small (∼ 10 kg), which is also reflected in small source mass discharge (∼ 3 g/day); (2) the plume is disconnecting, based on TCE concentration contours and TCE fluxes in wells along a longitudinal transect; (3) there is minimal biodegradation, based on TCE mass discharge of ∼ 6 g/day at a plume control plane ∼ 175 m from source, which is also consistent with aerobic geochemical conditions observed in the plume; and (4) residual TCE in the vadose zone provides episodic inputs of TCE mass to the plume during infiltration/recharge events. TCE flux data also suggest that the small residual TCE source mass is present in the low-permeability zones, thus making source treatment difficult. Our analysis, based on a synthesis of the archived data and new data, suggests that source treatment is unwarranted, and that containment of the large TCE plume (∼ 1.2 km long, ∼ 0.3 km wide; 17 m deep; ∼ 2000-2500 kg TCE mass) or institutional controls, along with a long-term flux monitoring program, might be necessary. The flux-based site management approach outlined in this paper provides a novel way of looking beyond the complexities of groundwater contamination in heterogeneous domains, to make intelligent and informed site decisions based on strategic measurement of the appropriate metrics.

0169-7722r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved.

A large scale groundwater remediation project using pump-and-treat (PAT) or pump-treat-inject (PTI) cannot be designed as a single time-step operation, because of uncertainties associated with the system. The changes in concentrations in... more

A large scale groundwater remediation project using pump-and-treat (PAT) or pump-treat-inject (PTI) cannot be designed as a single time-step operation, because of uncertainties associated with the system. The changes in concentrations in reality may differ significantly from predicted ones. Instead, a multi-stage decision process is formulated and solved as a two-level hierarchical optimization model. Cost serves as the objective function,

Oxidation of metal sulfide minerals is responsible for the generation of acidic waters rich in sulfate and metals. When associated with the oxidation of sulfide ore mine waste deposits the resulting pore water is called acid mine drainage... more

Oxidation of metal sulfide minerals is responsible for the generation of acidic waters rich in sulfate and metals. When associated with the oxidation of sulfide ore mine waste deposits the resulting pore water is called acid mine drainage (AMD); AMD is a known environmental problem that affects surface and ground waters. Characterization of oxidation processes in-situ is challenging, particularly at the field scale. Geophysical techniques, spectral induced polarization (SIP) in particular, may provide a means of such investigation. We performed laboratory experiments to assess the sensitivity of the SIP method to the oxidation mechanisms of common sulfide minerals found in mine waste deposits, i.e., pyrite and pyrrhotite, when the primary oxidant agent is dissolved oxygen. We found that SIP parameters, e.g., phase shift, the imaginary component of electrical conductivity and total chargeability, decrease as the time of exposure to oxidation and oxidation degree increase. This observation suggests that dissolution-depletion of the mineral surface reduces the capacitive properties and polarizability of the sulfide minerals. However, small increases in the phase shift and imaginary conductivity do occur during oxidation. These transient increases appear to correlate with increases of soluble oxidizing products, e.g., Fe 2+ and Fe 3+ in solution; precipitation of secondary minerals and the formation of a passivating layer to oxidation coating the mineral surface may also contribute to these increases. In contrast, the real component of electrical conductivity associated with electrolytic, electronic and interfacial conductance is sensitive to changes in the pore fluid chemistry as a result of the soluble oxidation products released (Fe 2+ and Fe 3+ ), particularly for the case of pyrrhotite minerals.

The past decade has seen considerable progress in the development of models simulating pesticide transport in structured soils subject to preferential flow (PF). Most PF pesticide transport models are based on the two-region concept and... more

The past decade has seen considerable progress in the development of models simulating pesticide transport in structured soils subject to preferential flow (PF). Most PF pesticide transport models are based on the two-region concept and usually assume one (vertical) dimensional flow and transport. Stochastic parameter sets are sometimes used to account for the effects of spatial variability at the field scale. In the past decade, PF pesticide models were also coupled with Geographical Information Systems (GIS) and groundwater flow models for application at the catchment and larger regional scales. A review of PF pesticide model applications reveals that the principal difficulty of their application is still the appropriate parameterization of PF and pesticide processes. Experimental solution strategies involve improving measurement techniques and experimental designs. Model strategies aim at enhancing process descriptions, studying parameter sensitivity, uncertainty, inverse parameter identification, model calibration, and effects of spatial variability, as well as generating model emulators and databases. Model comparison studies demonstrated that, after calibration, PF pesticide models clearly outperform chromatographic models for structured soils. Considering nonlinear and kinetic sorption reactions further enhanced the pesticide transport description. However, inverse techniques combined with typically available experimental data are often limited in their ability to simultaneously identify parameters for describing PF, sorption, degradation and other processes. On the other hand, the predictive capacity of uncalibrated PF pesticide models currently allows at best an approximate (order-of-magnitude) estimation of concentrations. Moreover, models should target the entire soil-plant-atmosphere system, including often neglected above-ground processes such as pesticide volatilization, interception, sorption to plant residues, root uptake, and losses by runoff. The conclusions compile progress, problems, and future research choices for modelling pesticide displacement in structured soils.

NSO heterocycles (HET) are typical constituents of coal tars. However, HET are not yet routinely monitored, although HET are relatively toxic coal tar constituents. The main objectives of the study is therefore to review previous studies... more

NSO heterocycles (HET) are typical constituents of coal tars. However, HET are not yet routinely monitored, although HET are relatively toxic coal tar constituents. The main objectives of the study is therefore to review previous studies and to analyse HET at coal tar polluted sites in order to assess the relevance of HET as part of monitored natural attenuation (MNA) or any other long-term monitoring programme. Hence, natural attenuation of typical HET (indole, quinoline, carbazole, acridine, methylquinolines, thiophene, benzothiophene, dibenzothiophene, benzofuran, dibenzofuran, methylbenzofurans, dimethylbenzofurans and xanthene) were studied at three different field sites in Germany. Compound-specific plume lengths were determined for all main contaminant groups (BTEX, PAH and HET). The results show that the observed plume lengths are site-specific and are above 250 m, but less than 1000 m. The latter, i.e. the upper limit, however mainly depends on the level of investigation, the considered compound, the lowest measured concentration and/or the achieved compoundspecific detection limit and therefore cannot be unequivocally defined. All downstream contaminant plumes exhibited HET concentrations above typical PAH concentrations indicating that some HET are generally persistent towards biodegradation compared to other coal tar constituents, which results in comparatively increased field-derived half-lives of HET. Additionally, this study provides a review on physicochemical and toxicological parameters of HET. For three well investigated sites in Germany, the biodegradation of HET is quantified using the centre line method (CLM) for the evaluation of bulk attenuation rate constants. The results of the present and previous studies suggest that implementation of a comprehensive monitoring programme for heterocyclic aromatic compounds is relevant at sites, if MNA is considered in risk assessment and for remediation.

Ethanol (EtOH), an emerging contaminant with potential direct and indirect environmental effects, poses threats to water supplies when spilled in large volumes. A series of experiments was directed at understanding the electrical... more

Ethanol (EtOH), an emerging contaminant with potential direct and indirect environmental effects, poses threats to water supplies when spilled in large volumes. A series of experiments was directed at understanding the electrical geophysical signatures arising from groundwater contamination by ethanol. Conductivity measurements were performed at the laboratory scale on EtOH-water mixtures (0 to 0.97 v/v EtOH) and EtOH-salt solution mixtures (0 to 0.99 v/v EtOH) with and without a sand matrix using a conductivity probe and a four-electrode electrical measurement over the low frequency range (1-1000 Hz). A Lichtenecker-Rother (L-R) type mixing model was used to simulate electrical conductivity as a function of EtOH concentration in the mixture. For all three experimental treatments increasing EtOH concentration resulted in a decrease in measured conductivity magnitude (|σ|). The applied L-R model fitted the experimental data at concentration ≤0.4 v/v EtOH, presumably due to predominant and symmetric intermolecular (EtOH-water) interaction in the mixture. The deviation of the experimental |σ| data from the model prediction at higher EtOH concentrations may be associated with hydrophobic effects of EtOH-EtOH interactions in the mixture. The |σ| data presumably reflected changes in relative strength of the three types of interactions (water-water, EtOH-water, and EtOH-EtOH) occurring simultaneously in EtOH-water mixtures as the ratio of EtOH to water changed. No evidence of measurable polarization effects at the EtOH-water and EtOH-water-mineral interfaces over the investigated frequency range was found. Our results indicate the potential for using electrical measurements to characterize and monitor EtOH spills in the subsurface.

To examine colloid transport in geochemically heterogeneous porous media at a scale comparable to field experiments, we monitored the migration of silica-coated zirconia colloids in a two-dimensional layered porous media containing sand... more

To examine colloid transport in geochemically heterogeneous porous media at a scale comparable to field experiments, we monitored the migration of silica-coated zirconia colloids in a two-dimensional layered porous media containing sand coated to three different extents by ferric oxyhydroxides. Transport of the colloids was measured over 1.65 m and 95 days. Colloid transport was modeled by an advection -dispersion -deposition equation incorporating geochemical heterogeneity and colloid deposition dynamics (blocking). Geochemical heterogeneity was represented as favorable (ferric oxyhydroxide-coated) and unfavorable (uncoated sand) deposition surface areas. Blocking was modeled as random sequential adsorption (RSA). Release of deposited colloids was negligible. The time to colloid breakthrough after the onset of blocking increased with increasing ferric oxyhydroxide-coated surface area. As the ferric oxyhydroxide surface area increased, the concentration of colloids in the breakthrough decreased. Model-fits to the experimental data were made by inverse solutions to determine the fraction of surface area favorable for deposition and the deposition rate coefficients for the favorable (ferric oxyhydroxidecoated) and unfavorable sites. The favorable deposition rate coefficient was also calculated by colloid filtration theory. The model described the time to colloid breakthrough and the blocking effect reasonably well and estimated the favorable surface area fraction very well for the two layers with more than 1% ferric oxyhydroxide coating. If mica edges in the uncoated sand were considered as favorable surface area in addition to the ferric oxyhydroxide coatings, the model 0169-7722/02/$ -see front matter D (J.N. Ryan). www.elsevier.com/locate/jconhyd Journal of Contaminant Hydrology 65 (2003) 161 -182

An optimization methodology for designing groundwater quality monitoring networks applicable to stochastic flow fields is presented and evaluated. The approach sets itself apart from previous techniques by incorporating the time dimension... more

An optimization methodology for designing groundwater quality monitoring networks applicable to stochastic flow fields is presented and evaluated. The approach sets itself apart from previous techniques by incorporating the time dimension directly into the objective function. This ...

The Balcova Geothermal Field (BGF) located in Izmir, Turkey is situated on an east-west directed graben plain within which the hot waters surface from a fault zone that cuts the Mesozoic aged Bornova Flysch. Due to the low permeability... more

The Balcova Geothermal Field (BGF) located in Izmir, Turkey is situated on an east-west directed graben plain within which the hot waters surface from a fault zone that cuts the Mesozoic aged Bornova Flysch. Due to the low permeability and porosity of the Bornova Flysch, the geothermal water cycles along the immediate vicinity of the Agamemnon fault and mixes with cold waters at different depths of this fractured zone. Within the scope of this study, the mixing patterns and the groundwater contamination mechanisms are analyzed by, hydrogeological and hydrogeochemical methods. Based on the results of this research, it has been found out that the hot geothermal water and the cold regional groundwater resources of the surficial aquifer mix within the fractured zone in Bornova Flysch and within the Quaternary alluvium aquifer due to natural and anthropogenic activities including (i) the natural upward movement of geothermal fluid along the fault line, (ii) the accelerated upward seepage of geothermal fluid from faulty constructed boreholes drilled in the area, (iii) the faulty reinjection applications; and, (iv) the uncontrolled discharge of waste geothermal fluid to the natural drainage network. As a result of these activities, the cold groundwater reserves of the alluvial aquifer are contaminated thermally and chemically in such a way that various toxic chemicals including arsenic, antimony and boron are introduced to the heavily used surficial aquifer waters hindering their use for human consumption and agricultural irrigation. Furthermore, the excessive pumping from the surficial aquifer as well as the reduced surface water inflow into BGF due to the dam constructed on Ilica Creek intensify the detrimental effects of this contamination. Based on the results of this study, it can be concluded that the groundwater pollution in BGF will expand and reach to the levels of no return unless a series of preventive measures is taken immediately.

The past decade has seen considerable progress in the development of models simulating pesticide transport in structured soils subject to preferential flow (PF). Most PF pesticide transport models are based on the two-region concept and... more

The past decade has seen considerable progress in the development of models simulating pesticide transport in structured soils subject to preferential flow (PF). Most PF pesticide transport models are based on the two-region concept and usually assume one (vertical) dimensional flow and transport. Stochastic parameter sets are sometimes used to account for the effects of spatial variability at the field scale. In the past decade, PF pesticide models were also coupled with Geographical Information Systems (GIS) and groundwater flow models for application at the catchment and larger regional scales. A review of PF pesticide model applications reveals that the principal difficulty of their application is still the appropriate parameterization of PF and pesticide processes. Experimental solution strategies involve improving measurement techniques and experimental designs. Model strategies aim at enhancing process descriptions, studying parameter sensitivity, uncertainty, inverse parameter identification, model calibration, and effects of spatial variability, as well as generating model emulators and databases. Model comparison studies demonstrated that, after calibration, PF pesticide models clearly outperform chromatographic models for structured soils. Considering nonlinear and kinetic sorption reactions further enhanced the pesticide transport description. However, inverse techniques combined with typically available experimental data are often limited in their ability to simultaneously identify parameters for describing PF, sorption, degradation and other processes. On the other hand, the predictive capacity of uncalibrated PF pesticide models currently allows at best an approximate (order-of-magnitude) estimation of concentrations. Moreover, models should target the entire soil-plant-atmosphere system, including often neglected above-ground processes such as pesticide volatilization, interception, sorption to plant residues, root uptake, and losses by runoff. The conclusions compile progress, problems, and future research choices for modelling pesticide displacement in structured soils.

A sand column leaching system with well-controlled suction and flow rate was built to investigate the effects on bacterial transport of air-water interface effects (AWI) correlated to water content, particle size, and column length.... more

A sand column leaching system with well-controlled suction and flow rate was built to investigate the effects on bacterial transport of air-water interface effects (AWI) correlated to water content, particle size, and column length. Adsorption of Escherichia coli strain D to silica sands was measured in batch tests. The average % adsorption for coarse and fine sands was 45.9 ± 7.8% and 96.9 ± 3.2%, respectively. However, results from static batch adsorption experiments have limited applicability to dynamic bacterial transport in columns. The early breakthrough of E. coli relative to bromide was clear for all columns, namely c. 0.15 to 0.3 pore volume earlier. Column length had no significant effects on the E. coli peak concentration or on total recovery in leachate, indicating retention in the top layer of sands. Tailing of breakthrough curves was more prominent for all fine sand columns than their coarse sand counterparts. Bacterial recovery in leachate from coarse and saturated sand columns was significantly higher than from fine and unsaturated columns. Observed data were fitted by the convection-dispersion model, amended for one-site and two-site adsorption to particles, and for air-water interface (AWI) adsorption. Among all models, the two-site + AWI model achieved consistently high model efficiency for all experiments. Thus it is evident from experimental and modeling results that AWI adsorption plays an important role in E. coli transport in sand columns.

Supercritical fluid extraction with CO was applied to the analysis of traces of pendimethalin, a 2 herbicide of the dinitroanilines group, in four different natural soils. The Supercritical Fluid Ž . Extraction SFE method was compared... more

Supercritical fluid extraction with CO was applied to the analysis of traces of pendimethalin, a 2 herbicide of the dinitroanilines group, in four different natural soils. The Supercritical Fluid Ž . Extraction SFE method was compared with the classical Soxhlet and shaking methods in terms of ease to run, extraction efficiency, selectivity and reproducibility. The influence of the physico-chemical properties of the soil matrix on herbicide extraction was then evaluated with the SFE method. The supercritical fluid extraction system used in the present study was found to be much easier to run than the other two methods, less time consuming and requires fewer operations as it was optimized for on-line sample clean up. SFE is the most selective of the three tested methods as fewer co-extracts are obtained in the final samples. SFE with CO is particularly 2 ) Corresponding author. Tel.: q41-21-785 9446; fax: q41-21-785 8553 0169-7722r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved.

A variety of column experiments have been completed for the purpose of selecting and evaluating suitable surfactants for remediation of nonaqueous phase liquids (NAPLs). The various NAPLs tested in the laboratory experiments were... more

A variety of column experiments have been completed for the purpose of selecting and evaluating suitable surfactants for remediation of nonaqueous phase liquids (NAPLs). The various NAPLs tested in the laboratory experiments were tetrachloroethylene (PCE), trichloroethylene (TCE), jet fuel (JP4) and a dense nonaqueous phase liquid from a site at Hill Air Force Base, UT. Both Ottawa sand and Hill field soil were used in these experiments. Surfactant candidates were first screened using phase behavior experiments and only the best ones were selected for the subsequent column experiments. Surfactants which showed high contaminant solubilization, fast coalescence times, and the absence of liquid crystal phases and gels during the phase behavior experiments were tested in soil column experiments. The primary objective of the soil column experiments was to identify surfactants that recovered at least 99% of the contaminant. The secondary objective was to identify surfactants that show low adsorption and little or no loss of hydraulic conductivity during the column experiments. Results demonstrated that up to 99.9% of the contaminants were removed as a result of surfactant flooding of the soil columns. The addition of xanthan gum polymer to the surfactant solution was shown to increase remediation efficiency as a lower volume of surfactant was required for recovering a given volume of NAPL. Based on these experimental results, guidelines for designing highly efficient and robust surfactant floods have been developed and applied to a field demonstration.

Laboratory and modeling studies were conducted to assess the potential performance of a permeable reactive barrier constructed of a natural zeolite material at the West Valley Demonstration Project in western New York State. The results... more

Laboratory and modeling studies were conducted to assess the potential performance of a permeable reactive barrier constructed of a natural zeolite material at the West Valley Demonstration Project in western New York State. The results of laboratory column tests indicated that the barrier material would be effective at removing strontium from groundwater under natural gradient conditions. Two one-dimensional contaminant transport models were developed to interpret the data. A single-solute retardation factor model provided good agreement with the column test data, but time-consuming extraction and analysis of the zeolite material was required to parameterize the model. A preliminary six-solute model was also developed based on the assumption of competitive cation exchange as the primary removal mechanism. Both models yielded similar predictions of the long-term performance of the barrier, but the cation exchange model predicted higher effluent concentrations during the first 1000 pore volumes of operation. The cation exchange framework has several advantages, including the ability to calibrate the model using only data from column effluent samples, and the ability to account for site-specific 0169-7722/$ -see front matter D differences in the groundwater cation composition. However, additional laboratory work is needed to develop a suitably robust model. D

The use of nanoscaled zero-valent iron particles (nZVI) to remediate contaminated soil and groundwater has received increasing amounts of attention within the last decade, primarily due to its potential for broader application, higher... more

The use of nanoscaled zero-valent iron particles (nZVI) to remediate contaminated soil and groundwater has received increasing amounts of attention within the last decade, primarily due to its potential for broader application, higher reactivity, and cost-effectiveness compared to conventional zero-valent iron applications and other in situ methods. However, the potential environmental risks of nZVI in in situ field scale applications are largely unknown at the present and traditional environmental risk assessment approaches are not yet able to be completed. Therefore, it may not yet be fully clear how to consider the environmental benefits and risks of nZVI for in situ applications. This analysis therefore addresses the challenges of comprehensively considering and weighing the expected environmental benefits and potential risks of this emerging environmentally-beneficial nanotechnology, particularly relevant for environmental engineers, scientists, and decision makers. We find that most of the benefits of using nZVI are based on near-term considerations, and large data gaps currently exist within almost all aspects of environmental exposure and effect assessments. We also find that while a wide range of decision support tools and frameworks alternative to risk assessment are currently available, a thorough evaluation of these should be undertaken in the near future to assess their full relevancy for nZVI at specific sites. Due to the absence of data in environmental risk evaluations, we apply a 'best' and 'worst' case scenario evaluation as a first step to qualitatively evaluate the current state-ofknowledge regarding the potential environmental risks of nZVI. The result of this preliminary qualitative evaluation indicates that at present, there are no significant grounds on which to form the basis that nZVI currently poses a significant, apparent risk to the environment, although the majority of the most serious criteria (i.e. potential for persistency, bioaccumulation, toxicity) are generally unknown. We recommend that in cases where nZVI may be chosen as the 'best' treatment option, short and long-term environmental monitoring is actively employed at these sites. We furthermore recommend the continued development of responsible nZVI innovation and better facilitated information exchange between nZVI developers, nano-risk researchers, remediation industry, and decision makers. (K.D. Grieger), asf@env.dtu.dk (A. Fjordbøge), nah@env.dtu.dk (N.B. Hartmann), eve@env.dtu.dk (E. Eriksson), plb@env.dtu.dk (P.L. Bjerg), anb@env.dtu.dk (A. Baun).

In contaminant travel from ground surface to groundwater receptors, the time taken in travelling through the unsaturated zone is known as the unsaturated zone time lag. Depending on the situation, this time lag may or may not be... more

In contaminant travel from ground surface to groundwater receptors, the time taken in travelling through the unsaturated zone is known as the unsaturated zone time lag. Depending on the situation, this time lag may or may not be significant within the context of the overall problem. A method is presented for assessing the importance of the unsaturated zone in the travel time from source to receptor in terms of estimates of both the absolute and the relative advective times. A choice of different techniques for both unsaturated and saturated travel time estimation is provided. This method may be useful for practitioners to decide whether to incorporate unsaturated processes in conceptual and numerical models and can also be used to roughly estimate the total travel time between points near ground surface and a groundwater receptor. This method was applied to a field site located in a glacial aquifer system in Ontario, Canada. Advective travel times were estimated using techniques with different levels of sophistication. The application of the proposed method indicates that the time lag in the unsaturated zone is significant at this field site and should be taken into account. For this case, sophisticated and simplified techniques lead to similar assessments when the same knowledge of the hydraulic conductivity field is assumed. When there is significant uncertainty regarding the hydraulic conductivity, simplified calculations did not lead to a conclusive decision.

The objective of this study was to characterize the temporal behavior of contaminant mass discharge, and the relationship between reductions in contaminant mass discharge and reductions in contaminant mass, for a very heterogeneous,... more

The objective of this study was to characterize the temporal behavior of contaminant mass discharge, and the relationship between reductions in contaminant mass discharge and reductions in contaminant mass, for a very heterogeneous, highly contaminated source-zone field site. Trichloroethene is the primary contaminant of concern, and several lines of evidence indicate the presence of organic liquid in the subsurface. The site is undergoing groundwater extraction for source control, and contaminant mass discharge has been monitored since system startup. The results show a significant reduction in contaminant mass discharge with time, decreasing from approximately 1 to 0.15 kg/d over five years. Two methods were used to estimate the mass of contaminant present in the source area at the initiation of the remediation project. One was based on a comparison of two sets of core data, collected 3.5 years apart, which suggests that a significant (~80%) reduction in aggregate sedimentphase TCE concentrations occurred between sampling events. The second method was based on fitting the temporal contaminant mass discharge data with a simple exponential source-depletion function. Relatively similar estimates, 784 and 993 kg, respectively, were obtained with the two methods. These data were used to characterize the relationship between reductions in contaminant mass discharge (CMDR) and reductions in contaminant mass (MR). The observed curvilinear relationship exhibits a reduction in contaminant mass discharge essentially immediately upon the initiation of mass reduction. This behavior is consistent with a system wherein significant quantities of mass are present in hydraulically poorly accessible domains for which mass removal is influenced by rate-limited mass transfer. The results obtained from the present study are compared to those obtained from other field studies to evaluate the impact of system properties and conditions on mass-discharge and mass-removal behavior. The results indicate that factors such as domain scale, hydraulicgradient status (induced or natural), and flushing-solution composition had insignificant impact on the CMDR-MR profiles and thus on underlying mass-removal behavior. Conversely, source-zone age, through its impact on contaminant distribution and accessibility, was implicated as a critical factor influencing the nature of the CMDR-MR relationship.

The effects of bentonite colloids on strontium migration in fractured crystalline medium were investigated. We analyzed first the transport behaviour of bentonite colloids alone at different flow rates; then we compared the transport... more

The effects of bentonite colloids on strontium migration in fractured crystalline medium were investigated. We analyzed first the transport behaviour of bentonite colloids alone at different flow rates; then we compared the transport behaviour of strontium as solute and of strontium previously adsorbed onto stable bentonite colloids at a water velocity of approximately 7.1·10 − 6 m/s-224 m/yr. Experiments with bentonite colloids alone showed thatat the lowest water flow rate used in our experiments (7.1·10 − 6 m/s)approximately 70% of the initially injected colloids were retained in the fracture. Nevertheless, the mobile colloidal fraction, moved through the fracture without retardation, at any flow rate. Bentonite colloids deposited over the fracture surface were identified during post-mortem analyses. The breakthrough curve of strontium as a solute, presented a retardation factor, R f~6 , in agreement with its sorption onto the granite fracture surface. The breakthrough curve of strontium in the presence of bentonite colloids was much more complex, suggesting additional contributions of colloids to strontium transport. A very small fraction of strontium adsorbed on mobile colloids moved un-retarded (R f = 1) and this fraction was much lower than the expected, considering the quantity of strontium initially adsorbed onto colloids (90%). This behaviour suggests the hypothesis of strontium sorption reversibility from colloids. On the other hand, bentonite colloids retained within the granite fracture played a major role, contributing to a slower strontium transport in comparison with strontium as a solute. This was shown by a clear peak in the breakthrough curve corresponding to a retardation factor of approximately 20.

Stable hydrogen isotopes of two chlorinated solvents, trichloroethylene (TCE) and 1,1,1trichloroethane (TCA), provided by five different manufacturers, were determined and compared to their carbon and chlorine isotopic signatures. The... more

Stable hydrogen isotopes of two chlorinated solvents, trichloroethylene (TCE) and 1,1,1trichloroethane (TCA), provided by five different manufacturers, were determined and compared to their carbon and chlorine isotopic signatures. The isotope ratio for d 2 H of different TCEs ranged between + 466.9xand + 681.9x , for d 13 C between À 31.57xand À 27.37x , and for d 37 Cl between À 3.19xand + 3.90x . In the case of the TCAs, the isotope ratio for d 2 H ranged between À 23.1xand + 15.1x , for d 13 C between À 27.39xand À 25.84x , and for d 37 Cl between À 3.54x and + 1.39x . As well, a column experiment was carried out to dechlorinate tetrachloroethylene (PCE) to TCE using iron. The dechlorination products have completely different hydrogen isotope ratios than the manufactured TCEs. Compared to the positive values of d 2 H in manufactured TCEs (between + 466.9xand + 681.9x ), the dechlorinated products had a very depleted d 2 H (less than À 300x ). This finding has strong implications for distinguishing dechlorination products (PCE to TCE) from manufactured TCE. In addition, the results of this study show the potential of combining 2 H/ 1 H analyses with 13 C/ 12 C and 37 Cl/ 35 Cl for isotopic fingerprinting applications in organic contaminant hydrogeology. D

Geophysical measurements, and electrical resistivity tomography (ERT) data in particular, are sensitive to properties that are related (directly or indirectly) to hydrological processes. The challenge is in extracting information from... more

Geophysical measurements, and electrical resistivity tomography (ERT) data in particular, are sensitive to properties that are related (directly or indirectly) to hydrological processes. The challenge is in extracting information from geophysical data at a relevant scale that can be used to gain insight about subsurface behavior and to parameterize or validate flow and transport models. Here, we consider the use of ERT data for examining the impact of recharge on subsurface contamination at the S-3 ponds 2 of the Oak Ridge Integrated Field Research Challenge (IFRC) site in Tennessee. A large dataset of time-lapse cross-well and surface ERT data, collected at the site over a period of 12 months, is used to study time variations in resistivity due to changes in total dissolved solids (primarily nitrate). The electrical resistivity distribution recovered from cross-well and surface ERT data agree well, and both of these datasets can be used to interpret spatiotemporal variations in subsurface nitrate concentrations due to rainfall, although the sensitivity of the electrical resistivity response to dilution varies with nitrate concentration. Using the time-lapse surface ERT data interpreted in terms of nitrate concentrations, we find that the subsurface nitrate concentration at this site varies as a function of spatial position, episodic heavy rainstorms (versus seasonal and annual fluctuations), and antecedent rainfall history. These results suggest that the surface ERT monitoring approach is potentially useful for examining subsurface plume responses to recharge over field-relevant scales.

In the Hesbaye region in Belgium, tracer tests performed in variably saturated fissured chalk rocks presented very contrasting results in terms of transit times, according to artificially controlled water recharge conditions prevailing... more

In the Hesbaye region in Belgium, tracer tests performed in variably saturated fissured chalk rocks presented very contrasting results in terms of transit times, according to artificially controlled water recharge conditions prevailing during the experiments. Under intense recharge conditions, tracers migrated across the partially or fully saturated fissure network, at high velocity in accordance with the high hydraulic conductivity and low effective porosity (fracture porosity). At the same time, a portion of the tracer was temporarily retarded in the almost immobile water located in the matrix. Under natural infiltration conditions, the fissure network remained inactive. Tracers migrated downward through the matrix, at low velocity in relation with the low hydraulic conductivity and the large porosity of the matrix. Based on these observations, Brouyère et al. (2004a) [Brouyère, S., Dassargues, A., Hallet, V., 2004a. Migration of contaminants through the unsaturated zone overlying the Hesbaye chalky aquifer in Belgium: a field investigation, J. Contam. Hydrol., 72 (1–4), 135–164, doi: 10.1016/j.conhyd.2003.10.009] proposed a conceptual model in order to explain the migration of solutes in variably saturated, dual-porosity, dual-permeability chalk. Here, mathematical and numerical modelling of tracer and contaminant migration in variably saturated fissured chalk is presented, considering the aforementioned conceptual model. A new mathematical formulation is proposed to represent the unsaturated properties of the fissured chalk in a more dynamic and appropriate way. At the same time, the rock water content is partitioned between mobile and immobile water phases, as a function of the water saturation of the chalk rock. The groundwater flow and contaminant transport in the variably saturated chalk is solved using the control volume finite element method. Modelling the field tracer experiments performed in the variably saturated chalk shows the adequacy and usefulness of the new conceptual, mathematical and numerical model.

Many countries intend to use compacted bentonite as a barrier in their deep geological repositories for nuclear waste. In order to describe and predict hydraulic conductivity or radionuclide transport through the bentonite barrier,... more

Many countries intend to use compacted bentonite as a barrier in their deep geological repositories for nuclear waste. In order to describe and predict hydraulic conductivity or radionuclide transport through the bentonite barrier, fundamental understanding of the microstructure of compacted bentonite is needed. This study examined the interlayer swelling and overall microstructure of Wyoming Bentonite MX-80 and the corresponding homo-ionic Na + and Ca 2 + forms, using XRD with samples saturated under confined swelling conditions and free swelling conditions. For the samples saturated under confined conditions, the interparticle, or so-called free or external porosity was estimated by comparing the experimental interlayer distances obtained from one-dimensional XRD profile fitting against the maximum interlayer distances possible for the corresponding water content. The results showed that interlayer porosity dominated total porosity, irrespective of water content, and that the interparticle porosity was lower than previously reported in the literature. At compactions relevant for the saturated bentonite barrier (1.4-1.8 g/cm 3 ), the interparticle porosity was estimated to ≤3%.

Though coliform bacteria are used world wide as an indication of faecal pollution, the parameters determining the transport of Escherichia coli in aquifers are relatively unknown, especially for the period after the clean bed collision... more

Though coliform bacteria are used world wide as an indication of faecal pollution, the parameters determining the transport of Escherichia coli in aquifers are relatively unknown, especially for the period after the clean bed collision phase brought about by prolonged infiltration of waste water. In this research, the breakthrough curves of E. coli after total flushing of 50-200 pore volumes were studied for various influent concentrations in various sediments at different pore water flow velocities. The results indicated that straining in Dead End Pores (DEPs) was an important process that dominated bacteria breakthrough in finegrained sediment (0.06-0.2 mm). The filling of the DEP space with bacteria took 5-65 pore volumes and was dependent on concentration. Column breakthrough curves were modelled and from this the DEP volumes were determined. These volumes (0.21-0.35% of total column volume) corresponded well with values calculated with a formula based on purely geometrical considerations and also with values calculated with a pore size density function. For this function the so-called Van Genuchten parameters of the sediments used in the experiments were determined. The results indicate that straining might be a dominant process affecting colloid transport in the natural environment and therefore it is concluded that proper 0169-7722/$ -see front matter D knowledge of the pore size distribution is crucial to an understanding of the retention of bacteria. D

Groundwater contamination by nitrate was investigated in an agricultural area in southern Quebec, Canada, where a municipal well is the local source of drinking water. A network of 38 piezometers was installed within the capture zone of... more

Groundwater contamination by nitrate was investigated in an agricultural area in southern Quebec, Canada, where a municipal well is the local source of drinking water. A network of 38 piezometers was installed within the capture zone of the municipal well to monitor water table levels and nitrate concentrations in the aquifer. Nitrate concentrations were also measured in the municipal well. A Water flow and Nitrate transport Global Model (WNGM) was developed to simulate the impact of agricultural activities on nitrate concentrations in both the aquifer and municipal well. The WNGM first uses the Agriflux model to simulate vertical water and nitrate fluxes below the root zone for each of the seventy agricultural fields located within the capture zone of the municipal well. The WNGM then uses the HydroGeoSphere model to simulate three-dimensional variably-saturated groundwater flow and nitrate transport in the aquifer using water and nitrate fluxes computed with the Agriflux model as the top boundary conditions. The WNGM model was calibrated by reproducing water levels measured from 2005 to 2007 in the network of piezometers and nitrate concentrations measured in the municipal well from 1997 to 2007. The nitrate concentrations measured in the network of piezometers, however, showed greater variability than in the municipal well and could not be reproduced by the calibrated model. After calibration, the model was validated by successfully reproducing the decrease of nitrate concentrations observed in the municipal well in 2006 and 2007. Although it cannot predict nitrate concentrations in individual piezometers, the calibrated and validated WNGM can be used to assess the impact of changes in agricultural practices on global nitrate concentrations in the aquifer and in the municipal well.

j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j c o n hyd zone. However, the sensitivity study showed that the inverse modelling approach provided a rather non-unique solution. More data available may reduce... more

j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j c o n hyd zone. However, the sensitivity study showed that the inverse modelling approach provided a rather non-unique solution. More data available may reduce the number of possible representations of the estimated source zone.

The true efficacy of a programme of agricultural mitigation measures within a catchment to improve water quality can be determined only after a certain hydrologic time lag period (subsequent to implementation) has elapsed. As the... more

The true efficacy of a programme of agricultural mitigation measures within a catchment to improve water quality can be determined only after a certain hydrologic time lag period (subsequent to implementation) has elapsed. As the biophysical response to policy is not synchronous, accurate estimates of total time lag (unsaturated and saturated) become critical to manage the expectations of policy makers. The estimation of the vertical unsaturated zone component of time lag is vital as it indicates early trends (initial breakthrough), bulk (centre of mass) and total (Exit) travel times. Typically, estimation of time lag through the unsaturated zone is poor, due to the lack of site specific soil physical data, or by assuming saturated conditions. Numerical models (e.g. Hydrus 1D) enable estimates of time lag with varied levels of input data. The current study examines the consequences of varied soil hydraulic and meteorological complexity on unsaturated zone time lag estimates using simulated and actual soil profiles. Results indicated that: greater temporal resolution (from daily to hourly) of meteorological data was more critical as the saturated hydraulic conductivity of the soil decreased; high clay content soils failed to converge reflecting prevalence of lateral component as a contaminant pathway; elucidation of soil hydraulic properties was influenced by the complexity of soil physical data employed (textural menu, ROSETTA, full and partial soil water characteristic curves), which consequently affected time lag ranges; as the importance of the unsaturated zone increases with respect to total travel times the requirements for high complexity/resolution input data become greater. The methodology presented herein demonstrates that decisions made regarding input data and landscape position will have consequences for the estimated range of vertical travel times. Insufficiencies or inaccuracies regarding such input data can therefore mislead policy makers regarding the achievability of water quality targets.

Hydrological responses in mountainous headwater catchments are often highly non-linear with a distinct threshold-related behavior, which is associated to steep hillslopes, shallow soils and strong climatic variability. A holistic... more

Hydrological responses in mountainous headwater catchments are often highly non-linear with a distinct threshold-related behavior, which is associated to steep hillslopes, shallow soils and strong climatic variability. A holistic understanding of the dominant physical processes that control streamflow generation and non-linearity is required in order to assess potential negative effects of agricultural land use and water management in those areas. Therefore, streamflow generation in a small pre-Alpine headwater catchment (Upper Rietholzbach (URHB), ~1km(2)) was analyzed over a 2-year period by means of rainfall-response analysis and water quality data under explicit consideration of the joint behaviors of climate forcing and shallow groundwater dynamics. The runoff coefficients indicate that only a small fraction of the total catchment area (1-26%) generates streamflow during rainfall events. Hereby, the valley bottom areas (riparian zones) were the most important event-water source...

The aim of this study is to gain a better understanding of the conceptual model of contaminant transport and fate in cases of NAPL pollution in mega-site contexts in order to improve the design of remedial strategies. The area where the... more

The aim of this study is to gain a better understanding of the conceptual model of contaminant transport and fate in cases of NAPL pollution in mega-site contexts in order to improve the design of remedial strategies. The area where the study was carried out is an unconfined aquifer of alluvial fans in the Tarragona Petrochemical Complex (Spain). Two boreholes were drilled and continuous cores were recovered in order to carry out a geological and hydrogeological testing at centimeter scale. A comprehensive sampling of subsoil materials was also undertaken. The biogeochemical heterogeneity occurring in the mega-site context is controlled by the existing conjunction of lithological, hydrochemical and microbiological heterogeneities. Biodegradation processes of the lightest compounds take place not only at the level of the dissolved fraction but also at the level of the fraction retained in the fine, less conductive materials. The quantification of this pollutant mass must be taken into account when designing remedial strategies in order to forecast back-diffusion. Sampling the low-conductivity levels contributes to the definition of the conceptual model of transport and fate from the spatial and temporal viewpoints.

This study numerically investigates the influence of initial water content and rain intensities on the preferential migration of two fluorescent tracers, Acid Yellow 7 (AY7) and Sulforhodamine B (SB), through variably-saturated fractured... more

This study numerically investigates the influence of initial water content and rain intensities on the preferential migration of two fluorescent tracers, Acid Yellow 7 (AY7) and Sulforhodamine B (SB), through variably-saturated fractured clayey till. The simulations are based on the numerical model HydroGeoSphere, which solves 3D variably-saturated flow and solute transport in discretely-fractured porous media. Using detailed knowledge of the matrix, fracture, and biopore properties, the numerical model is calibrated and validated against experimental high-resolution tracer images/data collected under dry and wet soil conditions and for three different rain events. The model could reproduce reasonably well the observed preferential migration of AY7 and SB through the fractured till, although it did not capture the exact depth of migration and the negligible impact of the dead-end biopores in a near-saturated matrix. A sensitivity analysis suggests fast flow mechanisms and dynamic surface coating in the biopores, and the presence of a plough pan in the till.

Variation in the ambient atmospheric pressure results in subsurface motion of air in porous and fractured earth materials. This is known as barometric pumping. We analyze this phenomenon for unfractured media and demonstrate that if... more

Variation in the ambient atmospheric pressure results in subsurface motion of air in porous and fractured earth materials. This is known as barometric pumping. We analyze this phenomenon for unfractured media and demonstrate that if hydrodynamic dispersivity is included, barometric pumping can significantly decrease the retention time of volatile subsurface contaminants. Formulae are derived which give analytically the dependence of the effect on the amplitude and frequency of the barometric pump as well as on the material properties. In addition, numerical modeling results using a method which careftilly avoids spurious numerica! dispersion are presented. Field data will appear to follow a standard diffusive transport model; but in the systems in which barometric pumping is significant, the value for D will need to be greater than that derived from isobaric tests. In addition to enhancing the diffusion, pumping also sweeps out pore gases near the surface and thus, reduces the distance a subsurface contaminant must diffuse before it mixes with the atmosphere. These barometric pumping mechanisms will be enhanced by the presence of fractures, which permit pressure variations to propagate deep into the ground. Because barometric pumping affects the rate of contaminant transport from the subsurface, this process may play an important role in the environmental remediation of volatile organic chemicals in the vadose zone.

The two-dimensional distribution of flow patterns and their dynamic change due to microbial activity were investigated in naturally fractured chalk cores. Long-term biodegradation experiments were conducted in two cores (~20 cm diameter,... more

The two-dimensional distribution of flow patterns and their dynamic change due to microbial activity were investigated in naturally fractured chalk cores. Long-term biodegradation experiments were conducted in two cores (~20 cm diameter, 31 and 44 cm long), intersected by a natural fracture. 2,4,6-tribromophenol (TBP) was used as a model contaminant and as the sole carbon source for aerobic microbial activity. The transmissivity of the fractures was continuously reduced due to biomass accumulation in the fracture concurrent with TBP biodegradation. From multi-tracer experiments conducted prior to and following the microbial activity, it was found that biomass accumulation causes redistribution of the preferential flow channels. Zones of slow flow near the fracture inlet were clogged, thus further diverting the flow through zones of fast flow, which were also partially clogged. Quantitative evaluation of biodegradation and bacterial counts supported the results of the multi-tracer tests, indicating that most of the bacterial activity occurs close to the inlet. The changing flow patterns, which control the nutrient supply, resulted in variations in the 0169-7722/$ -see front matter D 2005 Published by Elsevier B.V.

EDTA was percolated in laboratory columns through a soil polluted by heavy metals to investigate the efficiency of and processes involved in soil decontamination by chemical extrac-Ž y2 . tion. At high EDTA concentration 10 M , elution of... more

EDTA was percolated in laboratory columns through a soil polluted by heavy metals to investigate the efficiency of and processes involved in soil decontamination by chemical extrac-Ž y2 . tion. At high EDTA concentration 10 M , elution of Pb and Cd was very efficient for one pore volume, after which it decreased to almost zero due to depletion of available Pb and Cd and to competition with Ca and Fe slowly solubilized during the passage of the EDTA front. Clogging Ž y3 y4 . occurred after the end of the EDTA plateau. At lower EDTA concentrations 10 and 10 M , elution was less efficient, but extraction decreased little with the volume percolated; moreover no Ca above background values was dissolved. The optimum EDTA concentration for heavy metal extraction ranges between 10 y2 and 10 y3 M. The higher the concentration, the greater the extraction efficiency, but as the EDTA concentration is increased there is an optimum point at which clogging takes place and permeability decreases. q 0169-7722r00r$ -see front matter q 2000 Elsevier Science B.V. All rights reserved.

The removal of bacteriophages MS2 and PRD1, spores of Clostridium bifermentans R5 and Ž . Escherichia coli WR1 by deep well injection into a sandy aquifer, was studied at a pilot field site in the southeast of the Netherlands. Injection... more

The removal of bacteriophages MS2 and PRD1, spores of Clostridium bifermentans R5 and Ž . Escherichia coli WR1 by deep well injection into a sandy aquifer, was studied at a pilot field site in the southeast of the Netherlands. Injection water was seeded with the microorganisms for 5 days. Breakthrough was monitored for 93 days at 4 monitoring wells with their screens at a depth of about 310 m below surface. Within the first 8 m of soil passage, concentrations of MS2 and PRD1 were reduced by 6 log , that of R5 spores by 5 log and that of WR1 by 7.5 log . G. Medema , Ž . Ž . vogelaar@kiwaoa.nl A.J. Vogelaar , majid.hassanizadeh@ct.tudelft.nl S.M. Hassanizadeh . 1 Tel.: q31-30-606-9653. 2 Tel.: q31-30-606-9592. 3 Tel.: q31-15-278-7346.

Leaching of NO3-N from agricultural lands often occurs in well-defined hot spot areas when viewed across geographical regions of hundreds or thousands of km 2 and often appears as areas of high NO3-N concentrations in shallow underlying... more

Leaching of NO3-N from agricultural lands often occurs in well-defined hot spot areas when viewed across geographical regions of hundreds or thousands of km 2 and often appears as areas of high NO3-N concentrations in shallow underlying aquifers. Delineation of high-NO3-N zones can be achieved by combining models such the Nitrate Leaching and Economic Analysis Package (NLEAP) with Geographical Information System (GIS) technology to calculate the long-term potential mass of NO3-N leached from the crop root zone. Once identified, the hot spots can be further analyzed with the model to evaluate and rank appropriate alternative management techniques. A simulation analysis using the NLEAP model showed that long-term NO3-N leaching from corn (Zea mays L.) grown under furrow irrigation on a coarse-textured soil could be reduced by 53% with N management alone, while an 84% reduction in leached NO3-N was achieved for combined N and water management (sprinkler irrigation). This type of modeling analysis can be completed after a few weeks of effort, while comparable field studies would take several years to finish.

A stormwater infiltration basin in north-central Florida, USA, was monitored from 2007 through 2008 to identify subsurface biogeochemical processes, with emphasis on N cycling, under the highly variable hydrologic conditions common in... more

A stormwater infiltration basin in north-central Florida, USA, was monitored from 2007 through 2008 to identify subsurface biogeochemical processes, with emphasis on N cycling, under the highly variable hydrologic conditions common in humid, subtropical climates. Cyclic variations in biogeochemical processes generally coincided with wet and dry hydrologic conditions. Oxidizing conditions in the subsurface persisted for about one month or less at the beginning of wet periods with dissolved O(2) and NO(3)(-) showing similar temporal patterns. Reducing conditions in the subsurface evolved during prolonged flooding of the basin. At about the same time O(2) and NO(3)(-) reduction concluded, Mn, Fe and SO(4)(2-) reduction began, with the onset of methanogenesis one month later. Reducing conditions persisted up to six months, continuing into subsequent dry periods until the next major oxidizing infiltration event. Evidence of denitrification in shallow groundwater at the site is supported by median NO(3)(-)-N less than 0.016 mg L(-1), excess N(2) up to 3 mg L(-1) progressively enriched in δ(15)N during prolonged basin flooding, and isotopically heavy δ(15)N and δ(18)O of NO(3)(-) (up to 25‰ and 15‰, respectively). Isotopic enrichment of newly infiltrated stormwater suggests denitrification was partially completed within two days. Soil and water chemistry data suggest that a biogeochemically active zone exists in the upper 1.4m of soil, where organic carbon was the likely electron donor supplied by organic matter in soil solids or dissolved in infiltrating stormwater. The cyclic nature of reducing conditions effectively controlled the N cycle, switching N fate beneath the basin from NO(3)(-) leaching to reduction in the shallow saturated zone. Results can inform design of functionalized soil amendments that could replace the native soil in a stormwater infiltration basin and mitigate potential NO(3)(-) leaching to groundwater by replicating the biogeochemical conditions under the observed basin.

A model was developed simulating reactive transport in groundwater including bioclogging. Results from a bioclogging experiment in a flow cell with a two-dimensional flow field were used as a data base to verify the simulation results of... more

A model was developed simulating reactive transport in groundwater including bioclogging. Results from a bioclogging experiment in a flow cell with a two-dimensional flow field were used as a data base to verify the simulation results of the model. Simulations were performed using three different hydraulic conductivity vs. porosity relations published in literature; two relations derived from pore network simulations assuming the biomass to grow in discrete colonies and as a biofilm, respectively, and a third relation, which did not include pore connectivity in more than one dimension. Best agreement with the experimental data was achieved using a hydraulic conductivity vs. porosity relation derived from pore network simulation assuming the biomass to grow in colonies. The relation derived from pore network simulations assuming biomass to grow as a biofilm was unable to reproduce the experimental data when realistic parameter values were employed. With the third relation the clogging ability of the biomass was strongly underestimated. These findings indicate that the porous medium needs to be treated as a multi-dimensional medium already on the pore scale, and that biomass growth different than in a biofilm must be considered to get an appropriate description of bioclogging. D

Soil structure critically affects the hydrological behaviour of soils. In this paper, we examined the impact of areal heterogeneity of hydraulic properties of a structured soil on soil ensemble behaviour for various soil water flow... more

Soil structure critically affects the hydrological behaviour of soils. In this paper, we examined the impact of areal heterogeneity of hydraulic properties of a structured soil on soil ensemble behaviour for various soil water flow processes with different top boundary conditions (redistribution and drainage plus evaporation and infiltration). Using a numerical solution of the Richards' equation in a stochastic framework, the ensemble characteristics and flow dynamics were studied for drying and wetting processes observed during a time interval of ten days when a series of relatively intense rainfall events occurred. The effects of using unimodal and bimodal interpretative models of hydraulic properties on the ensemble hydrological behaviour of the soil were illustrated by comparing predictions to mean water contents measured over time in several sites at field scale. Although the differences between unimodal and bimodal fitting are not significant in terms of goodness of fit, the differences in process predictions are considerable with the bimodal soil simulating water content measurements much better than unimodal soil. We also investigated the relative contribution of the soil variability of each parameter on the variance of the water contents obtained as the main output of the stochastic simulations. The variability of the structural parameter, weighting the two pore space fractions in the bimodal interpretative model, has the largest contribution to water content variance. The contribution of each parameter depends only partly on the coefficient of variation, much more on the sensitivity of the model to the parameters and on the flow process being observed. We observed that the contribution of the retention parameters to uncertainty increases during drainage processes; the opposite occurs with the hydraulic conductivity parameters.

Water quality in the unsaturated and saturated zones of a waste rock pile containing sulphides was investigated. The main objectives of the project were (1) the evaluation of geochemical trends including the acid mine drainage... more

Water quality in the unsaturated and saturated zones of a waste rock pile containing sulphides was investigated. The main objectives of the project were (1) the evaluation of geochemical trends including the acid mine drainage (AMD)-buffering mechanism and the role of secondary minerals, and (2) the investigation of the use of stable isotopes for the interpretation of physical and geochemical processes in waste rock. Pore water in unsaturated zone was sampled from suction lysimeters and with piezometers in underlying saturated rocks. The investigation revealed strong temporal (dry period vs. recharge period), and spatial (slope vs. central region of pile) variability in the formation of acid mine drainage. The main secondary minerals observed were gypsum and jarosite. There was a higher concentration of gypsum in solid phase at Site TBT than at Site 6, suggesting that part of the gypsum formed at Site 6 in the early stage of AMD has been already dissolved. Formation of secondary minerals contributed to the formation of AMD by opening of foliation planes in waste rock, thus increasing the access of oxidants like O 2 and Fe 3 + to previously encapsulated pyrite. The behavior of several dissolved species such as Mg, Al, and Fe 2 + can be considered as conservative in the leachate. Stable isotopes, deuterium and 18 O, indicated internal 0169-7722/$ -see front matter D

Synthesis of rock-core sampling and chlorinated volatile organic compound (CVOC) analysis at five coreholes, with hydraulic and water-quality monitoring and a detailed hydrogeologic framework, was used to characterize the fine-scale... more

Synthesis of rock-core sampling and chlorinated volatile organic compound (CVOC) analysis at five coreholes, with hydraulic and water-quality monitoring and a detailed hydrogeologic framework, was used to characterize the fine-scale distribution of CVOCs in dipping, fractured mudstones of the Lockatong Formation of Triassic age, of the Newark Basin in West Trenton, New Jersey. From these results, a refined conceptual model for more than 55years of migration of CVOCs and depth- and strata-dependent rock-matrix contamination was developed. Industrial use of trichloroethene (TCE) at the former Naval Air Warfare Center (NAWC) from 1953 to 1995 resulted in dense non-aqueous phase liquid (DNAPL) TCE and dissolved TCE and related breakdown products, including other CVOCs, in underlying mudstones. Shallow highly weathered and fractured strata overlie unweathered, gently dipping, fractured strata that become progressively less fractured with depth. The unweathered lithology includes black hi...

The light nonaqueous phase liquid (LNAPL) oil pool in an aquifer that resulted from a pipeline spill near Bemidji, Minnesota, was analyzed for volatile hydrocarbons (VHCs) to determine if the composition of the oil remains constant over... more

The light nonaqueous phase liquid (LNAPL) oil pool in an aquifer that resulted from a pipeline spill near Bemidji, Minnesota, was analyzed for volatile hydrocarbons (VHCs) to determine if the composition of the oil remains constant over time. Oil samples were obtained from wells at five locations in the oil pool in an anaerobic part of the glacial outwash aquifer. Samples covering a 21-year period were analyzed for 25 VHCs. Compared to the composition of oil from the pipeline source, VHCs identified in oil from wells sampled in 2008 were 13 to 64% depleted. The magnitude of loss for the VHCs analyzed was toluene ≫o-xylene, benzene, C 6 and C 10-12 n-alkanes N C 7 -C 9 n-alkanes N m-xylene, cyclohexane, and 1-and 2-methylnaphthalene N 1,2,4-trimethylbenzene and ethylbenzene. Other VHCs including p-xylene, 1,3,5-and 1,2,3-trimethylbenzenes, the tetramethylbenzenes, methyl-and ethyl-cyclohexane, and naphthalene were not depleted during the time of the study. Water-oil and air-water batch equilibration simulations indicate that volatilization and biodegradation is most important for the C 6 -C 9 n-alkanes and cyclohexanes; dissolution and biodegradation is important for most of the other hydrocarbons. Depletion of the hydrocarbons in the oil pool is controlled by: the lack of oxygen and nutrients, differing rates of recharge, and the spatial distribution of oil in the aquifer. The mass loss of these VHCs in the 5 wells is between 1.6 and 7.4% in 29 years or an average annual loss of 0.06-0.26%/year. The present study shows that the composition of LNAPL changes over time and that these changes are spatially variable. This highlights the importance of characterizing the temporal and spatial variabilities of the source term in solute-transport models.

There is growing evidence that water seepage in thick unsaturated zones in fractured rocks may occur in non-volume-averaged fashion, as relatively 'slow' flow in the rock matrix, and 'fast' flow along... more

There is growing evidence that water seepage in thick unsaturated zones in fractured rocks may occur in non-volume-averaged fashion, as relatively 'slow' flow in the rock matrix, and 'fast' flow along localized preferential pathways in fractures. This poses difficult challenges for ...

Chromium (Cr) and Nickel (Ni) removal from secondary effluent has been evaluated in a four year research program to determine the effectiveness of Sub-Surface Flow (SSF) Constructed Wetlands (cw s ). Tests were performed in small scale... more

Chromium (Cr) and Nickel (Ni) removal from secondary effluent has been evaluated in a four year research program to determine the effectiveness of Sub-Surface Flow (SSF) Constructed Wetlands (cw s ). Tests were performed in small scale (10 l/h) and full scale (150 m 3 /d) SSF cw s . Metals removal was also assessed as a function of increased clogging that occurred in the cw s over the course of the study. Cr and Ni content were evaluated in sediments at various locations along the flow path and in plant tissues by sampling Phragmites australis roots, stems and leaves. Clogging was evaluated by measuring hydraulic conductivity at the same sampling locations at the beginning and at the end of the experiment. Residence Time Distribution (RTD) curves were also assessed at the beginning and after 48 months; the skewness of the RTDs increased over this period. Proportionality between increasing clogging and sediment accumulation of metals was observed, especially for Ni. Adsorption to the original matrix and the accumulated sediment is a removal mechanism consistent with available data.